Abstracts No.51: Inaugural Sprigg Symposium - The Ediacaran Revolution, 1998, University of Adelaide

Geological Society of Australia

ABSTRACTS Number 51

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INAUGURAL SPRIGG SYMPOSIUM The Ediacaran Revolution The University of Adelaide Department of Geology & Geophysics

June 24-25,1998.

Location Map Symposium Venue:

Department of Geology and Geophysics, Mawson Theatre mm* mut* asp^t*

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Symposium Dinner:

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4th Floor, Adelaide University Union Building

PUBLICATION SALES Copies of this volume can be purchased for $10 per copy, from: The Geological Society of Australia, Inc. 7th Floor 301 George Street Sydney, NSW 2000 Australia

GEOLOGICAL SOCIETY OF AUSTRALIA INC. SOUTH AUSTRALIAN DIVISION IN ASSOCIATION WITH THE UNIVERSITY OF ADELAIDE & UNIVERSITY OF SOUTH AUSTRALIAN

INAUGURAL SPRIGG SYMPOSIUM: THE EDIACARAN REVOLUTION June 24 -25,1998 The University of Adelaide Department of Geology and Geophysics Mawson Laboratories

ABSTRACTS & PROGRAMME

J.G. Gehling (Compiler) GEOLOGICAL SOCIETY OF AUSTRALIA ABSTRACTS No. 51 1998 ISSN 0729-011X © GEOLOGICAL SOCIETY OF AUSTRALIA, INC.

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Hosted by:

Sponsored by:

The University of Adelaide Department of Geology and Geophysics

• Petroleum Group, PIRSA

• Santos

• BORAL ENERGY

Spriggina floundersi Glaessner 1958

ACKNOWLEDGEMENTS The University of Adelaide, Department of Geology and Geophysics has sponsored the Geological Society of Australia by providing the Mawson Theatre and associated facilities as the venue for presentation of papers at the Inaugural Sprigg Symposium. The University of South Australia provided photocopying, electronic mail and telephone services in preparation for the symposium. John Drexel of Mines and Energy, PIRSA, made space available to advertise the Sprigg Symposium in the April issue of the MESA Journal. The "Pathways to the Past" guide to the geological heritage of the Fleurieu Peninsula was produced by The Geological Heritage Subcommittee of the GSA, South Australian Division. The "Brachina Gorge: A Corridor Through Time" guide to the Flinders Ranges National Park Corridor geological trail was donated by Mines and Energy, PIRSA, courtesy John Drexel. Margaret Fuller and Vicki Harris made the fossil replica for the plaque donated to the Sprigg family. Chris Nedin, Richard Jenkins, Ben McHenry, Ian Dyson and Jim Gehling loaned specimens for the display of Ediacaran and Cambrian fossils of South Australia. SPRIGG SYMPOSIUM COMMITTEE Jim Gehling Vic Gostin Doug Mason Robin Oliver

University of South Australia The University of Adelaide Mason Geoscience The University of Adelaide

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INAUGURAL SPRIGG SYMPOSIUM

DR. REG SPRIGG (1919-1994) Reg Sprigg has made notable contributions to Australian scientific and economic life. They manifest an enterprising and spectacular career. From 1944 to 1954, as Assistant SA Government Geologist, he participated, and inspired others, in extensive geological mapping of South Australia and in the conduct of a variety of resources surveys involving rocks ranging in age from Archaean to Pleistocene. During this period, his scientific interests led to the discovery, in 1946, on the western margin of the Flinders Ranges, of the Ediacara biota which has stimulated a world wide review of early animal life and its relationship to the base of the Cambrian — a revolution in fact which continues and which constitutes the theme of this Symposium. Impatient with the limitations provided by Government employment, Sprigg left the SA Mines Department in 1954 and set up the successful Geosurveys of Australia Pty Ltd to provide basic consulting geological/geophysical services previously not available to mining and exploration enterprises in Australia. In the course of this he made use of air photography, submersible vessels, SCUBA diving, acoustic sounding and seismic profiling. He took part in the formation of Santos Ltd and spearheaded exploration for petroleum in the Cooper Basin. In 1961 he formed Beach Petroleum N.L. Later, in 1968, increasing concern with the deterioration of the natural environment led to the innovative purchase of Arkaroola (Mount Painter) pastoral lease and its conversion into a wild life sanctuary and wilderness reserve centred on a comfortable but exhilarating tourist village. Reg's achievements were recognised early by the winning of the Tate Medal in the final year of his undergraduate study, and subsequently through the award of the Verco Medal of the Royal Society of South Australia, of the Lewis G. Weeks inaugural Gold Medal from APEA, of Honorary Doctorates of Science by the Australian National University and Flinders University, and by his appointment as an Officer of the Order of Australia. He was a Fellow of the Australian Academy of Technical Sciences and Engineering as well as Honorary Member of the Geological Society of Australia. Robin Oliver

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INAUGURAL SPRIGG SYMPOSIUM THE EDIACARAN REVOLUTION PROGRAMME Mawson Theatre, Geology Dept. (Mawson Laboratories)

Wednesday, June 24 8:00 - 9:00 am Registration and Dinner ticket sales : Tate Museum - Mawson Theatre 9:00 Opening and Introductions — Dr. Vic Gostin, Geological Society of Australia, SA Division, Chairperson 9:15 Tribute to Reg Sprigg — Bruce Webb, Chancellor, University of Adelaide 9:30 PROTEROZOIC EVOLUTION Chairperson : Vic Gostin 9:30 - 10:00 Keynote Speaker — Runnegar, B. (UCLA, USA): Proterozoic progress to megascopic complexity. 10:00 - 10:30 Brasier. M. D. (Oxford), & Lindsay, J. F. (AGSO): A billion years of 3 C stasis and the emergence of eukaryotes: new data from Northern Australia. 10:30- 11:00 Break 11:00 CHEMOSTRATIGRAPHY & NEOPROTEROZOIC ENVIRONMENTS Chairperson : Malcolm Walter 11:00 - 11:30 McKirdv, D,M., Jenkins, R.J.F., Michaelsen, B.H., Ayliffe, D.J., & Gostin, V.A. (Adel.): A coherent Ediacaran carbon isotope stratigraphy of South Australia and its use in interregional correlations. 11:30 - 12:00 Barovich. K. & Foden, J. (Adel.): Geochemical and Nd isotope constraints on sources of Neoproterozoic sedimentary rocks of centralsouthern Australia. 12:00 - 12:30 Corkeron, M.L. (Uni WA): Depositional environments and correlation of the Neoproterozoic succession in the Kimberley region, Australia. 12:30 - 1:30 Lunch 1:30 NEOPROTEROZOIC-CAMBRIAN TRANSITION Chairperson : Richard Jenkins 1:30 - 2:00 Narbonne. G.M., & MacNaughton, R. W. (Queen's, Canada): Terminal Neoproterozoic - Early Cambrian biostratigraphy of NW Canada: testing the effects of evolution and ecology. 2:00 - 2:30 Brasier, M. D., & McCarron, G. (Oxford): The transition from Neoproterozoic to Cambrian: new data from Mongolia to Oman. 13

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2:30 - 3:00 3:00 - 3:30 3:30 3:30 - 4:00 4:00 - 4:30 4:30 - 5:00 5:00

Gehling. J.G. (Uni. SA), Droser, M.L. (Uni. Cal., Riverside), & Jensen, S. (Cambridge): Similar cycles — different strokes : closing a taphonomic window across the Precambrian-Cambrian boundary. Break EDIACARAN PALAEOBIOLOGY & BIOSTRATIGRAPHY Chairperson : Jim Gehling Sun, W. (Nanjing, China): Primitive Ediacara-type fossils from the Late Proterozoic Xinmingcun Formation in northeast China. Grey, K. (WA Geol. Surv.): Ediacaran acritarch biozonation in Australia. Zang, W. (Min. Div. PIRSA): Ediacarian-Cambrian acritarch biostratigraphy in South Australia and global correlation. End of Wednesday Sessions

7:00 - 10:30 pm Sprigg Symposium Dinner —Uni. Adelaide Union Building, Level 4 Dinner Speaker: Emeritus Prof. Christopher Von der Borch. Thursday, June 25 9:00 am 9:00 - 9:30 9:30 - 10:00 9:30 - 10:00 10:00 - 10:30

10:30- 11:00 11:00 11:00 - 12:00

Mawson Theatre, Geology Dept. A TERMINAL PROTEROZOIC SYSTEM Chairperson : Wolfgang Preiss Keynote Speaker — Walter, M.R. (Vice Chairperson, IUGS Working Group): Progress in defining a new terminal Proterozoic System: a report for the IUGS Working Group. Walter, M.R., Veevers, J.J., Calver, C.R., Gorjan, P., & Hill, A.C. (Macquarie Uni.): Global Neoproterozoic chemostratigraphy. Jenkins. R.,J.F., & Nedin, C. (Uni. Adel.): The Ediacaran question: North and South. Christie-Blick. N. (Lamont-Doherty, USA), Kennedy, M. (UCLA), & Sohl, L. (Lamont-Doherty, USA): Proposed location of a terminal Proterozoic GSSP: Nuccaleena Formation, Flinders Ranges, South Australia. Break CAMBRIAN BIOSTRATIGRAPHY & SEDIMENTOLOGY Chairperson : Jim Jago Brock, G. A., & Engelbretsen* M.E. (Macquarie Uni.): Palaeobiogeographic patterns of Early Cambrian faunas from Australasia.

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11:30 - 12:00 12:00 - 12:30 12:30 - 1:00 1:00-2:00 2:00 2:00 -2:15 2:15 - 2:45 2:45 - 3:00 3:00 3:00 - 3:30 3:30 - 4:00 4:00 - 5:00

5:00 pm

Nedin, C- (Adel.): Paleobiology of the Early Cambrian Emu Bay Shale Fauna, Kangaroo Island, South Australia. Haines. P. (Uni. SA), Flottmann, T. (Uni. Adel.), Jago, J.B., & Gum, J.C. (Uni. SA): Forty five years of the Kanmantoo Group: a review of past and present concepts. Sun, Xiaowen. (NCPG&G, Adel.), & Jago, J. (Uni. SA): Cambrian biostratigraphy of eastern Warburton Basin (South Australia) and international correlation. Lunch GLOBAL EDIACARAN PALAEOBIOLOGY Chairperson : Guy Narbonne Hofmann. H J. (Uni. Montreal) & Mountjoy, E.W. (McGill): New macrofossil occurrence in Neoproterozoic Miette Group (Windermere Supergroup), western Canada. Rai. Vibhuti. (Lucknow, India): Paleobiology and evolutionary evidence from the terminal Proterozoic sequences of Himalaya and Peninsular India. Break NEOPROTEROZOIC SEDIMENTOLOGY & STRATIGRAPHY Chairperson: David McKirdy Lemon, N.M. (NCPG&G, Adel.): Sea level control on diapir emplacement: examples from the Enorama diapir. Lindsay, J.F. (AGSO): The Heavitree Quartzite, a Neoproterozoic (c. 800760 Ma) tidally influenced, ramp association, Amadeus Basin. FOSSIL DISPLAY & POSTERS — Mawson Laboratories Display of spectacular specimens from the Neoproterozoic Ediacara fauna and Cambrian Emu Bay fauna. Posters on Neoproterozoic and Early Cambrian Geology: Dalgarno, C.R. (Geol Surv. Vic.), & Dyson, LA. (NCPG&G, Adel.): Ediacaran diapirism at Mount Frome. Dyson, I.A. (NCPG&G, Adel.): Neoproterozoic salt tectonics and sequence boundary formation in the Adelaide Geosyncline. Dyson, LA. (NCPG&G, Adel.): Sequence stratigraphy and sedimenthosted mineralization in the Kanmantoo Group, Karinya Syncline. Dyson, LA. (NCPG&G, Adel.), & Dalgarno, C.R. (Geol Surv. Vic.): Salt glaciers and slumps in Neoproterozoic successions of the Adelaide Geosyncline. Sun, Xiaowen (NCPG&G, Adel.): Geochemistry and facies analysis of Cambrian volcanics in Warburton Basin and regional correlations, South Australia Mawson Lecture Theatre — Theme for 2000 Sprigg Symposium Closing Words -7-

PAPERS & POSTERS FOR PRESENTATION Page 10. Barovich, K., & Foden, J. (Adel.): Geochemical and Nd isotope constraints on sources of Neoproterozoic sedimentary rocks of central-southern Australia. 12. Brasier, M. D. (Oxford) & Lindsay, J. F. (AGSO): A Billion Years of d C stasis and the Emergence Of Eukaryotes: new data from Northern Australia. 13. Brasier, M. D., & McCarron, G. (Oxford): The transition from Neoproterozoic to Cambrian: new data from Mongolia to Oman. 14. Brock, G. A., & Engelbretsen, M.E., (Macquarie): Palaeobiogeographic patterns of Early Cambrian faunas from Australasia. 16. Christie-Blick, N. (Lamont-Doherty, USA), Kennedy, M. (UCLA), & Sohl, L. (Lamont-Doherty, USA): Proposed location of a terminal Proterozoic GSSP: Nuccaleena Formation, Flinders Ranges, South Australia. 18. Corkeron, M.L. (Uni WA): Depositional environments and correlation of the Neoproterozoic succession in the Kimberley region, Australia. 20. Gehling, J.G. (Uni. SA), Droser, M.L. (Uni. Cal., Riverside), Jensen, S. (Cambridge), & Runnegar, B. (UCLA): Similar cycles — different strokes: Closing a taphonomic window across the Precambrian-Cambrian boundary. 22. Grey, K. (WA Geol. Surv.): Ediacaran acritarch biozonation in Australia. 24. Haines, P. (Uni. SA), Flottmann, T. (Uni. Adel.), Jago, J.B., & Gum, J.C. (Uni. SA): Forty five years of the Kanmantoo Group: a review of past and present concepts. 25. Hofmann, H.J. (Montreal), & Mountjoy, E.W. (McGill, Canada): New macrofossil occurrence in Neoproterozoic Miette Group (Windermere Supergroup), western Canada 26. Jenkins, R.J.F., Nedin, C. (Uni. Adel.): The Ediacaran question: North and South. 28. Lemon, N. (NCPG&G, Adel.): Sea level control on diapir emplacement: examples from the Enorama diapir. 29. Lindsay, J. (AGSO): The Heavitree Quartzite, a Neoproterozoic (c. 800-760 Ma) tidally influenced, ramp association, Amadeus Basin. 30. McKirdy, D.M., Jenkins, R.J.F., Michaelsen, B.H., Ayliffe, D.J., & Gostin, V.A. (Adel.): A coherent Ediacaran carbon isotope stratigraphy of South Australia and its use in interregional correlations. 32. Narbonne, G.M., & MacNaughton, R.W. (Queen's Uni., Canada): Terminal Neoproterozoic - Early Cambrian Biostratigraphy of NW Canada: Testing the effects of evolution and ecology. 33. Nedin, C. (Adel.): Paleobiology of the Early Cambrian Emu Bay Shale Fauna, Kangaroo Island, South Australia. 34. Rai, V. (Lucknow, India): Precambrian paleobiology of the Indian Sub-Continent with special reference to the Terminal Proterozoic 36. Runnegar, B. (UCLA, USA): Proterozoic progress to megascopic complexity. l3

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37. Sun, W. (Nanjing, China): Primitive Ediacara-type fossils from the Late Proterozoic Xinmingcun Formation in northeast China. 38. Sun, X. (NCPG&G, Adel.), & Jago, J. (Uni. SA): Cambrian biostratigraphy of eastern Warburton Basin (South Australia) and international correlation. 40. Walter, M.R., Veevers, J.J., Calver, C.R., Goijan, P., & Hill, A.C. (Macquarie Uni.): Global Neoproterozoic chemostratigraphy. 41. Zang, W. (Petroleum Gp., PIRSA): Ediacarian-Cambrian acritarch biostratigraphy and global correlation. POSTERS 43. Dalgarno, C.R. (Geol Surv. Vic.), & Dyson, I.A. (NCPG&G, Adel.): Ediacaran diapirism at Mount Frome. [poster] 44. Dyson, I.A. (NCPG&G, Adel.): Neoproterozoic salt tectonics and sequence boundary formation in the Adelaide Geosyncline. [poster] 46. Dyson, I.A. (NCPG&G, Adel.): Sequence stratigraphy and sediment-hosted mineralization in the Kanmantoo Group, Karinya Syncline. [poster] 48. Dyson, I.A. (NCPG&G, Adel.), & Dalgarno, C.R. (Geol Surv. Vic.): Salt glaciers and slumps in Neoproterozoic successions of the Adelaide Geosyncline. [poster] 50. Sun, X. (NCPG&G, Adel.): Geochemistry and facies analysis of Cambrian volcanics in Warburton Basin and regional correlations, South Australia, [poster]

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GEOCHEMICAL AND Nd ISOTOPE CONSTRAINTS ON SOURCES OF NEOPROTEROZOIC SEDIMENTARY ROCKS OF CENTRAL-SOUTHERN AUSTRALIA BAROVICH, Karin M. & FODEN, John Department of Geology and Geophysics, University of Adelaide Nd isotope data from Neoproterozoic sedimentary rocks of the Adelaide Geosyncline, southern Australia, and to a lesser extent, the Amadeus Basin, central Australia, imply a significant component of younger primitive source material than the presently exposed Early Proterozoic/Late Archean Gawler Craton and Proterozoic Arunta/Musgrave terranes, respectively. Initial eNd values for Adelaidean and Amadeus sedimentary rocks range from -4 to -14, while the Gawler Craton values at Adelaidean time were -12 to -22, and the Arunta/Musgrave values ranged between -8 and -13. Yet, zircon geochronological evidence from both regions does not support the proposed existence of a widespread younger source terrane. The lack of younger detrital zircons in the Adelaidean sequence (as determined by the Pb-Pb Kober evaporation technique) suggests a mafic component, which did not supply a detrital zircon population to the sediments. It has been proposed that a widespread ca 800 Ma flood basalt province, formed as a result of mantle plume activity, provided the younger mafic source material required to substantially shift the initial eNd values of the Adelaidean and Amadeus sedimentary rocks away from the exposed basement values. Field evidence for this widespread flood basalt province exists in the 800 Ma Gairdner Dyke Swarm within the Gawler Craton and the Amata dyke suite in the Musgrave terrane of central Australia.

suggest that up to 70% of a Gairdner-like component is required to explain the eNd values of up to -4 for the Adelaidean samples. Physical sedimentary mixtures on this order should be reflected in the Sm/Nd ratios of the sediments, with isotopic Sm/Nd ratios of up to 0.1500 predicted by the mixing model. The isotopic Sm/Nd ratios of even the most anomalous Adelaidean and Amadeus sedimentary rocks are only slightly higher than the averages of their Proterozoic/Late Archean sources (0.125 compared with 0.115). Analysis of major element oxide data also does not indicate substantial contribution of a mafic provenance. Other geochemical criteria may indicate mixing with a mafic component (eg., Cr/Th vs. LREE/HREE, Th/U vs. Th, and initial eNd vs. Th/Sc), particularly for the Adelaidean sequence, but not to the extent required by the Nd isotope data. To further investigate the paradox highlighted by the results of the Sm/Nd mixing calculations, several fine-grained samples from the Adelaidean and Amadeus sequences (including those with the most anomalous Nd isotope compositions) and one coarse-grained sample from the Adelaidean sequence, whose Nd signature indicates a local basement provenance, were washed in HC1 to separate exchangeable Sm and Nd from those portions of the elements fixed in crystallographic sites in the minerals. Each component, leachate and residue, was analysed separately for its Nd isotope composition. Mass balance constraints dictate that the Sm-Nd isotope data for the leachate, whole rock (WR) and residue fall on a line on an isochron diagram. The leachates of the fine-grained samples in all cases have a higher Sm/Nd ratio than the WR, and a higher initial eNd value at age of deposition, while the residues have a lower Sm/Nd ratio and lower initial eNd value. Mixing lines formed by the leachate, residue and whole rock for the fine-grained samples yield ages on an isochron diagram that are intermediate between the average depleted mantle model ages of the older felsic source terranes and

To test the theory of a sedimentary mixing model between basement terrane and basaltic province to explain the anomalous e ^ values of the sedimentary rocks, Sm/Nd mixing calculations are made in order to evaluate their suitability as end-member components, and estimate the relative amounts involved of each component. An average Nd isotope composition of the Gairdner and Amata suites is used as one end-member (13.4 ppm Nd, e(800 ^ = 3.1) and Gawler Craton and Amnta/Musgrave average Nd compositions as the other (30 ppm Nd, e(800 Ma) = -15). The results -10-

the proposed 800 Ma mafic source province. We suggest that those phases available to dissolution during leaching, i.e., soluble minerals and adsorbed ions, reflect a preferential chemical mixing, rather than a physical mixing, of the more primitive Nd isotope signature of the mafic basalt province with the basement terrane.

Treatment of the coarse-grained sample from the Adelaidean sequence resulted in no separation of leachate and residue from the WR, and it appears these components are not reflecting different sources of Nd and Sm, as is the case for the fine-grained samples.

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A BILLION YEARS OF 813C STASIS AND THE EMERGENCE OF EUKARYOTES: NEW DATA FROM NORTHERN AUSTRALIA

1BRASIER, M.D. & ^LINDSAY, J.F. ^arth Sciences Department, Oxford University, Parks Road, Oxford, UK. Australian Geological Survey Organization, GPO Box 378, Canberra, ACT, Australia The Neoproterozoic to Cambrian (ca. 1.0 to 0.5 Ga) was a time of spectacular geological, environmental and biological revolutions. These were accompanied by major changes in the carbon cycle, in which the most positive 813c values may be taken to indicate widespread anoxia and rapid rates of carbon burial, broadly coincident with supercontinental amalgamation and the subsidence of orogenic and rift basins. So much CO2 may have been removed from the atmosphere by carbon burial at this time that marine glaciations developed, resulting in greater oceanic circulation, reduced organic carbon deposition, and negative 513C excursrons. The aim of this talk is to explore the possibility that the long interval between 2.0 and 1.0 Ga, called the dullest period in Earth history', may provide the key to our understanding of later biosphere evolution. We have studied carbon isotopes through 6 km of fully cored drill holes in 1.7 to 1.5 Ga carbonates of the Mount Isa and McArthur basins, Australia (which host the earliest known eukaryote biomarkers) to provide the most comprehensive and bestdated d!3c stratigraphy yet obtained from such ancient rocks. Both basins reveal remarkably stable temporal 813c trends

(mean of -0.6%o ± 2%o Pee dee belemnite) and confirm the impression of 813c stasis between 2.0 and 1.0 Ga, which, together with other evidence, suggests a prolonged period of stability in crustal dynamics, redox state of surface environments and planetary climate. This 813c stasis is consistent with great stability in the carbon cycle controlled, we suggest, by P limitation of primary productivity. Recent evidence shows that P depletion is a major factor in obligate associations between photosymbionts and host cells. We suggest here that the chloroplasts of the eukaryote cell were stabilised by photosymbiotic association during up to a billion years of 813C stasis spanning the Early to Middle Proterozoic. Remarkable and prolonged stability of the carbon cycle, in an interval without known glaciations, major phosphorites or mass extinctions, suggest that nutrient stability and P limitation nurtured these photosymbioses to the point at which chloroplasts became permanent organelles within the cell of eukaryotic autotrophs, and culminated in the radiation of eukaryotes at some time close to 1.0 Ga BP (Brasier and Lindsay, Geology, in press).

1

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THE TRANSITION FROM NEOPROTEROZOIC TO CAMBRIAN: NEW DATA FROM MONGOLIA TO OMAN BRASffiR, M.D. & McCARRON, G. Earth Sciences Department, Oxford University, Parks Road, Oxford, UK. The once favoured view of a sharp distinction given a Rb/Sr age of 554±10 Ma between terminal Neoproterozoic and have (Dubreuilh et al. 1992). U-Pb isochrons Cambrian biotas is now questioned by a igneous basement are currently being variety of new data, including stable isotopes from studied by the Bowring lab. at MIT while and geochronology. In this talk, volcanic interbeds are also being studied palaeontological and carbon isotopic data will by the Tucker lab. at St Louis. first be reviewed from phosphate-bearing successions in outer Mongolia and Iran, skeletal fossil Cloudina has been which suggest that skeletal fossils of The found in the Ara Formation, suggesting a 'Cambrian type (e.g. Anabarites, terminal Neoproterozoic to earliest hyolithellids, hexactinellid sponges), extend Cambrian age latter. A Pb/Pb down into rocks beneath negative carbon carbonate date forof the529±16 been isotope anomaly 'W', at the putative obtained from a major marker has the Precambrian - Cambrian boundary. The early Ara Formation of southernwithinOman appearance of phosphatic-siliceous facies in subsurface(unpublished PDO Report) and the Gobi-Altay Mountains successions of we have recently obtained a latest Mongolia suggests, along with other Neoproterozoic-earliest Cambrian U/Pb evidence, that these early skeletal remains age from the middle part of the were preserved along the outer, arc-fringed zircon correlated Fara Formation in the Oman margins of the ?Siberian craton. Mountains (R. Tucker, unpublished data). A succession with latest Neoporoterozoic Putative fossil markings (rare 'Intrites\ early skeletal fossils in the Elburz Mountains abundant 'ArumbericC) have been found of Iran likewise appears to have lain on the Masirah Bay Formation and outer margins, in this case of the Arabian within theocclusa occurs within Shuram craton. Over the last three years, detailed Nimbia Formation. In the Ara Formation, research has been undertaken on successions Cloudina is typically found associated with of comparable age (the Huqf Supergroup) thromboses (work of Stefan from the interior, evaporitic basins of the calcimicrobe Schroder and Albert Matter, Berne). Arabian craton, in Oman, by a research group Complex have also been found in at Oxford, Berne, Dublin and MIT, funded outcrops marking Ara age. Skeletal by Petroleum Development Oman. Detailed fossils andof possible trace fossils of Nemakitsedimentological and seismic studies, Daldynian or Tommotian type appear to be including biostratigraphy in conjunction with lacking in Oman, perhaps owing to carbon and strontium isotope widespread hypersaline conditions. chemostratigraphy, is being carried out with a view to elucidating the age and evolution of Carbon isotopes show negative-positive the succession. Sediments were here peaks three places: in the Cap carbonate, deposited upon rifted Pan-African basement. which inmay be correlative with those above The initial rift basins were infilled by thick, the 'Varanger 1' glaciation; in the Shuram multiple diamictites overlain by up to 12 Formation, which may be correlative with metres of Cap carbonate, now being studied units above the 'Varanger 2' glaciation; in detail by Jon Leather at Dublina and and in the Ara Formation, which may be Oxford. correlative with those at the Precambrianboundary. These new Further sagging enabled the deposition of Cambrian correlations suggest an older, mainly two siliciclastic/carbonate units before a Neoproterzoic age for the Huqf Group and second episode of rifting began, with with the generally accepted deposition of the Ara/Fara Formations. contrast correlations published hitherto. Granodiorite dykes beneath the diamictite 1

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PALAEOBIOGEOGRAPHIC AFFINITIES OF EARLY CAMBRIAN NONTRILOBITE SHELLY FAUNAS FROM AUSTRALIA BROCK, G.A., & ENGELBRETSEN, M.E. Centre for Ecostratigraphy and Paleobiology, School of Earth Sciences, Macquarie University, N.S.W., 2109 The lack of formal stage subdivisions for the East Avalonia, North China, Siberia and Early Cambrian in Australia has long Baltica each share four genera. The two frustrated high resolution regional and Gondwanan constituents, Central West intercontinental correlation. This picture is Africa and West Antarctica, each have three gradually changing with new genera in common with Australia. Affinities palaeontological and sequence stratigraphic with the Chinese blocks remained strong data challenging itraditionali biostratigraphic throughout the Early Cambrian, with North zonations. Because of their diversity, China sharing 33% and South China 42% of abundance, stratigraphic utility and relatively the Australian genera. widespread distribution, benthonic trilobites Early Cambrian micromolluscs show strong (e.g. Pilolla 1990; Lieberman 1997) and affinities to faunas in West Antarctica, South archaeocyathans (Maidanskaya et al. 1998) China, eastern Laurentia, Siberia, Mongolia, continue to be the most productive tools for Kazakhstan, and the southern European Early Cambrian biostratigraphic and platform (especially the Gorlitz palaeobiogeographic analyses. However, Synclinorium in Germany). Strong faunal trilobites and archaeo-cyathans iare not the links are apparent with South China at the only measure of faunal connectedness either species level based on the co-occurrence of between Early Cambrian continents or Stenotheca drepanoida, Pelagiella adunca, between different marginal segments of the tortilis and Pojetaia runnegari. same continentsi (Palmer & Rowell 1995, p. Beshtashella A particularly close relationship with Early 6). Cambrian sequences in Germany is based Description of non-trilobite shelly faunas on the shared occurrence of Beshtashella from Australia and around the globe has tortilis, Pojetaia runnegari, Yuwenia and provided opportunities to refine or develop Pelagiella. regional and intercontinental biostratigraphic Affinities of Early Cambrian small shelly correlation for the Cambrian using lingulate fossil species from Australia reinforce links and calciate brachiopods, molluscs, and suggested by archaeocyathan, brachiopod numerous problematic small shelly fossil and mollusc data. Dodecaactinella groups. The emerging biostratigraphic cynodontota, Microcoryne cephalata, potential of some of these groups provides Archiasterella hirundo and Allonia cf. independent avenues of palaeobiogeographic tripodophora from Atdabanian sequences in investigation during the Early Cambrian. South Australia are also known from Taxa of Atdabanian-Botomian age from approximately coeval strata in Germany. In Australia are almost entirely confined to addition, the heteract sponge Eiffelia intra- and epicratonic sedimentary packages araniformis has a widespread distribution in associated with the Adelaide Fold Belt Upper Atdabanian sequences from South (Arrowie and Stansbury Basins), Officer and central Australia, Kazakhstan, Siberian and Amadeus Basins. Toyonian (= Ordian) Platform, Mongolia, Germany, and South equivalent successions are also known from China. Eccentrotheca cf. kanesi from the intracratonic (Eastern Georgina, Wiso and Early Cambrian Todd River Dolomite has Daly Basins), epicratonic (Stansbury and also been recovered from the Early Arrowie Basins), marginal shelf (Gnalta Cambrian of Siberia and Avalonia. The Shelf, western N.S.W.) and probable island tommotiids Kennardia from the Early arc (Heathcote greenstone complex) Cambrian of central Australia and Dailyatia settings. from Yorke Peninsula and central Australia provide close links with approximately Early Cambrian lingulate brachiopod faunas coeval rocks in West Antarctica. The hyolith from Australia bear greatest affinity with Microcornus eximus in South China, Siberia Kazakhstan, with 50% of shared genera. and England strengthens faunal links with Southern/Central Europe, West Avalonia, South Australia. Laurentia and South China each share five genera with the Australian region. India, -14-

REFERENCES LIEBERMAN, B.S. 1997. Early Cambrian palaeogeography and tectonic history: A biogeographic approach. Geology 25, 10391042. MAEDANSKAYA, I.D., Debrenne, F., & Zhuravlev, A.Yu., 1998. Faunal migrations of archaeocyaths and Early Cambrian plate dynamics. Bulletin de la Socit Gologique de France (in press).

PALMER, A. R., & ROWELL, A.J., 1995. Early Cambrian trilobites from the Shackleton Limestone of the Central Transantarctic Mountains. The Paleontological Society, Memoir 6,1-28. PILLOLA, G.L., 1990. Lithologie et trilobites du Cambrien inferieur du SW de la Sardaigne (Italie): implications paleobiogeograph-iques. Comptes Rendus de I'Academie des Sciences Paris 310, Series H, 321-328.

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PROPOSED LOCATION OF A TERMINAL PROTEROZOIC GSSP: NUCCALEENA FORMATION, FLINDERS RANGES, SOUTH AUSTRALIA CHRISTIE-BLICK, Nicholas, 2KENNEDY, M.J., & ^OHL, L.E. department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964-8000, USA; ncb@ldeo.columbia.edu. department of Earth and Space Sciences, University of California, Los Angeles, CA 900951567, USA The late Neoproterozoic, from approximately 750-543 Ma, is a unique interval in Earth history, encompassing marked climatic oscillations, prominent variations in carbon and strontium isotopes, and distinctive paleobiology (including acritarchs, the Ediacara fauna and primitive trace fossils). In seeking to understand the relationships between these phenomena, we are particularly interested in how they may relate in time, and therefore in specific benchmarks that might be used to correlate precisely from one place to another, as well as to define formal chronostratigraphic units. While overall trends in historical geology are clear (for example, strata containing the Ediacara fauna appear to be broadly younger than those containing evidence for glaciation), the preserved record of both fossils and severe climate is sporadic or incomplete, and only limited chronology is available. Ultimately, the selection of benchmarks is a matter of judgement rather than discovery. The stratigraphic level that has emerged as a prime candidate for a terminal Proterozoic Global Stratotype Section and Point (GSSP) corresponds with the termination or late stages of the youngest Proterozoic glaciation in many areas (the Elatina Formation and correlatives in Australia and Ice Brook Formation of northwestern Canada). This level is marked by a thin but regionally extensive carbonate layer ("cap carbonate") that appears to correspond with a short-lived (< 105 years) global geochemical event. 513CCarb decreases upwards from values as large as +5 per mil in the glacial deposits to as low as - 5 per mil in the cap carbonate. Although absolute isotopic values vary from one section to another, owing at least in part to variations in paleogeographic position and diagenesis, overall trends are consistent between widely separated sections. Stratigraphic evidence for the duration of the event is preserved in the Amadeus basin of central Australia (Kennedy and ChristieBlick, in preparation). There the cap

carbonate passes laterally into a series of prominent unconformity-bounded units, each no more than a few tens of metres thick. These have been interpreted to be due to a combination of glacial-isostatic rebound and orbitally forced glacial-eustasy during the late stages of glaciation. Similar high-order unconformity-bounded units, also locally associated with a cap-like carbonate in nonglacial facies, and thought to be of the same age, have been described from the western United States (Christie-Blick, 1997). The proposed stratigraphic horizon for the GSSP (Nuccaleena Formation in South Australia) is drawn below the level of the Ediacara fauna in virtually all sections. Exceptions are the comparatively primitive Twitya disks of northwestern Canada, and a single pennatulid-like fossil or pseudo-fossil discovered immediately below the cap level in South Australia. The proposed placement of the GSSP is therefore consistent with the historical preference for making the Ediacara fauna a distinctive feature of any terminal Proterozoic unit. The proposed horizon is also located beneath the Pertatataka acritarch flora. The level of the cap carbonate is regarded as preferable to a horizon beneath one or more glacial units (e.g., Vendian) because we think that it is useful to distinguish intervals of markedly different climate and because in many sections the glacial strata overlie prominent unconformities most likely associated with significant hiatuses. The cap level is preferred to a younger horizon (e.g., Ediacaran of Jenkins, 1981) because we think that such a horizon may be more difficult to correlate at a global scale. The hypothesis that glaciation may have persisted at least locally to this level (Kaufman et al., 1997) is not consistent with the absence of evidence outside Australia for significant sea-level changes during this span (Jiang Ganqing and N. Christie-Blick, unpublished data from the Krol platform, northern India). Stratigraphic and sedimentological arguments for postNuccaleena glaciation in Australia are

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unconvincing in this context (DiBona, 1991; represents an extended interval of geological M. Corkeron, oral communication, 1998). time (several hundred thousand to several The Nuccaleena Formation is a distinctive, million years) and is most likely a composite readily mapped, pink to buff-coloured unit rather than the record of a single glacial laminated dolomite that can be traced over retreat. large areas of the Flinders Ranges of South Prime sections for a GSSP are located in the Australia, and correlated with confidence at central Flinders Ranges (Parachilna and least as far as central Australia. It Copley 1:250,000 scale geological map disconformably to unconformably overlies a sheets). Near Trezona bore, in the Flinders range of glacial and associated rocks (Elatina Ranges National Park, the Nuccaleena crops Formation), and it represents the basal unit of out widely within an impressive west-dipping a thick succession (> 3 km) of mainly homocline that includes strata from the upper terrigenous strata with minor carbonate part of the Sturtian-age glacial interval to the (Wilpena Group). Recent work suggests that Cambrian, including the main localities in the Nuccaleena Formation accumulated in which the Ediacara fauna has been found in relatively deep water during late glacial to the upper part of the Wilpena Group. post-glacial transgression. The sharp basal Chambers Gorge, located to the northeast of contact is ascribed to local glacial-isostatic the park, has the most spectacular outcrops of uplift and subaerial exposure (at sites that Nuccaleena, but overlies a fluvial sandstone were close to the ice sheet or overridden by unit of uncertain stratigraphic affinity. The it), followed by rapid drowning. In both the outcrop is also isolated from the principal Flinders Ranges and Amadeus basin, this Ediacara fossil sites. surface may be traced basinward into a relatively conformable, generally deeper- REFERENCES water succession. N., 1997, Stable isotopic studies of marine carbonates in CHRISTIE-BLICK, sedimentation and tectonics in the Flinders Ranges have met with variable Neoproterozoic success. Some formations appear to be west-central Utah: Brigham Young University pervasively altered, while others are less Geology Studies, v. 42, Part I, p. 1-30. affected by diagenesis. Intervals most likely DIBONA, P.A., 1991, A previously Late Proterozoic succession: to retain primary values include the unrecognised Upper Wilpena Group, northern Flinders Nuccaleena Formation, the Etina Formation Ranges, South Australia: Quarterly of the underlying Umberatana Group, the Notes, Geological Survey of Wearing Dolomite at the base of the Wonoka Geological Formation (middle part of the Wilpena South Australia, v. 117, p. 2-9. Group), and the upper part of the Wonoka. JENKINS, R.J.F., 1981, The concept of an The Nuccaleena shows consistent 8 C values 'Ediacaran Period' and its stratigraphic from stratigraphic profiles collected at several significance in Australia: Transactions, Royal locations in the Flinders Ranges. S C varies Society of South Australia, v. 105, p. 179from -1.5 to -3.0 per mil, with 5 0 rarely < 194. -8 per mil. 5 C is consistently depleted up- KAUFMAN, A.J., KNOLL, A.H., & section, indicating a general absence of G.M., 1997, Isotopes, ice homogenization and a retention of primary NARBONNE, ages, and terminal Proterozoic earth history: marine values, perhaps as a result of early Proceedings of National Academy of diagenetic stabilization to dolomite. Recent paleomagnetic work in the upper part Sciences, v. 94, p. 6600-6605. of the Trezona Formation and glaciogenic SOHL, L.E., CHRISTIE-BLICK, N., & Elatina Formation of the Flinders Ranges KENT, D.V., Paleomagnetic polarity confirms the previous low paleolatitude reversals in Marinoan (-600 Ma) glacial interpretation of these rocks (8.6° ± 3.3°; deposits of Australia: Implications for the Sohl et al., manuscript). Data from the duration and causes of low-latitude glaciation central Flinders Ranges have yielded a in the Neoproterozoic: Geological Society of positive regional-scale fold test (significant at America Bulletin, in review. 1 % level), and they demonstrate the existence of multiple polarity reversals in both the Trezona and Elatina. The reversals are significant in showing that the Elatina 13

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DEPOSITIONAL ENVIRONMENTS AND CORRELATION OF THE NEOPROTEROZOIC SUCCESSION IN THE KIMBERLEY REGION, AUSTRALIA. CORKERON, M. L. TSRC, Department of Geology and Geophysics, The University of Western Australia, Nedlands, WA, 6907 Two glacial events are preserved in the and Duerdin Groups record marine deposits Neoproterozoic record of the Kimberley of turbiditic mudstone and gradual region of northwestern Australia. The shallowing to coarse sandy subtidal Neoproterozoic succession in the Mount environments. Ramsay area contains two tillite bearing formations, the Landrigan Tillite at the base In contrast, the Egan Formation is the only of the Kuniandi Group and the Egan record of glacigenic rocks of the younger of Formation at the base of the unconformably the two glacial episodes and lithofacies are overlying Louisa Downs Group. East and distinctly different to those of the Moonlight west of the Mount Ramsay area, in the East Valley Glaciation. The Egan Formation Kimberley District and the Mount House was deposited on a shallow marine area respectively, only a single glacial carbonate platform. Carbonate rocks episode is recorded; the Fargoo/Moonlight characterised by intraclastic, stromatolitic Valley Tillites (lowermost formations of the and oolitic beds both underlie and overlie Duerdin Group) in the east Kimberley, and siliciclastic diamictite, conglomerate and the Walsh Tillite (lowermost formation of sandstone interpreted to be of glacigenic the Mount House Group) in the west origin. The glacigenic facies were Kimberley. These glacigenic formations deposited as subglacial outwash and are interpreted as equivalents of the current-reworked debris in front of an ice Landrigan Tillite, and together record the grounding line. Postglacial transgression is Moonlight Valley Glaciation, whereas the recorded by an overlying rhythmite facies glacial episode recorded by the Egan before a return to carbonate platform Formation is considered a separate and deposition. younger event. Correlation of Neoproterozoic successions Depositional models for the two glacial from the three geographic regions of the episodes vary significantly as indicated by Kimberley has been contentious. The distinctly different lithofacies preserved correlation proposed here is supported by from both glacial events. Deposits of the lithostratigraphic comparisons of the three Moonlight Valley Glaciation are distributed regions (Plumb, 1996), biostratigraphic over hundreds of thousands of kilometres evidence from the distinctive branching and record deposition from a broad stromatolite Tungussia julia identified in the continental ice sheet during glacial Egan Formation (Corkeron et al., 1996; recession. They preserve a terrestrialGrey and Corkeron, in press) and from marine transition. Glacially striated new chemostratigraphic evidence. 8 C basement underlies diamictite across the values of about -5 permil in 'cap entire depositional region recording icedolostones' above the Walsh and Landrigan induced erosion and scour of Kimberley tillites support the correlation of these units. Basin basement. The diamictite is A negative 8 C is also recorded in the 'cap interpreted as lodgement till and basal dolostone' above the Moonlight Valley meltout, and associated conglomerate and Tillite and although of smaller magnitude, sandstone deposits are interpreted as supports the correlation of this formation glaciofluvial meltwater outwash, both with the Walsh and Landrigan Tillites. deposited during glacial retreat. Overlying Similar negative trends observed in siltstone and shale, together with enigmatic Marinoan 'cap dolostones' of central and thin-bedded and regionally preserved South Australia support the proposal that dolostone, record post-glacial transgression the lower glacial event in the Kimberley is a in a marine regime. The remainder of the conformably overlying siliciclatic Marinoan Glaciation equivalent. 8 C formations of the Mount House, Kuniandi 13

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results are less definitive from the Egan Formation and Boonall Dolomite (nonglacial carbonate unit at base of Albeit Edward Group, east Kimberley) although similar trends of a positive to negative to positive curve are observed in both formations. This parallel trend, together with biostratigraphic control, supports the correlation of the Egan Formation and Boonall Dolomite and infers a younger than basal Marinoan glacial event in the Kimberley.

Neoproterozoic glacial episodes in the Kimberley region, northwestern Australia. 13th Australian Geological Convention, Abstracts, No. 41, p.97* GREY, K., & CORKERON, M., 1998. Late Neoproterozoic stromatolites in glacigenic successions of the Kimberley region, Western Australia: evidence for a younger Marinoan glaciation. Precambrian Research in press. PLUMB, K. A., 1996. Revised correlation of Neoproterozoic glacial successions from the Kimberley region, northwestern Australia. 13th Australian Geological Convention, Abstracts, No. 41, p.344.

REFERENCES CORKERON, M., GREY, L., LI, Z. X., & POWELL, C. McA., 1996.

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SIMILAR CYCLES — DIFFERENT STROKES: CLOSING A TAPHONOMIC WINDOW ACROSS THE PRECAMBRIAN-CAMBRIAN BOUNDARY iGEHLING, J. G., DROSER, M., JENSEN, S., & RUNNEGAR, B. University of South Australia, Levels Campus, Mawson Lakes, SA 5095; University of California, Riverside, USA; Cambridge University, UK; University of California, Los Angeles, USA. In Australia, North America, Russia and progradation are recorded in a single Namibia, siliciclastic formations spanning shallowing, coarsening upward cycle of the the Precambrian-Cambrian boundary Uratanna Formation, capped by the more provide limited taphonomic windows to widely distributed shore-face sandstones of early animal life. the Parachilna Formation (Figure 1). Relative falls in sea level are recorded in the The Wonoka, Ediacara, and Uratanna terminal Proterozoic to Early Cambrian sequences represent equivalent responses to succession in the Flinders Ranges by three rapid drowning of a limited part of the type-1 sequence boundaries featuring large Adelaide Geosyncline. These sequences are scale channel and valley incision into the distinguished by taxonomically and respective underlying formations (Figure 1). ecologically contrasting assemblages of In each case a low-stand sequence tract is body and trace fossils. overlain by a shallowing upward, high-stand sequence tract. Judging by the scale of one In the Wonoka sequence, there is little of these events, the incisions were products preserved evidence of mega-organisms. of relative falls in sea level controlled by During deposition of the Ediacara sequence, local tectonic movements or by evaporation sea floors were inhabited by passive and draw-down of sea level. The limited relatively immobile benthic organisms. evidence for transgressive sequence tracts Sediment processing animals were confined suggests a rapid restoration of sea level to two dimensional biotopes. Buried organic followed by renewed progradation from the remains and bedding lamination remained north and west out over an incised shelf. undisturbed, allowing the formation of death masks that facilitated preservation of the The Wonoka Formation was deposited over Ediacara fauna. The high-stand sequence a surface into which 1 km scale canyons had tract of the Uratanna sequence recorded the last Ediacaran-type fossils and the first been cut. Rare organic impressions were preserved in facies deposited between storm evidence of bioturbation in the form of and fair-weather wave-base. The Ediacara burrows that penetrated well below the water-sediment interface. The presence of a Member of the Rawnsley Quartzite filled valleys cut into the underlying shallow more complex and penetrating trace fossils in the Uratanna Formation indicates that the marine sandstones of the Rawnsley Quartzite. Fossils of the Ediacara fauna are Precambrian-Cambrian boundary lies near restricted to certain facies deposited below the underlying disconformity at the base of fair-weather wave-base in a prograding delta the Uratanna sequence. sequence. The Ediacara Member passes back into shore-face and tidal sand-flat Recent fossil discoveries in Namibia, sandstones of the upper Rawnsley Quartzite. Nevada and South Australia show that the A major eustatic fall in sea level truncated claimed "extinction" of the Ediacara fauna, deposition of the Rawnsley Quartzite well below the Precambrian-Cambrian marking a major disconformity throughout boundary, is an artifact of facies distribution. the Adelaide Geosyncline. In the northern Eventually, a Cambrian explosion of region, this sequence boundary features biological and ecological innovation put an incised valleys smaller in scale than the end to Ediacaran ecology and taphonomy in all but the most inhospitable of valleys filled by the Ediacara Member in the environments. underlying Rawnsley Quartzite. The subsequent transgression and then 2

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Stratigraphy Woodendinna Dolomite Parachilna Formation

Body Fossils

Trace Fossils

Algal Fossils

Uratanna Formation

Rawnsley Quartzite Ediacara Member

Bonney Sandstone

Wearing Dolomite Bunyeroo Formation *

I Acraman i ejecta

ABC Range Formation Brachina Formation

Figure 1 Generalized stratigraphy and characteristic mega-fossils of successive depositional sequences spanning the terminal Proterozoic — Early Cambrian transition in the Flinders Ranges, South Australia.

Nuccaleena Fm

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EDIACARIAN ACRITARCH BIOZONATION IN AUSTRALIA GREY, Kathleen School of Earth Sciences, Macquarie University, New South Wales, 2109

Current address: Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, Australia

Reg Sprigg's discovery of Ediacaran fossils raised the possibility of Proterozoic biostrat-igraphic correlation. Despite subsequent dis-coveries of numerous fossils, including metazoan body fossils, trace fossils, metaphytes, stromatolites, prokaryotic microfossils, and eukaryotic phytoplankton, only limited progress (restricted mainly to latest Neoproterozoic metazoan megafossils and trace fossils) was made towards Proterozoic biostratigraphy. The development of zonal schemes, similar to Phanerozoic ones, seemed unlikely because of taxonomic uncertainty, low species diversity, conservative evolution rates, morphological simplicity, and sporadic distribution patterns. Studies of the Centralian Superbasin and Adelaide Rift Complex indicate that Ediacarian biostratigraphic correlation is now possible using large, morphologically complex, acanthomorph acritarchs. Acritarchs are polyphyletic, organicwalled, acid-insoluble microfossils (mostly phytoplanktonic), extractable by palynological methods. They are ideally suited for biostrat-igraphy because of their complex morphology, abundance, short stratigraphic ranges, and wide geographic and lithofacies distributions. Prot-erozoic palynology gained momentum from improved preparation techniques, reconciliation of 'chert' and 'shale' microfossil taxonomy, the discovery of complex acanthomorphs in the Australian Ediacarian by Zang, and the need for improved Neoproterozoic correlation. Ediacarian acritarch assemblages in the Cent-ralian Superbasin and Adelaide Rift Complex are taxonomically diverse and demonstrate un-mistakable patterns of secular variation. Five assemblage zones and two palynofloras were recognised (Fig. 1). The zones are identifiable despite taphonomic and palaeoenvironmental complications, and are independent of lithology, lithostratigraphy, and sequence

stratigraphy (Fig. 2). The proposed Ediacarian stratotype in the Adelaide Rift Complex is too thermally mature for the preservation of identifiable acritarchs, but the section can be tied stratigraphically to the Stuart Shelf, which, in turn, provides biostratigraphic links to well-defined assemblage zones in the Officer and Amadeus Basins. Effective correlations between Australian basins have been demonstrated, but global extension of the scheme is not yet possible because only a few key species are known elsewhere. The Australian Ediacarian contains four east Siberian species, and has several genera in common with Siberia, Svalbard, Norway and China, indicating the potential for global correlation. Observed biotic changes are radical ones. The older SLP (Simple Leiospheredominated Palynoflora) is succeeded by the ECAP (Ediacarian Complex Acanthomorph-dominated palynoflora). The ECAP shows a marked and rapid increase in abundance, size, morphological complexity, and taxonomic diversity. More than 40 species and 20 genera appear for the first time in the middle Ediacarian. New body plans are introduced; and there are new lineages of green algae. These changes indicate significant evolutionary advances in the nature of the paly-noflora and a major evolutionary radiation. The actual or presumed position of the transition matches a negative 8 C excursion that coincides with the Acraman impact layer. Evidence for a relationship between the impact event and changes observed in acritarch assemblages is still largely circumstantial, but the effects of a large bolide impact supplies a plausible explanation for dramatic palynofloral changes that are otherwise difficult to explain. Further investigation is needed to test the possibility that the late Ediacarian diversification represents a recovery event following a bolide impact. 13

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org

Palynoflora

Proposed Assemblage Zone

Ediacarian New genus A sp. A/Ericiasphaera sp. A/Baltisphaeridiuml sp. A Complex Tanarium irregulare/ New genus A sp. B/ Mutifronsphaeridium pelorium Acanthomorph Tanarium conoideum/ Schizofusa sp. A/ Variomargosphaeridium litoschum Palynoflora Appendisphaera sp. A/Alicesphaeridium medusoidum/ Cavaspina sp. A (ECAP) Simple Leiosphaeridium jacutica/ Leiosphaeridium crassa Leiosphere Palynoflora (SLP) Figure 1. Proposed acritarch zones for the Centralian Superbasin and Adelaide Rift Complex. Open nomenclature is used to avoid nomen nudum.

Figure 2. Relationship of proposed Acritarch Assemblage Zones in the Officer Basin to lithostratigraphy, isotope chemostratigraphy and sequence stratigraphy. Cm = New genus A sp. A,Ea = Ericiasphaera sp. A, B?v = Baltisphaeridiuml sp. A, 77 = Tanarium irregulare, Cg = New genus A sp. B, Mp = Mutifronsphaeridium pelorium, Tc = Tanarium conoideum, Sr = Schizofusa sp. A, VI = Variomargosphaeridium litoschum, Ab = Appendisphaera sp. A, Am = Alicesphaeridium medusoidum, Cp = Cavaspina sp. A, Lj = Leiosphaeridium jacutica, Lc = Leiosphaeridium crassa, ECAP = Ediacarian Complex Acritarch Palynoflora, SLP = Simple Leiosphere Palynoflora. Parts of diagram incorporated with permission of Clive Calver and MESA

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FORTY FIVE YEARS OF THE KANMANTOO GROUP: A REVIEW OF PAST AND PRESENT CONCEPTS RAINES, P.W., FLOTTMANN, T., 'JAGO, J.B., & 'GUM J.C. 'Dept. of Applied Geology, University of South Australia, The Levels Campus, S.A. 5095 Dept. of Geology and Geophysics, University of Adelaide, Adelaide, S.A. 5005 The Cambrian Kanmantoo Group is a thick during the Delamerian Orogeny. Detrital (-7-8 km) succession of predominantly clastic zircon dating reveals major age peaks around metasediments that crop out in a -50x300 km 1000-1200 Ma and 500-600 Ma, indicating arcuate belt from western Kangaroo Island to that the sediment has nothing in common with the eastern Mount Lofty Ranges in South once proposed local basement sources or Australia. The group was defined by Sprigg underlying Neoproterozoic sediments. An and Campana (1953), who nominated a type active orogenic source in once contiguous section along the southern coast of Fleurieu Antarctica, perhaps reflecting an early phase Peninsula. In recent years it has become of the Ross Orogeny, is likely. The increasingly obvious that the Kanmantoo depositional basin may have been quite distal Group occupies a fundamentally important from the source. One model suggests that the position along the Palaeo-Pacific margin of accommodation space was created in response Gondwana. Understanding its significance to different subduction polarities along the may help to elucidate the history of the Ross- Australian and Antarctic segments of the Delamerian orogenies and the subsequent Palaeo-Pacific margin. Alternatively, strikedevelopment of the Tasman depositional and slip tectonics may have played a significant orogenic system to the east. The group also role. A fundamental lack of knowledge about has significant economic potential and is the nature and position of the eastern margin currently the subject of ongoing exploration. of the Kanmantoo Group has hampered a fiill Early workers focused on elucidating tectonic appraisal. stratigraphy, leading to several generations of As fossils thus far discovered are of no stratigraphic nomenclature, and on problems biostratigraphic value, the best current age of the base: ie. conformable, unconformable on the group are given by U-Pb or tectonic. The base is now known to be constraints for an underlying tuff (526±4 Ma) non-tectonic (although locally faulted) and zircona ages probable early syn-tectonic granitoid both unconformable and apparently and (516±4 Ma). This indicates very rapid conformable lower contacts are known. deposition and restricts the Kanmantoo Group Although the type section is now known to to the late Early Cambrian, long suffer from many structural complications not established views regardingchallenging perceived by earlier workers, stratigraphic stratigraphic position. Under oneitsnewregional model nomenclature dating from the early 1970's widespread red bed successions, traditionally still proves useful with some amendments. A correlated with the Kanmantoo Group and significant sequence boundary within the to extend into the Middle Cambrian, group, probably of tectonic origin, has been known are considered post-Kanmantoo early synrecognised for several years. Recent research tectonic deposits. has focused on depositional mechanisms, genesis of mineralisation within the provenance, age and regional correlations, The Kanmantoo Group has been the subject of basin tectonics, and controls on much debate. At present two major episodes mineralisation. of mineralisation are identified. A syngenetic A number of depositional mechanisms have event formed numerous small strata-bound been proposed in the past, but rapid Zn-Pb deposits, followed by an epigenetic sedimentation from high density turbidites event during the Delamerian Orogeny which now seems the likely explanation for a generated widespread vein-hosted Cu significant part of the Kanmantoo Group. mineralisation. Palaeocurrent studies suggest that most of the REFERENCE sediment entered the basin at the southern SPRIGG, R.C., & CAMPANA, B. 1953. The end, and sediment thickness and local age and facies of the Kanmantoo Group. redistribution was controlled by active growth Australian Journal of Science 16, 12-14. faults that were later reactivated as thrusts 2

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NEW MACROFOSSIL OCCURRENCE IN NEOPROTEROZOIC MIETTE GROUP (WINDERMERE SUPERGROUP), WESTERN CANADA. 'HOFMANN, H.J., & MOUNTJOY, E.W. *Dept. of Geology, University of Montreal, P.O. Box 6128, Sta. A., Montreal, Que. H3C 3J7, Canada. Dept. of Earth and Planetary Sciences, McGill University, 3450 University St., Montreal, Que. H3A 2A7, Canada. 2

2

Macrofossils have been recovered from siliciclastic beds in the the Miette Group in southeastern British Columbia. The units are older, and have a depositional setting somewhat deeper, than those from which a small Ediacaran biota and dubiofossils were previously reported (Hofmann et al., 1991). Preliminary work indicates that the new fauna includes charniodiscoid/ cyclomedusoid disks, as well as quilted bottom dwellers with fractal morphology. The latter have affinities with organisms referred to Bradgatia, which were previously known only in the Mistaken Point fauna in Newfoundland, and in the Charnian of England, and they thus constitute the first known representative of

such organisms in western North America. In addition, the Miette beds have yielded simple small and large, irregularly sinuous horizontal traces and burrows, including Planolites and Helminthoidichnites, as well as more systematically meandering traces with long limb segments reminiscent of Gordia marina Emmons. REFERENCE HOFMANN, H.J., MOUNTJOY, E.W., & TEITZ, M. 1991. Ediacaran fossils and dubiofossils, Miette Group of Mount Fitzwilliam area, British Columbia. Canadian Journal of Earth Sciences, v. 28, p. 1541-1552.

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THE EDIACARAN QUESTION: NORTH AND SOUTH JENKINS, R. F. J., & NEDIN, C. Department of Geology & Geophysics, University of Adelaide, S.A., 5005 Ideas concerning formal international equivalent of the Wearing Dolomite, thw chronostratigraphic divisions within the presently proposed GSSP placement. The wider Proterozoic have an extended history secular 9 CCARB isotopic record over these (e.g. Harland and Herod 1975). The intervals is strikingly similar in both "Ediacarien" Stage of Termier and Termier regions. (1960) emphasised the significance of the evolutionary appearance of megascopic The correlative stratigraphies of the Elatina soft-bodied metazoans near the close of the Formation through the later Neoproterozoic Proterozoic, and the same concept was in the Flinders Ranges and central Australia linked to the specific setting of the Flinders are so similar to the Vestertana Group of the Ranges with the nomination of an Ediacaran north Finnmark area of Norway as to System and Period by Jenkins (1981) and suggest the possibility that Baltica and the parallel consideration of an Ediacarian Australian Shield were conjugate at the System by Cloud and Glaessner (1982). time. There is a simple geometric solution The lower boundary of the System of to Australia occupying a "North Atiantic" Cloud and Glaessner reflects the popular placement during the later Neoproterozoic. idea that a closing glacigenic cycle within The Elatina Formation may be correlative the Proterozoic (the Elatina 'glaciation') with the Smalfjiord Formation of Finmark preceded major metazoan radiations. and the Bunyeroo and Olympic Formations are the homotaxial correlatives of the Two well recognised glacigenic intervals Mortensnes glacials. Harland and Herod are present in the local thick Neoproterozoic (1975) linked their Ediacaran to the close of succession, the 'Sturtian' and 'Elatina' the Varangian' glaciation, or by implication mixtites (or equivalents) of the Umberatana the top of the Mortensnes Formation, the Group, identified herein as "refrigerations" possible homotaxial equivalent of the I and II respectively. New evidence points proposed GSSP herein. to the Bunyeroo Formation representing a further possible refrigeration "111" within Rb-Sr measurements for shales the Wilpena Group and dropstones in part corresponding to the Bunyeroo and older of the Billy Springs Formation indicate yet Wonoka Formations in the Officer Basin another refrigeration 'TV". and on the Stuart Shelf may be interpreted as generating a 9 point model II errorchron Investigations by others in the Kimberley of of 646 ±16Ma (MSWD 2.0). The northwestern Australia (e.g. Plumb 1996a, alignment may be compared with a b) have led to the view that two 'Marinoan' plausible 'younger' regression of 648 ±26 (later Neoproterozoic) glacigenic intervals Ma (7 point model 3 errorchron, MSWD occur in sequence, the older represented by 3.7) for the data correlative with or near the the Walsh and/or Landrigan Tillites being upper glacigenic level in the Kimberley. the equivalent of the Elatina 'glaciation' in Thus the proposed GSSP is possibly of the the Flinders Ranges (Fig. 1). The younger order of 640-650 Ma old, making the Egan Formation shows parallels with the duration of the Ediacaran System c. 100 Ma Bunyeroo Formation in its general long. homotaxial placement, including its situation above an erosion surface The 3 C C A R B secular isotopic record developed on a local succession resembling synthesised from the Officer Basin (Dey the Sandison Subgroup. Similarly, in the Dey Mudstone through Munyarai northern Amadeus Basin of central Formation), not only correlates between the Australia, the discovery of several 'relict' Flinders Ranges succession (Bunyeroo to successions predating the glacigenic upper Wonoka-Billy Springs Formations) Olympic Formation or its lateral passage on the one hand, but gives a close match into conglomerates suggests that this with the Mackenzie Mountains of refrigeration corresponds to the Bunyeroo northwestern Canada (Keele through to mid Formation and its cap-carbonate is the 13

6

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Sheepbed Formations). The Wonoka and HARLAND, W.B., & HEROD, K.M., Twitia Formations are isotopic correlatives 1975. Geological Journal Special Issue, 6, and the presently proposed GSSP position 189-216. on the Wearing Dolomite corresponds to the JENKINS, R.J.F., 1981. Transactions of upper sharp boundary of the Rapitan Group the Royal Society of South Australia, 105, (Shezal Formation) and with the base of the 635-643. Twitia. The erosive surface below the KAUFMANN, A.J., KNOLL, A.H., & Narana Formation is equivalent to the basal NARBONNE, G.M., 1997. Proceedings Nama Group unconformity of Namibia, a of the National Academy of Science, USA, correlation supported by new sequential 94, 6600-6605. fossil finds in the Rawnsley Quartzite. In PLUMB, K.A. 1996a. Geological Society the Mackenzie Mountains this equivalence of Australia, Abstracts, 41: 344. is with the upper Sheepbed through Risky PLUMB, K.A. 1996b. 30th International Formations. Geological Congress, Abstracts, 2, 51. TERMIER, H., & TERMIER, G., 1960. Revue Generale des Sciences Pures et REFERENCES Appliquees, 67, 79-87. CLOUD, P., & GLAESSNER, M.F., 1982. Science, 217, 783-792. FIG. 1 KIMBERLEY, northwestern Australia, Mount Ramsey area.

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SEA LEVEL CONTROL ON DIAPIR EMPLACEMENT: EXAMPLES FROM THE ENORAMA DIAPIR LEMON, N.M. National Centre for Petroleum Geology and Geophysics University of Adelaide, SA, 5005. The Enorama Diapir, in the central conglomerates derived from the diapir and Flinders Ranges, now outcrops as an from formations below and local elongate breccia body, 10 km by 2 km. unconformities within the sequence show Signs of emplace-ment activity are seen that the diapir was still active. almost throughout the 4000m of section that outcrops around the margins and in The upper Etina Formation, largely that close proximity to the north-plunging section equivalent to the Wundowie body. Limestone, displays a series of shallow water sandy, stromatolitic and intraclastic The earliest signs of halokinesis are seen limestones interbedded with deeper water at the base of the Tapley Hill Formation. shales. Detail in the sedimentary section An unconformity on the Wilyerpa close to the diapir shows that, although the Formation has local conglomerates diapir was active throughout an extensive reworked from the underlying glacigenic period, there were pulses of activity tied to sequence. Throughout the Tapley Hill rises in sea level with equally many quiet Formation and overlying Sunderland periods when sea level fell. Formation, unconformities are developed close to the diapir associated with facies The 300m Patterton Member (informal) changes that show local shallowing and shale shows a series of slumps with diapirhigher energy conditions. The sequence at derived clasts above the underlying this level thins towards the diapir. limestone which increase in thickness and intensity toward the middle of the shale where 60m thick wedge of conglomerate Diapir emplacement activity increases up thins away from the diapir. As sea level section into the Etina Formation and decreases above this point, shallowing overlying Enorama Shale. Conglomerates towards the limestone band above, the flanking the current outcrop of the diapir bedding in the shale is largely undisturbed show that the diapir was exposed at the with one thin band of conglomerate. This time. Clasts were largely derived from the story is repeated about each of the three diapir itself with some addition from limestone bands equivalent to the reworking of the flanking sediments, Wundowie Limestone; numerous slumps cannibalised as the diapir uplifted and and conglomerates increasing in thickness deformed the section. and number as sea level rises towards the middle of the shale interval, with regular The upper half of the Etina Formation (as bedding and no conglomerates as the sea mapped on PARACHILNA 1:250,000), shallows towards the next limestone band. and the lower half of the Enorama Shale, thicken towards the diapir, filling the rim A major transgression ensued with the syncline above the zone of evacuation. deposition of the Enorama Shale. Thick Diapir emplacement activity appears to conglomerates are present at the base and diminish through the upper half of the through the lower half of the unit, Enorama Shale and up into the Trezona, interspersed with an algal reef complex Yaltipena and Elatina Formations that fringed the diapiric island. although local basin development,

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THE HEAVITREE QUARTZITE, A NEOPROTEROZOIC (C. 800-760 MA) TIDALLY INFLUENCED, RAMP ASSOCIATION, AMADEUS BASIN LINDSAY, John F. AGSO, Canberra, ACT 2609 The Neoproterozoic Heavitree Quartzite is widespread in the Amadeus Basin and has correlatives in all of the major central Australian intracratonic basins. The origin of the formation is enigmatic, not only because of its widespread sheet-like distribution and uniformity of composition, but also because intense sUicification makes facies studies difficult. Recently discovered exposures at the eastern end of the basin are relatively free of diagenetic quartz allowing a detailed study of sedimentary structures and an understanding of the sedimentary architecture of the formation.

plane beds. In the early stages of deposition, mud-dominated tidal-flat environments alternated with higher energy sand-dominated tidally influenced settings or upper-flow-regime settings involving storm-generated currents. Towards the top of the formation tidally-influence facies gradually decline and are eventually replaced by storm-generated facies deposited by unidirectional current flow. The transition to the shallow-marine, anoxic rocks of the Bitter Springs Formation is gradational and reflects increased accommodation in a ramp setting which lacked a clearly defined shelf break.

The formation, a massive, sheet-like unit that consists largely of pale tan or white quartzose sandstones interbedded with rare laminated mudstone and conglomerate intervals, was deposited in at least four depositional sequences. The sheet-like nature of the sandstones results from an abundant supply of sediments deposited in a high-energy environment on a slowly subsiding low-gradient ramp. Environmental settings switched both laterally and temporally between tidally influenced environments involving sand waves and storm generated unidirectional current environments involving dunes and

The Heavitree Quartzite was deposited as a direct response to the events surrounding the assembly and breakup of Rodinia, in particular peneplanation during regional uplift in response to a rising mantle plume followed by broad regional subsidence as the plume decayed prior to the breakup of the supercontinent. The large supply of quartz sand results from regional peneplanation associated with the rising plume and the lack of soil-stabilising vascular plants, an environmental setting with no modern analogue.

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A COHERENT EDIACARAN CARBON ISOTOPE STRATIGRAPHY OF SOUTH AUSTRALIA AND ITS USE IN INTERREGIONAL CORRELATIONS MCKIRDY, D.M., JENKINS, R.J.F., MICHAELSEN, B.H., AYLIFFE, D.J., & GOSTIN, V.A. Department of Geology and Geophysics, University of Adelaide, SA 5005 Stable isotopic analyses of syndepositional carbonate (calcite and/or dolomite) in thick sequences of well-preserved late Neoproterozoic marine sedimentary rocks from the eastern Officer Basin and northern Adelaide Fold Belt, when integrated with the recently revised lithostratigraphy of both successions, provide a coherent record of secular variation in the S C signature of the Ediacaran ocean. Overall, limestones and dolostones are uncommon in these local Ediacaran sequences, which also are not notably enriched in dispersed organic matter. Total organic carbon (TOC) contents rarely exceed 0.2% reflecting intense bacterial remineralisation of dead phytoplankton (comprising acritarchs and cyanobacteria) as they settled slowly through a deep, suboxic, water column. Even where the level of subsequent thermal maturation is not excessive (kerogen atomic H/C > 0.2), the residual organic matter preserved in these organically lean rocks is considered unlikely to encode a readily decipherable isotopic signal of the contemporary photoautotrophic biomass. Thus, our isotopic record is based largely on dolomicrites and calcareous and dolomitic siltstones containing 10-35% carbonate. Such Neoproterozoic rocks hitherto have been overlooked or discounted by chemostratigraphers. Nevertheless, in the case of those sampled for this study, their carbonate (particularly the dolomite fraction) appears to retain its primary carbon isotopic composition. Our samples come from six drillholes in the Officer Basin (Munyarai-1, Ungoolya-1, Karlaya-1, Meramangye-1, Observatory Hill-1 and Murnaroo-1) and from eight outcrop sections in the central and northeast Flinders Ranges. In addition, isotopic analyses of the carbonate in a suite of rock samples collected from Neoproterozoic exposures at Olympic Bore (near Ringwood) and Mount Capitor in the northeast Amadeus Basin allowed comparison with their supposed correlative units in the Adelaide Fold Belt.

Our composite Ediacaran C-isotope record provides a chemostratigraphic basis for correlation of the terminal Neoproterozoic record in South Australia with sequences of similar age in the Amadeus Basin, central Australia; Namibia; the Mackenzie Mountains, northwest Canada; and northeast Spitsbergen. The threshold to our 8 C arb curve is marked by a sharp positive excursion (-3 to +3 %o relative to PDB) in the upper 40 m of the Bunyeroo Formation which occurs at the top of the underlying Cryogenian sequence in the Adelaide Fold Belt. Similarly heavy carbonate (+2 to +4 %o) occurs in the Wilsonbreen Formation (Spitsbergen). Both these units contain evidence of glacial conditions (lonestones, diamictites). The basal Ediacaran unit, the 2 m-thick Wearing Dolomite, records an equally sharp return to negative values (-1 to -4 %o). This negative excursion is maintained at -6 to -8 %c throughout the lower Wonoka Formation (units 1-7) before a major excursion to higher values (-6 to +6 %c) in its upper part (units 8-11). The problematic C-depleted signature of the lower Wonoka carbonates (possibly enhanced by organic diagenesis) is mirrored by those of the Halfway Dam and lower Pertatataka Formations (Amadeus Basin); the lower Twitya Formation (N.W. Canada); and the lower Dracoisen Formation (Spitsbergen). The ensuing steady climb of 8 C b to values as high as +6 %c resembles similar positive excursions recorded in the upper Dey Dey Mudstone and lower Karlaya Limestone (Officer Basin: +6 %o); the Twitya-Keele transition and lower Keele Formation (N.W. Canada: +10 %o); and the upper Dracoisen Formation (Spitsbergen: +10

13

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The post-Wonoka Ediacaran sequence in the Adelaide Fold Belt is almost totally siliciclastic, except for parts of the Billy Springs Formation in the Mount Freeling -30-

excursion (-4 to +3 %o corresponding to that recorded in the Kuibis Subgroup, Namibia) and thereafter fluctuates irregularly (mostly between 0 and +2 %o). A short-lived negative excursion (to -4 %o) just below the Cambrian/Precambrian boundary is interpreted as a possible local manifestation of the 'Staraya Rechka event' recorded in sub-Tommotian carbonates of the western Anabar region, northern Siberia. The Narana Formation is considered to overlap the Pound Subgroup in the Adelaide Fold Belt/ The precise match of its carbonate isotopic record with that of the terminal Neoproterozoic record in the Mackenzie Mountains (N.W. Canada) is particularly striking. The demonstrable parallels between the secular 5 C a r b record described herein and those reported for terminal Proterozoic sequences elsewhere further strengthen the case for placement of the Ediacaran GSSP within the Wearing Dolomite, the cap carbonate for the Bunyeroo refrigeration, in the Flinders Ranges, South Australia.

Syncline. Therefore, the younger portion of our C-isotope curve is derived mainly from drillhole sections in the Officer Basin. Here § Qarb values decrease from +6 %o to -10 %o through the upper Karlaya Limestone and into the lower Tanana Formation, a negative excursion which in profile closely matches that in the upper Keele and Tepee Formations (N.W. Canada). A potential correlative of the intervening Ice Brook tillite is represented in the northeastern Flinders Ranges by diamictites in the Billy Springs Formation. Here the post-glacial S C rb record climbs from -8 to +7 %o paralleling that seen in the lower Sheepbed Formation (N.W. Canada). The corresponding positive excursion in the Officer Basin is more muted, attaining values of +4 % in the upper Tanana Formation, before declining erratically through the Munyarai Formation to +1 %o. Following a major down-cutting erosional event in the Officer Basin, the Narana Formation was deposited. Its carbonate Cisotope profile commences with a positive

9

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TERMINAL NEOPROTEROZOIC - EARLY CAMBRIAN BIOSTRATIGRAPHY OF NW CANADA: TESTING THE EFFECTS OF EVOLUTION AND ECOLOGY NARBONNE, Guy M. & MACNAUGHTON, Robert W. Department of Geological Sciences, Queen's University, Kingston, ON, K7L 3N6, Canada The Windermere Supergroup and overlying Neoproterozoic to subtrilobite Cambrian strata sub-trilobite Cambrian of the Mackenzie overlying the Windermere Supergroup Mountains provides a superb natural provide a test case for the current paradigm of laboratory for testing the relative roles of evolutionary stages in the development of the evolution and ecology in controlling early infauna. Three predominantly "biostratigraphic" zonation in this critical time siliciclastic formations (Ingta, Backbone interval. The fossiliferous succession is Ranges, and Vampire formations) collectively approximately 4 km thick, largely continuous, exhibit 13 facies associations representing and has been subjected to detailed sequence nonmarine to distal shelf environments, and stratigraphic and process sedimentologic can be subdivided into 18 simple sequences, analysis. The presence of an effectively each of 800,000 - 1,000,000 years duration. unaltered C-isotope record throughout the Trace fossil occurrences were digitized at the entire succession provides an independent level of simple (depositional) sequences and means of global correlation, and thus of plotted on a matrix with facies associations avoiding the circular reasoning inherent in (environment) on the x-axis and simple using biostratigraphy to measure/test sequences (time) on the y-axis. This analysis evolution. shows that evolution was a first-order control on trace fossil distribution, and that Ediacara-type fossils occur throughout the environmental factors exerted an important uppermost 2.5 km of the Windermere second-order control. Trace fossils were Supergroup, making this the thickest most abundant in normal marine environments fossiliferous succession of this age anywhere and less so in marginal-marine settings with in the world. A stratigraphic succession of fluctuating or brackish salinity. Eolian and three, increasingly diverse biotas can be fresh-water deposits were barren, presumably recognized. In contrast with the shallow because animals able to tolerate these marine environment characteristic of most conditions had not evolved, and turbulence occurrences, Ediacaran organisms in the restricted organisms in the shoreface zone. Mackenzie Mountains lived on a continental However, the key taxa used in biostratigraphy slope in water depths calculated to have been (e.g., Treptichnus and Rusophycus), show 1-1.5 km. Nevertheless, the biota of NW broad environmental tolerance across the Canada is remarkably similar to that of marine shelf. Trace fossils provide a shallow-water occurrences of the Ediacara consistent indicator of the Neoproterozoicbiota such as the Flinders Ranges and the Cambrian boundary in all marine facies of this White Sea, and most genera and even species study. Four evolutionary zones can be reported from the Windermere Supergroup are recognized: (I) Simple burrows, (II) also known from these shallow-water Treptichnus pedum Zone, (IE) Rusophycus successions. One notable exception is the avalonensis Zone, and (IV) Cruziana tenella extreme scarcity of dickinsoniids and apparent Zone. Global correlations imply that Zone I is absence of sprigginids and vendomids from terminal Neoproterozoic and the overlying NW Canada, suggesting that these groups three zones are subtrilobite Cambrian in age. may have been restricted to shallow-water These zones are present in the Newfoundland (photic?) environments. The comparatively Neoproterozoic-Cambrian boundary G S S P, low level of ecological and biogeographic the East European Platform, and elsewhere. control on the Ediacara biota significantly enhances its potential for global correlation, and supports calls for formal definition of a new geological period and system encompassing this distinctive biota. -32-

PALAEOBIOLOGY OF THE EARLY CAMBRIAN EMU BAY SHALE FAUNA, KANGAROO ISLAND, SOUTH AUSTRALIA NEDIN, C. Department of Geology & Geophysics, University of Adelaide, S.A., 5005 The exceptionally preserved fossils of the eyes on the head, and a proboscis may have Burgess Shale proved a watershed in the been present, showing possible affinities understanding of Cambrian palaeontology. with Opabinia from the Burgess Shale. However, the highly compressed nature of the fossils commonly hampered detailed There are two species of Anomalocaris palaeobiological analysis. More recent represented in the fauna, Anomalocaris finds of relatively undeformed, briggsi and Anomalocaris sp. The differing exceptionally preserved fossils such as appendages of these two species indicate those from Chengjiang in China and the that they occupied different ecological Emu Bay Shale have provided new impetus niches. The long spines and spinules on in the study of Cambrian palaeontology, the appendages of Anomalocaris briggsi, appear too delicate to allow a raptorial paleobiology and species interactions. method of hunting. Instead, they imply a method of sifting through fine sand and The Early Cambrian (Botomian) Emu Bay mud in order to trap small, non-mineralised Shale outcrops at two localities, Emu Bay invertebrates, with the appendage spines and Big Gully, on the north coast of and spinules acting as a net, trapping the Kangaroo Island. The latter outcrop, first prey between the appendages and then mapped by Reg Sprigg in 1952, contains a guiding the prey to the mouth. restricted fossil Lagerstatte, dominated by The appendages of A. sp. are similar to A. arthropods. Common elements of the canadensis from the Middle Cambrian assemblage are, Myoscolex ateles., the Burgess Shale and A. saron from the trilobites Redlichia takooensis and Hsuaspis Lower Cambrian Chengjiang fauna of bilobata, and the phyllocarids Isoxys China. They all appeared to have been communis and Tuzoia australis. Rarer raptorial hunters, grasping prey using the elements include Anomalocaris, Naraoia, appendages and 'biting' using a Xandarella, and the presumed worm combination of jaw and appendage Palaeoscolex. movements, allowing predation on even The usual mode of preservation is by the mineralised prey. The ability of precipitation of red stained, calcium Anomalocaris to prey on mineralised carbonate fibres, the notable exception organisms (durophagy) has been being Myoscolex, where preservation of contentious, given its lack of strong muscle tissues via phosphatization has mineralisation. However, other fossils occurred, representing the oldest occurrence from the lagerstatte, and elsewhere, provide of this phenomenon yet found. The supporting evidence for both the exceptional preservation has allowed methodology and durophagus ability of insights into the paleobiology and Anomalocaris. This has implications for palaeoecology of the fauna. the possible role played by predation in the evolution and elaboration of mineralised The enigmatic form Myoscolex possesses a exoskeletons and defence mechanisms such variable number of trunk somites with flapas enrollment. like appendages, possibly three or more

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PALAEOBIOLOGY AND EVOLUTIONARY EVIDENCES OF THE TERMINAL PROTEROZOIC SEQUENCES OF HIMALAYA AND PENINSULAR INDIA: AN ASSESSMENT RAI, Vibhuti Department of Geology, University of Lucknow, Lucknow 226007, U.P., INDIA The Proterozoic time represents the early in a relatively sterile lithology with little evolutionary phase of organic communities indication of diagenetic overprints on their that later diversified to complex morphology. Broadly, two specific evolutionary phases of early biosphere. The microbial communities can be identified end of the Proterozoic Eon (Terminal from the present assemblage (1) Acritarchs Proterozoic) witnessed the marked changes and (2) Cyanobacterial / algal assemblage. in the earth's physics, chemistry and biology which introduced profound The acritarchs from the Krol Formation are changes in environmental conditions and characterized by some very large-sized ecological realms resulting in evolution vesicles with diameter ranging from about diversification and extinction of various 100-500 microns. These are highly groups of organisms. This time span has ornamented acanthomorph genera also significance on account of its position belonging to Asterocapsoides, just below the Phanerozoic when Appendisphaera, Cavaspina, evolutionary patterns show quantum Cymatiosphaeroides and Ericiasphaera. In increase in taxonomic diversity and number addition to these a large number of new taxa of individuals. Evidences to these changes have also been recorded. Amongst the are recorded in sedimentary successions the small-sized acanthomorphic forms which world over. In India too, some are confined to the lowermost unit of the exceptionally well preserved successions in Tal Formation, a few characteristic forms are identified as Baltisphaeridium and the Lesser Himalaya and Peninsula provide Micrhystridium which appear at the end of an immensely useful sequence of events of Precambrian time. The assemblage closely the Terminal Proterozoic. resembles with the assemblage from the Pertatataka Formation of the Amadeus basin The Indian Scenario of central Australia, Doushantuo Formation Amongst the several communities of the of Yangtze gorge area of China and the Proterozoic, the microbial community is the Miroyedikha Formation of Siberia. most important community in throwing light on early evolution of organisms and The cyanobacterial fossil community of the constitutes the major tool in deciphering the Krol Formation has been categorized into various physical, chemical and biological three morphological groups viz. (1) events of the Phanerozoic explosion of life. Filamentous, (2) Coccoidal and (3) Bizzare In the Lesser Himalaya, the Krol Belt morphotypes. The important cyanobacterial documents a shallow marine sequence in fossil forms are Eomycetopsis, which exceptionally well-preserved Siphonophycus, Obruchevella, Salome, microbial community is recorded from the Myxococcoides, Gleodinopsis, Krol and Tal Formations. These two Eoentophysalis, Tetraphycus, lithounits are developed above the Blaini Eosynechococcus and Polybessurus which Formation (equivalent to the Varanger are common in the present collection. Those Glaciation) and demarcate the Terminal which occur in low numbers include Proterozoic (Vendian/Ediacarian) time span. Oscillatoriopsis, Palaeolyngbya and The Krol-Tal succession reveals a host of Polytrichoides. In addition, a very small biotic evidences with the cyanobacterialnumber of algal (non-cyanobacterial) algal-acritarch assemblage predominating in fossils, that show their affinity to green and the microbial community. These red algal groups, are also recorded from the communities are indicative of existence of a Krol assemblage. They are represented by well-defined biotope supporting biologic rare branching and non-branching forms entities. The preservation of these such as Palaeosiphonella cloudii, communities in the bedded syngenetic Archaeorestis, Ramavaginalis uralensis and cherts has added to their biostratigraphic Bangia. value. These delicate fossils are preserved -34-

Terminal-Proterozoic times, the microbial community had developed to a state where it created the ecological niches for the subsequent evolution of other biological communities including several animal phyla. It is also possible to conclude that in all these scattered basins of India, the sedimentation terminated close to the early Cambrian times as a result of global tectonic processes that might have influenced the depositional regime. The tectonism would have uplifted these intra-cratonic basins and caused disruption of deposition on a large scale. A note on the Terminal Proterozoic It is believed that in order to generate a precise stratigraphic scheme for the Late Proterozoic, the need is firstly to delineate various global events e.g. biological, evolutionary, tectonic and chemical (isotopes) in a chronostratigraphic scale. Since the involved time span is of considerable duration in the earth's history which covers a period of over a hundred million years for the Terminal Proterozoic alone, a subdivision of the Late Proterozoic is urgently required to facilitate formulation of an event related Late Proterozoic stratigraphic scheme. In my opinion, the top of the Varangerian glacial and coeval glacials around the world should be taken as the base of this new "Terminal Proterozoic" system. This would help in correlating the widely spaced basins that are now positioned on different continents on a much wider scale. The data generated from the biologic evidences such as OWMs, acritarchs assemblages (specially acanthomorphs), Ediacaran fossils, carbonaceous mega-fossils and trace-fossils; chemical evidences such as carbon-oxygen shifts, Sr-isotopes and Sisotopes should be used for further refinement of the lower boundary of the "Terminal Proterozoic'. The upper boundary of this Terminal Proterozoic obviously marks the lowermost boundary of the earliest Cambrian which is presently quite well established.

The Krol Formation shows presence of typical Vendian grazing traces, calcareous algal (microbial) fossil groups (Epiphyton, Renalcis, Gemma, Bija and Angulocellularia and a number of stromatolite form genera), and definite Ediacaran medusoid impressions, e.g. Cyclomedusa, Nemiana, Nimbia, Sekwia and Medusinites from the lower part of the Krol Formation. The fossil record of the upper part of the Tal Formation includes a number of earliest Cambrian faunistic remains such as trilobites, brachiopods, gastropods and small shelly fossils. Apart from these a rich assemblage of trace fossils has also been recorded from the sequence. The important Proterozoic successions of Peninsular India (the Bhima, Kaladgi, Kurnool, Vindhyan and Trans-Aravalli Vindhyan basins) show their development up to the Neoproterozoic times. Although these basins are separated from each other by a few hundreds to a few thousands of kilometres, many of these may represent continuity in sedimentation as part of a mega basin. These are intracratonic basins which show deposition of huge thicknesses of sediments (5000-6000 m thick) ranging in age from Mesoproterozoic to TerminalProterozoic. They essentially show deposits of sandstones, carbonates and evaporites in a shallow marine setting with the development of few fossiliferous horizons. Both megascopic and microscopic fossil groups have been recorded from these basins. The important megafossils are Grypania, Chuaria, Tawuia, Sinosabellidites, Protoarenicola and Pararenicola besides a number of stromatolites and trace fossils. Amongst the microscopic fossil groups, several mineralic, carbonaceous and Organic Walled Microfossils (OWMs) are recorded from shales and cherts. Acritarchs and large colonial vesicles are rare constituents in these fossil assemblages. From observations made on the entire assemblage, it appears that during the

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PROTEROZOIC PROGRESS TO MEGASCOPIC COMPLEXITY RUNNEGAR, Bruce Department of Earth and Space Sciences University of California, Los Angeles, CA 90095-1567, U.S.A. Paleontological evidence for the existence Newfoundland, Nevada, and South of animals as complex as Halkieria Australia. evangelista by the earliest Cambrian shows that the "Big Bang" of animal evolution was Few, if any, of the Ediacaran organisms well underway by the end the Proterozoic. belong to the crown groups of animal If phylogenetic trees based on 18S rRNAs phyla, none were cnidarian jellyfish, and are even approximately correct, most of the some of the best known forms extant animal phyla have invisible roots in (Dickinsonia, Ernietta, Phyllozoon, the Neoproterozoic and must have coexisted Pteridinium) are difficult to place in any with the problematical organisms of the extant animal or plant group. However, Ediacara fauna. even these "core vendobionts" differ significantly from each other in the Recent discoveries in Nevada and Namibia fundamental properties of construction, have taken core members of the Ediacara growth, mode of preservation, and fauna to the end of the Proterozoic, thus symmetry. closing the stratigraphic gap (Kotlin interval) that had been assumed to separate Together with the associated carbonate the Ediacaran biota from the Cambrian skeletons and trace fossils, the Ediacaran explosion. The times of origin of the organisms provide a glimpse of biodiversity Ediacaran organisms and the animal phyla at the close of the Proterozoic. It is the remain unknown but U-Pb ages on the ash synchronous appearance of distantly related bed that covered an already diverse clades of megascopic organisms that points Ediacaran assemblage at Mistaken Point, to the poverty of intrinsic versus extrinsic Newfoundland, are approximately 20 explanations for the nature of the Cambrian million years older than the base of the explosion of multicellular life. Cambrian. An argument based on the resolution of nodes in rRNA trees may be The terminal Proterozoic prelude to the used to suggest a significantly longer Cambrian explosion stands in stark contrast Precambrian history for the Metazoa, but to the limited fossil record of sizeable the first metazoan trace fossils are no older organisms during the preceding two billion than about 550 million years. years of Proterozoic time. However, there is good evidence for the existence of a variety of megascopic algae, including Key questions concerning the nature of the distinctive taxa such as Grypania and Ediacaran organisms remain unresolved but Longfengshania, from rocks younger than there is good morphologic and taphonomic about 1.8 billion years. New data from evidence for the presence of several major India shows that Grypania was probably clades (fronds, petalonamans, trilobozoans, cellular rather than coenocytic, thus etc.), that are uncomfortably united in increasing the probability that it is a crown Seilacher's extinct kingdom, the group eukaryote. This discovery makes the Vendobionta. Furthermore, old two billion delay in algal diversification one misconceptions are being discarded as we of the unexplained puzzles of Proterozoic learn more about these enigmatic organisms life. from recent discoveries in Namibia,

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PRIMITIVE EDIACARA-TYPE FOSSILS FROM THE LATE PROTEROZOIC XINMINGCUN FORMATION IN NORTHEAST CHINA SUN, Weiguo Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing, the People's Republic of China, 210008 Enigmatic discoid fossils of Liaoningella were sedentary and lived on surface discoida gen. et sp. emend, from the late diffusion and internal absorption. Most of Proterozoic (probably pre-Ediacarian) the individuals are solitary, but a few Xinmingcun Formation in the Jinzhou occur in twins with a clear separation in district, Dalian, southern Liaoning between, therefore an asexual Province, Northeast China, may be reproduction may be supposed. interpreted as a primitive form of the Ediacara-type metazoans. The individuals of Liaoningella are megascopic but their body configuration and living style appeared more like a The specimens are small, circular to subunicellular organism in many aspects. This circular discs with a complete margin and observation sheds fresh light on a few concentric ridges and grooves on the interpretation of the Ediacara-type surface, which is otherwise smooth. metazoans, especially those simple Although they are non-skeletal, they are medusiform fossils. The late preserved, like various Ediacara-type Neoproterozoic Ediacara-type metazoans fossils, as three-dimensional body casts may represent a primitive stage in the and external moulds in marine mud history of metazoan evolution and a deposits. Normally they lie flat on bedding specified adaptation to the low oxygen planes, but some are unusually situated at environment of that time. However, low angles to the bedding, thereby further data demonstrate that the Ediacaraindicating that the body was originally thin type creatures were not strictly confined to and tough or rigid. Despite the almost the late Neoproterozoic period but became perfect preservation, these fossils do not much less common in their conventional show any evidence for a digestive system shallow water habitats after the explosive or a locomotive apparatus. It seems radiation of the Cambrian life. possible that these enigmatic creatures

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CAMBRIAN BIOSTRATIGRAPHY OF EASTERN WARBURTON BASIN (SOUTH AUSTRALIA) AND INTERNATIONAL CORRELATION *SUN, Xiaowen & 2JAGO, Jim National Centre for Petroleum Geology & Geophysics, Thebarton Campus, University of Adelaide, SA5005. ^Department of Applied Geology, University of South Australia, The Levels, SA 5095 The eastern Warburton Basin unconformably underlies the petroleumproductive Cooper and Eromanga Basins. It is an Early Palaeozoic basin and contains more than 3500m of sedimentary and volcanic rocks (Gravestock & Gatehouse, 1995; Sun, 1996). The Cambrian to Early Ordovician Kalladeina Formation is more than 1700 metres thick and yields some fossiliferous beds. Eleven faunal assemblages, ranging from early Middle Cambrian (Late Templetonian/Floran) to Early Ordovician (Lancefieldian) have been established as a result of a systematic palaeontological study on specimens from the Kalladeina Formation (Sun, 1996). Among them, eight Middle to Late Cambrian faunal assemblages are correlated to the biostratigraphic zones of central Australia, Scandinavia and China (Figure 1). The Late Templetonian/Floran trilobite faunas of the Warburton Basin contain one faunal assemblage which can be subdivided into two sub-assemblages (la and lb in Figure 1). Faunal assemblage la includes Pentagnostus sp. cf. P. praecurrens, Peronopsis sp., Hypagnostus sp., Pagetia significans, Galahetes fulcrosus, Austrosinia sp. and Fuchouia fecunda. Faunal assemblage lb contains Goniagnostus (Criotypus) paenerugatus, Triplagnostus (T.) gibbus, Peronopsis sp., Fuchouia fecunda, Penarosa sp. cf. P. vittata, Pagetia sp. Diplagnostus sp., , Peronopsis sp. cf. P. tramitis, and Xystridura sp. cf. X. mile si* Undillan faunas in assemblage 2 occur in a packstone (Sun 1996) and include Hypagnostus clipeus, Doryagnostus magister, Triplagnostus (Aotagnostus) culminosus, Peronopsis laiwuensis, Valenagnostus sp. cf. V. imitans, Diplagnostus sp., Axagnostus sp., Utagnostus sp., Amphoton sp. cf. A. marginicrassa, Solenoparia sp., Dorypyge sp., and Anomocarella sp. with

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Solenopleura and Anomocarella recorded for the first time in Australia. Boomerangian trilobites occur in two faunal subassemblages (3a and 3b). Assemblage 3a contains Hypagnostus sp. cf. H. sulcifer, Valenagnostus sp. cf. V. velaevis, Dorypyge sp., Solenoparia sp., Amphoton sp. and Pianaspis sp. Assemblage 3b contains Lejopyge laevigata, L. armata, Agnostus sp., Peronopsis sp., Dorypyge sp. Mindyallan trilobites are found in two assemblages, 4 and 5. Assemblage 4 contains a small fauna, possibly from the Erediaspis eretes Zone. Assemblage 5 contains Clavagnostus sp. cf. C. burnsi, Proagnostus sp. cf. P. bulbus, Ammagnostus sp., Blackwelderial sp., Placosema sp. and Papyriaspididae gen. et sp. indet. Idamean trilobites of Assemblage 6 include Pseudagnostus idalis idalis, Pseudagnostus sp., Eugonocare sp. aff E. whitehousei, Proceratopyge (P.) sp. cf. P. (P.) lata, Pseudagnostus sp. cf. P. chinensis, and Oleninae gen. et sp. indet. Assemblage 7 is Iverian. It occurs in siltstone and shale which yields Oncagnostus (Strictagnostus) sp. cf. O. (5.) sp., Oncagnostus sp. cf. O. hoi, Neoagnostus sp. and Shirakiellidae gen. et sp. Indet. which is recorded in Australia for the first time. Assemblage 8 comprises Datsonian conodonts including Cordylodus proavus, Cordylodus sp. and Monocostodus sp. As with those of the Georgina Basin, the Warburton Basin trilobites have closer affinities with the shallow water faunas of the North China Platform and parts of Antarctica rather than with the more open ocean faunas of areas such as Tasmania, the Jiangnan Belt and Tian Shan of China, and Kazakhstan. Cosmopolitan agnostoid trilobites and conodonts provide the basis of the correlations shown in Figure 1.

REFERENCES GRAVESTOCK D.I. & GATEHOUSE C.G. 1995. Eastern Warburton Basin. In: Drexel J. F. & Preiss W. V. (eds). Geology of South Australia. Vol. 2, The Phanerozoic. South Australia. Geological Survey. Bulletin, 54, 31-34. SUN X. 1996. Sequence stratigraphy, sedimentology, biostratigraphy and

AGE Ma

Cambrian

496

Central Australia

China

Scandinavia

Warburton Basin

Stages/Zones

Stages/Zones

Zones

No Faunal assemblages

FENGSHANIAN

Acerocare

CHANGSHANIAN Kaolishania Maladioidella Changshania Chuangia

Leptoplastus Parabolina

DATSONIAN

491

palaeontology of the eastern Warburton Basin (Palaeozoic), South Australia. Ph.D. thesis, University of Adelaide, 313p, 2 Vols, (unpublished). YOUNG G.C. & LAURIE J.R. (eds) 1996. An Australian Phanerozoic Timescale. Oxford University Press, Melbourne, 279p.

PAYNTONIAN IVERIAN

8 Cordylodus proavus

Peltura 7

0. (Strictagnostus) /Neoagnostus

te

idalis Olenus 6 /Pseudagnostus Proceratopyge GUSHANIAN MINDYALLAN Glyptagnostus stolidotus Drepanura Agnostus pisiform is 5 Ammagnostus Cyclagnostus quasivespa Blackwelderia / Clavagnostus Erediaspis eretesLejopyge ZHANGXIAN 4 Erediaspis eretes Damesella laevigata Lejopyge laevigata BOOMERAN Yabeia 3b Lejopyge laevigata III C - GIAN II 3a Valenagnostus .5 Liopeishania 1 J. brachymetopa •O 500 E UNDILLAN CO Goniagnostus nathorsti Taitzuia - Poshania G. nathorsti 2 Doryagnostus magister O Doryagnostus notalibrae Amphoton P. punctuosus / T. (Aotagnostus) o Ptychagnostus punctuosus H. parvifrons "O 503 "O Late TEMPLETONIAN i /FLORAN 1b T. gibbus - Penarosa Euagnostus opimus Crepicephalina Acidusus atavus 1a Pentagnostus Acidusus atavus /Galahetes T. gibbus Triplagnostus gibbus IDAMEAN

08 -J

Figure 1 Faunal assemblages in eastern Warburton Basin and its international correlation. Time scale in that of Young and Laurie, 1996. -39-

GLOBAL NEOPROTEROZOIC CHEMOSTRATIGRAPHY

WALTER, M.R., VEEVERS, J.J., CALVER, C.R., GORJAN, P., & HILL, A.C. School of Earth Sciences, Macquarie University, NSW 2109 There are now sufficient chemostratigraphic studies of Neoproterozoic successions worldwide to allow global curves of the secular variation in the isotopic composition of seawater to be traced from 544 Ma to the 600 Ma and 700 Ma glaciations, and from 770-830 Ma. This has been attempted before, but there is now a large amount of new information from Australia, including improved control from acritarch and stromatolite biostratigraphy, as well as significant new information from other regions. The density of information is not uniform, but we recognise 29 features in the 9 C and ^ Ckerogen > two intervals of well-defined variation in Sr/ Sr and two peaks in the variation of 3 S ^ . Uncertainties remain in determining whether some of the successions are open marine, but progress has been made in recognising Neoproterozoic non-marine deposits and excluding them from our synthesis. Correlations between Canada and Australia are now firmly established. The -800 Ma Gillen Member of the Bitter Springs Formation is correlated with the upper Shaler Supergroup, the Sturtian glacials, about 700 Ma, with the 13

13

Rapitan glacials, and the Marinoan glacials, about 600 Ma, with the Ice Brook glacials. A network of correlations between these two regions and China, Mongolia, Siberia, Iran, Oman, Poland and Svalbard can also be proposed. The Neoproterozoic part of the Sr/ Sr curve resembles that of the Phanerozoic, but those of 9 C and 9 S do not. The 20.5 permil amplitude of 3 C and 35 permil of d S greatly exceeds the Phanerozoic 7.5 and 16 permil, reflecting radically reduced isotopic fractionation in younger times. Other striking features include the strong positive shifts in 5 S followed by d C between the Marinoan and Sturtian glacials. If these are truly global features, which the bulk of evidence seems to indicate, they must result from huge fluxes of C and S out of the oceans. A mechanism involving greatly enhanced organic productivity and sulfate reduction unlimited by organic carbon supply can be suggested. If this is correct, it means that during this time sulfate concentration in the ocean approached zero. 87

13

87

carbonate

34

86

34

su

34

13

c u r v e s

ate

12

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86

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l3

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EDIACARIAN SEQUENCES AND ACRITARCH BIOSTRATIGRAPHY IN SOUTH AUSTRALIA AND GLOBAL CORRELATION ZANG, Wen-long Mineral Resources Division, Primary Industries and Resources South Australia, PO Box 151 Eastwood, South Australia, 5063 Ediacarian (sensu Cloud and Glaessner, and Narana Formations, which contains a 1982) Wilpena Group in the Adelaide group of moderate-sized spinose acritarchs. Geosyncline was deposited on a rifted Generally, Ediacarian acritarchs reached continental platform. To the west it onlaps their peak diversification during deposition the Stuart Shelf which formed on the of the Wonoka Formation or equivalents, tectonically stable Gawler Craton and its whereas Early Cambrian species Skiagia eastern margin (eg. Torrens Hinge Zone) did not occur until in the middle Parachilna provides a geographic marker to estimate Formation. In association with the the palaeobathymetry. The sequence occurrence of acritarchs and Ediacara stratigraphy of the Wilpena Group is well faunas, the megascopic carbonaceous studied (Christie-Blick et al., 1988; Dyson, Chuaria - Tawuia assemblages have also 1992; Preiss, 1993) and two second-order been found in the ABC Range Quartzite and sequences are proposed to include eleven Wonoka Formation in the Adelaide third-order sequences and higher order subGeosyncline (Zang, 1997). sequences. Most of these sequences and sequence boundaries can be correlated from Assemblages 3 and 4 are also found in the the Adelaide Geosyncline to eastern Officer Pertatataka Formation in the Amadeus Basin in South Australia and the regional Basin, central Australia (Zang and Walter, maximum coastal onlap in the Ediacarian 1992) and similar assemblages have been succession occurred during deposition of reported from the latest Neoproterozoic the lower Brachina Formation. sediments in Russia (Moczydlowska et al., 1993) and China (Zhang, 1984; Awramik et Aciitarchs are abundant in the Wilpena al., 1985; Yin, 1987). Correlation between Group and equivalent sequences in the Australian Ediacarian sequences and the eastern Officer Basin and were collected upper Vendian in Siberia and upper Sinian mainly from transgressive and highstand in South China can be achieved by acritarch sediments. Five acritarch assemblages are biostratigraphy. Improvements in acritarch recognised. Assemblage 1 occurs in the biostratigraphy and integrated sequence upper Seacliff Sandstone and lower stratigraphy represent the hopeful Brachina Formation and contains poorly approaches for correlating Ediacarian preserved leiosphaerids, whereas the sediments worldwide (Fig. 1). appearance of moderate-sized spinose aciitarchs Micrhystridium sp. The author is grateful to W. V. Preiss for Goniosphaeridium sp. etc. and abundant his support and comprehensive discussion. Leiosphaeridia spp. in the upper Brachina Formation and its equivalent Meramangye REFERENCES Formation in the eastern Officer Basin marks assemblage 2. Assemblages 3-5 AWRAMIK, S. M., MCMENAMIN, D. were collected from the upper Wilpena S., YIN Chongyu, ZHAO Ziqiang, DING Group or equivalents and are dominated by Qixiu, & ZHANG Shusen, 1985. large, morphologically complex aciitarchs. Prokaryotic and eukaryotic microfossils Appearance of Comasphaeridium magnum, from a Proterozoic/Phanerozoic transition in followed by Hocosphaeridium China. Nature, 315, 655-658. scaberfacium and some 50-80 species marks assemblages 3 and 4 (Bunyeroo and CHRISTIE-BLICK, N., GROTZINGER, Wonoka Formations or equivalents). J.P., & VON DER BORCH, C.C., 1988. Assemblage 5 corresponds to the Ediacara Sequence stratigraphy in Proterozoic faunas and crosses the Precambrian successions. Geology, 16, 100-104. Cambrian boundary. In the eastern Officer Basin, assemblage 5 occurs in the Munyarai -41-

CLOUD, P. & GLAESSNER, M. F., 1982. The Ediacarian Period and System: Metazoa inherit the earth. Science, 217, 783-792. DYSON, I. A., 1992. Stratigraphic nomenclature and sequence stratigraphy of the lower Wilpena Group, Adelaide Geosyncline: the Sandison Subgroup. South Australia. Geological Survey. Quarterly Geological Notes, 122, 2-13. MOCZYDLOWSKA, M., VIDAL, G. & RUDAVSKAYA, V. A., 1993. Neoproterozoic (Vendian) phytoplankton from the Siberian Platform, Yakutia. Palaeontology, 36, 495-521. PREISS, W. V., 1993. Neoproterozoic. In: Drexel, J. F., Preiss, W. V. and Parker, A. J. (eds.), The geology of South Australia. Vol. 1. The Precambrian. South Australia. Geological Survey, Bulletin 54,170-203.

YIN LEIMING, 1987. Microbiotas of the latest Precambrian sequences in China. - In: Stratigraphy and palaeontology of systemic boundaries in China, Precambrian Cambrian boundary. 1, 415-494. ZANG, Wen-long, 1997. Megascopic carbonaceous Chuaria - Tawuia from late Neoproterozoic in South Australia. MESA Journal 4, 37-41. ZANG, Wen-long & WALTER, M.R., 1992. Late Proterozoic and Cambrian microfossils and biostratigraphy, Amadeus Basin, central Australia. Memoir of the Association of Australasian Palaeontologists, 12, 134p. ZHANG Zhongying, 1984. A new microphytoplankton species from the Sinian of the western Hubei Province. Botanica Sinica, 26, 94-98.

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EDIACARAN DIAPIRISM AT MOUNT FROME DALGARNO, C.R. & DYSON, LA. Geological Survey of Victoria, PO Box 500, East Melbourne, VIC 3002 National Centre for Petroleum Geology & Geophysics, University of Adelaide, S.A. 5005 The rift sequences of the Amadeus and Adelaide Fold Belt are normally separated from the Sturtian glacial record by unconformity resulting from regional extension. The latter record is marked in both basins by active diapirism driven by the earlier rift units. These phases of diapir uplift are marked by erosional intervals and flank unconformities that probably correspond to intervals of increased extension. Notable amongst these phases of diapir emergence are examples during the Ediacaran. In the northern Adelaide Fold Belt at this time a number of diapiric structures developed growth features such as eroded crowns, rim synclines and angular unconformities and down to basin faults on the flanks of the diapiric anticlines. Also prominent are debris trains on the crests of diapiric structures, which are interpreted as "salt glaciers". In the Amadeus Basin, Oaks et al. (1991) demonstrated that growth of salt structures was episodic and began by passive flow of salt to regional anticlinal cores. This was accelerated during the Petermann Movements with the formation of local unconformities adjacent to salt-cored structures. This involved units of the Pertatataka Formation, Arumbera Sandstone and Julie Formation that relate to the Ediacaran. Structures with documented diapir activity in this interval are the Goyder Pass structure, and Gardiner Range and Waterhouse anticlines. Various workers have documented a parallel history in the Ediacaran interval of

the Flinders Ranges in South Australia. Coats (1973) recorded unconformities and conglomerates associated with the Puttapa and Pinda diapirs in this interval and one of us (ID) has made recent studies of salt glaciers and unconformities at the base of the Wonoka Formation and Bonney Sandstone adjacent to the Pinda, Mucatoona and Beltana diapirs. Exposures of the Mount Frome Diapir provide classic examples of extensional faulting related to diapir activity during the Ediacaran interval. There are illustrations from the eastern flank of the structure of angular unconformity between the Wonoka and Bunyeroo Formations and the Bonney Sandstone and Wonoka Formation. An adjacent listiic fault with decollement in the underlying diapir shows evidence of growth during deposition of the Bonney Sandstone. REFERENCES COATS, R.P., 1973. COPLEY, South Australia. Explanatory Notes, 1:250 000 geological series, Geological Survey of South Australia. OAKS, R.Q., DECKELMANN, J. A., CONRAD, K.T., HAMP, L.T., PHILLIPS, J.O. & STEWART, A.J., 1991. Sedimentation in the northeastern and central Amadeus Basin, central Australia. In: Korsch, R.J. and Kennard, J.M. (editors), Geological and geophysical studies in the Amadeus Basin, central Australia. BMR Bulletin, 236, 73-90.

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NEOPROTEROZOIC SALT TECTONICS AND SEQUENCE BOUNDARY FORMATION IN THE ADELAIDE GEOSYNCLINE DYSON, I.A. National Centre for Petroleum Geology & Geophysics, University of Adelaide, S.A. 5005\ Depositional sequences of the Adelaide Geosyncline are defined as third-order tectono-eustatic cycles on which are superimposed higher frequency glacioeustatic cycles. Major unconformities are associated with the development of incised valley fills. The development of several prominent unconformities or sequence boundaries within the Umberatana and Wilpena Groups was associated with periods of active and passive diapirism, which in turn was related to major extensional events during break-up of the Neoproterozoic supercontinent (Dyson, 1996a). In particular, it is hypothesized that sedimentation is also driving the salt tectonics, and that this feedback mechanism results in the formation of allochthonous salt sheets during the passive stage of diapirism. There is an intimate relationship between salt glaciers, slumps and major sequence boundaries in the Neoproterozoic succession of the Adelaide Geosyncline and this relationship is most pronounced adjacent to diapirs. Salt glaciers are interpreted as event beds. The formation of salt glaciers within Neoproterozoic depositional sequences of the Adelaide Geosyncline appears to have been dependent on the relative effects of extensional tectonics versus sedimentary loading and sediment viscosity. High-frequency cycles in the Umberatana and Wilpena Groups are enhanced by high sediment supply on the falling limb of the relative sea level curve where accommodation rates are relatively low. Such cycles are found in the upper Trezona Formation, the Corraberra Sandstone Member of the Brachina Formation and the Rawnsley Quartzite and are represented by erosive-based shoreface sands. A relationship also exists between fourth-order sequences and third-order cyclicity on the rising limb of third-order eustatic cycles. These fourth-order sequences comprise the transgressive systems tracts of third-order sequences. Excellent examples are associated with the Seacliff Sandstone and the Wundowie Limestone Member of the Enorama Shale. Sharp-based shoreface

sands erosively overlie upward-sanding cycles of the Seacliff Sandstone at Hallett Cove and are attributed to forced regression during deposition of the transgressive systems tract in the lower Sandison Subgroup (Dyson, 1995). Three shalesandstone-conglomerate-limestone cycles comprise the Wundowie Limestone Member of the Enorama Shale adjacent to the Enorama Diapir (Dyson, 1997). Each cycle onlaps the margin of the diapir and comprises grey green shale and minor interbedded fine-grained sandstone that is overlain by fine to medium-grained, granulebearing and trough cross-bedded sandstone. In the lower two cycles, a clast-supported boulder conglomerate is erosive into the underlying sandstone and its base is interpreted as a high-frequency sequency boundary. An algal-laminated limestone erosively overlies the boulder conglomerate and its base is a ravinement surface. The sandstone and conglomerate units of each cycle are best developed adjacent to the diapir and thin dramatically in the interpreted offshore direction. However, the several metre-thick algal limestones thin rapidly and step-like towards the diapir. Away from the diapir, stromatolites are not well developed suggesting that they could not keep up with the relative rise in sea level. Cycles within the Wundowie Limestone Member appear to thicken away from the diapir with an accompanying increase in shale. Each cycle of the Wundowie Limestone Member is interpreted to represent a high-frequency sequence that was deposited as part of a transgressive sequence set near the base of the Enorama Shale. Deep-water dolomites overlie sequence boundaries that in a number of localities are marked by major erosional unconformities at the base of the Wilyerpa Formation, Tapley Hill Formation, Seacliff Sandstone and Wonoka Formation (Dyson, 1996b). They are associated with dolostones or dolomitic units of the Warcowie Dolomite, Tindelpina Shale, Nuccaleena Formation and Wearing Dolomite. Olistostromes and canyons are associated with the Warcowie Dolomite, -44-

related to major extensional events during passive margin development of the Adelaide Geosyncline following break-up of the Neoproterozoic supercontinent. The intimate association of diapirs and sequence boundary formation has important implications for how the development of extensional basins is interpreted. Thus, correlation of Neoproterozoic sequence boundaries on an extra-basinal scale will be difficult.

Tindelpina Shale and Wearing Dolomite. In each case, a deep-water sequence boundary may be related to the development of a wide palaeoshelf where subsidence on the outer shelf resulted in a relative rise of sea level. Underlying units such as the Bunyeroo Formation are very thick and fine-grained due to the increased subsidence, especially adjacent to diapirs that were active. This tectono-eustatic zone is one where deepwater dolomites are associated with maximum flooding of the shelf and retrogressive slumping.

REFERENCES The Neoproterozoic succession of the Adelaide Geosyncline was therefore highly influenced by tectonic factors in its subsidence and accommodation history, and by the type and rate of sediment supply. Sequence boundaries in the Umberatana and Wilpena Groups in the Adelaide Geosyncline have been previously attributed to glacio-eustasy. The origin and control of other depositional sequences remains problematic, especially for times lacking evidence of major glaciation. These models do not acknowledge the effects of tectonics on the development of sequence boundaries. Glacio-eustasy is thought to have been a significant control on the formation of unconformities that bound Sturtian and Marinoan glacial units. However, many of the sequence boundaries in the Umberatana and Wilpena Groups are most pronounced adjacent to diapirs and their formation was

DYSON, I.A., 1995. Sedimentology and stratigraphy of the Neoproterozoic Sandison Subgroup: a storm-dominated shallow marine sequence in the Adelaide Geosyncline, South Australia (unpub. Ph.D. thesis, Flinders University of South Australia). DYSON, I.A., 1996a. A new model for diapirism in the Adelaide Geosyncline. MESA Journal, 3, 41-48. DYSON, I.A., 1996b. Stratigraphy of the Neoproterozoic Aruhna and Depot Springs Subgroups, Adelaide Geosyncline. Trans. Roy. Soc. S. Aust., 120, 101-115. DYSON, I.A., 1997. Definition of the Artipena Dolomite Member, Enorama Shale. MESA Journal, 6, 33-35.

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SEQUENCE STRATIGRAPHY AND SEDIMENTED-HOSTED MINERALISATION IN THE KANMANTOO GROUP, KARINYA SYNCLINE DYSON, LA. National Centre for Petroleum Geology & Geophysics, University of Adelaide, S.A. 5005 The Karinya Syncline is a relatively simple folded, north-south structure that has undergone two deformation phases within the Delamerian Fold Belt. The Lower Kanmantoo Group in the Karinya Syncline consists of 3 depositional sequences, represented by a thick pile of siliciclastics that was deposited as a result of abundant sediment supply and sufficient accommodation during a phase of extensional tectonics (Dyson et al., 1994; Dyson, 1995). The Canickalinga Head Formation (CHF) appears to conformably overlie the Heatherdale Shale. However, the erosive base of a lenticular, mediumgrained sandstone up to 10m thick that displays horizontal-planar lamination and SCS is interpreted as a sequence boundary. It overlies a fine-grained succession of chloritic siltstone and chert. Volcaniclastics are not observed above the sequence boundary. The lenticular sandstone unit of shoreface origin is occasionally gossanous and overlain by some 20m of black shale, and is referred to as the Red Creek Formation. Together with the CHF, it constitutes a depositional sequence referred to as the Keynes Subgroup (Dyson, 1995). A series of T-R cycles comprise the highstand systems tract (HST) of the CHF. The Milendella Limestone overlies tidally crossbedded sandstone of the CHF, and consists of interlaminated shale and limestone or white to light grey marble that passes laterally into black shale. On the eastern limb, an 80m-thick succession of interbedded shale and shallow marine sandstone (Wyeroo Sandstone Member) is confined by two carbonate bands. This lenticular succession is interpreted as a lowstand prograding wedge (LPW), and its base is a sequence boundary (Dyson, 1996a). A maximum flooding surface is contained within or on top of the uppermost carbonate band which is gradationally overlain by shale of the Backstairs Passage Formation (BPF). The BPF consists of a series of T-R cycles associated with a HST that culminates in a tide-dominated but wave-influenced quartzitic sandstone (Dyson et al., 1996). The depositional

sequence that comprises the Milendella Limestone and BPF is referred to as the Sedan Hill Subgroup (Dyson, 1995). The BPF is erosively overlain by a lenticular sandstone of fluvial origin, c.a. 2-3m thick, that displays epsilon cross-bedding. This sandstone is up to 20m thick in the northern part of the syncline where it displays SCS and overlies the BPF with classic angular unconformity. The lenticular sandstone, referred to as the Malabena Sandstone Member of the Karinya Shale (Dyson et al., 1994, 1996) represents an incised valley fill (IVF) and is overlain by black shale that gradationally passes upward into interbedded fine-grained sandstone of the Tapanappa Formation. The Tapanappa Formation consists of a series of T-R cycles associated with deposition of a HST. The Karinya Shale and Tapanappa Formation constitute the depositional sequence referred to as the Silverton Subgroup (Dyson et al., 1996). The upper sequence boundary of the Tapanappa Formation is not found in the Karinya Syncline, but can be seen near Callington where a 70m-thick IVF of sandstone marks the base of the Tunkalilla Formation (Dyson, in Dyson et al., 1996). Base metal mineralisation is associated with at least 3 stratigraphic levels of the Lower Kanmantoo Group and can be related to different stages in the evolution of the Karinya Syncline. The mineralisation is thought to be both epigenetic and syngenetic in nature. Epigenetic Pb-Zn-Ag mineralisation occurs in fault zones up to 0.5 m thick. There is also potential for transpressional (syntectonic) Elura-style mineralisation in the northern Karinya Syncline sourced from basinal brines via the Palmer Fault, a major extensional feature that was reactivated during the Delamerian Orogeny. However, sandstonehosted Zn-Pb-Ag was first identified in the Karinya Syncline by Dyson et al. (1994, 1996) in the Malabena Sandstone Member, and may be explained by a stratal aquifer model. Sediment-hosted stratiform Cu-ZnAu mineralisation is found in lenticular gossans at the base of the Keynes -46-

Subgroup. A relationship between basic volcanics of the upper Heatherdale Shale and mineralisation can be demonstrated based on REE correlation (Abbott and Dyson, in prep). This is indicative of sedex-style mineralisation. The underlying volcanics are characterised by lapilli tuffs and volcaniclastic agglomerates, suggesting proximity to a major volcanic vent. Cu-PbZn mineralisation occurs in the LPW of the Milendella Limestone where it is adjacent to carbonate and black shale (Dyson, 1996). These occurrences suggest that sedimenthosted stratiform mineralisation in the Karinya Syncline is dominantly syngenetic to diagenetic. A volcanogenic/exhalative association has been established, and mineralisation is developed on major bounding surfaces within a sequence stratigraphic framework. This style of mineralisation has important implications for base metal exploration in the Kanmantoo Trough.

shallow marine sequence in the Adelaide Geosyncline, South Australia (unpub. Ph.D. thesis, Flinders University of South Australia). DYSON, I.A., 1996. The significance of a lowstand prograding wedge bounded by deep water carbonates of the Cambrian Milendella Limestone, Kanmantoo Trough, South Australia. Geol. Soc. Aust. Abstracts, 41, 124. 13th Australian Geological Convention, Canberra, 1996. DYSON, I.A., GATEHOUSE, C.G. AND JAGO, J.B., 1994. The significance of the sequence boundary at the base of the Early Cambrian Talisker Calc-siltstone and its relationship to mineralisation in the Kanmantoo Trough. Geol. Soc. Aust. Abstracts, 37. 12th Australian Geological Convention, Perth, 1994. DYSON, I.A., GATEHOUSE, C.G. AND JAGO, J.B., 1996. Sequence stratigraphy of the Talisker Calc-siltstone and its lateral equivalents in the Early Cambrian Kanmantoo Group. Quarterly geological Notes, Geol. Surv. S. Aust., 129, 27-41.

REFERENCES DYSON, I.A., 1995. Sedimentology and stratigraphy of the Neoproterozoic Sandison Subgroup: a storm-dominated

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SALT GLACIERS AND SLUMPS IN NEOPROTEROZOIC SUCCESSIONS OF THE ADELAIDE GEOSYNCLINE DYSON, LA. & DALGARNO, C.R. National Centre for Petroleum Geology & Geophysics, University of Adelaide, S.A. 5005 Geological Survey of Victoria, PO Box 500, East Melbourne, VIC. 3002 Breccias contained within the Neoproterozoic succession of the Adelaide Geosyncline have in the past been variously proposed as olistostromes and tectonic breccias related to thrusting or syn-depositional diapirism. More recently, allochthonous sheets of Callanna Group breccia interpreted as salt glaciers have been found adjacent to diapirs in the Flinders Ranges.

diapir activity. Perhaps the most spectacular features associated with slumping are the canyons at the base of the Wonoka Formation. Coats (1964) interpreted the Patsy Springs canyon as slump structures formed in a submarine environment. A brecciola at the upper boundary of the Bunyeroo Formation near Beltana was caused by local slumping of semi-consolidated sediments during deposition of the early Wonoka Formation. The brecciola was believed to have resulted in part by local instability caused by movement of the nearby Beltana Diapir (Leeson, 1970). These brecciolas represent slumping of limestone deposited on the upper slope prior to canyon infilling. Slumping was a possible precursor to canyon incision and occurred just prior to deposition of the Wearing Dolomite that was formed on a terrigenous-starved hiatal surface at the top of the Bunyeroo Formation. Slumping also occurred adjacent to the Pinda Diapir prior to deposition of the Wearing Dolomite, suggesting a possible relationship between incision of the Wonoka canyons and diapirism. It is significant because the base of the canyons have been previously interpreted as a major sequence boundary in the Adelaide Geosyncline. Slumps composed of Callanna Group breccia occur at the base of the Bonney Sandstone adjacent to the Frome and Beltana diapirs, and are interpreted to overlie a major sequence boundary.

Deposition of large-scale, unconformitybased slumps or olistostromes is thought to have occurred during periods of extensional tectonics and increased diapiric activity. For example, a megabreccia facies is contained with large channels near the top of the Skillogalee Dolomite at Worumba Diapir (Preiss, 1985). In the Willouran Ranges, similar features occur within the upper Skillogalee Dolomite north of Willouran Hill and in the vicinity of Breaden Hill. In the Willippa Anticline, an angular unconformity at the base of the Warcowie Dolomite is overlain by an olistostrome that was possibly deposited in the vicinity of an active fault scarp, along which Burra Group sediments were exposed. This unconformity is a major sequence boundary and is interpreted to have formed during a major extensional event, possibly related to the break-up unconformity. Large-scale slumping occurs in large erosional scours at or near the base of the Amberoona Formation in the Willouran Ranges (Coats and Dalgarno, 1983). Slumping of a lesser scale also occurs below and within the Wundowie Limestone Member of the Enorama Shale adjacent to the Enorama and Oraparinna Diapirs and is attributed to an increase in

An intimate relationship between slumping and deposition of allochthonous salt sheets may be observed at the Pinda Diapir where a tongue of Callanna Group sediments within the Bunyeroo Formation is some -48-

7km long and up to 500m thick. It is interpreted as a salt glacier that emerged as a salt fountain during a phase transgressive sedimentation. It displays characteristics similar to debris flows such as inverse and graded bedding that in turn suggest relatively low viscosity. A large synsedimentary fold occurs about two-thirds down the length of the tongue where overlying Bunyeroo shales are deformed together with the slumped breccia. The slump is thought to have been triggered by renewed diapiric uplift. As a result, the upper boundary of the Bunyeroo Formation was tilted prior to deposition of the Wearing Dolomite. This angular unconformity represents a deep-water sequence boundary. Another glacier is also found within the lower Bunyeroo Formation at nearby Mucatoona Diapir. At a similar stratigraphic level adjacent to the Beltana Diapir, two large olistostrome-like bodies of Callanna Group breccia were onlapped by shale and conglomerate of the Bunyeroo Formation. At Pinda Diapir, a small extrusion of breccia occurs about 200 m above the base of the Bonney Sandstone and represents an upper lateral of the Christmas tree diapir. The Breaden Hill Diapir in the Willouran Ranges is interpreted as an allochthonous sheet of breccia that was initially extruded at the cessation of Callanna Group sedimentation. The breccia was then episodically extruded at times of low sedimentation during deposition of the Burra and Umberatana Groups.

Adelaide Geosyncline are considered to represent gravity flow deposits of varying viscosity. The examples cited above suggest that there is an intimate relationship between deposition of salt glaciers and large-scale slumps and the formation of major sequence boundaries. Furthermore, this relationship is most pronounced adjacent to diapirs. REFERENCES COATS, R.P., 1964. Large scale Precambrian slump structures, Flinders Ranges. Quarterly geological Notes, Geological Survey of South Australia, 11, 1-2.

COATS, R.P. & DALGARNO, C.R., 1983. Large scale slumping in the Umberatana Group, Willouran Ranges. Geological Society of Australia Abstract, 10, 63-64. DALGARNO, C.R., 1983. Marinoan mud islands, Mount Frome, S. Aust. Geological Society of Australia Abstract, 10, 34-35. LEESON, B., 1970. Geology of the Beltana 1:63 360 map area. Geological Survey of South Australia Rept. Invest., 35. PREISS, W.V., 1985. Stratigraphy and tectonics of the Worumba Anticline and associated intrusive breccias. Geological Survey of South Australia Bulletin, 52.

Syn-sedimentary slumps and salt glaciers within Neoproterozoic successions of the

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GEOCHEMISTRY AND FACIES ANALYSIS OF CAMBRIAN VOLCANICS IN WARBURTON BASIN AND REGIONAL CORRELATIONS, SOUTH AUSTRALIA SUN, Xiaowen National Centre for Petroleum Geology & Geophysics, Thebarton Campus, University of Adelaide, SA 5005 The Warburton Basin is an Early Palaeozoic samples suggest that they belong to alkalipetroleum exploration frontier basin. The basalt of within-plate affinity, indicating eastern Warburton Basin contains at least renewed intra-plate extension. Association 3500m of flat-lying to folded volcanics, of basalt lava with deep-water carbonate carbonates and siliciclastics (Gatehouse, facies in several Gidgealpa wells, possibly 1986; Sun, 1996). Evolution of the with deep-water mudstone and shale in the Warburton Basin was influenced by Mudlalee to Kobari areas (Sun, 1996) volcanic activity. On the basis of the further supports a localised continuing rift geochemistry of the volcanics, two tectonic event. Trilobites in the Gidgealpa wells settings have been suggested, arc indicate that the age of the episodic basalt (Gatehouse, 1986) or rift (Shaw, 1991; ranges from prior to Late TempletonianBoucher, 1991; Sun, 1996). A rift setting is Floran to Mindyallan Stages. preferred based on detailed facies analysis These volcanics and associated sedimentary and bimodal geochemical characteristics. deposits indicate an initial and extensive The volcanics can be differentiated into two continental rift setting that was subjected to major phases, which can be divided into four major genetic groups of volcanic facies marine incursion, followed by a renewal of rifting on a local scale. This interpretation comprising nine facies. of the basin architecture will lead to a better understanding of petroleum systems in the The early phase volcanics, namely the Warburton Basin. Mooracoochie Volcanics, are widely distributed, comprising rhyolite and The rhyodacitic tuff of the Mooracoochie rhyodacite-dominated lava flows, Volcanics petrographically resembles the ignimbrites and associated volcaniclastic silicic ash-fall tuff of the Cymbric Vale rocks; they were emplaced rapidly and in Formation (Opik, 1975; Kruse, 1982; Zhou large volume. Twelve core samples were & Whitford, 1994), the tuff near the top of analysed and their immobile elements the Heatherdale Shale (Cooper et al., plotted in the rhyolite/dacite field. Two 1992), and the vitric tuff in the Billy Creek facies models suggest that a caldera existed Formation (Moore, 1979), being of Early in the Gidgealpa area; and a rhyodacitic Cambrian "Atdabanian-Toyonian" age. cryptodome or synsedimentary sill in the Although being similar petrographically and vicinity of Kalladeina 1 (Sun, 1996). The geochemically, the later phase volcanism is volcanics are overlain by basalt of the late younger than the Truro Volcanics in the phase volcanics (see below) in Gidgealpa Stansbury Basin (Forbes et al, 1972; wells. U-Pb zircon dating of the Gatehouse et al., 1993), and younger than Mooracoochie Volcanics in Malgoona 1 the basalt of the Mt Wright Volcanics well suggests a magmatic age at 517±9 Ma intercalated with archaeocyathan limestone (Armstrong, 1995). (Zhou & Whitford, 1994; Crawford et a/., 1997). Therefore, early phase volcanism in The late phase volcanics comprise the Warburton Basin correlates with porphyritic basalt, amygdaloidal basalt and volcanism in adjacent basins in South hyaloclastite, being episodically emplaced Australia and western New South Wales. only in deep-water environments. A submarine basalt facies model is interpreted (Sun, 1996). The analyses of ten core

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