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Geological Society of Australia

ABSTRACTS Number 38

AUSTRALASIAN SEDIMENTOLOGISTS GROUP CONFERENCE

COOL-WATER CARBONATES OF THE NORTHEASTERN OTWAY BASIN SOUTHEASTERN AUSTRALIA Geelong, Victoria, Australia 14-19 January 1995

GEOLOGICAL SOCIETY OF AUSTRALIA INC

Abstracts Number 38

Cool-water Carbonates of the Northeastern Otway Basin Southeastern Australia

Abstracts of a conference organised by the Australasian Sedimentologists Group Held at Geelong, Victoria, Australia 14-19 January 1995

Published by the Geological Society of Australia Inc ISSN 0729-OllX

CONTENTS

Page

TEMPERATE SHELF CARBONATES, TORQUAY, VICTORIA K. Arai, P. J. Davies, K. Konishil, and R. Maas

CARBONATE DEPOSITION OF THE SEASPRAY GROUP IN THE OFFSHORE GIPPSLAND BASIN T. Bemecker

COMPARISON OF THE GEOCHEMISTRY OF COOL-WATER CORALS, CORALLINE ALGAE AND BRYOZOANS FROM THE LACEPEDE SHELF, SOUTH AUSTRALIA WITH THEIR WARM WATER COUNTERPARTS (P) H. R. Bonab, Y. Bone, R. Moussavi-Harami, and K. Tumbull

COOL-WATER BRYOZOA AND STABLE ISOTOPES Y. Bone and N. P. James

STRATIGRAPmC PRINCIPLES AND PATTERNS OF COOL-WATER CARBONATE DEPOSITION: TERTIARY LIMESTONES, SE AUSTRALIA T. D. Boreen and N. P. James

LATE PALAEOZOIC COLD-WATER CARBONATES FROM EASTERN TASMANIA - DEPOSITIONAL ENVIRONMENTS PROCESSES J. K. Brooker and K. J. Woolfe

OMISSION SURFACES DEHNING CYCLICITY IN THE TERTIARY SECTION OF TORQUAY B. Buchbinder, T. Van der Linden, and P. J. Davies

SEA-LEVEL AS A CONTROL ON CARBONATE FACTORIES R. M. Carter

SEQUENCE STRATIGRAPHIC SIGNinCANCE OF PLEISTOCENE AND RECENT COOL-WATER CARBONATES FROM NEW ZEALAND (P) R. M. Carter, P. Gammon, A. R. Orpin and G. Saul

THE SOUTHWESTERN MARGIN OF AUSTRALIA: TRANSITION FROM COOL TO WARM WATER CARBONATES? L. B. Collins

CARBONATE SEDIMENT DISTRIBUTION PATTERNS OF A COOL-WATER EMBAYMENT; STREAKY BAY 7 SOUTH AUSTRALIA: A PRELIMINARY REPORT R. F. Daniel and C. C. Von Derborch

SOUTHEASTERN AUSTRALIA: A SEA-LEVEL DEPENDENT CARBONATE MARGIN M. A. Ferland and P. S. Roy

THE "LITTLE BARRIER REEF" OF SOUTHERN AUSTRALIA: THE RESULT OF WARMER-WATER INTERRUPTION TO PREVAILING COOL-WATER CONDITIONS D. A. Feaiy and N. P. James

(P)

Denotes Poster

GLACIO-EUSTATIC CONTROL OF COQUINA FACIES IN THE PLIOCENE PUKENUI LIMESTONE, NEW ZEALAND P. Ganunon

LATE QUATERNARY SEDIMENTS OF WANGANUI SHELF, NEW ZEALAND: A NON-TROPICAL CARBONATE-SILICICLASTIC MIXTURE J. L. Gillespie and C. S. Nelson

BRYOZOAN COLONIAL GROWTH FORMS AS PALEO-ENVIRONMENTAL INDICATORS: RE-EVALUATION OF METHODOLOGY AND PREDICTIVE UTILITY S. J. Hageman, Y. Done, B. McGowran and N. P. James

SKELETAL ASSEMBLAGES OF NEW ZEALAND CENOZOIC NON-TROPICAL CARBONATE SEDIMENTS S. Hayton, S. D. Hood and C. S. Nelson

COLD WATER REEFS AND BIOGENIC CARBONATES OF ARCTIC R. Henrich and A. Freiwald

PALEO-ENVIRONMENTS AND SEQUENCE STRATIGRAPHY OF THE CARBONATES AT SALE IN SOUTH GIPPSLAND, VICTORIA G. Holdgate and S. Gallagher

OVERVIEW OF CEMENTATION ENVIRONMENTS AND PATHWAYS FOR NEW ZEALAND CENOZOIC TEMPERATE-LATITUDE LIMESTONES S.D.Hood and C.S.Nelson

PALEOZOIC CRYOCARBONATES: CHARLATANS IN THE MIST? N. P. James

APPLICATION OF RECORDING NEPHELOMETERS TO SEDIMENTATION STUDIES ON THE MODERN SHELF (P) P. Larcombe and R. V. Ridd

A RAPID TRANSITION FROM WARM-WATER TO COOL-WATER CARBONATES IN THE UPPER ORDOVICIAN (CARADOCIAN) SECTION OF EASTERN NORTH AMERICA D. Lavoie

MISSISSIPPIAN COOL-WATER CARBONATE HYDROCARBON RESERVOIRS IN THE SOUTHERN FOOTHILLS OF THE CANADLVN ROCKY MOUNTAINS B. Mardndale and T. Boreen

THE NERITIC CARBONATE RECORD IN SOUTHERN AUSTRALIA: THE BIOGEOmSTORICAL FRAMEWORK B. McGowran, Q. Li and G. Moss

THE ORIGIN AND TIMING OF SIDERITE AND CALaTE CONCRETIONS IN EO-OLIGOCENE NON TO MARGINAL-MARINE FAOES OF THE TEKUITI GROUP, NEW ZEALAND (P) H. A. Moxham and C. S. Nelson

SOME PRELIMINARY OBSERVATIONS ON MARINE CEMENTS IN OLIZOMIOCENE SHELF LIMESTONES FROM NEW ZEALAND: AN ENIGMA OR THE NORM IN THE NONTROPICAL CARBONATE MODEL ? C. S. Nelson and N. P. James

BUIOAL DIAGENESIS OF SHALLOW-BURIED TERTIARY LIMESTONES, OTWAY BASIN, SOUTHEASTERN AUSTRALIA S. Nicolaides and M. W. Wallace

TEMPERATE-WATER DOLOMITE CEMENTED-CHIMNEYS FROM THE OUTER OTAGO CONTINENTAL SHELF, SOUTHERN NEW ZEALAND A. R. Oxpin

THE LEXINGTON LIMESTONE (LATE MIDDLE ORDOVICIAN) KENTUCKEY: A COOL WATER CARBONATE-CLASTIC RAMP IN A TECTONICALLY ACTIVE FORELAND BASIN M. C. Pope and J. F. Read

DISTRIBUTION AND SEDIMENTATION RATES OF BIOCLASTIC SAND ALONG THE COAST OF SOUTHERN NORWAY D. Ottesen and R. Boe

THE DERIVATION OF MASS TRANSPORT SEDIMENTS ON THE CONTINENTAL SLOPE OF THE OTWAY MARGIN, SOUTHEASTERN AUSTRALIA AND THE INFLUENCE OF SHALLOW-WATER SEDIMENTS V. Passlow

FAQES MODELS OF COOL TEMPERATURE SHELF CARBONATES, EASTERN TASMANIA, AUSTRALIA C. P. Rao and Z. Z. Amini

GLACIO-EUSTATIC CONTROL OF COQUINA TYPE AND SHELLBED STACKING ON QUATERNARY TEMPERATE SHELVES, NEW ZEALAND 0. Saul

FROM LIVING BRYOZOAN COMMUNITIES TO BRYOMOL DEPOSITS ON BOREAL-SUBARCTIC SHELVES OF THE NORTH ATLANTIC - AN ACTUALISTIC APPROACH P. Schafer and B. Bader

FAQES ANALYSIS OF A COOL-WATER CARBONATE FORMATION: THE OLIGOCENE-MIOCENE PORT VINCENT LIMESTONE, ST VINCENT BASIN - SOUTH AUSTRALIA B. Shubber, Y. Bone, B. McGowran and N. P. James 71 BRYOZOANS AS MAJOR COMPONENTS OF TEMPERATE CARBONATE SEDIMENTS A. M. Smith

SEDIMENTOLOGY OF CARBONATE MUD FROM A MODERN BACK-BARRIER LAGOON, LAKE REEVE, VICTOIUA (P) M. Smith and M. Wallace

I -

SEDIMENT BUNDLES IN THE TERTIARY OF TORQUAY, SOUTHWEST VICTORIA T. Van der Linden and P. J. Davies

SEDIMENTOLOGY AND GEOCHEMISTRY OF LATE PROTEROZOIC GLACUL-ASSOCIATED CAP DOLOMITES IN AUSTRALIA M. W. Wallace, M. Kennedy and C. Lavin

ELEMENTAL GEOCHEMISTRY OF NEW ZEALAND CENOZOIC LIMESTONES: A RECONNAISSANCE STUDY P. R. Winefield, C. S. Nelson and A. P. W. Hodder

A WINDOW ON THE PHYSICAL SEDIMENTOLOGY OF CARBONATES USING ENTROPY GROUPED LASER-DERIVED GRAINSIZE DATA (P) K. J. Woolfe

Temperate Shelf Carbonates, Torquay, Victoria K.Arai i, P.J.Davies2, K.Konishil, and R. Maas3 1. Kanazawa University, Kanazawa, Japan. 2. University of Sydney. NSW. 3. La Trobe University, Victoria.

This paper is a contribution arising from the joint research program of the Universities of Sydney and LaTrobe which is aimed at better understanding the relations between sedimentation and sealevel change in a section proposed as a classic sequence stratigraphic statement. Fifeteen detailed cliff sections have been measured over a 5.5km distance through the OligoMiocene Jan Juc Formation between Bells Beach and Bird Rock, to the southwest of Torquay, southern Victoria. Eight sedimentary facies have been defined from field and petrographic data. They are: glauconitic lag, cemented packstone, very fine packstone, glauconitic packstone, shell bed, fine packstone and heavily burrowed packstone. Their actual and inferred distribution are shown in Figure 1 and their detailed composition in Figure 2. Three sequence boundaries and a maximum flooding surface are inferred to occur within the sequence defined by Figure 1 (Reeckman and Partridge 1988) and have been assigned ages related to the 25.5Ma, 22.5 Ma and 21.0Ma eustatic sealevel shifts. However, Reeckman (in an unpublished manuscript) has changed these dates to 26.5Ma for the lower squence boundary and 25.5 Ma for the top sequnce boundary. Strontium dating has been conducted on twelve samples in a preliminary attempt to understand sediment/ process relationships. The dates are shown in Table 1. and with respect to dating, three points can be made: - dates on Glycimeris are internally more consistent than on Turritella. - the lower sequence boundary is consistently dated as older than 26.3Ma and may therefore define an event coincident with the proposed global eustatic low at 26.5ma. - two Glycimeris dates on the shell bed define its age as 25.7 and 25.8Ma. These are however at odds with the Turritella dates which indicate much older ages . In this paper, the Turritella dates are considered suspect. Assuming the Glycimeris dates are valid, a number of important conclusions alise. First, the time transgressive event up to the deposition of the shell bed was relatively rapid and deposited very littie sediment ie. a maximum of about 4m in the basin. Second, if the Bird Rock Cap defines another sequence boundary then it is most likely to equate with the proposed eustatic low of 25.5Ma. However, if this proves not be a sequence boundary, then the regressive section between the shell bed and the Pueblo Clay boundary is thicker than the transgressive and highstand section and formed in a much shorter period of time. This may say a great deal about the shape of the sealevel curve.

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Dead Man's Gully

Bell'sBeach r = f

6 7 8

9 10 11

x12

Fisherman's Steps

Bird Rock

Figure 1. Measured sections between Bell's Beach and Bird Rocks showing the fades variations determined from petrographlc studies. The positions of sequence boundaries previously defined by others are also shown.

glauconitic lag

facies A texture

packstone

structure grain component

fining upward burrows'.extensive

shell bed

facies E texture

packstone-grainstone

structure

fining upward SCS (section 1 &2)

grain component

grain size

gram size

gravel size skeletal within fine sand

granule-pebble

CaCOs content

50%

fades B texture

carbonate cemented

pgpkstpn^ packstone

structure grain component

massive burrows ;rare

66%

facies F

fine packstone

texture

packstone

structure

burrows;common

grain component

grain size

fine-very fine

fine plank, foram.

CaC03 content

CaCOa content

64%

-88%

facies C texture

very fine packstone -

miidMnnft packstone

structure

burrowsicommon

, grain component

facies G

heavily burrowed packstone

texture

structure

bent, foram. y

bivalves

packstone gastropods

burrows ;extensive

grain component scaphopods grain size

grain size

very fine-silt

fine

CaC03 content

56%

fades D

glauconitic packstone

texture

packstone

structure grain component

parallel lamina burrows;common

CaC03 content

58%

bryozoa

algae

echinoderms

1 I

others

terrigenous glauconite

grain size fine-medium

brown glauconite

CaC03 content

55%

Figure 2. Principal facies types, texlural character and component variation in the measured sections between Bell's Beach and Bird Rock.

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Table 1 Sr isotope data and "seawater curve" ages for Otway shells sample

87sr/86srj^

TS0701

0.708131±12

TS0702

0.708153±10*

TSllOl .

0.708185114

TS1102

^'^Sr/S^Sm-H

8SW age (Ma)

^^Sr/^^Sin-M 5SW

age (Ma)

0.708102

-154.5

27.3

0.708022

-105.1

26.3

0.708124

-151.4

26.5/26.7" 0.708044

-102.9

25.7

0.708098

-155.1

27.4

0.708018

-105.5

26.4

0.708206±10»

0.708119

-152.1

26.7

0.708039

-103.4

25.8

TS1301

0.708094120

0.708065

-159.8

28.6

0.707985

-108.8

27.2

TS1303

0.708182116

0.708095

-155.5

27.5

0.708016

-105.7

26.5

TS1401A

0.708028122

0.707999

-169.1

30.9

0.707919

-115.4

28.7

TS1401B

0.707996115

0.707967

-173.6

32.0

0.707887

-118.6

29.6

TS1401C

0.707994116

0.707965

-173.9

32.1

0.707885

-118.8

29.7

TS1402

0.708064110*

0.708066

-159.6

28.5

0.707986

-108.7

27.2

TS1403

0.708075110*

0.707988

-170.6

31.3

0.707908

-116.5

29.1

TS1404

0.707907115

0.707908

-181.9

34.1

0.707829

-124.4

31.3

• average of 2 separate runs of the same sample load or same Sr fraction ^ second age of 26.7 Ma derived from a second regression line (for the late Oligocene) given in Hess et al. (1989). Subscripts: m = measured; n-H =rcnormalizedHess el al.; n-M = renormalized Mobil OU. ^ ^ ratios have been corrected for mass fractionation using law.

using a linear

ratios are adjusted for machine bias from session to session using data for standard Sr

SRM987. "Seawater" ages have total errors of - d l m.y..

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Carbonate Deposition of the Seaspray Group in the offshore Gippsland Basin Thomas Bemecker School of Earth Sciences, The University of Melbourne ParkviUe VIC 3052

John A. Webb and Alan D. Partridge School of Earth Sciences, La Trobe University Bundoora VIC 3083 Oligocene to Recent carbonates of the Seaspray Group form the major regional seal to the giant oil and gas fields of the Gippsland Basin hydrocarbon province. Although the biostratigraphy of the ^oup has been extensively studied using planktonic foraminifera, surprisingly little work has been done on the lithological variations within the sequence. In the onshore part of the Gippsland Basin the Seaspray Group is divided into two formations: Lakes Entrance Formation and overlying Gippsland Limestone. The Lakes Entrance Formation consists of a lower sandy portion which is glauconitic in places, as well as an upper marl sequence. The Gippsland Limestone comprises a basal marl which grades into a thick limestone unit at the top. However, in the offshore basin both formations consist predominantly of marls, and have proved impossible to separate lithologically. Using drill cores from several wells in the central deep region of the offshore basin, new studies of the petrology and ostracod faunas have been carried out, supported by a synthesis of the foraminiferal data with the electric logs. This has led to the recognition that the Seaspray Group in the central deep can be subdivided into four lithological units. Through the Oligocene and most of the Early Miocene, marls (average 38% CaCOs) were deposited at very low depositional rates (10-40 mJMa) in water depths suggesting lower continental slope environments. Deposition was largely hemipelagic, under dysaerobic, presumably stagnant, deep water conditions. The bioclasts (mosdy planktonic forams) and pore-filling calcite cements are predominantiy composed of ferroan calcite, indicating that the pore waters were reducing. Across a regional but fairly subtie log marker in the late Early Miocene the sediments change to clay-rich wackestones to mudstones (av. 47% CaCOs) containing fine bioclastic debris representing a diverse fauna of planktonic and benthonic forams, as well as ostracods. Deposition probably occurred on the continental slope, largely from dilute fine-grained turbidity flows. This is supported by the marked increase in depositional rates to a maximum of about 180m/Ma. The diverse benthic fauna shows that the sea floor water was oxygenated; however the bioclasts and calcite cement are mostly ferroan. This indicates that the pore waters became reducing immediately after burial, due to the presence of finely dispersed organic material in the clay matrix. During the Middle Miocene a period of major channelling or submarine canyon formation commenced. Sediments filling these channels are wackestones/ packstones with very abundant bioclastic debris which is coarser than in the underlying unit, and contains bryozoan and echinoid fragments in addition to a diverse microfossil assemblage of forams and ostracods. Deposition probably occurred on the outer part of the continental shelf. The sea floor was well

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oxygenated, as shown by the diverse benthic fauna and non-ferroan calcite of both bioclasts and cement infills. The sediments are overall matrix-poor, probably reflecting periodic reworking by storm action. Average carbonate content is 48% whilst depositional rates are up to 250m/Ma. The period of channelling ended in the central part of the offshore basin at the beginning of the Late Miocene. The sediments from the Late Miocene to Recent succession were studied in less detail than the underlying strata. They comprise packstones and wackestones containing coarse bioclasts, mostly bryozoans, deposited mostly on the inner to mid shelf. Depositional rates fell below a maximum of lOOm/Ma except for the outermost shelf and continental slope. The present study has also shown that there is a marked difference between distinctly off-shore sediments, as described above from the central deep, and relatively near-shore sediments, typified by the cores from Barracouta-l well, which encountered Seaspray Group sediments with shallow marine affinities. Poorly fossiliferous outer shelf mudstones at the base are overlain by coarsegrained quartzose packstones/ grainstones containing large bryozoan f r a ^ e n t s . These are succeeded by bioclastic wackestones and packstones characterised by abundant skeletal grains as well as a high clay content. Bioclasts are derived from a relatively diverse fauna of forams, bryozoans, bivalves and ostracods. In Barracouta-l the high proportion of relatively intact skeletal grains indicates accumulation on a shallow shelf that was affected by episodic storm events. The prominent proportion of granule-sized quartz grains gives evidence that specific intervals were strongly influenced by terrigenous material. The Seaspray Group, whose sediments vBiy from 30% to 50% carbonate content, represents approximately 10,000 cubic kilometres of carbonate. There was an increase from low rates of deposition in the Oligocene to a peak in the Middle Miocene, corresponding to a substantial increase in the rates of carbonate production coupled with a transgressive maximum within the Gippsland Basin. This was probably related to changes in the oceanic environment and circulation impacting on the Gippsland Basin, as well as worldwide variations in palaeotemperatures. The authors gratefully acknowledge the financial support and access to data provided by MIM Petroleum Exploration Pty, Ltd, and ESSO Australia,

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Comparison of the Geochemistry of Cool-water Corals, Coralline Algae and Bryozoans from the Lacepede Shelf, South Australia with their Warm Water Counterparts HOSSAIN RAHMPOUR BONAB; YVONNE BONE; REZA MOUSSAVI-HARAMI AND KEITH TURNBULL Department of Geology and Geophysics, University of Adelaide, South Australia 5005 Many modem continental shelves are areas of carbonate-rich fauna and floral growth and subsequent sediment accumulation. These carbonate depositional environments can be subdivided into three major zones: (1) tropical/warm-water; (2) temperate/cool-water and (3) polar/cold water. Until recently research has been focused on the tropical environment, particularly in regard to the geochemistry and biomineralisation of Uving organisms. Our research has focused on the temperate environment. We have selected 45 samples of corals, coralline algae and bryozoans from dredged bottom samples from the Lacepede Shelf, South Australia. The skeletal fragments were analysed for mineralogy, oxygen and carbon isotopes, major, minor and trace elements. The isotope values of the ahermatypic corals show completely different values to mean isotopic values of their tropical counterparts. They are mostly in equilibrium with their environment in terms of S igO but not for ^13C i.e., there is a depletion for ^BC. Oxygen isotopic values of the coralline algae in the temperate environment show marked divergence from their tropical counterparts, with the former having ^180 values similar to the mean values for sea-water, and the latter showing a marked depletion. In the case of coralline algal carbon isotope values, samples from both areas show depletion, but this depletion is greater in the case of the tropical examples. Similarly, comparisons of the mean isotope values for bryozoans in tropical and temperate environments indicate that the bryozoans in cool-water are in almost complete isotopic equilibrium with their ambient sea-water, whereas the warm-water counterparts are depleted in S BC and are near equilibrium for S igO. This study shows that carbon isotope disequilibrium of carbonate-rich biota is of greater magnitude than is oxygen isotopic disequilibrium. Furthermore, our analyses show that isotopic ratios for similar organisms are quite differentfromone environment to another. Even more importantly, our research has shown that diverse organisms that live in the same environment may have dissimilar isotope values. This can be ascribed to a process termed the "vital effect" i.e. metabolic processes of individual species. In addition, even examples of the same species can have different isotope values when collected from different sites, e.g. the bryozoan Adeona sp., from different sites/depths. This difference may be related to extrinsic factors such as water depth, salinity, temperature, water

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turbidity, substrate, oxygen levels, etc. Our analyses show that those organisms with aragonitic mineralogy, such as corals and some bryozoans, have higher Sr and lower Mg concentrations than organisms with calcitic mineralogy, e.g. coralhne algae. On the other hand, the concentration of Fe and Mn is higher in the coralline algae than it is in the corals and the bryozoans. These differences may be a function of various combinations of the following processes: (a) discrimination of the mineralogy against some trace elements; (b) the skeletal formation process; (c) environmental variables such as temperature and (d) the physiology of the organism. In sununary, it can be concluded that the geochemistry and biomineralisation of cool-water carbonate fauna and flora show major differences to those of their warm-water counterparts.

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Cool-water Bryozoa and Stable Isotopes Yvonne Bone^ and Noel P. James^ ^Dept. of Geology and Geophysics, University of Adelaide, South Australia, 5005 ^Dept. of Geological Sciences, Queens University, Kingston, Ontario, K7L 3N6, Canada Introduction Our understanding of the formation of modem carbonate sediments in cool-water, open-shelf environments has advanced rapidly over the last few decades, with many of the studies taking place in New Zealand (Carter et al. 1985; Nelson ei al. 1981, 1988;) and along the southern margin of Australia (Connolly & von der Borch 1967; Wass et al. 1970; Marshall andDavies 1978; Collins, L. 1988; James et al. 1992 and references therein), the world's largest province of this type. These studies have enhanced our understanding of the bryozoan-rich Tertiary limestones in the Cenozoic Basins that are contiguous with the modem platform (James and Bone, 1991,1992; Boreen and James, 1993; James et al. 1994) and also allowed for extrapolations to be made even further back into the geological record (James and Bone, 1989). These modem sediments are dominated by bryozoans, molluscs and quanz particles, with a broad spectrum of associated accessory foraminifera, calcareous and siliceous invertebrates, calcareous algae and relict calcareous lithoclasts. Notwithstanding this variety, it is the bryozoans that the observer intuitively "sees" as the dominant roleplayer in the formation of any resultant limestone. This role of bryozoans as carbonate sediment producers has been addressed by Bone and James (1993) by looking at biyozoan colonies in terms of architectural shape. This is an artificial classification and is related more to ecology than phylogeny. It is an extended simplification of the scheme erected by Nelson et al. (1988), and takes bryozoans out of a morass of confusing terminology into a "user-friendly" scheme. It was found that bryozoans on the Lacepede Shelf, southem Australia could be divided, simplistically, into 9 morphotypes:- the erect rigid forms - (1) fenestrate, (2) foliose, (3) flat, robust, branching and (4) delicate, branching; the erect flexible forms - (5) articulated, branching and (6) articulated zooidal; and the generalised forms - (7) encmsting, (8) nodular/arborescent and (9) vagrant. The skeletal biogeochemistry of living and dead calcareous invertebrates is a web of complex extrinsic and intrinsic interactions e.g. sea-water temperature and composition in the case of the former, and vital affects controlling skeletal mineralogy in the latter. Bryozoans secrete their skeletal elements from either low Mg-calcite, intermediate Mgcalcite or aragonite, or from a regulated mix of these carbonates (Rucker 1968; Bone and James 1993). There is, however, a general tendency for constant mineralogy within each of the morphotypes, irrespective of taxonomic level. This gross generalisation has a number of exceptions, which are more of interest to paleontologists but which may also be critical to the geochemist e.g. Adeonellopsis sulcata . Stable Isotope Studies Forester et al. (1973), following on from the work of Urey et al. (1951), have shown that cheilostome bryozoans secrete their calcareous skeletons in isotopic equilibrium with sea-water and conclude that this implies that bryozoans could, therefore, be used for paleotemperature determinations. This would be advantageous in view of the ubiquity of bryozoans vs the frequent paucity of brachiopods in cool-water sediments. In this study, 97 bryozoan samples, representing 7 growth forms, were selected from bottom samples from 22 sites, obtained during CSIRO RV Franklin cruises FR3/89 and FR2/91. Their mineralogical and isotopic composition were determined by

Cool Climate Carbonate Conference (Page 9) Geelong 1994

standard X-ray diffraction (XRD) and stable isotope ratio analysis techniques. Representative samples were observed under cathodoluminescence (CL) and stained with Clayton Yellow in order to determine the exact location of different mineralogical features. In order to test whether there was significant species-specific vanation within growth form, 15 common species were selected and 43 samples from 4 sites were then analysed. Concurrendy, 98 brachiopods from 36 sites were analysed for comparative purposes. The affect of different sample preparation techniques was also investigated (treatment with Chlorox™ for different periods of time and at different strengths; different sample weights). The bryozoan samples, complete colonies or fragments of colonies, were examined under the binocular microscope to (a) determine their morphotype, (b) ensure that they were not encrusted by other organisms, including other bryozoans, (c) did not contmn contaminants within pore spaces, (d) did not have an undue number of kenozooids present, (e) determine whether they were living, recendy dead (white) or relict (brown) and (f) determine whether there was any other reason for discarding them as suitable samples for analysis. Results (1) There is sufficient variability in isotope values between ôwth forms to mask any value in their applicability for paleoenvironmental studies, if all results are plotted together. (2) Individual bryozoan growth forms show similar ^^C values with <l,0%c variation, regardless of sample site. Aragonitic flat, robust branching forms show up to l,5%c variation except for Adeonellopsis sulcata, which is bimineralic. (3) The iÔ values vary in response to water depth, which is in reality a proxy for water temperature. There is a consistent ^Ô enrichment with increased depth i.e. as temperature decreases. Actual XBT (expendable bathy-thermograph) recordings support calculated temperatures from brachiopod and intermediate-Mg calcite bryozoans. (4) The i^C content is species controlled, with <0.3%o difference in 14 of the 15 species analysed. The exception is Caleshara denticulata, with 0J%o range. (5) Aragonitic bryozoans are enriched and low-Mg calcite cyclostomes are depleted in i^C and to a lesser extent, ^Ô relative to brachiopod values. (6) The articulated branching cellarids, Cellaria rigida and Cellaria tenuirostris , which are often dominant in both modem sediments and Tertiary limestones, give values with no significant difference to co-existing brachiopods. (7) All samples should be treated with 1:10 strength Chlorox™ for 30 minutes, washed thoroughly in de-ionised water, filtered and dried, prior to analysis. Sample weights should not be <10 mgm. Conclusions Bryozoans are suitable for stable isotope analyses for paleoenvironmental studies. There is no significant difference from values obtained from co-existing brachiopods and individual growth forms (with minor exceptions e.g. articulated zooidal). Plots including all growth forms extend the positive and negative ranges of both isotopes and thus mask information. Aragonitic mineralogy accounts for isotope enrichment and low-Mg calcite for depletion. Acknowledgments This research is funded by the Australian research council and the Natural Sciences and Engineering Research Council of Canada. We thank CSIRO Division of Oceano^phy and the Captains and crews of RV Franklin. C. Bone laboured tirelessly in the laboratory in the early years. S. Hageman identified the bryozoan species and A. Mazzoleni and C. Staples "picked" in the recent developments.

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References Bone, Y. and James, N.P., 1993: Bryozoans as carbonate sediment producers, Lacepede Shelf, southern Australia. Sedimentary Geology, 86, pp. 247-271. Boreen, T.D. and James, N.P., 1993: Holocene sediment dynamics on a cool-water carbonate shelf: Otway, southeastern Australia. Journal Sedimentary Petrology, 63, pp. 574-588. Carter, R.M., Carter, L., Williams, J.J. and Landis, C.A., 1985: Modem and relict sedimentation on the South Otago continental shelf, New Zealand. Memoirs N.Z. Oceanographic Institute, 93, 43p. Collins, L., 1988: Sediments and history of the Rottnest Shelf, southwest Australia: a swelldominated, non-tropical carbonate margin. Sedimentary Geology, 60, pp. 15-49. Connolly, J.R. and von der Borch, C.C., 1967: Sedimentation and physiography of the sea floor south of Australia. Sedimentary Geology, 1, pp. 181-220. Forester, R.M., Sandberg, P.A. and Anderson, T.F., 1973: Isotopic variation of cheilostome bryozoan skeletons. In, G.P.Larwood (ed.) Living and fossil Bryozoa: Recent advances in research. Academic Press, London, pp-79-94. James, N.P. and Bone, Y., 1989: Diagenesis of Cenozoic, temperate water calcarenites. South Australia: a model for the meteoric/shallow burial alteration of Phanerozoic calcitic sediments. Journal of Sedimentary Geology, 59, pp. 191-203. James, N.P. and Bone, Y., 1991: Origin of a cool-water, Oligo-Miocene deep shelf limestone, Eucla Platform, southern Australia. Sedimentology, 38, pp. 323341. James, N.P. and Bone, Y., 1992: Synsedimentary cemented calcarenite layers in Oligo- Miocene cool water shelf limestones, Eucla Platform, southern Australia. Journal of Sedimentary Geology, 62, pp. 860-872. James, N.P., Bone, Y., von der Borch, C.C. and Gostin, V.A., 1992: Modern carbonate and terrigenous clastic sediments on a cool water, high energy, midlatitude shelf, Lacepede Shelf, southern Australia. Sedimentology, 39, pp. 877-903. James, N.P., Boreen, T.D., Bone, Y. and Feary, D., 1994: Holocene carbonate sedimentation on the west Eucla Shelf, Great Australian Bight: a shaved shelf. Sedimentary Geology, 90, pp. 161-177. Marshall, J.F. and Davies, P.J., 1978: Skeletal carbonate variation on the continental shelf of eastern Australia. Australian Bureau of Mineral Resources, J. Geology and Geophysics, 3, pp. 85-92. Nelson, C.S., Hancock, G.E. and Kamp, P.J.J., 1981: Shelf to basin, temperate skeletal carbonate sediments. Three Kings Plateau, New Zealand. Journal Sedimentary Petrology, 52, pp. 717-732. Nelson, C.S., Hyden, F.M., Keane, S.L., Leask, W.L. and Gordon, D.P., 1988: Application of bryozoan zooarial growth-form studies in facies analysis of nontropical carbonate deposits in New Zealand. Sedimentary Geology, 60, pp. 301-322. Rucker, J.B., 1968: Skeletal mineralogy of cheilostome Bryozoa. In, E.Annoscia (ed.) Proceedings of the First International Conference on Bryozoa, Atti. soc. ital. Sci. nat. 108, pp. 101-110. Urey, H.C., Lowenstam, H.A., Epstein, S. and McKinney, C,R., 1951: Measurements of paleotemperatures and temperatures of the Upper Cretaceous of England, Denmark and the southeastern United States. Geological Society of America Bulletin, 62, pp. 399-416. Wass, R.E., Connolly, J.R. and Macintyre, R.J., 1970: Bryozoan carbonate sand continuous along southern Australia. Marine Geology, 9, pp. 63-73.

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Stratigraphic Principles and Patterns of Cool-Water Carbonate Deposition: Tertiary Limestones, SE Australia Thomas D. Boreenl & Noel P. James^ 1 Home Oil Company Limited, Calgary, Alberta T2P 2Z5 Canada 2 Queen's University, Kingston, Ontario K7L 3N6 Canada Mid-Tertiary limestones, exposed as sea cliffs along the coast of Victoria, southeastern Australia, accumulated on the inner part of a cool-water, distally steepened ramp or open shelf. All sediments are bioclastic, dominated by particles of bryozoans, echinoderms, benthic foraminifers, brachiopods, and molluscs. Shallow, grainy facies also contain coralline algae, quartz, and glauconite while deep, muddy facies include ahermatypic corals, ostracodes, sponge spicules, planktic foraminifers, and terrigenous clays.

Stratigraphic Sedimentology The fundamental depositional unit is a meter-scale, subtidal cycle or rhythm (Figure 1). Shallow-shelf cycles are shallowing-upward, cross-bedded or burrowed grainstone capped by a marine-cemented hardground or quartz-granule lag while mid-shelf cycles are upward-coarsening and thickening, proximal to distal tempestites. Such cycles are interpreted to form by eustatically driven, climatically controlled oscillations in abrasion wave base and swell wave base. Deep shelf rhythms are interbedded bryozoan marl and calcareous clay, thought to be generated by climatically influenced fluctuations in carbonate productivity and terrigenous dilution. Lowstand systems tracts are depositional or erosional. Sequence boundaries are complex, multigeneration, mostly submarine surfaces (condensed cycle boundaries) that can be traced offshore into multiple omission surfaces and conformable contacts. Basinward facies shifts result in deposition of condensed lowstand wedges of stacked, shallowing-upward grainstone cycles. Transgressive systems tracts are thick bryozoan marl-calcareous clay rhythms associated with facies backstepping and abrupt deepening. Such rhythmites typically grade stratigraphically upward into tempestite cycles. Highstand systems tracts are highly progradational, wedge-shaped rock bodies of shallowing-upward grainy cycles. Dissimilarity in the relationship between thickness, duration, and accumulation rates of Holocene and Tertiary sediments points convincingly to cumulative nondeposition, erosion, and regional subsidence as important controls on long term net accumulation. On such bioclastic carbonate ramps autogenic factors such as the presence of broad facies belts, complex loose sediment mosaics, spatially variable and discontinuous hardgrounds, and energetic bottom currents cause a propensity for missed-beat, welded, and partially eroded cycles and makes preservation of complete Milankovitch pattems unlikely.

Sequence Stratigraphic Principles in Cool-water Bioclastic Systems Fundamental principles goveming the packaging of sediments in high-energy bioclastic systems have come to light on the basis of recent oceanographic work in the southern ocean (Von Der Borch et al 1970; Wass et al 1970; Davies and Marshall 1973; Collins 1988; Nelson 1988; Exon et al 1992; James et al 1992; Boreen and James 1993; Feary et al 1993) and analysis of onshore Australian Tertiary successions (Abele 1979; Reeckmann 1979; James and Bone 1991; Reeckmann 1994; Boreen and James in press). 1) Nearshore Nondeposition - On modem continental shelves of the southern ocean fair-weather wave base is at water depths of 100-130m. At the shallowest end of the fair-weather wave reworking zone, between the coast and 50 m depth, extreme wave and current energies form a nearshore zone of particle abrasion, nondeposition, and condensed sedimentation (Collins 1988; James and Bone 1991). Stratigraphic implication: Movement of the nearshore nondepositional zone offshore during falls of relative sea level can produce marine "condensed" sections that occur at the top of highstand systems tracts or that are syngenetic with lowstand wedge development. In such instances it is the shallowest relative sea level and the highest energy setting that creates the condensed section, not transgressive drowning as traditionally viewed. Cycle-capping hardgrounds, abrupt contacts between open marine and nearshore sediments, and complex lowstand and flooding surfaces can result.

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2) Deep-Water Sediment Supply - Aphotic carbonate producers, gentle shelf gradients, and mobile facies belts provide the potential for sediment production and accumulation through all phases of the sea level cycle (Boreen and James, 1993). Stratigraphic implication: Unlike tropical carbonate and siliciclastic depositional systems, which have highly variable sediment input at different points on the eustatic cycle, temperate-water bioclastic systems are steady-state and inherently prone to large scale platform progradation. This can produce highly-variable systems tract responses depending upon the rate of relative sea level fluctuation. 3) Caldte Mineralogy - Unlike tropical carbonates, which tend to have a large percentage of aragonitic components, sediments in cool-water carbonate systems are calcite-dominated and therefore relatively nonreactive. Stratigraphic implication: Lack of a strong vadose signature makes detection of lowstand exposure surfaces difficult. Rapid armoring in the meteoric environment does not take place (except for calcrete formation) and as a result loose sediment is susceptible to erosion, stripping, and reworking during subsequent sea-levelfluctuations(e.g., ravinement). 4) Deep-Water Grainstones - On the modern south Australian shelf cross-bedded, bioclastic grainstones are present at depths between 50 and 130 m (Collins 1988; James et al 1992). High-energy swell and storm waves give the bed forms a straight-crested ripple morphology, but superimposed geostrophic and oceanic currents, and coarse grain sizes contribute to internal "current-formed" stratification more typically associated with high-energy, shallow-water settings. Stratigraphic implication: Cross-bedded grainstones in the Tertiary sections described here have previously been interpreted as shoreface sands. Based on analogy with the modem south Australian offshore setting, it is more likely that the sediments were deposited at open shelf depths a considerable distance from the coeval shoreline. Misinterpretation of such cross-bedded grainstone deposits can significantly affect the reconstruction of paleoenvironmental models, determination of coastal onlap curves and estimation of the magnitude of paleo-sea-level fluctuations. The Tertiary limestones of southern Australia provide the critical link of stratigraphy between modem cool-water carbonate shelf deposits and the older Mesozoic and Paleozoic record of similar sediments. ABELE, C (1979) Geology of the Anglesea area, central coastal Victoria: Geological Survey of Victoria Memoir 31, 71 p. BOREEN, T.B. & JAMES, N.P. (1993) Holocene sediment dynamics on a cool-water carbonate platform: Otway, southeastem Australia: Joumal of Sedimentary Petrology, v. 63,574-588. BOREEN, T.B. & JAMES, N.P. (in press) Stratigraphic sedimentology of Tertiary cool-water limestones, SE Australia: Joumal of Sedimentary Petrology, 16 p. COLLINS, L.B. (1988) Sediments and history of the Rottnest Shelf, southwest Australia: a swelldominated, non-tropical carbonate margin: Sedimentary Geology, v. 60, 15-49. DAVIES, P.J. & MARSHALL, J.F. (1973) BMR Marine Geology cruise in Bass Strait and Tasmanian waters - Febmary to May, 1973. Record 1973/134, 9 p. EXON, N.G., LEE, C.S., FELTON, E.A., HEGGIE, D., MCKIRDY, D., PENNEY, C., SHAFIK, S., STEPHENSON, A. & WILSON, C. (1992) BMR Cruise 67: Otway Basin and west Tasmania sampling: Australia, Bureau of Mineral Resources, Report 306, 171 p. FEARY, D.A. et al (1993) Geological sampling in the Great Australian Bight, scientific post-cruise report, R.V. Rig Seismic Cruise 102. Australian Geological Survey Organization, Rec. 1993/18, 140 p. JAMES, N.P, & BONE, Y. (1991) Origin of a cool water, Ohg-Miocene deep shelf limestone, Bucla Platform, southern Australia: Sedimentology, v.38, 323-341. JAMES, N.P., BONE, Y., VON DER BORCH, C.C. & GOSTIN, V.A. (1992) Modem carbonate and terrigenous clastic sediments on a cool-water, high-energy, mid-latitude shelf; Lacepede, southern Australia: Sedimentology, v. 39, 877-903. NELSON, C.S., KEANE, S.L. & HEAD, P.S. (1988) Non-tropical carbonate deposits on the modem New 2^aland shelf: Sedimentary Geology, v. 60, 71-94. REECKMANN, S.A. (1979) Detailed stratigraphy of the Tertiary sequence: Torquay, Victoria - facies, environment and diagenesis [unpublished Ph.D. thesis] University of Melboume, 318 p. REECKMANN, S.A. (1994) Geology of the on-shore Torquay sub-basin: A sequence stratigraphic approach; NGMA/PESA Otway Basin Symposium, Melboume, Extended Abstracts, Australian Geological Survey Organization Record 1994/14, 3-6. VON DER BORCH, C.C., CONOLLY, J.R. & DIETZ, R.S. (1970) Sedimentation and stmcture of the continental margin in the vicinity of the Otway Basin, southern Australia: Marine Geology, v. 8,59-83. WASS, R.E., CONOLLY, J.R. & MACINTYRE, R.J. (1970) Bryozoan carbonate sand continuous along southem Australia: Marine Geology, v. 9, 63-73.

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SUBTIDAL CYCLES & RHYTHMS Iron-Stained

*AII cycles 1 -7 m thick

Hardground/Firmground " " ^ n r ^ Hard Thallasinoides ( Soft

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H.C.S.

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Pecten Bivalve

N (n "D 0)

Cross-bedded Grainstone

! l

Coarse bryozoan mollusc quartz grainstone

11 CO

CROSS-BEDDED GRAINSTONE CYCLES •Oft

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a)< SOC

Burrowed Grainstone & Minor HQS

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•oQ-

Cross-bedded Bryozoan Serpulid Grainstone

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OiU TD-J > 9 (^S

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BURROWED GRAINSTONEPACKSTONE CYCLES

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W Q.

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Figure 1. - Characterisitics and interpretations of metre-scale, subtidal cycles and rhythms in Tertiary strata from southeastern Australia (legend at upper left).

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Late Palaeozoic Cold-water Carbonates from Eastern Tasmania - Depositional Environments Jonathan K. Brooker and Ken J. Woolfe The Basal Beds are the oldest and most varied unit of the Late Palaeozoic Parmeener Supergroup exposed at Fossil Bay, Maria Island, eastern Tasmania. The sequence was deposited at palaeolatitudes of approximately 80® during the Gondwana Glaciation. Their upper part consists of fossiliferous and barren siltstone, diamictite, recrystallised limestone and shell beds. The sequence represents some of the best exposures of mixed glaciogenic and coldwater carbonates so far described from Australia. Facies architecture and lithofacies associations provide a record of both sea-level variations and changes in ice margin proximity. All of the units contain considerable ice-rafted debris (IRD), suggestive of a continuous proximal ice cover. The shell beds are unique in their ultra bundance of shells coupled with low taxonomic diversity (mostly brachiopods and pelecypods). The shells are abnormally large and thick (as large as 20 cm across and 5 cm thick). Bedding generally occurs on a decimetreto submetre-scale possibly indicating relatively low sedimentation rates. At this stage, limestone and diamictite (waterlain till or ultraproximal) facies are interpreted as glacial deposits whereas the shell beds and siltstones are inferred to be interglacial deposit with significant IRD. The absence of sedimentary structures other than wavy bed contacts implies restricted influence from waves, possibly suggestive of continous ice cover. Grain-size determinations using forward laser diffraction where carried out on carbonate-free residuals. Samples were digested in 10% HCI and ultrasonically dispersed in up water prior to analysis. Data was collected in 32 bins covering the 4 to 2000 micron size fractions. Entropy analysis of the resultant data matrix was then used to group the samples into minimum relative entropy clusters. These groupings (clusters) are then used to interpret process changes associated with variations in water depth and ice cover.

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Omission surfaces defining cyclicity in the Tertiary section of Torquay Benjamin Buchbinderl, Therese Van der Linden^, and Peter J. Davies 2 1. Geological Survey of Israel, Jerusalem, Israel. 2. University of Sydney, NSW. Abstract A continuous core taken from a drill hole 500 m south of Dead Mans Gully (Site # 9, 69.5 m depth ) consists of burrowed silty mudstones of Puebla Clay, grainstones of transitional Point Addis-Jan Juc sediments, calcareous sandy mudstones of the Angahook Formation and the uppermost 2.5 metres of Anglesea Sand. Specifically, the section is chai'acterised by surfaces or discontinuities defining the tops of metre scale cycles. The following surface types have been recognised (1) burrowed omission surfaces. (2) carbonate cemented omission surfaces (3) Feoxide cemented omission surfaces, (4) lithified omission surfaces lacking obvious erosion and burrowing features and (5) surfaces defined only by changes in lithology or grain size, but without a distinct omission surface. Most cycles are topped by a pronounced omission surfaces with large Thallassinoides burrows. Their outlines are accentuated by clear differences between the lithology of the host rock and that of the burrow fillings. The omission stage may be accompanied by varying (unknown) degrees of erosion and by initial compaction resulting in a firm-ground stage. Cementation may or may not follow. The Thallasinoides burrows are commonly filled with glauconitic sediments deposited when sedimentation resumed at the onset of the successive cycle. When an omission stage is accompanied by cementation, hardgrounds are formed. Reeckmann (1988, p. 213), attributes the hard layers in the temperate shelf carbonates of southeastern Australia to cementation by groundwater during periods of subaerial exposure. We agree that this is correct for the unconformity surface separating the lower and upper Point Addis Limestone (Reeckmann, 1979). However, we find that most other hardgrounds in the Tertiary section of Site 9 do not show evidence of subaerial exposure. Cementation of these other surfaces include poorly developed fringe isopachous cements, epitaxial growth on echinoderm grains and spaiTy calcite. The presence of sparry calcite cement by itself, is not necessaiily evidence for meteoric cementation. The origin of most of the hardgrounds could therefore be submarine. Hardground surfaces are typically common, but not restricted, to the Point Addis-Jan Juc transitional sediments. Omission surfaces free of hardgrounds are found in the siliciclastic sediments of the Puebla Clay and the Angahook Formation.

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Sea-level as a control on carbonate factories R.M. Carter Department of Earth Sciences James Cook University Townsville, Q.4811 One of the more unfortunate habits that bedevils sedimentology is that of classifying practitioners as either •'carbonate*' or •'clastic'* sedimentologists. Worse, within carbonate sedimentology an additional dichotomy into "tropical" and "cold-temperate" has emerged. Persons sometimes usesuch badges as an excuse for a lack of knowledge in their nonfavoured area. Leaving aside flocculation, all sedimentary grains above c.7 microns in size behave as clastic grains at the seafloor, irrespective of their mineralogy (and thus density). Which types and mixtures of carbonate or terrigenous facies are developed in a sedimentary sequence is a function of contemporary climate, geography (including tectonic setting) and sea-level, rather than mineralogically controlled. Climate operates both as an influence of rate of terrigenous supply (low in arid regions) and of type of carbonate material (coral-algal in the tropics, bryozoan-brachiopod-molluscan outside the tropics). Geography is important in controlling the delivery and deposition of terrigenous sediment (e.g. low to absent on offshore plateaus). And the position of 'sea-level* is a fundamental control on the location and extent of both carbonate factories and terrigenous sources.

Sea-level cycles produce different sedimentary responses in tropical and non-tropical regions. In the tropics, a sea-level high causes bank-top flooding and the initiation of active carbonate production and progradational shedding over a wide area of continental shelf. Conversely, a lowstand coincides with greatly reduced areas of carbonate production, a relative decline in carbonate supply, anddirect shedding of terrigenous sediment onto the slope and beyond. Outside the tropics, a high sea-level produces terrigenous sediment starvation over much of the continental shelf, thus stimulatingnon-tropical carbonate production. Many sedimentary sequences, whether tropical or non-tropical in origin, display major terrigenous and carbonate facies belts which shift, and hence interfinger, in response to sea-level changes. The mixed carbonate-terrigenous facies of the Great Barrier Reef shelf (tropical) will be compared and contrasted with carbonate-terrigenous facies developed within Pleistocene cyclothems from New Zealand (non-tropical). The correct interpretation of these and other ancient sequences has to be based on an appreciation of the principles of sequence stratigraphy, and an understanding of the whole spectrum of terrigenous and carbonate marine sediment facies.

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Sequence Stratigraphic significance of Pleistocene and Recent cool-water Carbonates from New Zealand Carter, R.M., Gammon, P., Orpin, A.R. & Saul, G. Department of Geology James Cook University Townsville Q'ld. 4811 Cool-water carbonate sediments occur in a variety of settings on the modem New Zealand shelf. In paralic and shoreline environments, shell hash accumulates in estuarine bars, channels and beaches, at high and low tide on ocean beaches, and as aprons adjacent to rocky shores or shoals. These inshore faunas are strongly affected by tide and wave-driven currents, and are dominated by mollusca. In nud-outer shelf environments, outside the shore-connected wedge of terrigenous sediment, and outside shelf mud depocentres, in situ shell hash accumulates as a widespread, thin (starved) sediment blanket. Sediment sorting is often poor, shell breakage is mostly of biogenic origin and in the absence of pervasive bioturbation - shells may be preserved in life position; faunas are dominated by molluscs, bryozoans and brachiopods, including the cold-water scallop Zygochlamys delicatula. Finally, oyster shellbeds (Tiostrea chilensis) occur in a wide variety of settingsfromparalic to mid-outer shelf Similar faunas and sediment facies are represented by coquina limestones and mid-cycle shellbeds (MCS) within uplifted, little-deformed, cyclothemic, Plio-Pleistocene sediments on the New Zealand mainland. Pliocene sediments mclude a barnacle-dominated coquina type (Te Aute Limestone facies) which accumulated around offshore rocky shoals, and which is uncommon on the modem shelf The invertebrate faunas contained in the modem shell hashes, and their fossil counterparts, are highly characteristic of depositional environment, leading to the recognition of (i) differing coquina facies for shell hashes deposited below or above the contemporary lowstand shortlme (Point X); and (ii) within any cyclothem, the presence of a systematic, homotaxial order for different shellbed/coquina types. Transgressive systems tract (TST), current-sorted coquinas (type A shellbeds) are capped by localfloodmgsurfaces which occur at the base of a condensed, mid-cycle shellbed (type B shellbed), and followed by terrigenous highstand systems tract (HST) siltstone. In some but not all cycles, the upper, shallowing HST may contain fiuther occurrences of inshore type A coquinas. Beds of Zdelicatula, traditionally used as a cold-water (i.e. glacial) indicator species in New Zealand, are instead mainly indicative of MCS and HST position within particular cycles, i.e. despite their undoubted cool-water ecology, the scallop beds are preserved in interglacial as well as glacial sediment.

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In contrast with the completely carbonate-dominated outer shelf cool-water sediments described from e.g. the Lacapede shelf in southern Australia, many New Zealand carbonates occur in intimate association with contemporaneous terrigenous sediments. In such a setting, the formation of major cool-water limestone units is dependent upon one or more of the following conditions being met: (a) a very high benthic productivity, leading to high rates of shell formation and burial; (b) prolonged highstand conditions (i.e. non-glacio-eustatic), allowing accumulation of significant thicknesses of outer shelf carbonate; (c) in times of glacio-eustasy, a mid-outer shelf palaeogeographic position combined with favourable long-term subsidence rates, allowing the superposition of stacked outer-shelf carbonate facies through several to many successive eustatic cycles. (ROV video footage by Alan Orpin of In situ modem outer shelf carbonate faunas and facies, including bryozoan and Zygochlamys delicatula communities, will be included in a poster display related to this paper.)

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The southwestern margin of Australia ; transition from cool to warm water carbonates? Lindsay B. Collins School of Applied Geology, Curtin University of Technology, GPO Box U1987, Perth,Western Australia

The passive continental margin of southwest Australia, from the North West Cape region in the north to Cape Leeuwin in the south, has a narrow shelf which is wave-dominated and predominantly open. Climatic conditions grade from subtropical in the north to more temperate in the south.over the latitudinal interval of 22-34°S (Fig.l). Though the character of the shelf sediments is poorly known in the north (latitudes 22 to 26°), coral reefs are developed at North West Cape (the Ningaloo Reef) and on the seaward margins of offshore islands at Shark Bay (Hatcher, 1991), and the embayment sediments at Shark Bay are distinctly warm water in ch^acter. Ooid shoals are well developed, and seagrass bank sediments are dominated by Halimeda, coralline red algae, molluscs and bryozoans (Logan et al., 1970). Shelf sediments in the south (32-34°S) are relatively well known (Collins, 1988), and are dominated by bryozoans and coralline red algae, with significant amounts of molluscs and foraminifera. These shelf sediments are distinctly cool water in character, and are similar to those of the cool water carbonate margin stretching across southern Australia (see Bone and James, 1993 ). The central part of the shelf, from latitudes 26 to 32°S, is poorly known, except for the region adjacent to the Houtman Abrolhos Islands and carbonate platforms, at 28 to 29.5°S. The shelf- edge reefs at the Abrolhos have Holocene growth rates which are comparable to those of tropical reefs (Collins et al., 1993), and mark the southerly limit of significant reef development. Cool water carbonate sediments, dominated by bryozoans and calcareous red algae, are found on the shelf surrounding, and to seaward of, the platforms (France, 1985). In contrast, sand sheets within the reef platform lagoons are composed of corals and coralline red algae, with significant amounts of molluscs, foraminifera, and bryozoans. However, warm water elements, such as Halimeda and ooids, are absent from these sediments. The existence of the Abrolhos reefs at relatively high southerly latitudes (28-29.5°S; compared to 24°S for the limit of reefs on the east coast of Australia ) has been attributed to the Leeuwin Current, a polewardflowing warm water stream, which flows along the continental margin (Collins et al., 1991). A biotic transition zone , between the Northern Australian Tropical and Southern Australian Temperate zones, occurs between the latitudes of 26 and 30'S ( Morgan and Wells, 1991). This zone is characterised by overlap of the two assemblages (Fig.l). A detailed and regional program of shelf sediment samplmg has been planned to identify the presence, latitudinal position, and assemblage characteristics of any transitionzone facies, and their environmental and palaeoenvironmental significance.

References

BONE, Y., & JAMES,N.P., 1993. Byrozoans as carbonate sediment producers on the cool-water Lacepede Shelf, southern Australia. Sediment. Geol., 86:247-271.. COLLINS, L.B., 1988. Sediments and history of the Rottnest Shelf, Southwest Australia: a swell dominated, non-tropical carbonate margin. Sediment. Geol., 60:15-49. COLLINS, L.B., WYROLL, K-H., & FRANCE, R.E., 1991. The Abrolhos Carbonate Platforms: geological evolution and Leeuwin Current activity. J.Roy.Soc. West. Aust., 74: 47-57.

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COLLINS, L.B., ZHU, Z.R., WYROLL, K-H., HATCHER, B.C., PLAYFORD, P.E., CHEN, J.H., EISENHAUER, A. & WASSERBURG, G.J., 1993. Late Quaternary facies characteristics and growth history of a high latitude reef complex: the Abrolhos carbonate platforms, eastern Indian Ocean. Mar. Geo]., 110:203-212. FRANCE, R.E., 1985. The Holocene geology of the Pelsaert reef complex, southern Houtman Abrolhos, Western Australia. Ph.D. Thesis, Univ. West. Aust. (Unpubl.). HATCHER, B.G., 1991. Coral reefs in the Leeuwin current - an ecological perspective. J.Roy. Soc. West. Aust., 74: 115-127. LOGAN, B.W., READ, J.F, and DA VIES G.R. (1970). History of carbonate sedimentation. Quaternary Epoch, Shark Bay, Western Australia. The American Association of Petroleum GeologistsMemoir 13:38-84. MORGAN,G.J., and WELLS, F.E., 1991. Zoogeographic provinces of the Humboldt, Benguela and Leeuwin Current systems. J.Roy. Soc. West. Aust., 74: 59-69.

Figure 1. Location map, also showing zoogeographic provinces and direction of Leeuwin Current flow ( open arrows).From Morgan and Wells (1991).

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Carbonate Sediment Distribution Patterns of a Cool-Water Embayment; Streaky Bay? South Australia: a Preliminary Report R. F. DANIEL and C. C.VON DERBORCH

Streaky Bay is situated on the western flank of the Gawler Craton which lies on the passive southern margin of South Australia. Granitic gneisses of the the Palaeo Proterozoic are encountered to the north, south and on the islands at the mouth of the bay. Overlying these rocks and surrounding the bay are aeolian calcarenites of the Bridgewater formation with isolated areas of the marine bioclastic Glanville formation. Streaky Bay is centrally located on one of the largest cool-water shelf carbonate provinces in the world extending from southern Western Australia to south eastern Victoria. The bay area is typified by a semi-arid climate of low terrestrial input with reworked sediments being derived from wave^ominant erosion at the distal cliff margins. Five near shore sedimentary facies are noted: (i) reworked calcareous aeolinite/molluscan sand; (ii) fine sandy molluscan/echinoid mud; (iii) molluscan sand; (iv) molluscan/ foraminiferal sand and (v) quartzose mixed bioclastic sand. The fauna present range from fresh to highly abraded in condition reflecting both the high wave energy at the mouth of the bay and the relict component in the sediment. The distribution of the biofacies is controlled mainly by water depth and substrate type: (a) <2m, near-shore and linear sandbanks- molluscan; (b) 2-7m, seagrass, medium sand- molluscs, encrusting bryozoans; (c) 7-12m, flne sandy mudmolluscs,echiniods; (d) > 12m, coarse sand to rocky bottom-molluscs, bryozoans, red algae, brachiopods, ophiuroids, ahermatypic corals and brown algae. The outer deep water (<40mlimit of study) is the predominant carbonate factory in the bay with large southwest swells providing nutients for iht fauna in this area and transportation to subsequent deposition site.

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^ •

Southeastern Australia: a sea-level dependent carbonate margin MARIE A. FERLAND, University of Sydney and PETER S. ROY, Geological Survey of New South Wales Fifty-eight vibrocores, collected in October 1992 from the mid and outer continental shelf of central New South Wales (NSW) (32.5 to 34.80S), contain the first subsurface sediments fi-om this region and record carbonate sedimentation during glacial lowstands. Prior to this survey, our knowledge of Quaternary sedimentation on the outer continental shelf had been constrained by a lack of subsurface data. Surface sampling on the NSW shelf (e.g., Shirley 1964; Davies 1979) provided evidence of three shore parallel zones divided approximately by depth, each with different sedimentary characteristics: (1) the shoreface and the inner shelf (< 60 m) is comprised primarily of quartzose sand, (2) the mid-shelf (60-120 m) is generally muddy with a mixed quartz-carbonate fine sand fraction, and (3) the outer shelf (120-150 m) is dominated by skeletal carbonate sand and shell gravel, much of which appears to be relict. The zonation of surficial sediment, and the increase in the proportion of carbonate with increasing water depth, were substantiated by the present suite of grab samples and vibrocores (Bickford et al, 1993). Coresfi-omthe inner shelf generally contain sediment comprised of <20 % carbonate, whereas outer shelf cores contain >65 % on average. The inner shelf quartzose sands are post-glacial deposits (<12,000 yrBP), usually <1-2 m thick, and represent reworking of various pre-existing deposits. In contrast, cores collected on the mid-shelf usually contain 2-4+m of muddy sand deposited during the late post-glacial marine transgression and stillstand periods. This fine to very fine-grained terrigenous and carbonate sediment, is characterized by the molluscs Mesopeplum caroli, Gazemeda gunii, Nemocardium thetidis, and Dentalium erectum, which indicate sedimentation in generally deep water (>60 m) where energy levels are lower than on the inner shelf Vibrocores fi-om the boundary region between the mid and outer shelf (c. 115-130 m w.d.) are characterized by thin deposits of Holocene mid-shelf muddy sediment overlying relict deposits. Several cores contain sequences of surfzone and shoreface bivalves (primarly Glycymeris) which yield radiocarbon ages of 15,000 to 18,000 yrBP, and thus confirm deposition during the last glacial maximum when sea level was about 120 to 130 m below present (Chappell & Shackelton 1986; Fairbanks 1989). The bivalves are in a matrix of clean, fine-grained sand which we believe was derivedfi^omreworking of the regressive (or older) shelf deposits. The outer shelf surface is composed of skeletal carbonate sand and shell gravel, long assumed to be relict, given the shallow water mollusc assemblage and degree of encrustation on the surfaces of shells (Smith & Iredale 1924; Marshall & Davies 1978). Radiocarbon-dates fi-om this study show that the rate of sediment accumulation on the outer shelf during highstands is slow, with shells of 11-12,000 yrBP occurring at, or just 45 cm below, the seabed. (Winnowing by ocean currents probably contributes to the slow accumulation rates.) Vibrocores fi-om the outer shelf, especially between 135 and 150 m w.d., are characterised by predominantly carbonate sand and shallow-marine molluscs, with a minor terrigenous clastic component (< 20-35%) and little mud. Ten cores contain alternating sequences of two distinctly different lithologic units: (1) finegrained skeletal carbonate sand and (2) a coarser unit comprising densely-packed bivalves in a

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carbonate sand matrix. The molluscan species indicate that the two units were deposited under different environmental conditions. The fine-grained skeletal sand is generally deficient in whole shells, although it does contain some bivalves, such as M caroli and N, thetidis that are sometimes articulated. These bivalves live on the mid shelf today, however their enclosing sediment in outer shelf cores is more calcareous and less muddy than their modem mid-shelf counterpart. The coarser unit is characterised by mainly shallow water, robust bivalves including Pecten fumatus (dominant), Tawera gallinula and Bassina jacksoni, in a matrix of skeletal carbonate sand. These latter species typically occur today in the cooler waters of southern Australia and mainly in water depths of 20-50 m. Most of the valves in both units are extremely well-preserved, unabraded and oflen retain their original color. Radiocarbon dating of P. fumatus bivalves in 9 outer shelf cores yield last glacial maximum ages of 13,000 to 28,000 yrBP (n = 11). Many of these shells are fi-om <lm below the seabed, whereas shells at >2m depth in these cores yield background radiocarbon results (>40,000 yrBP). Thus, much of the sediment preserved in the 3-5 m long cores from the present outer shelf was deposited in a shallow shelf setting during, or prior to, the last glacial sea-level lowstand, which was approximately 120 m below present sea level at about 18-20 Ka (Chappell & Shackelton 1986; Fairbanks 1989). The presence of cool-water molluscs, representative of shallow-water conditions, supports the radiocarbon evidence. Amino acid racemisation analyses on P. fumatus shells which were beyond the range of radiocarbon, indicate that there are two older groups of bivalves: those with minimum ages of 94,000 yrBP (assigned to oxygen isotope stage 6) and those with minimum ages of 212,000 yrBP (assigned to oxygen isotope stage 8) (Ferland, Roy & Murray-Wallace, submitted, Murray-Wallace et al., 1994). The vibrocores provide the framework for a model of shelf sedimentation which shows that the composition of shelf sediment in different water depth zones varies with changing sea levels. During periods of high sea level, the inner shelf is dominated by quartzose sediment and characterized by reworking, while the mid shelf undergoes deposition of muddy mixed siliciclastic and carbonate fine sands, and the outer shelf is largely non-depositional. In contrast, during periods of low sea level (>100m below present sea level), the present inner shelf and some of the mid shelf are subaerially exposed, the outer part of the mid-shelf is reworked by surfzone and shoreface processes, and the outer shelf is dominated by carbonate deposition in a high-energy, shallow shelf environment (c. 25-50 m w.d.). We believe that there has been a long-term (?Quatemary) partitioning of sediment, with siliciclastic sediment confined primarily to the inner shelf, while the outer shelf has been dominated by carbonate deposition primarily during low and intermediate sea level positions. This is contrary to many generally accepted basin fill models which shows transgressions and regressions producing a lateral migration of facies across the shelf In this way, the present distribution and composition of sediment on the shelf surface is not a reliable indication of the sedimentary pattern which existed at low sea levels. The sedimentologic data for the outer shelf indicates that both interstadials and lowstands are characterised by carbonate sedimentation, while highstands are essentially non-depositional. The predominance of carbonate sedimentation is thought to result from both increased carbonate production, possibly due to changes in the East Australian Current and a cooler glacial ocean, and a decreased supply of siliciclastic sediment. The siliciclastic sediment which is present in the outer shelf cores is generally very fine to fine-grained sand and was probably derived fi-om a combination of reworking of the regressive midshelf fine-grained sands and from deposition of a small amount of fine-grained suspended sediment delivered to the coast by lowstand rivers. At low sea levels, shelf morphology is such that the largest decrease in bed gradient for rivers that drained the Sydney Basin, occurred on the present inner shelf, which resulted in deposition of

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coarser quartz sand landward of the lowstand coast. It is also likely that increased aridity during glacials resulted in less terrigenous sediment being supplied to the continental shelf. The relatively limited supply of terrigenous sediment to the shelf during late Quaternary periods of low sea level has important implications for models of shelf sedimentation and for the composition of the outer shelf Cainozoic sediment wedge (Davies 1979). Our data indicate that the upper portion of the wedge is not comprised of lowstand fluvial deltas, but is instead primarily a carbonate province formed under high-energy, inner shelf conditions during multiple lowstands. Furthermore, cores from the upper slope contain Neogene calcareous silts and muds vAth little or no terrigenous material (Bickford et al 1993), and support our hypothesis that little terrigenous sediment has been discharged beyond the continental shelf edge through much of the Quaternary.

References BICKFORD G., HEGGIE D., BIRCH G.F., JENKINS C., FERLAND M.A. KEENE J.B. & ROY P.S. 1993. Preliminary Results of AGSO RV Rig Seismic Survey 112 Leg B: Offshore Sydney Basin Continental Shelf and Slope Geochemistry, Sedimentology and Geology. Australian Geological Survey Organisation Record 1993/5, 121 pp (plus Appendices). CHAPPELL I , SHACKELTON N.J. 1986. Oxygen isotopes and sea level. Nature, 324, 137140. DAVIES P. J. 1979. Marine geology of the continental shelf off southeast Australia. Bureau of Mineral Resources Bull 195. FAIRBANKS R.G. 1989. A 17000 year glacio-eustatic sea level record: influence of glacial melting rates on Younger Dryas event and deep ocean ciruculation. Nature, 342, 637642. FERLAND M.A., ROY P.S. & MURRAY-WALLACE, C.V. {Submitted), New evidence for glacial lowstand sedimentation on the outer continental shelf, southeastern Australia. Quaternary Research. MARSHALL J.F., DAVIES P J. 1978. Skeletal carbonate variation on the continental shelf of eastern Australia. Bureau of Mineral Resources, Journal of Australian Geology and Geophysics, 3, 85-92. MURRAY-WALLACE C.V., FERLAND M.A. & ROY P.S. (1994). Aminiostratigraphy of Quaternary outer shelf sediments. New South Wales, Australia. In Advances in the Study of the Sydney Basin, Twentyeighth Newcastle Symposium, Department of Geology, University of Newcastle, 188-195. SHIRLEY J. 1964. An investigation of the sediments on the continental shelf of New South Wales, Australia. Journal of the Geological Society of Australia, 11, No. 2, 331-343. SMITH T.H., IREDALE T. 1924. Evidence of a negative movement of the strand line of 400 feet in New South Wales. Journal of the Royal Society of New South Wales, 58, 157-168.

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The ^Xittle Barrier Reef ^ of Southern Australia: The Result of Warmer-Water Interruption to Prevailing Cool-Water Conditions

David A. Feary (AGSO, Dept. of Geology 8c Geophysics, University of Sydney) and Noel P. James (Dept. of Geological Sciences, Queen's University, Kingston, Ontario)

The Cenozoic record of the southwestern Eucla Basin in the western Great Australian Bight is predominantly one of interrupted cool-water carbonate deposition. Seismic stratigraphic analysis of an extensive grid of high quality seismic data across the western Great Australian Bight reveals a succession of seven unconformity-bounded seismic sequences. Most of these sequences are inferred to have been deposited within cool-water, shelf and upper slope carbonate depositional environments. This has resuhed in a series of sequences characterised by aggradational or very highly obliquely progradational ramp geometries. One of the most striking characteristics within many of these sequences is the presence of broad, low relief mounds, inferred to be br,vozoan? sponge mud mounds. Unconformities separating these sequences represent depositional hiatuses probably corresponding to lower sea-level periods, but there is also possible truncation of reflectors by erosive, cold-water currents. The most spectacular feature on seismic profiles across the shelf of the western Great Australian Bight is a reefal build-up (see figure), lying beneath the central part of the modem shelf and parallel to the modem shelf edge. This feature extends for more than 475 km, and is up to 300 m high. The geometry of this seismic sequence, together with the characteristics of stacked reefs which form the reefal escarpment, indicates that the Little Barrier Reef represents an episode of warmer-water (warm subtropical or tropical) carbonate deposition, interrupting the prevalent temperate or cool subtropical carbonate regime responsible for most of the remainder of the Cenozoic succession. The Little Barrier Reef probably represents deposition during the latest Early Miocene or early Middle Miocene climatic optimum, and we speculate that it may have resuhed fi-om a combination of this global warm episode together with a warm-water current flow, perhapsfi-oma proto-Leeuwin Current.

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0.70

Airgun seismic profile and line drawing interpretation showing stacked reefs which grew in warm-water ('rim phase'), and which formed the extensive western Great Australian Bight "Little Barrier Reef". The underlying 'ramp phase' mounds are interpreted as cooler-water build-ups which grew in a broad, gentlysloping shelf environment.

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Glacio-Eustatic control of coquina facies in the Pliocene Pukenui Limestone, New Zealand Paul Gammon Geology Department James Cook University of North Queensland Townsville Q'ld 4811

Mangaopari Stream is situated in the southeast comer of North Island, New Zealand. The sequence studied is Pliocene to early Pleistocene in age, and records the progressive tectonic uplift of a forearc basin from bathyal depths to subaerial exposure. Within this overall regressive sequence, the Pukenui Limestone is a formation showing marked facies variations which are able to be related to glacio-eustatic sea-levelfluctuations.In the south (Clay Creek section), Pukenui Limestone is inferred to have been deposited entirely below the contemporary lowstand shortline position (Point X). Sequence boundaries are disconformities overlain by winnowed shell concentrations and sandy lowstand sediment. Sea-level rise, the transgression, is marked by a local flooding surface (LPS) above which occur in situ, outer shelf, Zygochlamys delicatulabryozoan-branchiopod sheUbeds. Further north (Popes Head section), towards the palaeoshoreline, the Pukenui Limestone was deposited in shallower water, above Point X. Cycles within the limestone here are similar to previously described inner shelf mid-Pleistocene cyclothemsfromWanganui. Lateral lithological and faunal changes in the Pukenui Limestone are used as the basis for a conceptual facies model of a palaeo-temperate-carbonate shelf The Zdelicatula fauna is of coldwater origin, and has a close counterpart on the modem New Zealand mid-outer shelf Previously considered to be a significant palaeoclimatic indicator species, with its FAD marking the basePleistocene, the Mangaopari section shows that the delicatula fauna is in fact controlled by both depth (more strictly, absence of terrigenous sediment) and water temperature. Fu-st appearing well down in the late Pliocene, the fauna occurs particularly within the outer shelf parts of the transgressive and highstand system tracts. Accurate discrimination of the different types of temperate-water coquina Umestone that characterise New Zealand Plio-Pleistocene cyclothems requires correct identification of both faunal elements and systems tract position.

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Late Quaternary sediments of Wanganui shelf, New Zealand: a non-tropical carbonate-siliciclastic mixture Jeanette L. Gillespie and Campbell S. Nelson Department of Earth Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand Shallow-marine, non-tropical carbonate sediments are presently most widespread on the New Zealand continental shelf where levels of terrigenous-sediment input are relatively low. One of the smaller occurrences is located on Wanganui shelf, in central New Zealand's Greater Cook Strait. Evidence from surficial sediment samples and short piston cores shows that a lense of skeletal-carbonate sediments, mixed with siliciclastic material, has been accumulating in this location since at least the last post-glacial sea-level rise following about 18,000 y BP. The lense migrated to its present position as sea level rose. These late Quaternary sediments are considered to be good modem analogues of uplifted Plio-Pleistocene cyclothemic deposits exposed onland in the Wanganui region. From a synthesis of textural and compositional data, five surficial sediment facies have been defined for Wanganui shelf (Table 1). These sediments also occur in piston cores (max. penetration 2.5 m) collected from the shelf. Facies 1 (Bivalve-bearing gravelly sand) is a terrigenous-dominated, inner shelf facies (< 50 m water depth) containing both modern (< 6,500 y BP) and relict components. Facies 2 (Skeletal-dominated sandy gravel) comprises sediments containing > 50 % CaCOs, and presently occurs on the inner to mid shelf (-30-90 m water depth) where levels of terrigenoussediment input are reduced. The carbonate fraction is dominated by bivalves and bryozoans. Facies 3 (Bivalve-bearing muddy sand) is a terrigenous-dominated facies that occurs at mid-shelf depths (--75110 m). It represents a transition from Facies 2 to Facies 4 (Mud). The latter constitutes the northern reaches of the Cook Strait Basin mud depocentre. Both Facies 3 and 4 receive terrigenous sediment from dual North and South Island sources. Facies 5 (Micaceous sand) is derived chiefly from west oast South Island material swept into Greater Cook Strait by wind-induced currents aided by oceanic (Westland and D'Urville) currents. The nature and distribution of the terrigenous siliciclastic components are chiefly controlled by: 1) the region's active tectonic setting and onland geology - North Island volcanics and easily-eroded mudstones and siltstones, and South Island plutonic and metamorphic rocks; 2) the episodic, postglacial rise in sea level which initially allowed sediments to be deposited and then left them stranded to become relict and palimpsest; and 3) the present hydraulic regime of Greater Cook Strait - stormdominated with an additional tidal component. The nature and distribution of skeletal components reflects: 1) the distribution of terrigenous material, bivalves dominating in areas receiving a high terrigenous input and bivalves/bryozoans occurring in subequal amounts in the more terrigenous-

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sediment-starved areas; 2) substrate type; 3) water depth; and 4) the shelf s storm-dominated hydraulic regime. The late Quaternary Wanganui sediments can be discussed in terms of the developing model of shallow-marine, non-tropical carbonate sedimentation. In conmion with other non-tropical carbonates they contain bryomol and bimol (bivalve mollusc) skeletal assemblages; exhibit both calcitic and aragonitic carbonate mineralogies - the former mainly dominating over the latter; include mixtures of living, fresh, and degraded skeletal material; have low-positive stable isotope signatures ( 3 0 . 9 8 2.04;

0.80 - 2.05), and occur in association with terrigenous sediments. Bivalve molluscs in

particular provide favourable substrates for attachment and encrusting by epifauna - evidence of taphonomic feedback. The deposits are subject to destructive diagenetic processes such as bioerosion. Radiocarbon dating of sediments supports the observation that the use of shell physical appearance as the sole criterion for differentiating modern/relict and young/old skeletons in non-tropical environments is unreliable. The Wanganui sediments also exhibit a number of characteristics that are less typical of the large platform deposits on which much of the non-tropical carbonate model has so far been based. These include: moderately high total mud and carbonate-mud components; abundant living, and diverse fauna in areas with otherwise moderately high terrigenous-mud inputs; sedimentation rates (10-100 cm/ky) greater than that typically reported of 1-2 cm/ky; and lack of rocky substrate. These differences imply that it may not be appropriate to make generalisations about temperate-latitude carbonates based solely on the larger, more conspicuous platform occurrences such as those that occur at Three Kings and Snares off northern and southern New Zealand, respectively.

I e I

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Table 1.

Descriptive parameters (mean values) for the 5 surficial facies. Textural parameters relate to w h o l e samples, while compositional data are for the coarse skeletal fraction.

Facies 1

Average water depth (m)

Facies 2

Facies 3

Facies 4

Facies 5

100

30 67 3 Sandy gravel

28 45 27 Gravelly muddy sand

10 51 39 Gravelly muddy sand

1 37 62 Sandy mud

0 92 10 Sand

bivalves

Subfacies la

Subfacies lb

Subfacies 2a

Subfacies 2b

Subfacies 2c

Texture Weight % gravel Weight % sand Weight % mud Folk classification

2 95 3 Sand

15 85 0 Gravelly sand

31 67 2 Sandy gravel

Weight % CaC03

Composition Major skeletal groups Minor skeletal groups

bivalves

Weight % bivalves Typical bivalve assemblage

82 Glycymeris

96 Glycymeris; Scalpomactra; Dosinia; Myadora; Saccella

88 Glycymeris; Tucetona

45 Tucetona

50 Chlamys; Tucetona; Cardita; Barbatia; Venericardia; Mesopeplum

70 Chlamys; Tiostrea; Corbula; Venericardia; Nemocardium

92 Chlamys

41 ENml; ERfe

38 ERde; ERro

9 ERde; ERro

Maoricolpus

Homotrema

Waltonia

Bivalve-bearing muddy sand

Mud

Micaceous sand

Weight % bryozoans Dominant growth forms * Other

Species diversity

Facies name Subfacies name

Bivalve-bearing gravelly sand Yellow-brown sand

Bivalve-bearing, volcanogenic gravelly sand

Bivalve-dominated sandy gravel

bivalves; bryozoans bivalves; bryozoans bivalves foraminifera bryozoans; brachiopods

Skeletal-dominated sandy gravel Bryozoan/bi valvedominated sandy gravel

Bryozoan/bivalvedominated muddy sandy gravel and gravelly muddy sand

* ENml = encrusting multilaminar; ERfe = erect rigid fenestrate; ERde = erect rigid delicate branching; ERro = erect rigid robust branching.

Bryozoan colonial growth forms as paleoenvironmental indicators: reevaluation of methodology and predictive utility Steven J. Hagemanl, Yvonne Bonel, Brian McGowranl and Noel P. James^ iDept. of Geology & Geophysics, University of Adelaide, SOUTH AUSTRALIA 2Dept. of Geological Sciences, Queen's University, Kingston Ontario, CANADA Introduction Correlation between bryozoan colonial growth forms and environments in which the organisms lived, allows for potential application of growth forms as paleoenvironmental indicators. A number of workers have demonstrated this potential in ecological, paleontological and sedimentological studies. However, problems encountered in methodology (data collection and analysis) and unanswered questions about controls over bryozoan distributions, currentiy restrict the utility of bryozoan colonial growth forms as paleoenvironmental indicators.

Growth Form Classincation Over the years many biyozoan colonial growth form types have been recognized, each of which traditionally has been given the name of the genus that typifies the form. Schopf (1969) made a significant contribution when he proposed a hierarchical, classification of bryozoan colonial growth forms with four basic types (erect rigid, erect flexible, encrusting and free-living). This approach emphasizes functional morpholo^c and biomechanical similarities of morpho-ecologically related groups rather than splitting forms into discrete groups based on differences. Nelson et al. (1988) and Bone and James (1993) refined this approach by providing descriptive names for basic growth form types, making apphcation more accessible for nonspecialists.

Validity of methodology from first principles Stach's (1936) original arguments about correlation of bryozoan colonial growth form and environment are so elegant and intuitive that they have long enjoyed wide acceptance among ecologists. Stach's work was based on empirical observations, but it is difficult to argue with, based simply on theoretical grounds. Optimal environmental settings for virtually every growth form are intuitive. However, relatively liAe is known about controls that exclude growth forms from their non-optimal environments. It might, therefore, be as important to know why a bryozoan colonial growth form is absent from a setting as it is to document its presence. Parameters controlling the restriction of growth form distributions are far less intuitive and should be an important area for future study.

Predictive Utility Even though relationships between bryozoan colonial growth forms and environments are intuitive, interpretations remain ad hoc. In order for bryozoan growth forms to have utility in paleoenvironmental analysis, it must be demonstrated that they have predictive value in known settings. The relationships between environmental factors and bryozoan growth form distributions are complex (they co-vary). It is, therefore, misleading to evaluate single ecologic factors outside the context of others. When developing predictive models, the natural distribution of the bryozoans must first be recognized (e.g. geographic distribution in a study area). Environmental factors can then be compared to this distribution (which inherentiy has the greatest predictive utility for the bryozoans at hand). Note that while developing predictive modes, it is also misleading to compare bryozoan growth form distributions to any other aCDLQli distribution (e.g. traditional bio-lithofacies). Any number of a priori facies distributions may be correlated with the bryozoan distribution, but we are interested in the factors that are the most correlated (= greatest predictive utility). Once the natural distributions of growth forms have been more fully evaluated in the context of interrelated environmental factors, we will be able to interpret individual environmental parameters with much greater confidence.

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Methodology

Methodological differences among workers are probably the greatest difficulty encountered in current application of bryozoan colonial growth forms to paleoenvironmental interpretations. For any setting, growth forms can be evaluated by looking at changing abundance (volumetric or numerical) or changing diversity (species within growth form). Each of these can be evaluated by changes in absolute or relative values. Relative values can, in turn, be evaluated for changes within growth fomis or among growth forms. Attempts can also be made to combine abundance and diversity into a single analysis. Thus, there are at least 10 lo^cal and theoretically valid methods in which a single data set could be compiled and interpreted, likely with varied conclusions. Indeed, workers have employed a variety of these methods, making their studies and conclusions incompatible for comparison (e.g. Stach 1936, Cheetham 1963, Lagaaij and Gautier 1965, Schopf 1969, Cook 1965, Bone and James 1993, Moissette 1994, Hageman et al. in preparation). At this time, the relative merit of each of these different methods is unknown.

Conclusions

1. Methodology needs to be more fully tested and standardized in modem settings before bryozoan colonial growth forms can be applied to paleoenvironmental studies. It must be demonstrated that objective analysis is possible in known settings before the methodology can be applied subjectively in unknown settings. 2. Relationships among environmental factors that control the distribution of bryozoan colonial growth forms need to be better constrained. This should be accomplished in the context of the natural distribution of bryozoans and the covariance of environmental factors, rather than a prior comparisons with specific factors. 3. General trends of environmental variation are possible with bryozoan colonial growth forms, but categorical statements of specific environmental conditions (e.g. absolute water depths) are premature. 4. Although this paper appears to present more problems than solutions, the outlook for application of bryozoan colonii growth forms to paleoenvironmental analyses remains optimistic. Problems raised here are all testable. The resolution of these problems will allow bryozoan colonial growth forms to achieve their full potential as paleoenvironmental mdicators.

References

9 9

BONE, Y. & JAMES, N.P. (1993) Bryozoans as carbonate sediment producers on the cool-water Lacepede Shelf, southem Australia. Sedimentary Geology 86,247-271. CHEETHAM, A.H. (1963) Late Eocene zoogeography of the Eastern Gulf Coast Region. Geological Society of America, Memoir 91, 879 p. COOK, P.L. (1965) Bryozoa (Polyzoa) from the Coast of tropical West Africa. Atlantide Report 10, 115-262. HAGEMAN, S.J., BONE, Y., MCGOWRAN, B., & JAMES, N.P. (in preparation) Analysis of bryozoan fades on the cool-water Lacepede Shelf, southem Australia. LAGAAIJ, R & GAUTIER. Y.V. (1965) Bryozoan assemblages from marine sediments of the Rhone delta, France. Micropaleontology 11,39-58. MOISSETTE, P. (1994) Bryozoan assemblages in Messinian deposits of westem Algeria. Lethaia 26, 247-259. NELSON, C.S., HYDEN, P.M., KEANE, S.L, LEASK, W.L. & GORDON, D.P. (1988) Application of bryozoan zoarial growth-form studies in facies analysis of non-tropical carbonate deposits in New Zealand. In: C.S. Nelson (Editor), Non-Tropical Shelf Carbonates—Modem and Ancient. Sedimentary Geology 60,301-322. SCHOPF, T.J.M. (1969) Paleoecology of ectoprocts (bryozoans). Journal of Paleontology 43, 234-244. STACH, L.W. (1936) Correlation of zoarial form with habitat. Joumal of Geology 44, 60-65.

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Skeletal assemblages of New Zealand Cenozoic non-tropical carbonate sediments Shaun Hayton, Steven D. Hood and Campbell S. Nelson Department of Earth Sciences, University of Waikato, Hamilton, New Zealand The Cenozoic non-tropical limestones of South Island, New Zealand are constructed of whole and fragmented skeletal material. Petrographic analysis determined the abundance of different skeletal types in samples and these data were subjected to a complete linkage cluster analysis to group the limestones into compositionally similar types. Subsequent comparison of the clusters with previously defined modem and ancient cool-water skeletal assemblages found that six established categories and one new one were required to define the samples. The seven assemblages are: (A) Bamamol - bamacle/bivalvedominated; (B) Bimol = bivalve-dominated; (C) Bryomol = bryozoan/bivalve-dominated; (D) Echinofor = echinoderm/benthic foraminifera-dominated; (E) Nannofor = nannofossil/planktic foraminiferadominated; (F) Rhodechfor = calcareous red algae/bryozoan/benthic foraminifera/echinodermdominated; (G) Rhodalgal = calcareous red algae-dominated. The seven assemblages are subdivisions of the Foramol superassemblage of Lees and Buller (1972), used to describe the typically skeletal-rich shallow-marine carbonate sediments of non-tropical shelves. Skeletal Assemblage Composition

Relative abundance in New Zealand

• • •

B 20

Bryozoans Bivalves Echinodemis Benthic foraminifera Planktic foraminifera Calcareous red algae Barnacles

Average Composition %

Development of a method by which samples can be correctly and simply classified was the logical extension of this work. A "multiple" triangular diagram was derived that considers the three dominant skeletal contributors in a sample. Development incorporated 90% of the samples used in the cluster analysis to define the assemblage zones within the triangular diagram. As a check of the utility of the diagram for New Zealand Cenozoic carbonates, more than 150 independently analysed samples from

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6 9

the Cenozoic limestones of North Island, New Zealand were used. Over 85% of these samples were able to be plotted on the diagram and classified. Benthic foraminifera

Planktic foraminifera *

Bamamol

Bimol

Bryomol Echinofor

Bryozoans

Nannofor

•

Rhodechfor

QRhodaigal Q

No Samples Plotted

Bivalves

Bamacles

Bryozoans

Echinoderms

Bryozoans

The correlation between the skeletal assemblage system developed here, and groupings of modem and ancient non-tropical bioclastic sediments described in the literature (e.g., from New Zealand (Nelson et al 1988b); Scotland (Scoffm 1988); southern Australia (James etal 1992); and northem Italy (Scudeler Baccelle & Reato 1988)) suggests that these assemblages are able to be extensively applied to nontropical carbonate sediments more generally. This comparability amongst modem and ancient nontropical occurrences suggests that the skeletal assemblages may be broadly related to particular environmental settings. Idealised across-shelf and three-dimensional models are proposed to show possible relationships between the distribution pattems of the seven skeletal assemblages.

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^" - • • . .

Off-shore high

Sea level

Sea-way

Rhodalgal

The application of this classification system should allow the use of consistent terminology for naming Foramol-type non-tropical skeletal carbonate deposits, modem and ancient. This will improve communication between workers in the field of non-tropical carbonates, benefit inter-study comparisons, and assist with the advancement of facies models for non-tropical carbonate deposits.

References JAMES, N.P., BONE, Y., VON DER BORCH, C.C. & GOSTIN, V.A. (1992) Modem carbonate and terrigenous clastic sediments on a cool water, high energy, mid-latitude shelf: Lacepede, southern Australia. Sedimentology 39, 877-903. LEES, A. & BULLER. A.T. (1972) Modem temperate water and warm-water shelf carbonate sediments contrasted. Marine Geology 13, M67. NELSON, C.S., KEANE, S.L. & HEAD, P.S. (1988) Non-tropical carbonate deposits on the modem New Zealand shelf. Sedimentary Geology 60, 71-94. SCOFFIN, T.P. (1988) The environments of production of carbonate sediments on the shelf west of Scotland. Sedimentary Geology 60, 125-134. SCUDELER BACCELLE, L. & REATO, S. (1988) Cenozoic algal biostromes in the eastem Veneto (northem Italy): a possible example of non-tropical carbonate sedimentation. Sedimentary Geology 60, 197-206.

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Cold water reefs and biogenic carbonates of the Arctic Riidiger Henrich & Andre Freiwald Faculty of Geosciences - University of Bremen, Klagenfurter StraBe, D-28334 Bremen, Germany Traditionally, reefs constructed by accretion of colonial carbonate secreting organisms are considered to be suggestive of subtropical and tropical climatic conditions. Recently discovered reefs well beyond the Arctic circle contradict with conventional views on biogenic carbonate accumulation concepts, eg. shallow water coralline algal reefs in the skerries of northern Norway, azooxanthellate coral reefs of mid-Norway and deep water siliceous sponge/bryozoan/serpulid buildups and biogenic mats on an dmost perannually sea-ice covered sea mount in the central Greenland Sea. Controlling parameters leading to the formation of these modem arctic reefs and buildups display important forcing parameters yet unknown from their tropical counterparts. The arctic red algal reefs grow on skerry plateaus in very shallow, medium agitated clear water. A major precondition for active reef accretion is intensive grazing by echinoids and limpets, which prevents overgrowth of last growing brown algae. Such an overgrowth by brown algae would rapidly interrupt the reef construction process. In the surroundings these reefs wide extended intertidal carbonate flats are observed. During the Holocene, multiple phases of reef accretion and destruction occurred in response to local high frequency sea level oscillations. These were induced by complex interactions of postglacial isostatic uplift rates of the Fermoscandian Craton and the stepwise Holocene eustatic sea level rise. Deep water construction of the sea mount Vesterisbanken reveal a variety of depth related siliceous sponge/bryozan/scrpulid buildups, which are controlled by food transfer from downwelling water masses with a maximum supply from seasonal ice edge blooms. Additionally, intensive recycling of food and nutrients by bacteria is of particular significance. In situ collapse of such siliceous/carlcareons buildups results in parautechthonous spiculite formation, a process which may be of specific relevance for the interpretation of fossil analogues. Corals thrive well in deep and cold waters along the northwestern European continental margin. Due to their dendroid colonial growth habit, these scleractinian corals provide the potential to construct spatially extended reef ecosystems with exceptionally large standing stock. Although many deep water coral reef locations are known for long time, basic questions concerning their environmental controls, such as betho-pelagic coupling, successfiil turnover during reef growth, and initial reef development are still longing for an answer. In this context, some new observations from two Norwegian sites will be discussed.

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With respect to aerial coverage a fourth type of biogenic carbonates is of specific relevance in the Arctic, eg. polygenetic carbonate lag deposit which formed in response to isostatic uplift and resultant changes in current regimes. Here, a thin veneer of an current excaved and winnowed arctic mollusc infauna was inhabited by a secondary hard substrate epifauna mainly balanids.

References: Freiwald, A. (1993): Coralline maeri pavements - islands within the phaeophytic kelp beltPacies, 29:70-104. Freiwald, A.; Henrich, R: Schafer, R & H. Willkoman (1991): The significance of highboreal to subarctic maerl deposits in Northern Norway to reconstruct Holocene climatic changes and sea level oscillations.-Fracies, 25:315-340. Freiwald, A. & Henrich, R. (1994): Reefal; coralline algal buildups within the Arctic Circle; morphology and sedimentary dynamics under extreme environmental seasonality Sedimentology, 41:963-984. Henrich, R.; Hartmann, M. Reitner, J. Schafer, P. Freiwald, A. Steinmetz, S. Dietrich, P. & J. Thiede (1992): Facies behs and communities of the Arctic Vesterisbanken seasonal Fades 27:71-104.

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Palaeoenvironments and sequence stratigraphy of the Tertiary carbonates at Sale in South Gippsland, Victoria

Guy Holdgatel & Stephen Gallagher 2 ^ Department of Earth Sciences, Monash University, Clayton. Victoria 2 School of Earth Sciences, University of Melbourne, Parkville, Victoria This contribution represents the results of an initial study on two bores, Wurruk Wurruk-1 and Wurruk Wurruk-13 and adjacent outcrops near Sale in South Gippsland. Each bore consists of C.500 metres of shallow marine temperate carbonates of Oligocene to Late Miocene age, laterally equivalent to economic brown coal deposits in the LaTrobe Valley. The succession in the bores comprises the Seaspray Group that is the major reservoir se^ of economically significant hydrocarbon deposhs in the offshore Gippsland Basin. The aim of this paper is to present our earlier results on the palaeoenvironments and sequence stratigraphy of the Tertiary c^onates at Sale in South Gippsland derived from analyses of wireline logs, seismic and core logs, in conjunction with studies of the foraminiferal distribution. The initialfindingsare as follows > *

The Seaspray Group comprises five main sequences; two in the Lake Entrance Formation and three in the Gippsland Limestone.

The Lower Lakes Entrance Formation sequence occurs towards the end of flie Lower Oligocene and is poorly represented in the bores.

The upper Lakes Entrance Formation sequence corresponds to the high sea level period in Ae early Lower Miocene and hence the Upper Oligocene is absent.

The base of the Lower Miocene Gippsland Limestone is a major sequence boundary and is overlain by a number of parasequences recording successivefluctuationsin sea level.

Analyses of benthic foraminiferal distribution using Ae palaeodepth range chart of Bsyvmd (1990) in conjunction with analyses of planktonic/benthonic ratios has revealed (on a broad scale) fluctuations in sea level at the base of Ae Gippsland Limestone recording vertical changes from middle shelf (50-100m) to inner shelf depAs (0-50m).

Foraminiferal distribution studies has also revealed minor sea level fluctuations wiAin individual beds.

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Overview of cementation environments and pathways for New Zealand Cenozoic temperate-latitude limestones Steven D. Hood and Campbell S. Nelson Department of Earth Sciences, University of Waikato, Hamilton, New Zealand Current mcxlels of shallow-marine limestone cementation have evolved mainly from studies of tropical carbonates. In the marine realm these carbonates typically experience constructive diagenetic processes, such as seafloor cementation and preservation of metastable carbonate phases. However, on carbonate shelves at higher latitudes, the cooler water temperatures, lesser degree of carbonate saturation, higher CO2 content, lower sediment accumulation rates, and instability of metastable carbonate phases, promote a predominantly destructive early diagenetic regime. The primary mixed mineralogy skeletal sediment is subject to mechanical abrasion, bioerosion, varying degrees of dissolution with partial to total loss of metastable aragonite, and incongruent dissolution of high Mg-calcite. Cenozoic limestones are widely distributed in New Zealand, especially in the Oligoceneearliest Miocene in both islands, and the Plio-Pleistocene in North Island. A spectrum of limestone types exists, but all are skeletal-dominated (>70%), with usually <20% interparticle cement-matrix and <10% siliciclasts, and they have the facies attributes typical of nontropical carbonates. The diagenesis of these limestones has been strongly influenced by the composition and degree of preservation of the original metastable skeletons, by the chemistry of the pore fluids, and by the period of residency of these pore fluids. In turn these factors were controlled by a combination of different temperate-latitude depositional settings, their basinal tectonic histories, and the degree of influence of (glacio-) eustatically-induced sea-level fluctuations. Together these factors have been responsible for the evolution of contrasting cementation environments and pathways. The wide range of diagenetic features identified from field and petrographic work, namely the fabric and mineralogy of the cements, their significance in terms of pore fluid chemistry, and the paragenesis of cement sequences, have been used to identify for the New Zealand limestones a small number of cementation scenarios associated with four broad diagenetic environments or classes: Class I - seafloor; Class II - shallow-marine burial; Class III combined shallow burial-meteoric; Class IV - deep subsurface burial (Fig. 1). Class III involves a relative emergence (regressional) situation in which the limestones were subjected to meteoric waters and subaerial exposure relatively soon after deposition, while Classes I, II, and IV involve an overall submergence (transgressive) situation, in which the limestones progressed directly into the burial setting with tn^ped formation waters.

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Class I diagenesis is rare and involved early seafloor cementation and possible hardground development wherever conditions of non-sedimentation and high energy conditions were conducive to a high seawater flux in the sediment. Cements are typically non-ferroan, non- to dull luminescent, fibrous to bladed, isopachous, inter- and intragranular sparite rinds, often with porosity occlusion by micrite cement/matrix, but also by sparite regionally sourced by later pressure-dissolution. These rare limestones are typically coarse calcarenites to fine calcirudites with open to moderately open fabrics, and are well lithified and of Oligo-Miocene age. Class II diagenesis involved slow tectonic subsidence and shallow burial (10s of m) of predominantly calcitic skeletons where marine porewaters (and later varying degrees of meteoric fluids) were non-reactive due to the absence of metastable aragonitic skeletons. Shallow burial depths prohibited die production of pervasive pressure-dissolution-derived cements and the resulting calcarenites and calcirudites, of Oligo-Miocene age, have open fabrics and are poorly cemented and porous. These cements are characteristically dull to bright luminescent, ferroan to non-ferroan, often substrate specific bladed to dog-toothed scalenohedral fringes or syntaxial rim cements. Class III diagenesis initially involved shallow-marine burial (10s of m to 100+ m) followed by rapid and profound mineral-controlled phreatic meteoric diagenesis of aragonitic skeletons in eastern North Island Plio-Pleistocene limestones because of differential uplift in an active forearc basin setting. Precipitation of calcite was impelled by dissolution of aragonite resulting in the redistribution of porosity from inter- and intra-skeletal to new bio-mouldic pores. Cements are characteristically non-ferroan to ferroan, variably luminescent, typically fine to coarse, dnisy, clear, equant sparite. The degree of neomorphic stabilisation is variable, depending on reaction rates (controlled by grain size, porosity, and permeability) and residency time, so that some original skeletal aragonite may be preserved. Limestones are poorly to very well cemented calcirudites with open to moderately open fabrics. Class IV diagenesis involved dominantiy stable calcitic skeletons with low diagenetic potential. Cementation occurred during modest rates of subsidence and moderate to deep burial (1001000+ m) with initiation of pressure-dissolution at grain contacts to form commonly ferroan, dull luminescent, clear, dnisy, equant sparite. Porosity typically decreases with increasing burial with fabrics becoming increasingly tight and highly pressure-dissolved with associated stylolitisation and fracturing. Limestones are characteristically crystalline, very well cemented, calcarenites to calcirudites of Oligo-Miocene age. The cementation characteristics of New Zealand Cenozoic limestones are consistent with currently developed models of temperate-latitude shallow-marine carbonate sedimentation. However, they also demonstrate a diversity and complexity of diagenetic features, such as seafloor marine cements and meteoric cements, which have not yet been incorporated fully into models of temperate carbonate diagenesis. Clearly there is a future demand for more sophisticated fecies and diagenetic models to encompass the broad spectrum of temperatelatitude limestone varieties. Interestingly, die spectrum of diagenetic possibilities known for tropical carbonates also occurs for temperate carbonates, but differ in terms of the carbonate phases precipitated and their extent.

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Fig. 1 - Diagenetic environments, pathways, and classes for New Zealand Cenozoic limestones SEAFLOOR DIAGENESIS uppermost few m primary skeletal sediment having mixed mineralogies (typically calcite»aragonite) * skeletal abrasion, bioerosion, dissolution * marine cementation (fibrous spar, homogenous micrite, peloidal micrite) * rare internal sedimentation of microbioclastic micrite

aragonite lost

aragonite retained

SHALLOW BURIAL DIAGENESIS * substrate specific cements (includes dog-tooth, bladed and syntaxial rim fabrics) metastable mineral phases neomorphosed completely (long residence) or incompletely (short residence) * mild pressure-dissolution at bioclast contacts, grain alignment and fracture

MODERATE - DEEP BURIAL DIAGENESIS 100- 1000+ m * pressure-dissolution cementation * stylolitisation vemmg

Class i seafloor /

Class IV deep subsurface burial

METEORIC DIAGENESIS * aragonite dissolution and reprecipitation as equant calcite sparite

Class II shallow-marine burial

Class III combined shallow burial-meteoric

PALEOZOIC CRYOCARBONATES: CHARLATANS IN THE MIST? Noel P. James, Queen's University, Kingston, Ontario K7L3N6, Canada The concept of cool-water marine carbonates comes largely from the modem ocean. Such sediments, here called Cryocarbonates (platform carbonates formed in waters too cold for abundant photic symbionts), typically develop where the temperature of seawater is less than 20°C. Thermocattonates, in contrast, form in waters that are warmer than 20®C and characterize modem "tropical" platform environments. Frigid seawater eliminates green algae and organisms with photic symbionts, and inhibits the precipitation of particles such as ooids and lime mud crystallites. The calcareous biota is typified by filter- and detritus-feeders such as molluscs, bryozoans, annelids, barnacles, hydrozoans, echinoderms, and protists with lesser numbers of brachiopods and ahermatypic corals. Coralline algae are ubiquitous in the photic zone. The non-carbonate biota is dominated by abundant sponges and ascidians. There are three overlapping sediment provinces in this depositional realm. Temperate cryocarbonates form in waters around 20°C and the cryocarbonate biotic assemblage is augmented by high numbers of coralline algae, together with low numbers of thermocarbonate elements such as hermatypic corals, large foraminifers and green algae. Cool cryocarbonates form in environments with bottom temperatures between 5°C and 20®C and are characterized by sediments composed of abundant and diverse cryocarbonate elements. Cold cryocarbonates develop on platforms bathed by polar waters of less than 5"C and the cryocarbonate biotic assemblage is locally increased by abundant brachiopods. Similar limestones are common in the rock record, but are they true cryocarbonates or are they charlatans in the mist of time? Such ancient carbonates generally form ramps or unrimmed platforms, usually during periods when large reef-building metazoans were absent. These limestones can confidently assumed to be true cryocarbonates when at high paleolatitudes, when interbedded with glacial sediments and/or when containing glendonite-group minerals. But similar sediments can be produced during times of major evolutionary change, nutrient excess, pronounced thermocline development and/or excursions of high-latitude oceanic currents into low latitudes. Three end-member platform models are currendy envisaged; 1) cryocarbonate platform model (mid-high latitude, high energy, cool-cold seawater, cryocarbonate throughout), 2) upwelUng platform model (low-mid latitude, low/high energy, warm-cool seawater, cryocarbonate + ooids & green algae) and 3) thermocline platform model (low-mid latitude, low/high energy, strongly temperature-stratified seawater, inboard temperate cryocarbonate & thermocarbonate, outboard cryocarbonate). Permian limestones from several areas contain attributes that strongly suggest they were true cryocarbonates. Similar Mississippian and Ordovician limestones, however, are more equivocal and likely formed on upwelling and/or thermocline platforms. Recognition of these different types of shelves and ramps and their correct interpretation is crucial to any actualistic portrayal of Paleozoic oceanography or platform dynamics and any prediction of subsurface facies trends. Cool Climate Carbonate Conference (Page 43) Geelong 1994

Application of Recording Nephelometers to sedimentation studies on the modern shelf

P. Larcombe & R. V. Ridd Marine Geophysical Laboratory Geology Department James Cook University of North Queensland Townsville Qld 4811 Data on water suspended sediment concentrations (SSC) are of importance in a range of shelf studies, including erosion, resuspension and deposition analyses of sediments, and ecological studies. Recording optical backscatter (OBS) devices such as nephelometers, allow continuous measurement of SSCs in marine waters, but their deployment periods are often limited by biofouling to just a few days. Instrumentation developed at JCU not allows collection of long term-series OBS data (weeks-months). We show data from tropical mbced siliclastic/carbonate shelf environments, with methods directly applicable to cold water carbonate environments. Winds, waves, currents and SSCs were measured continuously over a period of 4 months at a range of sites near fringing coral reefs on the inner shelf of the Great Barrier Reef A total of 30,000 hours of nephelometer data (measured 30cm above bed) was collected, with over 500 water samples, 250 sediment traps and 25 sea-bed cores. Measured SSCs on the inner shelf were between 5mg/l and ca. 300 mg/1, although most commonly 10-50 mg/1. They are controlled mostly by long wavelength waves (swell) generated by the regional wind regime. In contrast, at the adjacentfringingreefs, SSCs were much lower, only rarely attaining 40-50 mg/1, achieving periods of over a day with SSCs > 20 mg/1. SSCs are controlled by short wavelength wind-waves, generated locally. These data indicate that: 1.

Corals can clearly thrive in conditions thought previously to be above "exceedance limits" of SSC;

In combination with core data, ancient ecological conditions may be inferred, which for the inner shelf of the central GBR, are likely to have been similar since 6000 by B.P.

Clearly, time series SSC data are powerful tools in understanding sedimentary processes in modem shelf environments.

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A rapid transition from warm-water to cool-water carbonates in the Upper Ordovician (Caradocian) section of eastern North America Denis Lavoie. Quebec Geoscience Center, Geological Survey of Canada, 2700 Einstein Street, P.O. Box 7500, Ste-Foy, Quebec, Canada GIV 4C7. The Upper Ordovician Trenton Group of southern Quebec (eastern Canada) represents the last Taconian foreland basin carbonate unit in the Quebec Reentrant, prior to final collapse of Laurentia's continental margin and its burial under syn-orogenic flysch. The Trenton Group either conformably or unconformably overlies the lower Upper Ordovician Black River Group (carbonates) and is in turn conformably overlain by the Upper Ordovician Utica Shales. The tripartite Trenton unit records progressive deepening from 1) very shallow to shallow carbonate ramp, 2) shallow to deep carbonate ramp and 3) shallow to deep outer shelf. Regional facies distribution, lithotectonic elements and thicknesses variations indicate that the Trenton shelf was dissected by extensional faults delineating blocks subsiding at various rates. From regional considerations, it has been shown that tectonism played a key role in the demise of carbonate sedimentation at the continental margin. The Trenton Group has a distinctive coarse-grained middle unit, the Deschambault Formation. Lithofacies of the Deschambault are dominated by coarse-grained bioclastic/intraclastic grainstone and rudstone,finer-grainedlithofacies are ubiquitous but subordinate. The complete spectrum of lithofacies indicate sedimentation ranging from above fairweather- to below stormwave base. Accretion rates from areas of continuous sedimentation are low (<14 cm/103 years). Skeletal components in the Deschambault are dominated by bryozoans, brachiopods, crinoids and red algae. This faunal association is similar to the m^em temperate-water bryomol association, non-skeletal elements are represented by peloids and intraclasts. From sedimentologic and faunal evidence, it is proposed that the Late Ordovician Deschambault ramp was bathed by temperate waters. The proposed facies model compares favourably with modem cool-water shelves rimming the southern edge of the Australian continent. In contrast, however, the immediately underlying unit, the Black River Group, is characterized by oolitic grainstones, coral-stromatoporoid-algal bindstones and ubiquitous green algae. The latter faunal and sedimentologic evidence are rather suggestive of warm-water conditions. Paleomagnetic data locate southern (Quebec in a low latitudinal (tropical) setting in Late Ordovician. Upper Ordovician litho- and biofacies distribution in eastern North America and Late Ordovician progressive disappearance of some faunal provinces are used to conclude that the initiation of the Late Ordovician glaciation that covered most of Gondwana was instrumental in easing northward movement of cold oceanic currents. This resulted in the n^id contraction (<1 m.y.) of the southern hemisphere warm-water tropical belt from a 30® latitudinal-wide zone in earliest (Taradoc to a 15° zone in early Caradoc.

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Mississippian Cool-Water Carbonate Hydrocarbon Reservoirs in the Southern Foothills of the Canadian Rocky Mountains Bill Martindale & Tom Boreen, Home Oil, Calgary, Alberta Canada T2P 2Z5 Regional Setting and Sedimentology. Mississippian (=Lr. Carboniferous) sediments in the Western Canada Sedimentary Basin were deposited on the downwarp^ western margin of the ancestral North American plate, in a back arc/foreland basin setting formed by plate convergence during the late Devonian/early Carboniferous Antler orogeny (Richards 1989). Upward-shallowing cyclical carbonate and siliciclastic sediments on the ramp-like margin prograded west into the subsiding foredeep forming a series of regressive wedges which were punctuated by several transgressive events. (Second and third order) cycles consist of basal fine grained bioturbated siliciclastic mudstones overlain by mixed cherty carbonate and siliciclastic wackestones and packestones with brachiopods, bryozoans and a variety of echinoderm remains. These are overlain by graded and crossbedded crinoid grainstones and interbedded bryozoan/echinoderm packstones. Cycles are capped by ooid grainstones, laminated mudstones, nodular anhydrite and fenestral mudstones with pedogenic fabrics and pisoids. Framebuilding organisms such as corals are rare. Facies tracts withm each cycle are lO's to lOO's of km wide and lOO's of km long. Depositional slopes are estimated (R. Brandley, Pers. Comm.) at 0.1®, except in the region of local depocentres.

Tropical v. Cool-Water Characteristics of the Mississippian Palaeogeographic reconstructions of the western margin of N. America during the Mississippian suggest a location between the palaeoequator and 25® N (review in Richards 1989) and it has therefore been generally assumed that Mississippian carbonates were of warm-water origin. Richards (1989) and Mundy (1992) have suggested that durmg the latter part of each upward-shallowing cycle, the ramp evolved into a low relief nearshore platform as a consequence of crinoid/bryozoan shoal accumulation in warm, relatively shallow waters. In their models, warm shallow lagoons formed behind the shoal and fronted a low-energy shoreline characterized by sabkhas and ephemeral ponds. Upward-fining grainstones in distal settings were interpreted as shoal-derived turbidite flows, transported downslope where they are now interbedded with distal low-energy carbonate wackestones and mudstones. While a warm-water model has considerable merit in the mte^retation of nearshore facies, there are many features of the Mississippian which are more characteristic of cool-water, high-energy, open-shelf environments. These include: 1). Deposition m an open oceanic, continental margin setting characterized by an unrimmed shelf and a lack of significant phototrophic firamebuilders. 2). A depositional system characterized by large scale platform progradation rather than aggradation. 3). Broad facies belts continuous over lO's to lOO's of kms with the zone of most active carbonate production some distance from the shoreline. 4). Sediments dominated by the remains of non-phototrophic, nutrient-dependent organisms (echmoderms, bryozoans). 5). Original sedunent compositions which were mostly calcitic (High and Low Mg) not aragonitic. 6). Cycles dominated by tempestites and bioclastic grainstones packaged in metre-scale, cross-bedded cycles that mimic siliciclastics in their hydrodynamic zonation and distribution. 7). Warm water diagenetic features such as oiids, aggregate precipitates, submarine cementation and vadose fabrics are rare and restricted to peritidal areas. 8). Scouring, micritization and abrasion of shelf sediments which indicate that seafloor diagenesis was largely destructive. 9). Pseudomorphs of Dcaite (CaC03.6H20) (Pauly 1963, R. Brandley Pers. Comm. 1994) present in deeper water mudstones. Ikaiite has been reported in deep oceanic settings and is stable only at temperatures of 0-3 ®C when levels of orthophosphate (from breakdown of organic matter) inhibit precipitation of calcite and aragonite. 10). Deep water facies which are bryozoan-rich and include bryozoan mud mounds, fenestrate bryslzoan wackestones/packstones, and ramose bryozoan grainstones.

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Conversely, there are some features which do nm fit a cool-water, high-energy model. These include: 1). Presence of proximal warm water and arid subaerial facies and fabrics including ooid grainstones, laminated microcrystalline dolostones (?primary), rooted horizons, fenestral mudstones, vadose overprint on pisolites deposited in ephemeral ponds and nodular and chickenwire anhydrite. 2). An absence of coarse-grained lag deposits representing condensed sedimentation m high-energy nearshore zones.

Temperature Stratifiled Shelf - the Best of Both Worlds! To account for the factors listed above, a stratified warm shallow/cold deep shelf model is proposed for the Mississippian in the Southern Rocky Mountains. Palaeo-oceanographic reconstructions of the Mississippian (Parrish 1982) place the west coast of North America in an equatorial or low latitude position. Typically, that would result in warm surface waters separated from deeper, cooler waters by a thermocline at 100-200m and a zone of phototropism well above the thermocline. Modeling by Hay et al (1990), however, suggests that the Pangean continent at these latitudes would have had arid, offshore winds. Interraction of these winds with nearshore waters induced equatorial or coastal upwelling of cold, nutrient-rich waters from below the thermocline. In the temperature stratified model proposed here, upwelling promoted the growth of nutrient-dependent bryozoans and echinoderms in wide facies belts across the Mississippian shelf. However, a combination of low shelf gradient and offshore winds reduced the intensity of oceanic swell and storm waves, which would explain the absence of a high energy, shaved nearshore shelf. Thus the depositional setting of the Mississippian shelf in the southern Rockies was much like that of the present day south coast of Australia but was of lower energy and was temperature stratified, exhibting both warm and cool water characteristics (Fig. 1).

ORIQINAL MINERALOQY RESERVOIR OUAUIY

Sromtlictls. Bryo-rtoh SMjswiti PfWIARY miosmr

Mud-dombiaid Sddlmenti TIGHT

DolomHizationof Mudf.Le«chinoof CtlcHBAIIoohemt SECONDARY POROSmr

Exiinsivt Syniudai CementB TOKT (flXOBpt W4>6W I dolofiMztd) 01 R§mfvokFBciBi

MutfKtofninaM MMOR PRMMiY POROSITY

Figure 1 - Generalized depositional model of an Early Carboniferous carbonate ramp, S.Rocky Mountains, Canada.

The Mississippian as a Hydrocarbon Reservoir In the southern Rocky Mountain Foothills, Mississippian carbonates host significant oil and gas reserves which have been the focus of exploration since the 1920's. Exploration success depends on structural settmg and reservoir quality, which in turn is a function of diagenetic modification.

Diagenesis of Mississippian Carbonates Early, marine phreatic diagenetic fabrics include micritization of allochems and precipitation of fibrous isopachous marine cements. Vadose and evaporitic fabrics are confined to peritidal sediments and include pedogenic fabrics, meniscus cements and precipitation of nodular anhydrite. Prunary dolomite may have precipitated in sabkha settings. Marine (? and meteoric) phreatic shallow burial diagenesis is dominated

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by precipitation of syntaxial calcite on echinoderm grains and by reflux dolomitization of hypersaline brines generated in overlying sabkha sequences. Dolomitization may be partial, affecting only the fine-grained mud matrix of wackestones and packstones, leaving calcitic allochems unaffected or may be pervasive, dolomitizing both matrix, allochems and syntaxial cements. In general, dolomitization is fabric retentive. During deeper burial, calcitic allochems were preferentially leached, resulting in significant mouldic porosity locally. Oil emplacement and thermochemical sulphate reduction occurred at high temperatures during deep burial (Jurassic/Cretaceous Laramide orogeny) and generated methane, saddle dolomite, calcite, anhydrite, H2S, sulphur and pyrobitumen. Structural Setting The Front ranges andFoothills of the Rockies are the eastern-most expression of the compressional Laramide and Cordilleran orogenies of W. Canada. They consist of west-dipping, highly imbricated thrust sheets of Pre-Cambrian to Tertiary rocks with over 150km. of shortening. The southern Foothills in Alberta consist of highly deformed Mesozoic and Tertiary clastics underlain by deeper thrust sheets carrying Mississippian to Cambrian carbonates. Locally, imbrication of a number of deeper thrust sheets has carried palaeozoic carbonates to surface, where they form broad anticlinal outliers. Reservoir Quality Hydrocarbons are reservoired in structural culminations at the leading edges of thrust sheets. Porosity is developed withm both limestones and dolostones and consists of primary interparticle and secondary intercrystalline and biomoldic pore systems. Primary porosity is rare and is conEmed to crmoid /bryozoan grainstones and packstones where the fibrous skeletal structure of bryozoans resists cementation and mhibits complete occlusion of porosity by syntaxial cements. Secondary intercrystalline porosity is developed in dolomitized shallow lagoonal mudstones and in crinoid grainstones. The most effective porosity is biomouldic in crinoid/bryozoan packstones and wackestones. Here, calcitic allochems which survived dolomitization, are preferentially leached resulting in porosities of up to 10%. Ironically, m many fields, the best reservoirs are in muddier intervals which are preferentially dolomitized and leached. Grainier intervals ^ e syntaxially cemented early, resist dolomitization and remain tight. Overall, however, Mississippian reservoir quality is poor and only becomes effective at or close to the leading edges of thrust sheets wherefracturessignificantly improve permeability. Exploration History & Production Gas and oil seeps from Mississippian outliers and mapping of surface anticlines provided the incentive for exploration as early as the 1920's. The first significant gas and condensate discovery was in 1924 from the Mississippian at Turner Valley, Alberta. At that time, there was no market for gas and most was flared. Oil was discovered in Turner Valley in 1936 and until the late 1940's, the Turner Valley field was the largest in Canada and the British Commonwealth. Original reserves were 81 x lO^m^ (2.8TCF) gas and (132 X 10^ bbls) oil. Today the Turner Valley field continues to produce oil via waterflood and 22 X has recently been the focus of enhanced recovery using horizontal drilling techniques.There are 19 Mississiopian gas fields in the southern Alberta Foothills with total initial reserves of approximately 453 xlO^ m3 (16 TCF). Light oil and condensate are found downdip of the gas at Turner Valley and in a recently discovered pool at Moose Mountain, a gas-producing palaeozoic outlier with a colourful exploration history dating back to 1929. Bibliography HAY. W.W., BARRON, E.J. & THOMPSON, S.L. (1990) Results of global atmospheric circulation experiments on an earth with a meridional pole-to-pole continent. J. of the Geol. Soc. London, 147, 385-392. MUNDY, D.J.C. (1992) Sedimentology, Structural Geology and Exploration History of the Mississippian at Moose Mountain, S.W. Alberta Foothills. Field Trip Guidebook, A.A.P.G Annual Convention, Calgary. PARRISH, J.T. (1982) Upwelling and petroleum source beds, with reference to Palaeozoic. A.A.P.G. Bull. 66, 750-774. PAULY, H. (1963) "Ikaite", a new mineral from Greenland. Arctic, 16, 263-264. RICHARDS, B.C. (1989) Upper Kaskaskia sequence: uppermost Devonian and Lower Carboniferous. In: Western Canada Sedimentary Basin. A Case History (Ed. Ricketts, B.D.). C.S.P.G. 165-210.

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The neritic carbonate record in southern Australia: the biogeohistorical framework Brian McGowran, Qianyu Li, and Graham Moss Dept Geology & Geophysics, The University of Adelaide, SOUTH AUSTRALIA 5005 The neritic stratigraphic record sorts into four "sequences" which resemble the putatively global second-order sequences based on sequence stratigraphy. The Cainozoic record of global climatic deterioration is sharply punctuated by four sharp coolings ("chills") and they too are chronologically consistent with the regional neritic record. Correlations and age determinations are limited by the facies, the extratropical situation, and the lack of a local or regional geomagnetic pattern. The record is highly incomplete at the second order (especially by a 9Ma gap in die Eocene; poor and restricted records of the early Oligocene and late Miocene); and at the third order, where hiatus is becoming more not less apparent; at lower orders cycles are obvious everywhere. In this interrupted regional succession we have had to move from regional stages only loosely based on fossils, to biostratigraphic ranges and formal zones (of planktonic foraminifera), to faunal associations based on transgressions and regressions, so that we are now but a short step from sequence bio stratigraphy and a revision of the regional stages. For this geochronological scaffolding is important not only to the neritic realm itself, but also to the neritic-oceanic link and ODP drilling in one direction, and to the terrestrial environmental and palaeobiological realm in the other. In the oldest sequence the sediments are marginal marine siliciclastics with several very brief transgressions (ingressions) with marine microfaunas and rare macrofossils but no limestones. Extratropical carbonates begin very suddenly at the Wilson Bluff transgression which is the Khirthar restoration of the IndoPacific region. At the same time the Leeuwin Current is switched on for the first time. Both are due to the sudden acceleration of Australia/Antarctica separation. The Leeuwin Current becomes a recurring theme in enhancing the global record of warm climatic pulses by injecting warm water and warm biota into this extratropical realm. This effect reaches its late Palaeogene maximum at the Tortachilla transgression and its Neogene zenith in the BatesfordianBalcombian at the Miocene climatic optimum. The third order of biogeohistory is the focus of biostratigraphy, sequence stratigraphy, and climatic fluctuation and the ecostratigraphic succession. We have progressed accretionally from sealevel change and water depth, to climatic change and tropical-type biotic incursions, to the trophic resource continuum and fluctuations in nutrient supply. All of these variables make sense not merely locally and regionally, but globally. Ecostratigraphic change is seen in quantified foraminiferal profiles. The main ratios are between planktonic groups, planktonics/benthics, shallow/deep benthics, and infaunal/epifaunal benthics. Warm incursions are oligotrophic; signals at the eutrophic end of the spectrum are most cogent where the planktonic and benthic patterns run in parallel, implying an environmental not a taphonomic cause. Our third order patterns by and large are consistent with both the putative global sea level patterns and the glacial cycles inferred from third order 5180 cycles.

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geochronology

transgressions

regional stages

mega-sequences

GLANVILLE

PLEISTOCENE

CHILL IV

WERRIKOOIAN

L PIACENZIAN

PLIOCENE E ZANCLEAN

MESSINIAN

HALLEHCOYE

KALIMNAN

WHALERS BLUFF

CHELTENHAMIAN

N17

global climate 2nd-order sequences

i\r

TB3

MITCHELUAN

L TORTONIAN

BAIRNSDAUAN

SERRAVALLIAN

CADELiyBALCOMBE MORGAN/BATESFORD BATESFORDIAN

LANGHIAN

UPPER MANNUM/ LONGFORD

BURDIGALIAN

LONGFORDIAN

CLIFTON

P22 L

Miocene optimum TB2

AQUITANIAN

CHILL III

TBI

JANJUKIAN

CHATTIAN P21b P21« -30

RUPELIAN

P20 P19

WILLUNGAN

CHILL II

ALDiNGA LPRIABONIAN

hii

TUIT P15

TUKETJA

P14 TORTACHILLA

BARTONIAN

-40

"piT

TA4

ALDINGAN

JOHANNIAN

WILSON BLUFF

Khirthar restoration

P12

LU LU

LUTETIAN

TA3

P11

CHILL I 50

YPRESIAN

BURRUNGULE P7

WANGERRPIAN

RIVERNOOK-A PEBBLE POINT

UU m o

PRINCETOWN RIVERNOOK

TA2

L SELANDIAN

o UJ

KINGS PARK 26

TA1

DANIAN Pib

CEDUNA MAASTRICKTIAN

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The origin and timing of siderite and calcite concretions In EoOligocene non- to marginal-marine facies of the Te Kuiti Group, New Zealand Heather A. Moxham * and Campbell S. Nelson *Department of Earth Sciences, University of Melbourne, 3029, Parkville, Melbourne, Australia Department of Earth Sciences, University of Waikato, Private Bag 3102, Hamilton, New Zealand

Introduction

Because concretions may develop before, during, or following sediment compaction they can provide useful information about the evolution of pore fluids during diagenesis. Diagenetically early carbonate concretions occurring within the lower two formations of the transgressional Te Kuiti Group in New Zealand, record the transition from carbonate precipitation from purely meteoric fluids, to precipitation from marine fluids and a shifting carbonate carbon source across this transition.

Geologic setting

The Te Kuiti Group comprises a predominantly transgressive sequence of late Eocene to earliest Miocene sedimentary formations ranging upwards from fresh-water coal measures to brackish to marginal-marine siliciclastic deposits to fully marine mixed carbonate-siliciclastic and pure carbonate formations that are widespread throughout central western North Island of New Zealand. Concretionary structures are common in the lowest formations of the Group, being dominantly sideritic in the non-marine Waikato Coal Measures (WCM) to brackish Glen Afton Claystone Member (GAC) of the Mangakotuku Formation and calcitic in the more marine-influenced Rotowaro Siltstone Member (ROS). Samples for this study come mainly from five opencast coal mines and one underground coal mine in the Huntly region.

Timing

Cementation was initiated during very early diagenesis in all of the concretions examined, ie within the first few metres of burial and probably in many instances just beneath the sediment water interface, as evidenced by the high inferred porosities at the time of cementation (60 - 90%), and from field observations that (1) laminated host sediments drape over concretions indicating formation prior to compaction, (2) fragile fossils for example hydridella, and echinoid spines are preserved undeformed in many of the concretions observed, and (3) individual carbonaceous laminae when they occur within erratically cemented horizons are up to three times the thickness in cemented regions as in non-cemented intervening regions. Comparison of inferred carbonate precipitation depths with estimated sedimentation rates, suggest that the bulk of cementation

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occurred within several hundred ky of sediment deposition. However in some of the larger concretions cementation continued (although at a reduced rate) for up to 5 My,

Geochemistry Trace elements - The degree of Ca and Mg substitution for Fe in the siderite cements increases both on passage from the WCM through the GAC to the ROS (Fig 1) and from the central to marginal cements within individual WCM concretions, reflecting the transition from precipitation from meteoric fluids to fluids with an increasingly marine influence and therefore higher levels of and Ca^^ relative to Fe2+ levels (Mozley 1989). Matrix cements in the Rotowaro Siltstone concretions are mainly non-ferroan, mildly magnesian calcite, comprising 2.0 - 5.6 mol % MgCOs. The Fe-poor nature of the calcite cements coupled with the presence of abundant pyrite in concretion cores is suggestive precipitation in the sulphate-reduction zone, where the formation of pyrite is removing most of the reduced iron in solution (Raiswell, 1976). CtCQs

- 20

CtaCOt

(Fe+MiOCO, KEY •WCMcmre • WCMnin 4.GAC ORGS

MfCOi

•i r ;•

/ /

/ / / / +

• SMarite-WCM « C«lcito • WCM a C«ici1« -WCM + +

• S<d«ite-ROS

• • / 100% (Fe + M n ) C 0 3

r-r— --15 -20

iW'"' MgC03

for siderites analysed by electron microprobe.

—10 —20 ^-30

sssr.'^ • excite- ROSi

-10

-5

5"0

Figure 2 . v s for carbonate cements from the WCM, GAC and ROS. Inset continental and marine fields for siderite (from Mozley and Wersin 1992).

Stable isotopes - Central carbonate cement values indicate precipitation from fluids increasingly enriched in S^^O on transition from the WCM (-5.7 to -L0%o PDB) through GAC (-1 to l%o PDB) to ROS (-1 to l%o PDB) (Table 1, Figure 2). Near surface temperatures for carbonate cements are obtained for all concretionary materials if meteoric formation fluids are assumed for WCM (6w -7 SMOW, Bums, 1980), mixed meteoric marine fluids are assumed for GAC concretions (ie 5w -4 SMOW) and marine parent fluids are assumed for ROS concretions (ie 5w -1 SMOW, Bums and Nelson, 1981). Marginal cements in all of the larger concretions (>30 cm across) are characterised by lower inferred porosities and more depleted oxygen isotopes consistent with concretion growth outwards from centre to margin. Oxygen isotope variations and petrographic relationships indicate that calcite septaria within WCM and ROS concretions started to develop during the later stages of concretion growth. Carbon isotopes also exhibit a marked dependence on the environment of deposition with WCM concretions exhibiting positive values 1.6 to 12.8 PDB) suggestive of precipitation within the methanogenic zone. Calcite septarian cements in WCM concretions have variable but often highly depleted carbon isotope values (S^^C -16.3 to 3.1 PDB) suggestive of carbonate contribution from methane oxidation. The presence of

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moulds after aragonite in the brackish GAC, coupled with the uniform marine carbon isotopic values for the siderite concretions in this unit (S^^C -1.8 to 1.1 PDB), is suggestive of aragonite dissolution being the primary source of concretion carbonate. Calcite concretions within the more fully marine ROS have depleted carbon isotopic compositions (S^^C -31.7 to -6.5 PDB) indicating carbonate production within the sulphate reduction zone. TABLE 1. CARBONATE SOURCE FOR MAJOR CEMENT TYPES Cement

ai80

O source

ai3C

Fomiation

C source

Depth (m) Temp ( C) WCM siderite -matrix c

-5.9 to-1,0 meteoric to mixed meteoric 3.9 to 12.3 /marine. siderite - matrix m -2.3 to -5.7 meteoric to mixed meteoric 2.8 to 12.8 Miarine at elevated temp. calcite - veins -7.9 to -9.4 meteoric to mixed meteoric -16.3 to 3.1 /marine at elevated temp. GAC siderite -matrix c

-1.4 to 1.0

siderite - matrix m -0.6

Time (ky)

methanogenesis

<10

6to25

>90% grown

methanogenesis

<50

10 to 24

300 to 1000 growth completed 1300 to 5000

methanogenesis methane oxidation

23 to 300

19 to 26

mixed meteoric/marine

-1.8 to 0.9

aragonite dissolution

<0.5

9tol8

>90% grown 15 to 50

mixed meteoricAnarine

-0.7

aragonite dissolution

growth completed

marine

-31.7 to-12.1 sulphate reduction

<10

6tol3

>90% grown

ROS calcite - matrix c

60 to 200 -0.8 to 0.9

170 to 330 calcite - matrix m

-1.0 to-3.8

calcite - vein G1

marine to marine at elevated temp. -0.6 to-1.0 marine

calcite - veinG2

-3.3 to -7.7

marine at elevated temp. possible meteoric mixing.

14 to 27

sulphate reduction

<80

-26.4 to-19.5 sulphate reduction

6 to 95

12 to 14

600 to 1800

25 to 48

-31 to -6.5

-10.0 to 0.7

mixed sulphate reduction

growth completed 1360 to 2640

and methanogenesis

References BURNS, D.A., (1980). Aspects of the stable isotope geochemistry of some New Zealand sediments. Unpublished M.Sc. Thesis, University of Waikato, Hamilton, New Zealand. 122 pp. BURNS, D.A„ NELSON, CS., (1981) Oxygen isotopic paleotemperatures across the Runangan Whaingaroan (Eo-Olig) boundaty in a New Zealand shelf sequence. New Zealand Joumal of Geology and Geophysics, v. 24,529-538. MOZLEY, PS., (1989a) Relation between depositional environment and the elemental composition of early diagenetic siderite: Geology, v. 17,704 - 706. MOZLEY, PS., WERSD^ P., (1992) Isotopic composition of siderite as an indicator of depositional environment. Geology, v. 20, 817 - 820. RAISWELL, R., (1976) The microbiological formation of carbonate concretions in the Upper Lias of N.E. England. Chemical Geology, v. 18,227-244.

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Some preliminary observations on marine cements in OlizoMiocene shelf limestones from New Zealand: an enigma or the norm in the nontropical carbonate model? Campbell S. Nelson^ and Noel P. James^ ^Department of Earth Sciences, University of Waikato, Hamilton, New Zealand ^Department of Geological Sciences, Queen's University, Kingston, Canada It is now appreciated that shallow-marine carbonate deposits can be widely developed on modem cool- or cold-water shelves as well as the more familiar setting of warm topical seas. To aid in the distinction between tropical and nontropical limestones in the Phanerozoic record a variety of textural compositional, skeletal, and diagenetic properties have recently been formulated (e.g. Nelson 1988). Amongst these it has been suggested that synsedimentary marine cements are mainly absent or rare in nontropical carbonates, due mainly to temperate waters being colder and having a lower or more variable degree of carbonate saturation compared to tropical waters, where a variety of inorganic precipitates occur. Indeed, seafloor diagenesis in cool-water settings has been labelled potentially 'destructive', involving processes such as grain bioerosion, maceradon, and dissolution, rather than cementation. New Zealand Cenozoic limestones share the majority of attributes typical of nontropical carbonate deposits (Nelson 1978). Maximum development was during the Oligocene-earliest Miocene when the New Zealand landmass was topographically subdued and largely submerged, accumulating mixed siliciclastic-carbonate and skeletal carbonate deposits upon a vast, shallow oceanic, ramped platform. The resulting limestones are predominantly bryozoan-rich and dominated by burial cements sourced from varying amounts of pressure-dissolution between skeletal grains, reflecting the diflferent burial histories of the deposits. However, some preliminary petrological work indicates that marine cements are locally developed in many of the Oligo-Miocene platform limestones, including those in the North Wanganui, South Taranaki, West Coast, South Canterbury, and Southland basins. In the field and in handspecimen the marine-cemented limestone units are often conspicuous because they are coarse-grained, include well abraded and reasonably well sorted skeletal material, are often macrofossiliferous, may contain scattered terrigenous pebbles and carbonate clasts, may be associated witb Fe-Mn-P04 •'^lineralisation^ and frequently preserve spar-filled moulds of former aragonitic molluscan and bryozoan biofragments, an otherwise rare or absent feature in the majority of associated limestones. Moreover, despite later burial, the marinecemented limestones typically preserve an open grain fabric, largely unaffected by significant pressure-dissolution, with relatively large interparticle pore volumes of 15-40% or more. Locally the marine-comcnted limestones support hardground faunas, mcluding encrusting oysters, solitary corals, and serpulids, and their upper surfaces may be truncated and bored. In thin section the most distinctive of the marine cements is an isopachous rind of fibrous to bladed, nonferroan, low-Mg calcite crystals lining, but rarelyfilling,both intra- and interparticle pores. The calcite rinds are 50-200^m thick, inclusion-rich, and have dull or blotchy cathodoluminescence. The fibrous cements are overiain by micrite or equant spar. The micrite is of three types:

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(1)

(2)

(3)

Microbioclastic micrite - a heterogeneous mix of pasty brown micrite and fine silt-sized skeletal detritus, interpreted as internal sediment pumped into pore spaces interconnected with the sea bed; Homogeneous micrite - a pale to deep brown, dense uniform "paste" comprising an interlocking mosaic of irregular (sub)equant cryptocrystals (<4|im across), interpreted mainly as a marine cement; Peloidal micrite - vague to distinct micritic clots, from 5-15|im or larger in size, set in usually subordinate amounts of very fine microspar, also interpreted as marine precipitates

Pore spaces may be occluded by these micrite types, with or without the initial formation of isopachous spar rinds about grains, or they are occluded by equant calcite spar of later burial origin. In rare cases the pore spaces porewards of the isopachous rinds have remained empty and such samples retain a high primary porosity. A feature of the marine cements is the wide variability m their nattlre, distribution, and degree of development, both within and between samples. Based on the evidence of variably neomorphosed fabrics and a relative enrichment in Mg of the marine cements compare to both their substrate grains and later burial calcite spar, it is inferred that the primary mineralogy of the marine cements was probably ( ? moderate-) Mg calcite. The 5 and 6 ^^C values of bulk limestones with marine cements fi-om a particular locality are always more positive than the associated burial-cemented limestones, consistent with a phase of early sea floor lithification. The least buried (<300m) of the marine-cemented limestones are fi-om the South Canterbury region, and these probably best reflect the primary isotope signature of the marine cements, the small positive 6 ^^O and 5 ^^c values near 1 to 2% being those anticipated fi-om equilibrium precipitation of carbonate fi-om cool shallow marine waters (e.g. Rao and Nelson 1992). The age of the sampled marine-cemented limestones ranges fi-om early Oligocene to early Miocene, mainly fi-om late Oligocene to earliest Miocene, about 30 - 20 Ma (includes the Duntroonian, Waitakian, and part Otaian New Zealand stages; intemational ages Chattian, Aquitanian and part Burdigalian). The marine-cemented limestones seem to be developed at specific stratigraphic positions, such us within rare in situ oyster or bryozoan mounds, at the tops of units possibly representing subtidal carbonate cycles, and particularly associated with certain unconformities. The petrographic and stratigraphic evidence suggest that some combination of high environmental energy level and slow or arrested sedimentation are potentially conducive conditions promoting the marine cementation. More problematic in nontropical settings is the requirement for circulating sea water to be supersaturated with respect to calcium carbonate. Formation is suggested to have been favoured during times of relatively lowered sea level. TUis would have provided the necessary increased energy conditions at the sea floor, a warming of sea water due to shallowing, a probable intensification of upwelling of nutrient-enriched oceanic waters onto the Oligo-NCocene ramped platform where wanning and loss of CO2 would favour precipitation of marine cements (and also any phosphatisation, glauconitisation, etc.), and the potential for associated unconformity development as the sea floor was brought into the zone of open ocean wave abrasion (cf James et al. 1992; James and Bone 1994).

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During the Oligocene, New Zealand lay in the path of rapidly evolving, new oceanic current systems in the Southern Ocean, developing because of a rapid, but fluctuating, build up of ice on Antarctica. Increasingly higher resolution marine 6 records for the Oligocene-early Miocene arc beginning to demonstrate variations consistent with Milankovitch-type glacioeustaticallydriven sea-level fluctuations on the order of several tens of metres or more (e.g Miller et al. 1991). The possible interrelationship between such eustatic cycles, sedimentary cyclothems, unconformity development, and the New Zealand marine-cemented limestone horizons deserves fuller study, especially since similar features are recorded m the Oligo-Miocene limestones of southern Australia (James and Bone 1993, 1994) and elsewhere, and may represenl "eorrelative events" (e.g Vella 1967). However, the situation in New Zealand is likely to be complicated because the late Oligocene-early Miocene was also a time of major tectonic change associated wilh the inception of the convergent Pacific-Australian plate boundary through the subcontinent. JAMES, N.P. & BONE, Y (1992) Synsedimeniary cemented calcaronite layers in Oligo-Miocene shelf limestones, Eucla Platform, southern Australia Jl. Sediment. Petrol. 62, 860-872. JAMES, N.P. & BONE, Y. (1994) Paleoecology of cool-water, subtidal cycles in mid-Cenozoic limestones, Eucla Platform, southern Australia. Palaios 9, 457-476. JAMES, N.P., BONE, Y., VON DER BORCH, C.C. & GOSTIN, V.A. (1992) Modem carbonate and terrigenous clastic sediments on a cool water, high energy, mid-latitude shelf: Lacepede, southern Australia. Sedimentology 39, 877-903. MILLER, K G., WRIGHT, J.D, & FAIRBANKS, R.G. (1991) Unlocking the ice house: Oligocene-Miocene oxygen isotopes, eustasy, and margin erosion. Jl. Geophys. Res. 96, 68296848. NELSON, C.S. (1978) Temperate shelf carbonate sediments in the Cenozoic of New Zealand. Sedimentology 25, 731-771. NELSON, C.S. (1988) An intoductory perspective on non-tropical shelf carbonates. Sediment. Geol. 60, 3-12. RAO, C.P. & NELSON, C.S. (1992) Oxygen and carbon isotope fields for temperate shelf carbonatesfi-omTasmania and New Zealand. Marine Geol. 103, 273-286. VELLA, P. (1967) Eocene and Oligocene sedimentary cycles in New Zealand. N. Z. Jl. Geol. Geophys. 10, 119-145.

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Burial diagenesis of shallow-buried Tertiary limestones^ Otway Basin, southeastern Australia Stelios Nicolaides and Malcolm W. Wallace School of Earth Sciences, The University of Melbourne, Parkville, VIC. 3052, AUSTRALIA

Introduction

The burial diagenetic environment, in which limestones spend most of their geological existence, is the least understood. Studies in the past (eg, Choquette & James, 1987) have recognised two major burial processes which transform carbonate sediments to carbonate rocks: cementation and compaction. It is important to understand these lithification processes and utilise them as prediction tools for the development of good reservoir rocks, hydrocarbon accumulation, and sediment-hosted mineralisation. This study documents the cementation and compaction history of the Heytesbuty Group, a subsurface temperate carbonate succession from the Otway Basin, southeastern Australia (Fig. 1). An advantage of this study is that the Heytesbury Group is undergoing burial diagenesis now for the first time and there are no complications due to subsidence or uplift. The Heytesbury Group is also important to investigate because it is a temperate carbonate succession. Our current knowledge on the diagenesis of temperate carbonates is far from complete (Nelson, 1988). Methods used include transmitted-light microscopy, cathodoluminescence, and trace element analysis.

Geological setting

The Otway Basin originated in the Late Jurassic as a result of the separation between Australia and Antarctica. Sedimentation began in the basin with volcaniclastic and fluvial deposits, followed by coastal and shallow marine clastic deposits. A significant cooling event occurred across the Eocene-Oligocene boundary which affected the biological bdance in the southern Australian continental shelf Cool-water, open marine conditions prevailed during the Oligocene with a reduction in terrigenous input and deposition of the carbonate-dominated succession of the Heytesbury Group (Fig. 2), as a result of increased seafloor spreading. PORT C A M P B E L L EMBAYMENT ||Depo8. setting SEAWARD LANDWARD—^ I & lithoiogy t ^ Newer Volcanics^ ^l Basalt Terrestrial sand First major development of shelf carbonates. Calcarenlte & marl

First near-shore to open manne succession. Mudstone, marl, sandstone

F i g . 1 . Location and generalised geological map of the study area. Modified from Glenie (1971).

F i g . 2 . Stratigraphical position of the Heytesbury Group (with maximum thicknesses). Modified from Tickell (1992).

etal.

Composition

The basal Clifton Formation is a relatively porous, coarse-grained, skeletal grainstone with less porous clay-rich intervals. The intermediate Gellibrand Marl is a muddy, non-porous and impermeable bioclastic argillaceous limestone. The upper Port Campbell Limestone typically consists of a friable, porous and

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permeable bioclastic grainstone with occasional clay-rich interbeds. The skeletal components include bryozoa, echinoderms, benthonic and planktonic foraminifera, serpulid worm tubes, gastropods, bivalves, ostracods, brachiopods, sponge spicules, calcareous red algae, and possible calcispheres. Occasional very-fine sand-sized sihciclastic grains (mostly quartz) and rare glauconite pellets make up the rest of the grains.

Cementation

Cementation is limited and includes: 1) scalenohedral calcite (non-luminescent to bright, Mn- and Fepoor, in inter- and intraparticle porosity); 2) blocky equant calcite (dull, Mn- and Fe-rich, in interparticle porosity); 3) syntaxial calcite overgrowths on echinoderm particles (non/bright/dull-zoned); 4) euhedral dolomite (in the inte^article pore space of the Port Campbell Limestone); 5) bladed-prismatic calcite (ferroan, in planktonic foraminifera); and 6) glauconite and iron oxides (only in intraparticle porosity). All of the petrographically-interpreted late CaCO^ cements are low-Mg calcites (<4 mol% MgC03). The cements observed in the Heytesbury Group (Fig. 3) appear to have formed in three successive diagenetic environments (Nicolaides, 1995): 1) early shallow burial (early Fe- and Mn-poor, nonluminescent syntaxial overgrowths and non-luminescent scalenohedral calcite, under oxidising conditions); 2) late shallow burial (bright, more Mn-rich—than the initial non-luminescent—syntaxial overgrowth zone, and bright scalenohedral calcite, under moderately reducing conditions); and 3) moderate burial (ferroan, dull blocky calcite and dull syntaxial overgrowth zone, under reducing conditions). Pressure-dissolution was the main cement-producing mechanism during burial, although seawater and minor aragonite dissolution could account for the precipitation of the early nonluminescent cements. Scarcity of early interparticle cements may have been caused by the calcite-rich character of the original sediments.

Compaction

Mechanical compaction features, including grain reorientation and grain deformation, occur in most grainstones and packstones of the Heytesbury Group. However, it is extremely difficult to identify pure mechanical compaction features in the wackestone intervals because the allochems are not in contact with one another. Bryozoa, serpulid tubes, and brachiopods are the most affected bioclasts, whereas echinoderm clasts show very little, if any, mechanical compaction features. Grain reorientation and deformation appear to have begun at depths of less than 160 m (shallowest sample). Pressure-dissolution features (Bathurst, 1987) include interpenetration of grains, fitted fabric, dissolution seams, and microstylolites. Stylolites are not present. Petrographic observations suggest that there is a difference between the types of pressure-dissolution features in the various lithologies. While fitted fabric and microstylolites are recognised in the grainy limestones, dissolution seams are identified in the argillaceous carbonate sediments (cf. Railsback, 1993). Pressure-dissolution at grain contacts is by far the most common feature occurring in almost all of the samples, from depths of approximately 160 to 670 m. Fitted fabric and microstylolites are observed in the deeper grainstone samples at a depth of approximately 550 m, whereas dissolution seams are observed in the clay-rich wackestones at depths less than 190 m.

Pressure-dissolution and cementation

It is petrographically evident that there is a decrease in interparticle porosity and an increase in cementation with depth (Fig. 4). Samples taken from shallow depttis (less than 430 m) lack cementation whereas samples taken from deeper parts of the succession (deeper than 500 m) contain significant amount of calcite cement in their interparticle pore space (Fig. 4). These volumetrically important calcite cements appear to coincide with the development of pressure-dissolution features, especially fitted fabric and microstylolites. Thus pressure-dissolution appears to be the primary cement-producing mechanism in these shallow-buried temperate carbonates.

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The degree of interparticle compaction is indicated by measuring the interparticle porosity plus interparticle cements (compaction curve, Fig. 4). Thus, in the depth interval between 0 and 226 m the interparticle compaction is estimated at 45% (from estimated 40 to actual 22%), between 226 and 430 m at 64% (from 22 to 14.2%), whereas a further 29.6% of interparticle compaction is estimated between 430 and 550 m, resulting in a total interparticle compaction of 74% (75% in 670 m). Percentage DIAGENETIC EVENTS

SHALLOW BURIAL EARLY LATE

MODERATE BURIAL

Non-lum. Scalenohedral Bright Scalenohedral Glaucx)nlte Cement Non-lum. Synt. Overgr. Bright Synt. Overgr. Dull Synt. Overgr. Dull Blocky Equant Mechanical Compaction Pressure Solution APPROXIMATE DEPTH (m)

7100-200

7400-500

Fig. 3. Schematic paragenetic sequence of the Clifton Formation.

700 Fig. 4. Relationship between interparticle porosity, cementation, and compaction.

Conclusions and implications

It is concluded from the above that early cementation (marine to early burial) was negligible possibly due to the calcitic character of the sediments. The majority of cements originated in the burial environment as a result of pressure-dissolution. These conclusions imply that temperate limestones can retain their primary porosity during early burial and can be potential reservoirs.

References

BATHURST, R.G.C. (1987) Diagenetically enhanced bedding in argillaceous platform limestones: stratified cementation and selective compaction. Sedimentology, 34, 749-778. CHOQUETTE, P.W. & JAMES, N.P. (1987) Diagenesis #12. Diagenesis in limestones - 3. The deep

burial environment. Geoscience Canada, 14, 3-35. Geology, 60, 3-12. NICOLAIDES, S. (1995) Cementation in Oligo-Miocene non-tropical shelf limestones, Otway Basin, Australia. Sedimentary Geology (in press). RADLSBACK, L.B. (1993) Lithologic controls on morphology of pressure-dissolution surfaces (stylolites and dissolution seams) in Paleozoic carbonate rocks from the mideastem United States. Journal of Sedimentary Petrology, 63, 513-522. NELSON, C. S. (1988) An introductory perspective on non-tropical shelf carbonates. Sedimentary

Acknowledgments

This work was carried out while the first author was receiving an Australian Postgraduate Research Award. We would like to thank the Geological Survey of Victoria for providing the drill core material.

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Temperate-Water Dolomite Cemented-Chimneys from the Outer Otago Continental Shelf, Southern New Zealand

Alan R. Oxpin Department of Geology James Cook University of North Queensland Townsville QLD 4811

Authigenically cemented chimneys and edifices represent submarine fluid escape structures associated with the expulsion of porefluidsat or near ambient temperatures at the sediment-sea water interface. An extensive suite of dolomite cemented chimneys, slabs, and a small fault scarp occur on the outermost continental shelf, east of the Otago Peninsula, on a terrace around 1 km^ at 200m depth, approximately 50 m deeper than the general shelf break. Detrital sediment grains comprise more than 50 wt% in the chimneys. Bioturbation which occurred before cementation, indicate that cementation took place below the sediment water interface. The intense encrustation and boring of chimneys and irregular-shaped carbonatecemented debris suggests that the chimneys have been exhumed, i.e. are relict features. The dolomite cement isfinegrained, poorly ordered, calcic (53 mole% CACO3), cathodoluminescent, depleted in 13C values (-4.9 to -12.8% PDB) indicate that some of the carbon was derived fi-om the biogenic degradation of organic matter. The biSO composition of the cement (+5.9 to +6.4% PDB) is the highest yet recorded for a New Zealand marine dolomite cement. Expulsion of fluid delivered fi-om well below the sediment-water interface is responsible for generating and maintaining conditions favourable for dolomiteprecipitation. Calculated temperatures for dolomite precipitation range fi-om 3® to 5°C, which is significantly cooler than the modem sea bed temperature (8®-10®C). The colder temperatures of precipitation, and a maximum radiocaiton age of 33,000 ± 550 yr. BP of the chimneys, are compatible with cementation during a period of glaciation. The expelledfluidswere composed largely of sea water, possibly modified by a lens of "perched" ground water derivedfi-omthe exposed inner-mid shelf as the shoreline regressed, culminating in the -120m last-glacial shore line (20 ka BP).

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The Lexington Limestone (Late Middle Ordovician) Kentucky: A Cool Water Carbonate-Clastic Ramp In A Tectonically Active Foreland Basin Michael C. Pope and J. Fred Read, Department of Geology, Virginia Tech, Blacksburg, VA 24061-0420

The Late Middle Ordovician Lexington Limestone of Kentucky, U.S.A. records cool water deposition on a high-energy ramp in an active foreland basin. The Lexington Limestone is the basal unit of the thick Lexington to Cincinnatian sequence (lower Trenton Group). TTie ramp sloped gentiy eastward from a forebulge (Cincinnati Arch) into the Appalachian foreland basin and passed abruptiy westward, across a faulted margin, into the narrow Sebree Trough. The Lexington Limestone is composed dominantly of subtidal limestone and shale with rare tidal flat- and skeletal shoal-facies, which developed on structurally controlled highs on the peripheral bulge. Brachiopods and bryozoans are the most abundant faunal elements in the Lexington Limestone. This faunal association, the presence of low-Mg calcite marine cements, the abundance of iron and phosphatic stained hardgrounds, and the abundance of phosphate (up to 2.4 wt. percent), andtiielow accumulation rates (1.4-2.5 cm/kyr); in addition totiielack of warm-water features such as a chlorozoan fauna, ooids, and evaporites, indicate dominantiy cool water deposition. Stromatoporoid and coral horizons in late highstands may indicate warmer conditions during these periods. The major facies developed are: 1) tidal flat facies: laminated/fenestral lime mudstones or skeletal wackestones with karstic features and evidence of early meteoric diagenesis; 2) lagoonal/restricted facies: nodular-irregularly bedded whole skeletal wackestone/packstone with stromatoporoids, corals, pelecypods, gastropods, and red algae (less than 20 m deptii); 3) tidallv influenced skeletal shoal facies: bipolar cross-bedded fine-coarse grainstone; 4) intermediate ramp facies: nodular-irregularly bedded skeletal wackestone/packstone and shale; 5) deep ramp facies: regular bedded shale and limestone storm beds; 6) basinal facies: even bedded calcisiltite and shale (probably > 50 m water depth). The facies commonly are arranged into shallowing-upward cycles. Subtidal cycles, the dominant cycle type, are asymmetric to symmetric, 1-7 m thick, and composed of deep-shallow ramp facies. These high-frequency cycles indicate moderate amplitude sea level fluctuations (a few tens of meters) which caused alternate rapid shallowing and deepening of the ramp. Tidal flat cycles occur in 3rd order late highstands or lowstands and show smaller sea level fluctuations. The available biostratigraphic and chronostratigraphic data indicate the average cycle duration ranges from 40-130 k.y. The Lexington Limestone and the equivalent lower Trenton Group in the Appalachian Basin suggest that cool oceanic waters were present to paleolatitudes of 10-30^ S during the Late Middle Ordovician. The change to cool water carbonate deposition following Early - and Early Middle Ordovician warm water carbonate deposition may be related to volcanic outgassing associated with regional bentonite deposition; regional tectonism creating arelativelydeeper, cooler water setting in a stratified epeiric sea; southward migration of North America into cooler latitudes; or global coolingrelatedto the onset of Gondwana glaciation. The moderate amplitude sea level fluctuations indicated in the subtidal cycles may be due to glacio-eustatic sea level changes associated with waxing and waning of Gondwana ice sheets during a time of global greenhouse climate.

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Distribution and sedimentation rates of bioclastic sand along the coast of Southern Norway

Dag Ottesen & Reidulv Bee, Geological Survey of Norway, P.O.B0X 3006-Lade, N-7002 Trondheim, Norway. In spite of extensive e}q>loitation of marine caibonate sand (as fertilizers for agricultural purposes) along the western coast of Norway, little attention has been drawn to these cool wats* carbonate d q ) 0 ^ in the geological literature. Some work has been carried out on their geochanical composition and quality as soil fotilizers (Sve et al. 1990), but littie work has dealt witii the sedimentology and sedimoitation rates of carbonate sand depo^. The examined carbonate sand is bioclastic, typically dominated by molluscfi^agmentswiiich make up more than 90 % of the sediment. Serpulids, barnacles and echinoids are present in minor amounts. The calcareous red alga Lithothamnium may also occur, but rardy in large quantities in Southern Norway.

Occurrence 5«E

rS0YA

11°E

hWN ^Ctoondhi

Cool water, modem carbonate deposits in Europe are described from the coast of Brittany in northwestern France, from the western part of the English Channel and in Cornwall, along the western coast of Ireland and the western and northern coast of Scotland. In Scandinavia, caibonate sand deposits occur in Denmark and along the western coasts of Sweden and Norway. Regional moping (shallow sdsmic and grab san^ling) by the Geological Survqr of Norway has shown that carbonate sand depoats occur in a narrow coastal bdt, with thousands of islands and skerries^ along the outermost part of the southern and western coasts of Norway ^ig. 1). The seabed within this coastal bdt has irregular relief and oftai drops down to the i|ord bottom at several hundred metres water depth. Carbonate sand depoi^ are normally situated between 0 and 50 metres water depth. Due to moderate landuplift of the coastal areas after the degladation (Svendsen & Mangerud 1987), carbonate sand is rarely located above sea level in southmi Norway.

Fig. 1. Carbonate sand and gravel deposits along the coast of Norway from lindesnes to Lysoya. The stippled line represoits the ^proximate landward boundary of areas with large carbonate sand deposits. Dots show msj or carbonate sand deposits to the south of Stadt.

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Description and results The shoreline along the western coast of Norwayfecesthe North Sea, and is exposed to westerly winds. There is little input of terrigenous matoialfrommôr rivers to these coastal areas, and thisfevorsthe growth of lime-secreting organisms. Skeletal grains accumulate to form carix)nate sand and gravel depo^. The commonly bare rock surfece along the southern and western coast of Norway in general fevours hard bottom, benthic communities. This is also reflected in the bioclastic composition, with the byssaly attached Modiolus modiolus often as a môr consituent. Six vibrocores (maximum length 270 cm) were taken at water depths between 7 and 64 m in Austevoll and Sund (Fig. 1). The top and bottom of these cores were dated by the ^^C-method. The ages and computed sediment accumulation rates are shown in Fig. 2. The sediment accumulation rate in Sund varies beêen 43 and 57 cm/1000 years, and in Austevoll between 35 and 130 cm/1000 years. A locality at Lys0ya in Sar-Trendelag (Figs. 1), comprises an almost pure carbonate sand deposit lying between 0 and 15 m above the present sea levd. The thickness of cartonate sand reaches more than 10 metres. The sedimentary succession at the back-wall of the pit is from bottom to top: 1) 0.5 m of gladomarine clay with dropstones and a few molluscfragments.2) a 2 m thick transition zone layers of siliclastic sand and gravel with an upward increasing content of carbonatefragments3) 10 m of almost pure, stratified carbonate sand and gravel with erosive troughs up to 20 cm deep infilled with cross-bedded sand and gravel in the uppermost 3 m of the section. kyr

LYS0YA m

Kyr

SUND 11

\ ^

(D STORE VAflOBY ® STORE RIS0Y ® F/ER0Y

AUSTEVOLL m

10-

11 12

CARBONATE SANO/^VEL MKElTaWBdNAfE" AND TERRIGENOUS SEDIMENTS

kyr 5

The sedimentary succession is interpreted as a shallowing upwards sequence. A molluscfi-agmentfrom the clay near the bottom of the pit has been dated by the AMS method to 10140±85 years BP (Rg. 2), which represents the latest part of the Yoimger Dryas cold period. At that time the front of the inland ice was situated about 40 km east of Lysaya. The sediments of the tran^on zone above the days were deposed during Preboreal time (10 000-9000 years BP) (Fig. 2). Carbonate sand accumulation started in the beginning of the Prd)oreal, and increased throughout the period. The sandy carbonate matrix of a coarse beach deposit with cobbles and boulders is ^^C-dated to 4015±90 years BP (T-11167). The sediment represents the transition from of&hore to foreshore conc^ons at this locality. The deposit This means that shell production lasted for about 6000 years,fromabout 10 000 years BP to about 4000 years BP, when the locality rose above sea levd. The carbonate sand accumulation rate at the Lysoya locality variesfrom150 cm/1000 years to 390 cm/1000 year (Fig. 2).

Fig. 2. Sediment accumulation rates (cm/1000 years)fix)mSund, Austevoll and Lysoya.

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Discussion During the maximum of the last gladation (ca. 20 000 years BP), inland ice covered the whole of the Scandinavian peninsula and reached the shelf edge. During this peri(^ exten^e ero«on occurred, and most of the older deposits in the coastal areas were removed. Thus, it was not until the end of the gladal period that conditions were suitable for carbonate production and preservation. Dating by the ^^C-method shows that the nuyority of Norw^ian carbonate sand d q x ) ^ are of Holocene age. The distribution of the carbonate sands and gravels at Lyseya suggests that t h ^ were tran^rted by waves and currents through narrow sounds and concentrated as small fens and wash-over deposits to the south-east (on the lee side) of the skerries. This process of deposition may probably explain the high accumulation rates. Farrow et al. (1984) measured sedimentation rates of carbonate sand on the Orimey shelf to be 10 cm/1000 years, and on the Scottish shelf to be 3 cm/1000 years. The sedimentation rates in Sund and Austevoll, on the western coast of Norway, are 4-11 times higher than the sedimentation rates on the Orkney shelC while the sedimentation rates at Lysay are 15-40 times higher.

Acknowledgement We thank Mike Talbot forcommatts.

References Farrow, G. E., Allen, H & Akpan, E. B. 1984: Biodastic Carbonate Sedimentation on a Kgh-Latitude, Tide-dominated Shelf: Northeast Orknqr Islands, Scotland. J. ofSed Petr. 54,373-393. Sve, D., Erstad, K.J., Lyngstad, I. 1990: Quality of shell sand for agricultural liming in Western Norway.

NorskLandbruk^(Wskning4,65-72. Svendsen, J.I., & Mangerud, J. 1987: Late Wdchsdian and Holocene sea-level history for a cross-section of western Norway. iVbr. GeoL Tidsskr. 70,111-134.

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The Derivation of Mass Transport Sediments on the Continental Slope of the Otway Margin, southeastern Australia and the Influence of Shallow-water Sediments Vicki Passlow Australian Marine Quaternary Program Department of Geology, Australian National University

Introduction This study of sediments from the Otway margin is based on a series of cores taken by the then Bureau of Mineral Resources from two transects across the continental slope (Exon et al., 1992). The cores examined range from around 1000 to 4000 metres water depth. Shelf sediments in this region belong to the cool-water carbonate province, which extends along the entire southern margin of Australia (Wass et aL, 1970). The sediments of the continental shelf and upper slope in the Otway region have been documented in some detail by Boreen et al. (1993). Von der Borch & Hughes-Clarke (1993) have shown that significant mass transport of sediments occurs on the upper slopes in this region. Examination of Late Quaternary sediments of the upper slope indicates that they have been dominated by downslope-transported facies to depths of between 2300 and 2500 metres (Passlow, 1994). The sources of these sediments and the extent to which shelf sediments contribute to transported sediments are examined here.

Sediment Facies Five sediment facies can be identified from slope sediments. Of these, four are attributed to mass transport processes. These are a debris flow facies, two mud flow facies and a turbidite facies. Hemipelagic sediments comprise the other facies present. Muddy bryozoan sand facies These debris flow sediments, olive in colour, typically occur in thin beds at the base of mud flow sediments. The sand-sized fraction is dominated by branching bryozoans and fragments derived from them. Other components include planktic and benthic Foraminifera, ostracods of the shelf and upper slope, echinoid spines and test fragments, gastropods, and scaphopods. These sediments can be correlated with the "robust branching bryozoan muddy sand" identified by Boreen et al. (1993) from the upper slope in water depths of 250 to 350 metres. Laminated olive-grey bryozoan mud facies The mud flow sediments of this facies are widespread over the upper and middle slope. The sand-sized fraction of the sediment includes fragments derived from bryozoans, planktic and benthic Foraminifera, echinoid spines, spicules and fine-grained mica and quartz. A high proportion of fecal pellets is typical. The proportion of bryozoan-derived fragments typically decreases with depositional depth. The equivalent upper shelf facies described by Boreen et al. (1993) is the pelleted skeletal mud, found in depths of 350 to 500 metres on the upper slope. A decreasing proportion of bryozoan fragments in the deeper mud flow sediments indicates that the pelagic muds found below 500 metres are also being transported by mud flows. Laminated foram-nanno ooze This second mud flow facies is closer in composition and appearance to hemipelagic sediments. The bulk of the sand-sized fraction is composed of planktic and benthic Foraminifera, with deep-sea ostracods, echinoid spines, radiolarians and diatoms also present. The deep-sea ostracod fauna indicates that the sediment is derived from a range of slope depths. In contrast to other sediments facies, the shallow-water component, composed predominantly of fine-grained mica and quartz, biogenic spicules and shallow-water ostracods, is strongly size-sorted.

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The degree of sorting suggests that it is derived from fines thrown into suspension in the high energy zone above the shelf break and carried downslope in density flows. This facies is restricted in its distribution, occurring predominantly during transgressive phases (Passlow, 1994). The examination of the last the deglaciation by Boreen and James (1993) indicates that this was a period of considerable reworking of shelf material. There is no equivalent shelf facies, although Boreen et al (1993) have recorded some suspension deposition in the "pelagic ooze" facies below 500 metres water depth. Yellow-grey sand and mud facies The turbidites of the lower slope are composed of a mix of planktic Foraminifera and bryozoans; minor components include benthic Foraminifera, ostracods, echinoid spines, mica, quartz and accessory minerals. The occurrence of turbidites in this region is restricted to low sea-level stands and subsequent transgressions (Passlow, 1994). Several studies in the region have provided evidence that turbidity are not currently active (von der Borch & Hughes-Clarke, 1993; Boreen & James, 1993; Feary et aL, 1992). The colour contrast between the olive-grey muds occurring on the slope and the yellow-grey of most turbiditess suggests that turbidites have been sourced elsewhere. The most likely source is reworked dunes, which were present on the shelf during the low sea-level stand of stage 2 (Boreen & James, 1993). Further supporting evidence comes from the significant presence of Tertiary nannofossil taxa in turbidites (Exon et al, 1992; Appendix 2). Tertiary sediments were exposed and eroded during the high sea-level stand of stage 3 and are a component of sea-floor lag sediments (Boreen & James, 1993).

Conclusions Two of the facies of the slope can be directiy correlated with facies occurring on the upper slope. These are the muddy bryozoan sand facies and the laminated olive-grey bryozoan mud facies. The latter facies is widespread, dominating sedimentation on the slope to depths of around 2300 to 2500 metres, both in the present-day and through the Late Quaternary. The laminated foram-nanno ooze sediments are derived maily from slope material, but include a shallow-water component transported from the shelf break region by density flows. In contrast, turbidites appear to have ^ e sourced from reworked beach sediments exposed onthe continenda slope during low sea-level stands.

References BOREEN, T., JAMES, N., WILSON, C. & HEGGIE, D. ( 1 9 9 3 ) Surficial cool-water carbonate

sediments on the Otway continental margin, southeastern Australia. Marine Geology.112 : 35-56. BOREEN, T . D . & JAMES, N.P. (1993) Holocene sediment dynamics on a cool-water carbonate shelf: Otway, Southeastern Australia. Journal of Sedimentary Geology,63{4): 5 7 4 - 5 8 8 . ExoN, N.F., LEE, C.S., FELTON, E.A., HEGGIE, D., MCKIRDY, D., PENNEY, C., SHAHK, S., STH>HENSON, A. & WILSON, C. (1992) BMR Cruise 67: Otway Basin and west Tasmanian sampling. Bureau of Mineral Resources, Geology and Geophysics Report 306. FEARY, D., BOREEN, T . D . , JAMES, N.P., BONE, Y . , BIRCH, G., LANYON, R. & SHARK, S..

(1992) Preliminary Post-cruise Report, Rig Seismic Research Cruise 1991 Sediments of the Great Australian Bight. Bureau of Mineral Resources Southern Margin Project 121.27 PASSLOW, V. (1994) Late (Juateraary History of the Southern Ocean Offshore southeastern Australia, Based on Deep-Sea Ostracoda. Unpublished PhD Thesis, The Australian National University. VON DER BORCH, C.C. & HUGHES-CLARKE, J.E. ( 1 9 9 3 ) Slope morphology adjacent to the coolwater carbonate shelf of South Australia: GLORIA and Seabeam imaging. Australian Journal of Earth Sciences AO: 5 7 - 6 4 . WASS, R . E , CONOLLY, J . R . & MACINTYRE, R J . ( 1 9 7 0 ) Bryozoan carbonate sand continuous along Southern Australia. Marine Geology.9 : 6 3 - 7 3 .

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FACIES MODELS OF COOL TEMPERATE SHELF CARBONATES, EASTERN TASMANIA, AUSTRALIA C. Prasada Rao and Zahra Z. Amini Department of Geology, University of Tasmania, Hobart, Australia 7001

Tasmania,

Cool temperate carbonates predominate over siliciclastics on the shelf off eastern Tasmania. Calcite content (mean, 59%) is greater than that of quartz (33%) and aragonite (8%). The grain size of sediments is mostly sand (52%) and fine sand (35%) with minor amounts of gravel (12%) and fines (<62|i; 2%) and thus sediments are moderate to well sorted. The major biota in bulk sediments are bryozoa (32%), foraminifera (11%) and mollusca (6%) and the remaining fauna occurs in small amounts. Debris (41%) and skeletal fragments (15%) occur in significant amounts. Pellets (7%) and intraclasts (4%) are minor. Biota type varies with sediment grain-size, with the dominance of bryozoa and mollusca in the gravel fraction; mixtures of bryozoa, foraminifera and mollusca in the sand fraction; and mainly bryozoa and foraminifera in the fine sand fraction. Fines {<61\i) are comprised of micrite and mostiy spicules debris. Bryozoans are excellent producers of sand- and gravel-size grains. The percentile distributions of rotaliids, miliolinids and planktonics in sand, fine sand and bulk sediments are similar because these foraminifera have not been appreciably broken and redistributed. The amounts of Sr and Na increase and Fe decreases with increasing water depth of bulk carbonate. High concentrations of Fe (mean 4,009 ppm) and Mn (57 ppm) indicate dysaerobic conditions. The S^^o values of bulk carbonates indicate bottom shelf seawater temperatures range from 7 to 12°C and these are similar to measured Tasmanian seawater temperatures. Latitudinal and depth distribution of constituents in bulk sediment, gravel, sand and fine sand fractions, minerals and chemical compositions indicate carbonate and bryozoa contents increase with decreasing water temperatures. Low b^^C values and high contents of intraclasts, skeletal fragments and debris suggest that strong currents, waves and influx of large volumes of tropical. Coral Sea water rework sediments off northeastern Tasmania. Influx of cold Subantarctic water around Tasmania in winter provides nutrients for luxuriant growth of fauna, particularly bryozoa in cool waters. Two facies models are proposed. The first facies model (Fig. 1) based on bulk sediment constituents illustrates three major microfacies, namely coastal siliciclastics, modem bryozoa carbonate facies up to 130m and mixed bryozoa carbonates below 130m water depth. The second facies model (Fig. 2) based on variations of constituents in gravel, sand and fine sand fi-actions indicate 5 major microfacies. In order of increasing water depth, these are siliciclastic facies, bryozoa and mollusca facies, bryozoa and foraminifera facies, bryozoa facies and mixed bryozoa facies. This second facies model depicts better the variations in Tasmanian shelf environments and thus evaluation of both grain-size and types of constituents is necessary in facies analysis.

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•

Increasing carbonate % Decreasing insoluble residue % Gravel %

Gravel % Sand % Decreasing fine sand % Increasing bryozoa % Decreasing mollusca % Foraminifera % Sponges Echinoderms %

Decreasing Quartz % Increasing Calcite %

Uniform aragonite % Increasing Sr and Na ppm Decreasing Fe ppm '

Increasing

and

PDB

Figl Cool Climate Carbonate Conference (Page 67) Geelong 1994

MSL (Recent)

Siliciclastics Q. 0) •c k. 0)

Modern & relict carbonate

MSL 18,000 B.P.

130

Increasing bryozoa % —•

Q) >

Decreasing Quartz % Decreasing intraclasts %

Echinoderms % Bivalves %

1 Increasing bryozoa %

•0

Increasing Rotaliids %

(0 0)

Sponges %

Intraclasts % Quartz % Increasing skeletal fragments

(1) " 2

.Eg IL (/)

Increasing sponges % Decreasing Quartz %

Fig 2 Cool Climate Carbonate Conference (Page 68) Geelong 1994

Glacio-eustatic control of coquina type and shellbed stacking on Quaternary temperate shelves, New Zealand Gordon Saul Geology Department James Cook University of Nth Queensland Townsville Q'ld 4811 Sedimentation within the foreland Wanganui Basin, western North Island New Zealand, reflects Plio-Pleistocene sea-level change. Part of an overall regressive sequence, the PlioPleistocene Nukumaru Group comprises repetitive fine sand and pebbly lenticular shellbed (coquina) facies deposited in temperate-water, inner shelf to shoreface environment. Faunas within these shellbeds include variety of estuarine to offshore assemblages which indicate deposition of the limestone facies entirely above contemporary lowstand shorelines (Point X). For the more offshore shellbeds, simple sediment starvation, and bypassing, are the main condensation mechanisms, and result in in situ (biocoenotic, or Type B: e.g. Mangamoko Shellbed) shellbeds. In inshore, shallower water, the high energy processes of wave and tidal current winnowing dominate shellbed development, resulting in transported amalgamations of mbced faunal assemblages (thanatocoenotic, or Type A beds; e.g. Nukumaru Limestone). Field observations from the Pleistocene Nukumaru Group are compared with knowledge of modem shelf shell assemblages in developing a process-model for shellbed (coquina) development for Quaternary cold-temperate shelves.

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From living bryozoan communities to BRYOMOL deposits on boreal-subarctic shelves of the North Atlantic - an actualistic approach Priska Schafer & Beate Bader Geological-Palaeontological Institute, Kiel University, Germany Suspension feeding communitites dominated by bryozoans and bivalve molluscs are a widely distributed phenomenon from low to high latitudes on outer shelves of the North Artlantic. Temperate ^rittany, France) to subarctic settings (North Norway) along the oceanic gradient of the North Atlantic Current are chosen for the study of living benthic communitites and associated BRYOMOL deposits with special regard to influences of environmental changes on carbonate production and sedimentation. In contrast to constantly oligotrophic conditions in tropical oceans, suspension feeding communitites on mid and high latitude shelves face distinctly higher and predominantly seasonal variations in food supply. A strong bentho-pelagic coupling, indenpendancy from light and the lack of competition with benthic algae are considered to be the major reasons for the dominance of bryozoan-molluscan communities in the aphotic zone on deeper shelf banks. BRYOMOL assemblages reveal only a very biased picture of the former living benthic community that depends on skeletal parameters and habitat zonation, on physical stress exposure and on the degree of sediment redeposition. Formation of BRYOMOL deposits on boreal-arctic shelves is largely controlled by regional variations in the interaction of isostatic uplift and sea level fluctuations in Holocene times. Despite a patchy distribution of living communitites and a generally poor cover with BRYOMOL deposits locally large accumulations on open shelves oflEBrittany and North Norway occur either as large megaripple fields or in leeward eddies on the upper shelf slope.

The following topics are concerned with in the present study: (1) the impact of oceanography, climate and biology on colonization and growth patterns of living bryozoan communitites and on the formation of BRYOMOL carbonates; (2) adaptive strategies of bryozoans to overcome seasonal changes in environmental parameters, and environmental signals in bryozoan skeletons; (3) (palaeo)oceanographic and fades models that explain regional differences in the formation of boreal-subarctic BRYOMOL carbonates; (4) analysis of biological and physical phenomena based on a comparison of living communities and sediment assemblages to provide a tool for the interpretation of the BRYOMOL carbonates in the fossil record.

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Fades analysis of a cool-water carbonate formation: The Oligocene-Miocene Port Vincent Limestone, St.Vincent Basin - South Australia. I B. Shubber, l Y.l Bone, B. McGowran and 2 N.P. James ^Department of Geology and Geophysics, University of Adelaide, South Australia 5005, Australia. ^Department of Geological Sciences, Queen's University, Kingston, Ont. K7L 3N6, Canada.

Introduction

Cool-water skeletal carbonate rocks and sediments comprise the major portion of the stratigraphic record in the Tertiary St. Vincent Basin of South Australia. Several units are exposed along coastal cliffs on both the eastern and western sides of the basin, and can be traced off-shore via boreholes.

The Port Vincent Limestone is an Oligocene-Miocene unit exposed for 50 km along the coastal cliffs on the eastern side of Yorke Peninsula, which is on the western border of the basin. The unit is dominated by the bryomol assemblage and so is mainly a bryozoan calcarenite enriched in foraminifers, echinoids, coralline algae, bivalves and brachiopods. Lithologically the unit exhibits contrasting physical characteristics, with soft and friable, highly porous bryozoan calcarenites, being punctuated by several sharp and distinctive, 0.5 - 1 m thick, layers of hard, low- porosity bryozoan calcarenites. Generally, most bryozoan remains are delicate branching cyclostomes, articulated branching cheilostomes, and less commonly fenestrate, flat robust branching, encrusting, and vagrant bryozoan growth-forms. Based, mainly, on the relative abundance of bryozoan growth-forms and foraminiferal content, two main groups of facies were recognised; 1) Group C - representing cool-water facies, and composed of 70% vol. bryozoa and 0-10% vol. matrix. 2) Group W - representing warm-water facies, and composed of 35% vol. bryozoa, 50% vol. cement and matrix. Group C corresponds to the soft and friable calcarenites whereas group W corresponds to the hard lithologies.

Facies description

Facies analysis and interpretation of the Port Vincent Limestone suggest a shallow marine depositional environment extending from the inner shelf to the outer middle shelf. Facies succession for the studied formation are as follows: (1) Facies CI "Miliolid echinoidal bryozoan packstone - rudstone" This facies is dominated by abundant benthic foraminifer, with miliolids reaching sizes up to 2 mm; common echinoderms and a variety of bryozoan zoareal growth-forms, less common are coralline algae, very rare planktonic foraminifer; all embedded in a patchily distributed micritic matrix. This facies typifies deposition on a shallow inner shelf with limited access to the sea. (2) Facies C2 "bryozoan bivalve floatstone" is dominated by flat robust branching, delicate branching with common articulated branching, and encrusting bryozoan growth-forms. The benthic and planktonic foraminifers Cibicides, Subbotina, Chiloguembelina and Guembelitria, as well as coralline algae and echinoids, are common. This

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facies forms a shallow bivalve shoal, limiting the effect of the open sea and providing an ideal protection for the inner shelf facies. (3) Facies C3 "cross bedded bryozoan grainstone"

dominated by well sorted delicate branching and articulated branching bryozoan growth-forms. Cibicides, Spirillina, Notorotalia, Guembelina, Chiloguembelina and rare Crespinina occur throughout. Occasional scattered quartz-rich horizons occur in upper levels. Coralline algae and benthic foraminifers increase in abundance and size towards the top of the facies. This facies is devoid of any carbonate mud, and was deposited on the inner-middle shelf. (4) Sub-fades C3a "bryozoan algal foraminiferal grainstone"

This sub-facies contrasts with the underlying facies

C3, in the noticeable increase in the abundance and size of coralline algae and benthic foraminifers. These minor variations are attributed to the development of a marine hardground capping the top of facies C3. (5) Facies W1 is a "bryozoan Amphistegina grainstone" which represents the hard layers that punctuate the sequence several times. It is dominated by a variety of bryozoan growthforms including: articulated branching, flat robust branching, delicate and vagrant growth-forms, together with common Amphistegina, other common benthic and planktonic foraminifer, bivalves and echinoids. (6) Facies C4 "fine highly abraded bryozoan bioclastic grainstone" is composed of fine grained, highly abraded delicate, and articulated branching bryozoan growth-forms and broken unidentified bryozoan bioclasts, Cibicides, fine grained coralline algae, echinoid grains and calcareous sponge spicules. This facies was deposited on the outer parts of the middle shelf.

Conclusions The facies succession indicates that the Port Vincent Limestone was deposited in a transgressive cool-water carbonate shelf environment, with warm water interruptions occurring several times during the deposition. Lithological and facies variation are originally depositional, and have been further accentuated by selective diagenesis. Evidence suggests that periodic incursion of warmer water into the cool-water environments represents a climatically imposed effect, which is correlatable with regional observations across Southern Australia.

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Bryozoans as major components of temperate carbonate sediments Abigail M. Smith Department of Marine Science, University of Otago Campbell S. Nelson Department of Earth Sciences, University of Waikato Most modem marine bryozoans have calcified body walls, so the colony that remains after the decay of soft parts is a preservable skeleton. Bryozoans are consequently well known as fossils, persisting from the Ordovician to the present. Modem bryozoans are suspension feeders, and occupy a wide variety of environments, from the tropics to the poles. Many species are intertidal; still more live subtidally. They are most abundant on the continental shelf, although bryozoans have been found down to 6000 m water depth. Usually minor components of tropical reef environments, bryozoans are abundant in temperate shelf carbonate sediments, but not acknowledged in the foramol/chlorozoan classification of Lees & Buller (1972). Nelson et al. (1988) used the new term "bryomol" to characterise the typical temperate carbonate sediment of the Pacific: dominated by bryozoans and/or bivalve molluscs, with variable contributions from bamacles, echinoids, worm tubes, gastropods, and foraminifera. This nomenclature has been expanded by Hayton et al. (this volume); their bryomol assemblage (with a mean of 60% bryozoans) is commonly found in Cenozoic limestones of New Zealand. The main sedimentological role of bryozoans in both tropical and temperate settings is as producers of carbonate sediment (Table 1). Most bryozoans deposit CaCOs extracellularly on a chitinous and proteinaceous cuticle. Carbonate mineralogy varies considerably, and may be low-Mg calcite, highMg calcite, or aragonite (Smith et al., in prep). Indeed, a single colony may lay down calcite and aragonite at different times in its life cycle. Table 1. Sedimentological roles of bryozoans in tropical and temperate carbonates Tropical (Cuffey, 1974) Principal ftame-builders Bryozoans alone Bryozoans with other organisms Accessory frame-encrusters Dead-reef veneers Encrusters Cavity dwellers and fillers Sediment formers Sediment-movement inhibitors Sediment binders Sediment trappers Sediment destroyers (borers)

0 0 0

Temperate (Smith, 1992)

• o —

• 0 •

•

o o

•

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Calcification rates for individual bryozoans fall in the range of 25 to 736 mg CaCOs/y (Smith & Nelson, 1994a). Areal carbonate production varies from a few tens or hundreds of g/m2/y up to many thousands in particularly favourable conditions. In Hauraki Gulf, New Zealand, accumulation of bryozoan carbonate is on the order of 4 to 40 cm/ky (Smith & Nelson 1994a). Dominantly-bryozoan carbonates accumulate at rates of 1-10 cm/ky off southem Australia (James et al., 1992); and cool-water bryozoan limestones have been shown to accumulate at about 1-3 cm/ky (James and Bone 1991). Bryozoan colonies occur in a wide range of growth forms, from encrusting to erect to free-living, which may reflect environmental conditions (e.g., see Nelson et al., 1988). In some temperate environments, erect bryozoans may grow together to form elaborate structures. Off New Zealand these "bryozoan meadows" are composed of a few large bryozoan species and numerous epibionts, including polychaete worms, encrusting bryozoans, bivalves, and crustaceans (Bradstock and Gordon, 1983). Some encrusting bryozoans are typically found on rock or shell substrate, where they add structure and volume and may enhance the preservation potential of the substrate. Others may encrust algal fronds or human-derived materials; bryozoans are some of the most tenacious foulers in the marine realm (Soule and Soule 1977). In addition to the constructional roles listed, bryozoans may be destructive. Only a few species occur as borers, and they are not very common. After death, bryozoan sediments are subject to a variety of potentially destructive early sea-floor diagenetic processes, including abrasion, dissolution, and bioerosion (Figure 1). Such processes remove bryozoan skeletons from the sedimentary record, and at least abrasion and dissolution are selective in their effects (Smith and Nelson, 1994b). The result is that certain growth forms have greater preservation potential than others, which indicates that paleoenvironmental analysis based on colonial growth forms (after the method of Stach, 1936) must be applied with due attention to possible taphonomic effects of early-sea floor diagenesis (Smith & Nelson, 1994b). Postdepositional diagenesis may well remove even more bryozoans from the fossil record, particularly those with metastable aragonite skeletons. Nevertheless, bryozoan limestones formed in temperate shelf environments are quite widespread, at least in the Cenozoic of New Zealand and Australia.

References BRADSTOCK, M. AND GORDON, D.P. (1983) Coral-like bryozoan growths in Tasman Bay, and

their protection to conserve conmierciaJ fish stocks. New Zealand Journal of Marine and Freshwater Research 17, 159-163. (1974) Delineation of bryozoan constructional roles in reefs from comparison of fossil bioherms and living reefs. Proceedings of the Second International Coral Reef Symposium, Brisbane, 357-364. HAYTON, S., HOOD, S.D. AND NELSON, C.S. (1995) Skeletal assemblages of New Zealand Cenozoic non-tropical carbonate sediments. This volume. JAMES, N.P., AND BONE, Y. (1991) Origin of a cool water, Oligo-Miocene deep shelf limestone, Eucla Platform, southem Australia. Sedimentology 38, 323-341. CUFFEY, RJ.

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JAMES, N.P., BONE, Y., VON DER BORCH, C.C., AND GOSTIN, V.A. (1992) Modem carbonate

and terrigenous clastic sediments on a cool water, high energy, mid-latitude shelf: Lacepede, southern Australia. Sedimentology 39, 877-903. LEES, A. AND BULLER, A.T. (1972) Modem temperate-water and warm-water shelf carbonate sediments contrasted. Marine Geology 13, M67-M73. N E L S O N , C.S., HYDEN, F.M., KEANE, S.L., LEASK, W.L., AND G O R D O N , D.P. (1988) Application of bryozoan zoarial growth-form studies in facies analysis of non-tropical carbonate deposits in New Zealand. Sedimentary Geology 60, 301-322. SMITH, A.M. (1992) Aspects of the sedimentology of New Zealand bryozoans and mixed carbonate-clastic deposits: a contribution to the temperate shelf carbonate model. D. Phil Thesis, University of Waikato (Earth Sciences), Hamilton, New Zealand. SMITH, A.M. AND NELSON, C.S. {1994a) Calcification rates of rapidly colonising bryozoans in Hauraki Gulf, northern New Zealand. New Zealand Journal of Marine and Freshwater Research 28, 227-234. SMITH, A.M. AND NELSON, C.S. (1994/?) Selectivity in sea-floor processes: taphonomy of bryozoans. In: Biology and Palaeobiology of Bryozoans (Eds. Hayward, PJ., Ryland, J.S., and Taylor, P.D.). Proceedings of the 9th International Bryozoology Conference, Olsen & Olsen, Fredensborg, 177-180. SMITH, A.M., NELSON, C.S. AND SPENCER, H.G. in prep. Skeletal carbonate mineralogy of New Zealand bryozoans. SOULE, J.D. AND SOULE, D.F. (1977) Fouling and bioadhesion: life strategies of bryozoans. In: Biology of Bryozoans (Eds. Woollacott, R.M. and Zimmer, R.L.). Academic Press, New York, pp. 437-458. STACH, L.W. (1936) Correlation of zoarial form with habit. Journal of Geology 44 60-65.

cementation lithification

Figure 1: A budget for bryozoan carbonate sediments.

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Sedimentology of carbonate mud from a modern back-barrier lagoon, Lake Reeve, Victoria. Michelle Smith and Malcolm Wallace School of Earth Sciences, University of Melboume, Parkville, 3052. Introduction

Lake Reeve is an ephemeral back-barrier lagoon located amongst Quaternary sediments in the Gippsland Lakes area, southeastern Victoria. The lagoon is narrow and shallow, extending for 65km parallel to the Gippsland coastline, and separated from the open ocean by a modem, barrier complex (Davis et ai, 1977; Bird, 1978). It has been the site of carbonate precipitation throughout the late Holocene. The carbonate precipitation in Lake Reeve is controlled by a complex combination of factors. The geomorphic setting, hydrodynamics and prevailing climatic regime are important factors, which have seen the water chemistry significantly modified during the Holocene. Increasing restriction, and evaporative losses not offset by fluvial and groundwater inputs or precipitation have resulted in the lagoon becoming increasingly ephemeral and hypersaline. These features, combined with an abundance of photosynthetic organisms and low terrigenous sediment influx have resulted in carbonate precipitation.

Carbonates and their distribution

Carbonates in Lake Reeve are typically white muds containing little or no organic debris or terrigenous sediment. X-ray diffraction of samples collected along the length of the lagoon indicates the predominant mineralogy is low Mg-calcite, with occasional samples displaying aragonite peaks of biogenic origin. Unlike the modem carbonate sediment in the somewhat analogous Coorong lagoon in South Australia, no dolomite has been observed in Lake Reeve. Stable isotope analysis of the recent carbonate sediments shows the Lake Reeve calcites typically display light values (613C -7.3 to + l.l%o PDB) and relatively heavy 5 is O (5 i® O -2.1 to + 2A%o PDB). Such an isotopic signature suggests precipitation from waters with a distinct meteoric influence. The heavy b^^O values may result from evaporation. Carbonate mud layers in Lake Reeve vary in thickness from a few cm to 40 cm, but are typically 10-15 cm thick. The carbonates generally occur on mudflats or beneath a thin algal veneer, but are also observed in the salt marsh environments, beneath organic layers associated with the stabilising

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vegetation. Carbonate mud is found occurring along the entire length of the lagoon, with the exception of those areas of perennial lagoon.

Sedimentology and depositional environments of Lake Reeve The modern sedimentary environments of Lake Reeve are varied, reflecting changes in the dominant hydrologic conditions. Parts of the lagoon remain constantly inundated, parts are subject to intermittant inundation, while other parts remain dry throughout the year. All of these environments have distinctive sediment types. The regions which are subjected to periodic wetting are of particular interest, as they are commonly covered by extensive algal mat growth, and are the sites of the carbonate mud precipitation. This carbonate mud environment occurs as extensive mudflats around the margin of Lake Reeve. When conditions are dry, these mudflats form characteristic polygonal mudcracks and dessicated algal mats.

Climate and hydrology Weather systems from the west or south west predominantly influence the Gippsland region, with the Gippsland Lakes situated in the rainshadow of the South Gippsland and the Eastern Highlands. The rainfall is distinctly seasonal, reaching 624mm annually. Evaporation is quite high, with average evaporation higher than rainfall for most months of the year. Such a prevailing climatic regime is largely responsible for producing the ephemeral nature of Lake Reeve. These conditions combined with insignificant fluvial input into the lagoonal system has seen the waters become more saline with time. Groundwater contribution to the lagoon is indicated by isotopic analyses of the carbonates. Seawater seepage may be a further hydrologic component to Lake Reeve.

Holocene stratigraphy and the significance of the carbonate precipitation Lake Reeve preserves an essentially continuous Holocene sedimentary sequence formed in response to the last major marine transgression in southeastern Australia. These sediments contain organisms and foraminiferal assemblages which enables the palaeoenvironmental changes affecting this coastal setting to be documented. The fauna from these sediments indicate a depositional environment which has become lower in energy, increasingly restricted and more saline throughout the Holocene. The basal unit of the Holocene sequence in Lake Reeve contains terrigenous, shelly marine sediment with a diverse, open marine macro and micro-fauna. Up sequence, the fauna gradually changes indicating increasing restriction and salinity conditions. In the uppermost section of the sedimentary sequence, a marked change in sedimentation occurs, from predominantly terrigenous quartz-rich sediments to the carbonate muds commonly observed in the modem lagoonal environment. With this distinct change in grain size and composition, there is a corresponding change in the faunal assemblages, from a diverse, marine assemblage to a restricted hypersaline fauna.

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References BIRD, E.C.F. (1978). The Geomorphology of the Gippsland Lakes; Environmental Studies Series No. 186, Ministry for Conservation, Vic., 158pp. DAVIS, R.A., DELPORTE, B.C. and MARSDEN, M.A.H. (1977). Morphology, surface facies, and sediment distribution in Gippsland Lakes, Victoria; Environmental Studies Series No. 146, Ministry for Conservation, Vic., 49pp.

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Sediment bundles in the Tertiary of Torquay^ southwest Victoria Therese Van der Linden, Peter J.Davies Department of Geology and Geophysics, University of Sydney. and B.Buchbinder Geological Survey of Israel, Jerusalem, Israel. Abstract This paper is a contribution arising from the joint research program of the Universities of Sydney and LaTrobe which is aimed at better understanding the relations between sedimentation and sealevel change in a section proposed as a classic sequence stratigraphic statement. Detailed sedimentologic analysis of Drill hole 9 between Deadman's Gully and Bells beach has defined ninety three sediment packages from just below the top of the Anglesea Sands and the top of the exposed Pueblo Clay, a time frame presumed to be about 5 million years. Within this section, 19 packages occur in the Pueblo, 12 in the Jan Juc Upper Transitional sediments, 27 in the Lower Carbonates, 32 in the Angahook and three at the top of the Anglesea Sands. Packages are separated by the types of surface reported in Buchbinder etal (this volume). Packages are either homogenous or variants on coarsening and fining upward sections of differing grain sizes and mineralogy in combination with the presence and/or absence of glauconite, buiTOwing, cementation, Fe staining, and dispersed or aggregated gravel. Actual and /or interpreted ages for the boundaries of the major stratigraphic sequences indicate that sediment packages define sub 80,000 year depositional units in the Jan Juc and Lower Carbonates and sub 40,000 year depositional units in the Angahook. The depositional origin of the packages will be discussed and defmed.

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Sedimentology and Geochemistry of Late Proterozoic Glacial-associated Cap Dolomites in Australia Malcolm W. Wallace School of Earth Sciences, University of Melbourne, Parkville, Vic. 3052, Australia Martin Kennedy Department of Biological Sciences, Section of Ecology and Systematics, Cornell University, Ithaca NY, 14850, USA and Ciaran Lavin Geology Department, Monash University, Clayton, Vic. , Australia

INTRODUCTION Thin (<15m) enigmatic dolomite units overlie Late Proterozoic glacial sequences throughout the world. The occurrence these "cap dolomites" has prompted interest in their paleoclimatic significance (Williams, 1979). These cap dolomites have also been used as a means of lithostratigraphic correlation in many Late Proterozoic sequences. However, despite the significance of these dolomites as lithostratigraphic markers and paleoclimate indicators, their origin remains poorly constrained. GEOLOGICAL SETTING Within many late Proterozoic successions, two major glacial sequences are present (the lower Sturtian-Rapitan and upper Marinoan-Varanger), both with thin cap carbonate units (Preiss, 1987). In Australia, cap dolomites occur within the Adelaide fold belt, as well as the Amadeus, Ngalia and Kimberley regions. The finely laminated and finely crystalline (-5-50 ^im) nature of many of these "cap dolomites", together with the presence of teepee structures and stromatolites has led many researchers to suggest a shallow peritidal environment of deposition for these dolostone units. In this paper, we present sedimentological and geochemical data from the Marinoan cap dolomites of the major Australian late Proterozoic basins in order to better define the origin of these problematic dolostone units. RESULTS Late Proterozoic (Varangian or Marinoan) cap dolomites from the Amadeus Basin, the Adelaide Fold Belt, the Ngalia Basin and the Kimberley region consist of three major types of carbonate: 1. detrital carbonates; 2. early diagenetic nodular carbonates; and 3. stromatolitic carbonates. The detrital and early diagenetic carbonates almost invariably

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consist of finely crystalline dolomicrite. The stromatolitic carbonates may consist of dolomite or calcite. Sedimentary structures in the detrital carbonates indicate a predominantly deep water environment of deposition. Well-defined Bouma sequences and unidirectional flute marks indicate deposition predominantly below storm wave base. Iron oxide-rich stromatolites overlying these dolostone units have a many similarities with previously described subtidal or deep water stromatolites. The total absence of tidal features, dessication structures or fenestral fabrics is inconsistent with a shallow water or peritidal origin. The general lack of lonestones within the cap dolomites indicates that ice rafting was not significant and that the environment was probably not periglacial. Synsedimentary fracturing, soft sediment deformation and brecciation are commonly present in the Marinoan cap dolomites. Synsedimentary fractures (neptunean dykes and sills) are commonlyfilledwith dolomicrite internal sediments and fibrous inclusion-rich dolomite cements. Thefibrouscements are commonly overlain by dolomicrite intemal sediments, indicating the cements are of synsedimentary origin. Stratigraphically, a predominandy deep water origin for the cap dolomites is consistent with deglaciation and the overall transgressive nature of the sequence. In sequence stratigraphic terms, the cap dolomites may represent a condensed transgressive system tract, with the deep water stromatolites representing the highly condensed downlap surface below the prograding mudstones of the overlying high-stand sediments. The Marinoan cap dolomites are characterised by light carbon isotopic compositions =-0.5 to -5.5 %o) and moderately to very light oxygen isotopic compositions (S^^O =-4.0 to -11.0 %o). At any one locality, stratigraphic profiles generally display lightening upwards trends for both the carbon and oxygen isotopic composition. However, while the stable isotopic compositions at individual localities show relatively uniform compositions with consistent stratigraphic trends, large variations in the stable isotopic composition are recorded at different localities. The consistent stratigraphic variations in isotopic composition are significant and indicate that the primary marine chemistry of these dolomites is at least partially preserved at most localities. A synsedimentary or very early diagenetic marine origin for the dolomites is consistent with: LThefinely crystalline nature of the dolomites; 2. The presence of synsedimentary dolomite cements; 3. The ubiquitous preservation of Marinoan c ^ carbonates as dolomites globally; and 4. the preservation of consistent stratigraphic trends in isotopic composition.

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1 i

CONCLUSIONS Marinoan cap dolomites were: 1. deposited during deglaciation and marine transgression; 2. most commonly deposited in deep water settings below storm wave base; and 3. either deposited as dolomites, or were subject to synsedimentary or very early diagenetic marine dolomitization. These distinctive and widespread cap dolomites appear to record changes in the carbon cycle brought about by, and/or causing long term global climate change, deglaciation and consequent transgression. REFERENCES Preiss, W. V., 1987, The Adelaide Geosyncline- Late Proterozoic stratigraphy, sedimentation, palaeontology and tectonics: Geological Society of South Australia Bulletin, no. 53, 438p. Williams, G. E., 1979, Sedimentology, stable isotope geochemistry and paleoenvironment of dolostones capping lat Precambrian glacial sequences in Australia: Geological Society of Australia Journal, v. 26, p. 377-386.

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Elemental geochemistiy of New Zealand Cenozoic limestones: a reconnaissance study Peter R. Winefield, Campbell S. Nelson and A. Peter W. Hodder Department of Earth Sciences, University of Waikato, Hamilton, New Zealand

A significant problem in studies of ancient carbonates is the clear distinction between tropical and temperate limestone facies. Recent tropical carbonates have been well-studied and there exists a number of criteria for their recognition in the geological record. Modem temperate carbonates differ from their tropical counterparts in their skeletal grain composition, mineralogy, diagenesis, and geochemistiy, including the range of major and minor elements and the oj^gen and carbon isotope composition.

There is a relatively limited database on the elemental chemistry of temperate carbonate deposits, and none for the widespread occurrences of New Zealand temperate limestones of Cenozoic age. This study involved the geochemical analysis of approximately 570 samples from both the North Island and South Island of New Zealand (Figure 1). Bulk powders of samples were analysed by Atomic Absorption spectroscopy. Results from the analysis of New Zealand Cenozoic limestones give average Ca values of 420,000ppm, av. Mg 5450ppm, av. Na 1450ppm, av. Fe 2620ppm, av. Sr 550ppm and av. Mn 510ppm. Also approximately 150 samples were analysed for

and S"C, with the average values for bulk skeletal limestones being -1.89 per

mille and 0.34 f>er mille respectively.

As the chemical composition of a limestone reflects the physicochemical conditions pertaining at the time of formation and diagenesis (Moore, 1989), it should be possible to differentiate New Zealand temperate limestones from tropical carbonates and to gain some understanding of chemical diagenetic processes from their elemental chemistry. Considering the above New Zealand average values, the Mg and Sr contents are typically lower than occurs in many tropical carbonates, while the contents of Na, Fe and Mn are relatively higher.

Several element versus element plots have been suggested for discriminating between tropical and temperate carbonates (e.g. Rao, 1991). For example, a Na versus Sr plot for the New Zealand Cenozoic limestones groups them well outside the area of tropical carbonates and

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within a temperate field having Sr values between 100 and lOOOppm and Na values of 500 to SOOOppm (Figure 2). Sr and Mn values can be particularly influenced by meteoric diagenetic processes. Sr has a relatively high concentration in seawater compared to meteoric water, and Mn vice versa. Brand and Veizer (1980) found that meteoric diagenesis is characterised by a decease in Sr with a corresponding increase in Mn concentration. The wide range in plots on the Sr versus Mn diagram for the East Cape-Poverty Bay limestones, North Island (Figure 3), illustrate that the limestones have been subject to varying degrees of meteoric diagenesis associated with differential uplift of parts of the region soon after carbonate deposition, thereby allowing a variable input of meteoric water into some limestone formations but not others. Stable isotope-element trends are also helpful in elucidating diagenetic trends. For example, Brand and Veizer (1980) and Rao (1991) demonstrated that an increasing degree of meteoric alteration is associated with an increase in Mn content, and a decrease in S^^O values. This trend is evident in the same suite of East Cape-Poverty Bay limestone samples referred to above, and supports a range of diagenetic influences from predominantly marine to increasingly meteoric (Figure 4). While this study is still underway, and results remain incomplete, the elemental relationships in the New Zealand Cenozoic limestone dataset appear promising for developing further criteria for distinguishing between temperate carbonates and their tropical counterparts, and for gaining an understanding of chemical diagenetic processes. References BRAND U. & VEIZER, J. (1980). Chemical diagenesis of a multicomponent carbonate system -I: trace elements. Journal of Sedimentary Petrology, 51, 1219-1236. MOORE, C.H. (1989). Carbonate Diagenesis and Porosity. Developments in Sedimentology, 46. Elsevier, Amsterdam.

1 RAO, C.P. (1991). Geochemical differences between subtropical (Ordovician), temperate

(Recent and Pleistocene) and sub-polar (Permian) carbonates, Tasmania, Australia. Carbonates and Evaporites, 6, 83-106.

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10.000-1Subtropical

raffoniia

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Figure 2: Plot of Na(ppm) versus Sr(ppm) for New Zealand Cenozoic limestones, with Tasmanian subtropical and subpolar data (from Rao, 1991) for comparison

Figure 1: Sample location map

2.000

m m *

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Figure 3: Plot of Sr(ppm) versus h^n(ppm) for East Cape/Poverty Bay limestones

^ ^ Increasing meteoric influence

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Figure 4: Plot of S O versus Mn(ppm) for East Cape/Poverty Bay limestones

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A window on the physical sedimentology of carbonates using Entropy Grouped Laser-derived Grainsize Data

KenJWoolfe Department of Geology James Cook University of North Queensland Townsville Q'ld 4811 It is often difiBcult to unravel the physical sedimentology of clastic caibonates, because the grain size distribution of bulk samples commonly reflects artefacts of the preserved biota rather than the physical processes of transport and sorting. The problem is further compounded by the large sample sizes which need to be prepared if the silicate fraction is to be analysed using traditional grain size methodology. The increasing acceptance of laser diffraction technology now enables very small samples (less than 500 mg) to be analysed with confidence. Consequently, even a relatively small carbonate sample will yield sufficient silicate material on dissolution in HCI for grain size analysis. Rapid acquisition and management of high quality grainsize data from carbonate samples was fecilitated by establishing a DDE-Link between a Malvern Mastersizer X laser particle sizer and EXCEL for WINDOWS. The resultant data set was grouped, using ENTROPY a BASIC entropy analysis program, to deliminate grainsize facies for samples collected from a section of the Great Barrier Reef shelf and the Devonian Burdekin Limestone. This technique offers a direct window to the physical sedimentology of modem and ancient carbonate provinces. A window which until recently was open, has beenfirmlyclosed.

Cool Climate Carbonate Conference (Page 86) Geelong 1994