Issuu

Geological Society of Australia

ABSTRACTS Number I Q

ADELAIDE GEOSYNCUNE SEDIMENTARY ENVIRONMENTS AND TECTONIC SETTINGS

SYMPOSIUM A.M.F. Adelaide Dec 9, 1983

GEOLOGICAL SOCIETY OF AUSTRAUA (SOUTH AUSTRAUAN DIVISION)

ADELAIDE GEOSYNCLINE SEDIMENTARY ENVIRONMENTS AND TECTONIC SETTINGS SYMPOSIUM

AGSETS December 9,1983 Australian Mineral Foundation, Adelaide ABSTRACT VOLUME

Convenor R. Dalgamo

GEOLOGICAL SOCIETY OF AUSTRAUA ABSTRACTS No. 10 1983

SYMPOSIUM COMMITTEE

Convenor

C . R . Dalgarno

Deputy Convenor

D r . A.J. Parker

Secretary

E.A. Dubowski

Treasurer

R.B. Flint

Excursion Organiser

J.G. Gehling

Committee

D.B. Hilyard Ms. N. Oreskes P.C. Smith

••S.A. Liaison

ACKNOWLEDGEMENTS The Publication Drafting Section of the South Australian Department of Mines and Energy provided location slides and diagrams in addition to titled cards for all posters.

PUBLICATION SALES Copies of this volume can be purchased from: Geological Society of Australia, Inc., Challis House, 10 Martin Place, Sydney, N.S.W., 2000.

PREFACE The extended abstracts in this volume are of two types: Key speakers under the three sessions, "Rift Setting", "Tectonic Development" and "Clastic and Carbonate Deposition", are permitted summary papers and 30 minutes for presentation, viz.. Dr. Andrew White, Dr. Wolfgang Preiss, Dr. John Parker and the joint paper by Drs. Richard Jenkins and Victor Gostin. Other abstracts are to support poster presentations for which most authors have been allotted 10 minutes for brief presentation, and the opportunity during breaks in the formal proceedings to attend their posters for discussion. The posters are intended to be retained by the Geological Society (S.A. Division) to be rotated amongst Universities as a portfolio of educational material on the Adelaide Geosyncline.

Requests should be made to the

Regional Geology Branch, S.A.D.M.E. for use of the material. At the rear of this volume is a Proforma for a tabulation of significant localities in the Adelaide Geosyncline. This is a request from the Committee of the AGSETS for general assistance in the preparation of a catalogue of localities

pertaining

synsedimentary

unconformities, sedimentary features, etc.

structures,

growth

faults,

Assistance from all interested in

such a compilation would be appreciated. Finally, I would like to make a personal tribute to the late James Eric Johnson, who died in October this year, for his assistance to me in developing a love for the theme of this symposium.

Jim dedicated his life to the geology and

mineralogy of the Adelaide Geosyncline and its basement.

R. Dalgarno Convenor, AGSETS Committee

ADELAIDE GEOSYNCUNE SEDIMENTARY E N V I R O N M E N T S A N D T E C T O N I C SETTINGS SYMPOSIUM A T A M F GLENSIDE O N D E C E M B E R 9, 1983 Programme

Ref.

C h a i r m a n : Bob Dalgarno

" R I F T SETTING"

9.00-9.30

30 mins.

Andrew White "Speculations on the E v o l u t i o n of the Adelaide R i f t " .

9.30-10.00

2 X 10 mins.

A l a n Webb et al. "Geochronological F r a m e w o r k - Adelaide Geosyncline".

D a v i d H i l y a r d "Wooltana M e t a b a s a l t Tectonic Setting".

Wolfgang Preiss " D e p o s i t i o n a l & T e c t o n i c C o n t r a s t s between Burra Group and Umberatana Group Sedimentation".

Robin U p p i l l "Dolomite-Magnesite F a d e s , Mundallio Subgroup".

Bob W i l t s h i r e "Basement Blocks U m b e r a t a n a Group, D i a r y " .

Genesio C i r c o s t a et al. " S t u r t i a n Glacials, Ironstone and F a u l t i n g Yednalue, C e n t r a l Flinders Ranges".

10.00-10.30

10.30-11.15

mins.

11.15-11.45

Break.

C h a i r m a n : Bren Thomson

"TECTONIC DEVELOPMENT"

11.45-12.15

30 mins.

John Parker " T e c t o n i c D e v e l o p m e n t of the Adelaide F o l d B e l t " .

12.15-13.00

4x10

Tim O'Driscoll "Leigh CreekFreeling Heights Structural Corridor".

10.

T r e v o r Mount " A r k a b a D i a p i r " .

11.

Bob Dalgarno " M a r i n o a n Mud Islands, Mt. Frome".

12.

John Cann, et ah "Enorama C o n t a c t Relationships".

13.00-14.00

mins.

Luncheon.

Diapir

C h a i r m a n : Brian D a i l y

Ref.

"CLASTIC AND CARBONATE DEPOSITION"

14.00-14.30

mins.

13.

Richard Jenkins and Vic Gostin " M a r i n o a n and Ediacaran type sections in the c o n t e x t of t e c t o n i c cycles in the Adelaide Geosyncline".

14.30-16.00

7 X 10 mins. plus discussion

14.

D a v i d Tonkin and George W i l l i a m s " P e r i g l a c i a l Structures, C a t t l e G r i d Mine".

15.

Ian Dyson "Storm Sedimentation, Brachina Subgroup, H a l l e t t C o v e " .

16.

Chris von der Borch and A l e x Grady "Submarine Canyons, Wilpena Group".

17.

J i m Gehling " E d i a c a r a M e m b e r P r o x i m a l Turbidites".

18.

Peter Haslett "Cambrian Syndepositional Wirrealpa".

16.00-18.30

Tectonics,

19.

David Gravestock "Lower Facies and A r c h a e o c y a t h a " .

Cambrian

20.

Ian L a m b e r t , et al. " M e t a l l o g e n y of the Adelaide Geosyncline - Stuart Shelf Copper P r o v i n c e " . Drinks

SATURDAY, DECEMBER 10 - Field Trip to Haiiett Cove Area SUNDAY, DECEMBER 11 - Deiamerian Discussion (venue to be announced)

CX3MPLETE UST OF CONTRIBUTING AUTHORS AND TITLES Ref. No.* 1.

Text Page A.H. White "SPECULATIONS ON THE ADELAIDE RIFT AND THE ORIGIN OF DIAPIRS" pp3-6

A.W. Webb, R.P. Coats, C.M. Fanning and R.B. Flint "GEOCHRONOLOGICAL

FRAMEWORK

THE

ADELAIDE

GEOSYNCLINE" pp7-9 3.

D. Hilyard "WOOLTANA METABASALT - STRATIGRAPHY, PALAEOENVIRONMENT, TECTONIC SETTING" pp 10, 11

W.V. Preiss "DEPOSITIONAL AND TECTONIC CONTRASTS BETWEEN BURRA GROUP AND UMBERATANA GROUP SEDIMENTATION" pp 13 - 16

R. Uppiil "DEPOSITIONAL ENVIRONMENTS OF THE DOLOMITE-MAGNESITE FACIES ASSOCIATION OF THE MUNDALLIO SUBGROUP pp 17, 18

R.G. Wiltshire "BASEMENT BLOCKS IN UMBERATANA GROUP - OLARY" pl9

G. Circosta, D.New and V.A. Gostin "STURTIAN

GLACIATION,

PENECONTEMPORANEOUS

IRONSTONE

FAULTING,

NORTHERN

DEPOSITION YEDNALUE

ANTICLINE, CENTRAL FLINDERS RANGES, SOUTH AUSTRALIA" p21 *

Reference Numbers shown on Location Diagram and Stratigraphic Table.

A.J. Parker "TECTONIC DEVELOPMENT OF THE ADELAIDE FOLD BELT" pp 23 - 28

E.S.T. O'Driscoli "THE

LEIGH

CREEK-FREELING

HEIGHTS

STRUCTURAL

CORRIDOR" PP29-31 10.

T.J. Mount "DIAPIRS AND DIAPIRISM IN THE ADELAIDE 'GEOSYNCLINE' SOUTH AUSTRALIA" pp 32, 33 R. Dalgarno

11.

"MARINOAN MUD ISLANDS, MOUNT FROME, SOUT^^ AUSTRALIA"

26.

"EDIACARAN EXTENSIONAL FAULTS, MT. FROME"

27.

"STURTIAN AND CAMBRIAN GROWTH FAULTS, ORAPARINNA

pp34,35 p70 DIAPIR" pp71,72 • 'i •

12.

J.H. Cann, I.F. Clark, B.J. Cook and W.G. Shackleton "ENORAMA DIAPIR CONTACT RELATIONSHIPS" pp36-38

13.

R.J.F. Jenkins and V.A. Gostin "MARINOAN AND EDIACARAN TYPE SECTIONS IN THE CONTEXT OF TECTONIC CYCLES IN THE ADELAIDE GEOSYNCLINE" pp 39 - 44

14.

D.G. Tonkin and G.E. Williams "FOSSIL PERIGLACIAL STRUCTURES IN THE CATTLE GRID MINE, MOUNT GUNSON" pp45-48

15.

I.A. Dyson "THE SIGNIFICANCE OF HUMMOCKY CROSS-STRATIFICATION IN THE LATE PRECAMBRIAN BRACHINA SUBGROUP, HALLET COVE, SOUTH AUSTRALIA" pp49,50

16.

C.C. von der Borch and A.E. Grady "SUBMARINE CANYONS - WILPENA GROUP" p51

17.

J.G. Gehling "THE

EDIACARA

MEMBER:

SHALLOWING

UPWARD

SUMBARINE FAN SEQUENCE, WITHIN THE POUND SUBGROUP" pp52-54

18.

P.G. Haslett "LOWER CAMBRIAN SYNDEPOSITIONAL TECTONICS" PP 55, 56

19.

D.I. Gravestock "FACIES CHANGES AND ARCHAEOCYATHID DISTRIBUTION IN EARLY CAMBRIAN CARBONATES, FLINDERS RANGES, SOUTH AUSTRALIA" PP 57, 58

20.

I.B. Lambert, T.H. Donnelly, J. Knutson, H. Etminan "METALLOGENY OF THE ADELAIDE GEOSYNCLINE - STUART SHELF COPPER PROVINCE" PP 59, 60

21.

B. Cooper "HISTORICAL PERSPECTIVE"

PP 22.

R.B. Flint "ADELAIDEAN

SEDIMENTS

THE

PEAKE

AND

DENISON

RANGES" PP 61, 62

23.

R.P. Coats and R. Dalgarno "LARGE

SCALE

SLUMPING

THE

UMBERATANA

GROUP,

WILLOURAN RANGES" pp63,64 24.

G.E. Williams "CYCLIC

L A M I N A T I O N IN THE L A T E P R E C A M B R I A N

ELATINA

F O R M A T I O N A N D ITS P A L A E O C L I M A T I C SIGNIFICANCE" pp 65 - 67 25.

I.A. Dyson and C . C . von der Borch "EVIDENCE

EVAPORITE

MINERALS

THE

LATE

P R E C A M B R I A N B R A C H I N A SUBGROUP, H A L L E T T COVE, SOUTH AUSTRALIA" pp 68, 69 28.

R.B. Major and J.F. Drexel "MOUNT PAINTER B R E C C I A S " pp 73 - 75

29.

C.H.H. Conor "MYLONITIZATION A N D THE F O R M A T I O N OF THE

ECONOMIC

KYANITE/SILLIMANITE, K A O L I N I Z E D SILLIMANITE A N D BRITTLE M I C A DEPOSITS N E A R WILLIAMSTOWN, SOUTH A U S T R A L I A " pp 76, 77 30.

P.D. Fleming and A . J . R . White "MIGMATITE

FORMATION

RELATION

HISTORY OF THE P A L M E R A R E A : ONSET

AND

LATER

STRUCTURAL

EVIDENCE F O R THE E A R L Y

PERSISTENCE

PARTIAL

MELT

CONDITIONS IN THE MT. L O F T Y R A N G E S , SOUTH A U S T R A L I A " pp 78, 79 31.

L P . Youles "STURTIAN

SUBMARINE

ESCARPMENT

DELAMERIAN

DECOLLEMENT?" p80 " R E - I N T E R P R E T A T I O N OF A G E DATES, R A D I U M RIDGE BEDS, MT. P A I N T E R " (Poster only)

NORTH FLINDERS RANGES 19

27 WILPENA GROUP

HAWKER GROUP 1 8

BURRA GROUP

HAWKER GROUP

CALLANNA GROUP

HAWKER GROUP EQUIVS.

SOUTH FLINDERS RANGES EASTERN FACIES

TORRENSIAN

SOUTH FLINDERS RANGES WESTERN FACIES

WILLOURAN

STURTIAN

MARINOAN

(EDIACARAN

NORMANVILLE GROUP

STUART SHELF

UMBERATANA GROUP

ADELAIDE REGION 21

HISTORICAL PERSPECTIVE Barry Cooper South Australian Department of Mines and Energy The Adelaide Geosyncline occupies an important place witJiin geological thinking in South Australia. The region encompasses the natural focus of human activity in the state, and as a result contributes to the unique South Australian geological outlook. If, for example, the principles of stratigraphy had been formulated in Adelaide rather than Western Europe, there is no doubt that our perception of the world geological succession would have been radically different. Sediments from the Adelaide Geosyncline have been discussed since the earliest period of European settlement (Finniss, 1843; Burr, 1846) although geological understanding of the region was long impeded by structural complexity, lack of fossils and the perceived necessity to correlate with classic British sections. The general absence of fossils in a relatively unmetamorphosed sequence was especially perplexing to early workers. The desire to discover them encouraged geologists of the calibre of Edgeworth David and Howchin to describe "fossils" that are now considered to be inorganic. Professor Walter Howchin (1845-1937) must be regarded as the Father of Adelaidean Geology. After almost twenty years of research, first on Cretaceous/Tertiary fossils then ancient glaciations and their deposits, this British trained clergyman and geologist recognised that the Sturt Tillite provided an excellent lithological marker within the geosyncline. This discovery culminated in two classic papers on "The Geology of the Mount Lofty Ranges" (Howchin, 1904, 1906) ,r in which the stratigraphic succession in the Adelaide region was correctly determined and lithological units were described. Howchin had previously described Lower Cambrian fossils from the region and as a result always doubted whether any of the basin was of Precambrian age. Sir Douglas Mawson (1882-1958) became the authority on the Adelaide Geosyncline after Howchin's death. Following formal education at the University of Sydney, Mawson had been first appointed to the University of Adelaide in 1905. Subsequently, he began mineralogical studies in the Flinders Ranges, which slowly expanded to embrace stratigraphic studies of this entire region (Mawson, 1942). Mawson (1940) encouraged use of the term "Adelaide Series", which was first proposed by David (1922), and this gained wide useage especially after a Precambrian age for most of the succession was accepted. Mawson was also the first to appreciate the real problems of lithological correlation within the Adelaidean that are so apparent today. As a student of Mawson, Dr. Reg. C. Sprigg became the first South Australian born geologist to make a significant contribution to the understanding of the Adelaide Geosyncline. Remapping of Howchin's classic sections was undertaken, and with Mawsoi a standard subdivision of the Adelaidean was proposed (Mawson & Sprigg, 1950). As head of the regional mapping group at the Geological Survey of South Australia (1946-1953), Sprigg initiated and supervised systematic geologic mapping of the fold belt. As part of this work, he also proposed the first dynamic model of deposition within the geosyncline (Sprigg, 1952)•

In the cxxarse of the past 30 years, detailed mapping of the entire Adelaide Geosyncline has been carried out. The basin is now known to contain one of the best exposed, most complete and most accessible sections of Late Proterozoic and Early Cambrian strata in the wrld. It is also relatively little deformed. The fold belt has special significance because it is the type area for Ediacara-type fossils and the Ediacar(i)an period. Also notable are widespread Late Proterozoic glacial deposits as well as valuable reference sections for late Proterozoic stromatolites and Early Cambrian faunas. Peculiar, and possibly unique, tectoiic breccias are equally important. They have been interpreted, but not unanimously regarded as having a diapiric origin. References Burr, T., 1846. Ronarks on the geology and mineralogy of South Australia. Andrew Murray, Adelaide 32 pp. David, T.W.E., 1922. Occurrence of remains of small crustacea in the Proterozoic(?) or Lower Cambrain(?) rocks of Reynella near Adelaide. Trans. R. Soc. S. Aust. 46:6-8 Finniss, B.T., 1843. The geology of South Australia. S. Aust. Mag. 2:225-232. " —^ Howchin, W., 1904. The geology of the Mt. Lofty Ranges, Part 1. Trans. R. Soc. S. Aust. 28:253-280. Howchin, W., 1906. The geology of the Mt. Lofty Ranges, Part 2. Trans. R. Soc. S. Aust. 30:227-262 Mawson, D., 1940. The Adelaide Series. Aust. J.

3:25-27.

Mawson, D., 1942. The structural character of the Flinders Ranges. Trans. R. S^. S. Aust. 66:262-272. Mawson, D., & Sprigg, R.C., 1950. Subdivision of the Adelaide System. Aust. J. Sci. 13:69-72. Sprigg, R.C., 1952. Sedimentation in the Adelaide Geosyncline and formation of the continental terrace. Mawson Anniv. Vol. pp. 153-159. _

SPECULATIONS ON THE ADELAIDE RIFT AND THE ORIGIN OF DIAPIRS A.H. WHITE Consultant Geologist, Adelaide, South Australia RIFTING Von der Borch (1980) has summarised much convincing evidence that the Adelaide Geosyncline is in fact a failed rift in the central and northern parts and a rifted passive continental margin in the southeastern part of the geosyncline. The rift is supposed by several authors to contain more than 24,000 metres of sedimentary fill and von der Borch's hypothesis of rifting implies that basement consists of continental crust. The rifting occurred between early Proterozoic/Carpentarian platforms; the Curnamona Nucleus/Willyama Block to the east and the Gawler Craton to the west. The rifting hypothesis is supported by the gross structural and geophysical features of the geosyncline. Firstly, the geosyncline is bounded by and contains a number of major sub-parallel lineaments, many of which have proved to be normal faults. Thrusting has not been noted except in the M t . Painter Block in association with the Paralana Fault. Instead of a Bouguer gravity low reflecting 24,000 m of sediments there is generally an axial positive Bouguer gravity ridge, a feature which is characteristic of other well-documented rift systems (Baker et al., 1978; Ramburg, 1976). Thick wedges of Adelaidean sediments which the writer suggests were deposited in half grabens on either side of the axial high are indicated by Bouguer gravity lows flanking the high. Preiss (this volume) and von der Borch (op.cit., p.120) make similar interpretations. This conclusion is supported by a seismic profile south of Parachilna. Further speculation based on the gravity is that there are east-west arches or blocks disrupting the north-south continuity of the half grabens. Thrusting in the M t . Painter area is considered to be related to movement on an east-west transform fault of which the Paralana Fault is part. The hydrothermal breccias in the M t . Painter complex are considered by the author to be part of one or more large igneous ring complexes or cauldron subsidences, - which is in accord with von der Borch's thesis that the M t . Painter area was a hot spot. Analogous ring complexes occur at the triple junction in the failed continental Limpopo Rift (Sawkins, 1976). Still further evidence of the rift origin of the geosyncline is the abundance of copper enriched alkaline basalts in the basal parts of the geosynclinal fill, analogous with the basal sequence in the Keweenawan Rift (Norman, 1978). The regional total magnetic intensity data (SADME, 1976) also allows for some speculative interpretation consistent with von der Borch's tectonic model of the Adelaide Geosyncline. The same regional trends occur in the magnetics as in the gravity. High frequency magnetic anomalies occur in the otherwise magnetically quiet rift where von der Borch (op.cit.. Fig. 2b) has postulated hot spots associated with triple junctions. The southeas tern rifted passive continental margin of the geosyncline is bordered by elongate, high frequency, high amplitude magnetic anomalies. These are analogous to those in the western part of the Hodgkinson Basin and the Lachlan Geosyncline where fore-arc trench systems were formed as a result of collision of oceanic plates with continent. The inference is that the zone

bordering the rifted continental margin and now concealed beneath younger sediment, Is also a belt of fore-arc trench sediments, volcanlcs and Intruslves. Seismic studies (Stewart, 1972) Indicate that the crust thickens from the margins towards the centre of the rift by one to two kilometres to a total of 34 kilometres, and therefore the axial gravity highs are best explained by the presence of a basic Igneous mass In the crust. Tucker and Brown (1972) estimate from aeromagnetlc data that magnetic basement, which the author speculates to be the top of the basic Igneous mass. Is at a depth of about six kilometres In the central Flinders Ranges, ORIGIN OF "DIAPIRS" Much has been written about the so-called "dlaplrs" In the Adelaide rift, and controversy still rages about their origin. The author has examined approximately twenty large and small dlaplrs on the COPLEY and MARREE 1:250 000 sheet areas and makes the following general observations. The "dlaplrs" are Invariably Intrusive, and consist of xenollth-rlch breccias which grade Into massive, spectaculary flowbanded dolomite. The predominant llthology other than massive dolomite Is polymlct dlamlctlte containing abundant xenollths, ranging to raft size, of Adelaldean sedimentary rocks, gneisses and granites, and altered mafic and ultramaflc, peralkallne Igneous rocks In a matrix that Is mostly dolomltlc, but locally calcltlc or both. Petrographlc studies by Whitehead (1972) and the author Indicate that most of the xenollths exhibit replacement to some degree by dolomite, quartz or mlcrocllne. Whitehead (op.clt., p.15) wrote that carbonate Is the only mineral which has been Introduced Into the breccia In significantly large amounts and has migrated from an undetermined source. Dykes and sills of dolomltlc carbonate a few millimetres to many metres wide Intrude the host rocks around most breccia bodies. Thomson (1965) has already pointed out the structural control of Intrusion of the "dlaplrs" along faults and other zones of weakness. The breccias have been Intruded under high pressure, as evidenced by the rarity of vughs In the breccias. The breccias Indiscriminately Intrude, brecclate and stope all formations In the Adelaldean sequence up to Middle Cambrian. They contain a wide range of eplthermal metamorphlc minerals (Mount, 1975; Whitehead, op.clt.). Apart from dolomite the breccia masses exhibit marked enrichment of some minerals; copper and baryte In subeconomlc amounts are associated with almost every breccia examined, and Iron, phosphorous, fluorine, zircon and tltanlum-bearlng minerals were noted In breccias by Mount (op.clt.) and Whitehead (op.clt.). The formation of mlcrocllne In the matrix Indicates that potassium may be enriched In the breccias. Although the breccias are Intrusive and contain an abundance of eplthermal minerals, no contact thermal effects appear In host rocks and the breccias examined, with the exception of a 10 cm wide zone of Incipient hornfelsed Bunyeroo Formation at the contact of the Puttapa "Dlaplr" west of the Puttapa zinc mine. Several other authors (e.g. Coats, 1973) mention detritus derived from "dlaplrs" being entrained In younger Adelaldean sediments. Despite careful search for such occurrences, the author has failed to find breccia fragments so entrained; rather the specific cases cited by other authors were pebble conglomerates associated with marine transgressions, or were Intrusive sills of breccia showing no signs of reworking.

The author contends that all the above phenomena are best explained if the "diapirs" are in fact carbonatite breccia pipes or plugs. Recent work suggests that carbonatite magmas originate as a result of liquid immiscibility of peralkaline fractions in mantle-derived magmas, and that this particularly applies to large, slow cooling magmas (Philpotts, 1976; 1978). Strontium distributions in coexisting silicate and carbonate liquids indicate that carbonatites and peralkaline silicates are not differentiates one from the other but derive from separate (immiscible?) liquids (Koster van Groos, 1975). The writer therefore speculates whether the carbonatite breccia pipes are crystallised from carbonate melts separated by liquid immiscibility from the vast basic igneous body inferred from gravity to occupy the rift axis. The basic igneous mass could well be a concealed analogue of the Bushveld Complex/Great Dyke basic igneous system associated with the Limpopo Rift in South Africa. The altered peralkaline ultramafic and mafic igneous xenoliths in the breccia pipes are most probably samples brought to the surface of this basic igneous body. The xenoliths of gneiss and granite are probably fragments of the continental crustal basement above the mantle. The spectacular degree of brecciation, and the appearance of the breccias as classic breccia pipes containing a jumble of xenoliths from all levels of crust through which they have passed, suggests that they intruded under very high vapour pressure. Fenitisation of a type associated with carbonatites elsewhere, was found to be widespread in the Adelaide rift, but perhaps because of its subtle nature and not the widespread potassium flooding usually taken to indicate fenitisation, has hitherto been overlooked. Apart from dolomite replacement of xenoliths, and abundant microcline in the breccias, there is regional fenitisation in the form of abundant specular hematite-dolomite-baryte-quartz, and baryte-quartz veining and fracture filling, throughout the Adelaide rift. Hematised and dolomitised joints are common. Specular hematite, carbonate and quartz-baryte joint fillings are features of the outer zone of fenitisation around the Callander Bay alkaline carbonatite complex in Ontario, Canada (Currie and Ferguson, 1970). The lack of widespread pervasive potash metasomatism of country rock commonly associated with other carbonatites suggests that the vapour in the Adelaide rift carbonatites, was dry. It is deduced from the overwhelming dolomite emplacement associated with the breccia pipes that the dominant vapour was CO2 and introduced massive quantities of Ca and M g . The breccia pipes may be classified as sovites. Barium, copper and iron are strongly enriched, and titanium, fluorine and phosphorous are moderately enriched in the breccias, however the characteristic enrichment of Ce, Re and Nb in other carbonatites has not yet been found. Some of the carbonatite breccia pipes cut across folds in the Adelaide rift and others are intruded in cores of domes or anticlines. It is apparent therefore, that the carbonatites were intruded after the Delamerian (late Cambrian-early Ordovician) folding of the sedimentary strata.

REFERENCES Baker, B.H., Crossley, R., Goles, G.G., 1978: Tectonic and magmatic evolution of the southern part of the Kenya Rift Valley, in Neumann, E.R., and Ramberg (eds.), Petrology and Geochemistry of Continental Rifts. D. Reidel Publ. Co., Dordrecht, pp. 29-50. Coats, R.P., 1973: Copley 1:250 000 Geological Series - Sheet SH/549 Explanatory Notes. Geol. Surv. S. Australia. Currie, K.L. and Ferugson, J., 1971: A study of fenitisation around the alkaline carbonatite complex at Callander Bay, Ontario, Canada. Can. Jour. Earth Sciences, 8; pp. 498-517. Roster van Gross, A.F., 1975: The distribution of strontium between coexisting silicate and carbonate liquids at elevated pressures and temperatures. Geochem. et Cosmochim. Acta 39pp. 27-34. Mount, T.J., 1975: Diapirs and diapirism in the Adelaide 'Geosyncline', South Australia. Unpubl. thesis. Dept. of Geology and Mineralogy, Univ. Adelaide, S. Australia. Norman, D.I., 1974: Ore deposits related to the Keeweenawan Rift. I" Neumann, E.R., and Ramberg, I.E., (eds). Petrology and Geochemistry of Continental Rifts. D. Reidel Publ. Co.. Dordrecht, pp. 245-254. Philpott, A.R., 1978: Rift associated igneous activity in eastern North America. ^ Neumann, E.R., and Ramberg, I.B., (eds.) Petrology and Geochemistry of Continental Rifts. D. Reidel Publ. Co., Dordrecht, pp. 133-154. Ramberg, I.B., 1976: Title not published. Norges Geol. Under., 325, 1) 1976• Sawkins, F.J., 1976: Metal deposits related to intracontinental hotspot and rifting environments. J. Geol. 84; pp. 653-671. South Australia Department of Mines & Energy, 1978: Total Magnetic Intensity Map South Australia, 1:1 000 000 scale. S. Aust. Dept. Mines and Energy. Stewart, I.C.F., 1972: Interpretation of crustal structure. South Australia. J. Geol. Soc. Aust. 19; pp. 351-362. Thomson, B.P., 1965: Geology and Mineralisation of South Australia. Jn McAndrew, J., (ed.) Geology of Australian Ore Deposits, 1, 2nd Ed., 8th Commonwealth Mining and Metallurgical Congress, Aust. I.M.M., Melbourne, pp. 270284. Tucker, D.H. and Brown, F.W., 1973: Reconnaissance helicopter gravity survey in the Flinders Ranges, S. Australia, 1970. Bur. Min. Res. Geol. and Geophys. Rec. 1973/12 (unpubl.). von der Borch, C.C., 1980: Evolution of Late Proterozoic to Early Paleozoic Adelaide Fold belt, Australia: Comparisons with Post-Permian Rifts and Passive Margins. Tectonophys., 70: pll5. vmitehead, S., 1972: Investigation of diapiric rocks in the Flinders Ranges, South Australia. S. Aust. Dept. Mines report 72/214 (unpubl.).

GEOCHRONOLOGICAL FRAMEWORK OF THE ADELAIDE GEOSYNCLINE 1

A.W. Webb , R.P. Coats , C.M. Fanning

and R.B. Flint

^Australian Mineral Development Laboratories, PO Box 114 Eastwood ^Department of Mines & Energy, PO Box 151 Eastwood SA

INTRODUCTION The Adelaide Geosyncline has proved to be one of the most difficult regions of the Australian Precambrian in which to determine a time framework on the basis of isotopic dating. Several factors have contributed to this problem. Firstly, the definition of the base of the Adelaide System has been a topic of dispute until quite recently, when extensive drilling on the Stuart Shelf has provided much more information on the stratigraphic relationship between pre-Adelaidean and early Adelaidean strata. Secondly, the overprinting effects of the Cambro-Ordovician Delamerian Orogeny are widespread and have been recognised, or at least invoked, by the universal isotopic disturbance found in rocks within the Adelaidean sequence to the east of the Torrens Hinge Zone. Thirdly, most of the rocks within the Adelaide Geosyncline are of sedimentary origin. Igneous rocks comprise only a very small percentage of the total sequence and these rocks are generally strongly altered basic volcanics, confined to the lowermost lithostratigraphic unit. Only under the most favourable conditions have sedimentary rocks proved to be suitable for isotopic dating and altered volcanic rocks, too, have been found to yield extremely unreliable dates. Fourthly, the K-Ar and Rb-Sr techniques have been used almost exclusively in attempts to date the Adelaidean sequence. Possibly, in the future, U-Pb analyses may prove to be of greater use. Thus we are left with only limited means to obtain a geochronological framework for the sequence of deposition within the Adelaide Geosyncline. Two methods have been used: a maximum age of deposition may be provided by the crystalline rocks of the basement inliers and depositional (or diagenetic) ages may be determined on the essentially undeformed, but incomplete sequence of sediments on the Stuart Shelf. A number of geological ages shown on the legend of the Geological Map of South Australia (1980) have not appeared in formal geological literature and one of the aims of this paper is to give some background information on the source and reliability of these dates. In addition, new data produced over the past 18 months, although still in preliminary stages of evaluation, are presented to give further insight into the present extent of the investigations. PRE-ADELAIDEAN BASEMENT In the geosynclinal zone, several inliers of crystalline basement rocks are exposed and the assumption could be made that the last major deformation or recrystallisation event pre-dated the lowermost overlapping strata in any particular area. In addition, on the Stuart Shelf, pre-Adelaidean rocks recovered by exploratory drilling have presented the opportunity to set a maximum age for deposition in this region.

(a) Houghton Inlier: The only precise date in the Barossa Complex is the Rb-Sr total rock isochron of 849±32 Ma for the "Houghton Diorite" (Cooper & Compston, 1971). The basement here is overlain by the Burra Group and the conventional interpretation of Cooper & Compston is that the metamorphic event registered by the 849 Ma date occurred before the deposition of the Burra Group. (b) Peak and Denison Inlier: Within this inlier, the basement Wirriecurrie Granite is overlain by the Callanna Group but there is a marked disruption between the top of the Callanna Group and the overlying Burra Group. K-Ar biotite ages from the Wirriecurrie Granite fall between 960 and 1090 Ma (Ambrose, Flint & Webb, 1981), but there is no indication whether the event registered by the K-Ar dates is pre- or post-deposition of the Callanna Group. (c) Musgrave Block: On the northeastern margin of the Officer Basin, strata equivalent to the Burra and Umberatana Group unconformably overlie a metamorphic and granitic basement of the Musgrave Block which registers a widespread 1100-1000 Ma event by both the K-Ar and Rb-Sr methods. Thus, the crystalline basement dates within the geosyncline suggest an age younger than 1100 Ma for the oldest Callanna Group and 850 Ma for the Burra Group. (d) Gawler Craton: On the eastern margin of the Gawler Craton, one of the younger basement units is the Roopena Volcanics. This was dated by Compston et al. (1966) at 1320±25 Ma (Rb-Sr isochron). Later investigations by SADME and AMDEL tend to confirm this date but the significant scatter of the data about the isochron indicates that these strongly altered rocks have not remained isotopically closed systems since the time of extrustion. Overlying the Roopena Volcanics, and underlying the earliest Adelaidean strata, is the Pandurra Formation. Shaly bands within this unit from two localities have given a well-fitting Rb-Sr total rock isochron of 1425±51 Ma (5 samples, MSWD=1.5) (Fanning et ai., in prep.) If this is accepted as a minimum age of deposition, the validity of the 1325 Ma date for the Roopena Volcanics is brought into question. ADELAIDEAN STRATA (STUART SHELF) (a) Callanna Group: The Beda Volcanics on the Stuart Shelf are the equivalents of the Wooltana Volcanics of the Callanna Group. Several samples from a single, dense, fresh to moderately altered flow have been dated by the total rock, Rb-Sr method. Although there is some scatter of the data, the three most divergent points can also be identified on other chemical grounds (see poster and Webb & Coats, 1980) and when excluded from the regression a model 1 isochron of 1076±33 Ma is obtained. An earlier Rb-Sr total rock date of the Beda Volcanics (Webb & Horr, 1978) of 700 Ma is considered not to be an age of extrusion. This flow is amygdaloidal and very extensively altered and it is now believed that the Rb-Sr data possibly reflect an alteration event. (b) Umberatana Group: The Tapley Hill Formation in Woomera No. 1 gives a Rb-Sr total rock age of 750±53 Ma (5 samples, MSWD»2.4). The Willochra Subgroup from

SLT 101 gives an age of 724±40 Ma (5 samples, MSWD=2.4) but the inclusion of a sixth total rock sample from this core produces an age of 686±59 Ma (MSWD=4.7). The sixth sample was lithologically different from the other five and the legitimacy of its inclusion is open to debate. These units bracket the Brighton Limestone, which is the uppermost unit of Sturtian age and thus give reasonable control on the age of the Sturtian-Marinoan boundary. The Marinoan glaciation must therefore have occurred later than 724 Ma ago. (c) Wilpena Group: The Woomera Shale and the stratigraphically equivalent Brachina Formation, have both been dated. The Woomera Shale (Woomera No. 1) gives a model 3 Rb-Sr total rock age from six samples of 676±200 Ma (MSWD= 4.1). The large error is due to the lack of variation in Rb/Sr ratios. The Brachina Formation from BMW lA-1 gives a model 1 age of 601±68 Ma (5 samples) but although this result can not be distinguished statistically from the Woomera Shale date, it may be suspect because samples of the underlying Angepena Formation from the same core give an age of only 6181136 Ma (c.f. 724140 Ma for the Willochra Subgroup in SLT-101). The Yarloo Shale in SCYW-IA has an age of 588135 Ma (7 samples, MSWD= 8.8). This date may be slightly too young as it leaves only a short interval for the deposition of the upper part of the Wilpena Group (which includes the Edicara Fauna) before the commencement of the Cambrian ca.570 million years ago. The ages presented are generally consistent with the stratigraphic sequence although their accuracy remains to be verified, e.g. by dating the same stratigraphic unit in several locations. ACKNOWLEDGMENTS The results reported here, not attributed to other authors, were obtained at AMDEL for the South Australian Department of Mines & Energy and are published with the permission of the Director-General, SADME. The authors wish to thank Dr W.V. Preiss and B.P. Thomson for their assistance and encouragement over the course of these investigations. This paper is published with the approval of the Director-General, SADME and the Managing Director of AMDEL. REFERENCES AMBROSE, G.J., FLINT, R.B. and WEBB, A.W. (1981): Precambrian and Palaeozoic Geology of the Peake & Denison Ranges. Bull. Geol. Surv. S. Aust. No. 50. COMPSTON, W., CRAWFORD, A.R. and BOFINGER, V.M. (1966): A radiometric estimate of the duration of sedimentation in the Adelaide Geosyncline, South Australia. J. Geol. Soc. Aust. 13, 229-76. COOPER, J.A. and COMPSTON, W. (1971): Rb-Sr dating within the Houghton Inlier, South Australia. J. Geol. Soc. Aust. 17, 213-9. FANNING, C.M., FLINT, R.B., and PREISS, W.V.: Geochronology of the Pandurra Formation. Q. Geol. Notes, Geol. Surv. S. Aust. (in prep.). WEBB, A.W. and COATS, R.P. (1980): A reassessment of the age of the Beda Volcanics on the Stuart Shelf, South Australia. S. Aust. Dept. Mines & Energy Rept. Bk No. 80/6. WEBB, A.W. and HORR, G.M. (1978): The Rb-Sr age and petrology of a flow from the Beda Volcanics. Q. Geol. Notes, Geol. Surv. S. Aust. 66, 10-13.

WOQLTANA METABASALT - STRATIGRAPHY^ PALAEOENVIRONMENT, TECTONIC SETTING David Hilyard

School of Applied Geology, South Australian Institute of Technology, P.O. Box 1, Ingle Farm, South Australia 5098.

The Wooltana Metabasalt crops out discontinuously for approximately 60km along strike, adjacent to the southern and western margins of the Lower-Middle Proterozoic Mount Painter Inlier, N.E. Flinders Ranges. It is the uppermost formation of the Callanna Group in that area, overlain unconformably by Burra Group sandstones. Metabasalt is the predominant lithology in the eastern exposures, with subordinate tuff, dolerite-gabbro, quartz sandstone, calcsilicate metasediments, and breccia. Basalts are massive coherent flows l-20m thick with amygdaloidal oxidized tops. The flows are lens-shaped with a lateral extent up to 1km. There is no evidence of submarine eruption. Lateral equivalents west of the Mount Painter Inlier contain abundant intercalated calc-silicate metasediment, and represent a facies deposited further from the eruptive centre. Thickness changes in the formation indicate substantial block faulting during deposition, continuing into the Torrensian. Preliminary geochemistry indicates a continental tholeiitic composition. In conjunction with sedimentary facies and structural setting this attests to the rift nature of the early Adelaide Geosyncline. WOOLTANA VOLCANICS:

'30 20'S

Fine amygdaloidal basalt

^^^

Sandstone Tuff, very fine basalt Breccia Dolerite Dolerite dykes in basement Crystalline basement Fault

T39°25'E "Wooltana"

WOOLTANA VOLCANICS SUMMARY G E O L O G I C A L MAP

Arkaroola Vi I lage

WEST I EAST

O O P

A I

J—v

V_1 I V

•00000

Yudnamutana Hill

•••44vvvvv

- 600m Mt Painter

A. A •••••*

•tH^M . VVV

A A l z Paralana Quartzite

ALL SECTIONS

v vy •

400

200

rrt

fOOLTANA L f i J v OLCANICS

Arkarool^ Village

AAA

Umberatana Group

OOO

Burra Group

VVV;'

WOOLTANA VOLCANICS: WEST A A A Amphibolite — calcA A A silicate (metabasalt)

LOCATION OF SECTIONS

AAA

"Wooltana"

—

• V/W

Massive and banded calc— silicate (metasediment)

o o oooo

EAST Fine amygdaloidal basalt Very fine basalt, tuff

A ^ V P Breccia

•

• •

• • !

v. -f4'. • ••••

Sandstone

Lava

/s^jy Dolerite —

• • • »• Sandstone

gabbro yvv

Wywyana Formation

WOOLTANA VOLCANICS GENERALIZED STRATI GRAPHIC SECTIONS

vyvv

—V"

Unconformity Thickness uncertain

Composite section: base of exposed sequence

- 13 -

DEPOSITIQNAL AND TECTONIC CONTRASTS BETWEEN BURRA GROUP AND UMBERATANA GROUP SEDIMENTATION W.V. Preiss South Australian Department of Mines and Energy, Adelaide Long continued subsidence in the Adelaide Geosyncline during the late Proterozoic to Middle Cambrian period allowed the accumulation of extremely thick deposits of varied lithology, uninterrupted by major orogeny until the penetrative deformation of the sequence during the Delamerian Orogeny. Nevertheless, on two occasions epeirogenic movements caused sedimentation to cease entirely, and when reestablished, sedimentation reflected a new palaeogeography and tectonic setting. Changes in the distribution of sedimentary facies and in the relative importance of syndepositional tectonism in the Adelaide Geosyncline and adjacent platforms, i.e. the Stuart " S h e l f , to the west and the Curnamona Cratonic Nucleus to the north-east, especially between the Warrina and Heysen Supergroups, reflect evolution of the basin from an early rifting phase to a later stage of broad downwarping (Fig. la). Elsewhere in the world, similar changes are recorded in sequences developed on and adjacent to evolving passive continental margins (Fig. lb), and the former existence of a continental margin in the still enigmatic southeastern extension of the Adelaide Geosyncline remains a speculative possibility. Although most of the stratigraphy of the Adelaide Geosyncline has been deciphered within the Delamerian Fold Belt, important data delimiting the extent of formations have become available only from recent extensive drilling by mineral exploration companies. Deposition of the Warrina Supergroup was essentially restricted to an extensive rifted basin, bounded to the west by the Torrens Hinge Zone and to the north-east by faults marking the edge of the Curnamona Cratonic Nucleus. Although rifting began with the sedimentation and volcanism of the Callanna Group, (the volcanics extending also a short distance west of the Torrens Hinge Zone) the tectonic contrasts are most clearly illustrated by the Burra and Umberatana Groups. The Burra Group is confined to the Adelaide Geosyncline, transgressing on to the basement high near Adelaide that had remained emergent during Callanna Group deposition. In the Umberatana Group, which includes deposits of the Sturtian and Marinoan glaciations, sedimentation commenced in well defined graben within the Adelaide Geosyncline and later spread across its full extent, and eventually on to the adjacent platforms. Deposits more extensive (Fig. 1).

the

lower

Wilpena

Group

are

even

During deposition of the Burra Group, the Torrens Hinge Zone was a region of normal faulting, with the uplifted eastern edge of the Gawler Craton supplying quartzo-feldspathic clastics into the rifted basin. The base of the Burra Group is poorly known, except in marginal areas where it transgresses unconformably on to older rocks; elsewhere a conformable transition from the more evaporitic sequences of the Callanna Group is likely. The first sand sheets of the Burra Group are interpreted mainly as broad, coalescing alluvial fan deposits, with local marine reworking. The remainder of Burra Group deposition is cyclical, with repetitions of four major facies associations: (i) black shales; (ii) laminated fine sandy silts; (iii) medium to coarse grained cross-bedded feldspathic sandstones; (iv) micritic dolomite, partly associated with desiccation features.

14 ~

stromatolites, and sedimentary magnesite. These associations are interpreted to represent, respectively, relatively deep, sediment starved basinal depressions, prograding delta front sediments, lobate delta top-sets and distributary channels, and paralic to lagoonal carbonate muds, in part also deposited into deeper water. The stratigraphy of the lower and middle Burra Group is broadly similar in the northern and southern outcrop areas. Although no Burra Group is known from the central Flinders Ranges, sedimentation was probably continuous across this region up to and including the Skillogalee Dolomite. Thereafter the sedimentary histories of the two regions diverged, and no clear progradational cycles are recognised in the north. Although most of the Skillogalee Dolomite represents tectonic quiescence and extremely low depositional slopes, syndepositional faulting became active late in Skillogalee deposition north of lat. 32°. This resulted in the formation of wedges of megabreccia intertonguing southward with a thick Skillogalee sequence. The central Flinders Ranges region may have been uplifted at this time, acting then as a barrier dividing the Burra Group into northern and southern depositional domains. In the mid-North and Willouran Ranges regions, Burra Group sedimentation was further differentiated at various times into sub-basins by active syndepositional faults. After Burra Group deposition, sedimentation ceased for a period of unknown duration. The Warrina Supergroup was lithified and exposed to erosion, but mostly not deformed, except in the central Flinders Ranges region where there was faulting and tilting of the Burra Group and diapirism, and perhaps even thrusting, of the Callanna Group. In the central Flinders Ranges, the remaining Burra Group was probably stripped off either regionally, or on diapiric domes, in some of which the Umberatana Group is now seen unconformably overlying disrupted Callanna Group. In the early stages of the Sturtian glaciation deposition resumed only in relatively deep troughs, probably fault controlled, adjacent to the western margin of the Curnamona Cratonic Nucleus, while the remainder of the Adelaide Geosyncline region was still emergent. Glacially-derived clastics, probably mostly from the Curnamona Cratonic Nucleus, were shed into these troughs. Sedimentary ironstones occur as facies variants of both diamictite and laminated siltstone units. It is still uncertain whether the very thick glaciomarine and ?turbidite sequence of the Yudnamutana Subgroup, which lacks ironstones and was deposited at the northeast extremity of the Adelaide Geosyncline belongs to this or the younger Sturtian glacial phase. After minor tectonic movements and erosion, a more widespread and uniform sheet of glaciomarine diamictites, with associated reworked conglomerates, grits, sandstones and siltstones was deposited, probably largely from western source areas, in shelf environments adjacent to the platforms. Across north-west trending faulted hingelines, flysch-like clastics were dumped into a trough encircling the Curnamonc Cratonic Nucleus. This trough runs perpendicular to and is masked by the local Delamerian fold trends, but extended eastward into western NSW. By the end of the Sturtian glaciation syndepositional faulting was no longer dominant. The former graben had all been filled by sedimentation, and with the post-glacial eustatic rise in sea level.

- 15 -

-STUART

12-

f ...

LEGEND Morinoon glociols Grey and green silfsfones Redbeds Topley Hill Fmn - lominafed siltsione Sfurflon glociols Sedimentary ironstones Skillogolee Dolomite Evaporitic closfics ond carbonates Basic volcanics Turbidifes Limestone Dolomite Sands,coarse to fine Diapir Pre-Adelaideon rocks Unconformity Syndepositional foult

300 KILOMETRES

SADME S 16923

Fig. 1, Comparison of Adelaidean sediments of the Adelaide Geosyncline with the Mesozoic-Cainozoic Atlantic continental margin of the United States. (a) A depositional cross-section of Adelaidean sediments of the Stuart "Shelf" and Adelaide Geosyncline. The region of the Delamerian Fold Belt has been palinspastically expanded by 30% perpendicular to fold axes. Horizontal scale as for (b). (b) A generalised model of U.S. Atlantic margin, redrawn from data illustrated in Watts (1981).

the Adelaide Geosyncline and the eastern part of the Stuart "Shelf" were Inundated, perhaps to a depth of several hundred metres. Deposition of finely laminated organic-rich silts of the Tapley Hill Formation occurred throughout this region, but as the basin filled, the palaeogeography of the Adelaide Geosyncline became differentiated into a western shelf area and deeper water regions in the south-east and north. The central Flinders Ranges region maintained a shelf character though most of the interglacial period, with the deposition of thick shelf carbonates in its depocentre. The Torrens Hinge Zone at this time marked the site of substantial easterly thickening of the Umberatana Group, rather than of notable facies changes, which took place at the shelf margin some 60-100 km further east. The persistence of sedimentation on the Stuart "Shelf" after the relatively deeper water Tapley Hill Formation suggests that glacioeustatic sea level rises are insufficient to account for the lateral spread of the Umberatana Group on to the platforms. Indeed, the Curnamona Cratonic Nucleus was not transgressed until the latter part of the interglacial period. Tectonic subsidence of the platforms must therefore have been involved. In the Marinoan glaciation, the same shelf-basin palaeogeography persisted. Reworked fluvioglacial sands were spread into the basin from a western cratonic source, (coarse Whyalla Sandstone on the Stuart "Shelf" and finer Elatina Formation in the Flinders Ranges). Associated gritty siltstones and local lenticular diamictites indicate limited glacial activity. At the same time, massive diamictites and associated dropstone facies were deposited in the eastern and northern basinal regions, with erratics probably derived from the Curnamona Cratonic Nucleus and perhaps from the Muloorina Ridge. On the Stuart "Shelf" the upper Umberatana Group oversteps the Tapley Hill Formation. The succeeding lower Wilpena Group extends further west and north again, as the Brachina Formation reflects another post-glacial eustatic sea level rise, but again further subsidence allowed deposition to continue. The progressive onlap of younger and younger units of the Heysen Supergroup on to the Gawler Craton may be compared with the coastal onlap of post-rift sediments on modern passive continental margins (Fig. lb). This may be produced by sediment loading of a basement whose flexural strength increases with age after heating during rifting (Watts, 1982). Application of this model to the Adelaide Geosyncline and Stuart "Shelf" suggests that the unconformity separating the Warrina and Heysen Supergroups could be regarded as the "breakup unconformity" separating rift and post-rift sequences, rather than the unconformity at the base of the Cambrian as previously suggested (von der Borch, 1980). REFERENCES von der Borch, C.C., 1980. Evolution of Late Proterozoic to Early Palaeozoic Adelaide Foldbelt, Australia: Comparisons with Post-Permian Rifts and Passive Margins. Tectonophysics, 70:115-134. Watts, A.B., 1981. The U.S. Atlantic Continental Margin: Subsidence History, Crustal Structure and Thermal Evolution. In: A.W. Bally, A.B. Watts, J.A. Grow, W. Manspeizer, D. Bernoulli, C. Schreiber and J.M. Hunt. Geology of Passive Continental Margins. Am. Ass. Petrol. Geol. Education Course Note Series 19: Tulsa, Oklahoma: 324 pp.

DEPOSITIONAL ENVIRONMENTS OF THE DOLOMITE-MAGNESITE FACIES ASSOCIATION OF THE MUNDALLIO SUBGROUP Robin K. Uppill Western Mining Corporation Limited, P.O. Box 3906U, Winnellie, N.T. 5789 INTRODUCTION The formations within the Mundallio Subgroup comprise three major facies associations: (1) the generally clastic dominated sequence with some dolomite of the lower Mundallio Subgroup, widespread in the northern Flinders Ranges (Nankabunyana Formation, Camel Flat Shale and Tilterana Sandstone), but becoming more lenticular and dolomitic in the southern Flinders Ranges (Nathaltee Formation); (2) dolomite-shale association of the Mt Lofty Ranges in which few facies are present and they occur as thick internally homogeneous units (Castambul Formation, Skillogalee Dolomite and Woolshed Flat Shale); (3) the widespread association of dark-grey dolomites, intraclastic magnesite and dolomitic sandstone (Yadlamalka Formation and Montacute Dolomite) and the laterally equivalent sequence of dark-grey dolomites, siltstones and sandstones (Mirra Formation). The third association is the subject of this poster presentation and generally occurs as rather monotonous sequences characterised by rapid vertical facies changes on a small scale, and in which all major facies occur throughout. Outcrops of this facies association are confined to the southern and northern Flinders Ranges, and occur very locally near Adelaide. FACIES DESCRIPTIONS Grey to dark-grey laminated to thin bedded dolomite mudstones form 50-80^ of outcrop in most areas. The flat even to slightly wavy and lenticular lamination, small erosional scours, minor cross laminae and common terrigenous laminae, suggest deposition of dolomite largely as detrital carbonate mud. Mudstones with more wavy irregular lamination may reflect the influence of algal trapping of sediment. Evidence of exposure during deposition in the form of desiccation cracks, tepees and fenestral fabrics is generally minor, indicating deposition in predominantly submerged environments. Indications of evaporites are rare in most areas. Dolomite grainstones are a minor component of this facies association, and include intraclastic dolomite, oncoid grainstones, peloidal grainstones, and rare ooid grainstones. Stromatolitic dolomites, also a relatively minor facies, occur largely as extensive biostromes and less commonly as bioherms. Columnar forms dominate with the exception of the Depot Creek area where domal forms are more common. Biostromes reflect a uniform depositional substrate and moderate energy conditions, while bioherms developed under more persistent wave agitation. The above dolomite facies are characterised by relatively simple diagenetic histories with lithification and compaction occurring without significant destruction of primary depositional textures. However sequences in the south-central Flinders Ranges contain interbeds of massively outcropping dolomite, the textures of which suggest complex

diagenesis involving dissolution and precipitation under subaerial conditions due to the presence of dilute groundwaters. This facies may reflect local uplift as also suggested by the presence of synsedimentaiy breccias within the Yadlamalka Formation in this area. Magnesite, forming up to 21% of this facies association, occurs as magnesite mudstone, nodular magnesite and intraclastic magnesite. Rarely magnesite is interlaminated with dolomite, but most magnesite contains minor intimately admixed dolomite, while intraclastic magnesite may have a dolomite matrix. Magnesite mudstones are laminated, extremely finegrained, often contain small tepees, and were deposited on shallow mud flats or in lagoons. They may be partly or completely replaced by white nodular magnesite, leading to the formation of beds of close-packed coalescing nodules. The nodules disrupt and cross-cut lamination indicating displacive and replacive growth within the sediment. Nodular magnesite may have formed during prolonged periods of non-deposition following exposure of the magnesite mudflats. Subsequent erosion either by sheet-flooding or wave-undercutting associated with minor transgressions, resulted in the deposition of laterally extensive beds of intraclastic magnesite, the dominant magnesite facies. Clastic sediments are dominantly medium- to coarse-grained dolomitic sandstones in the southern Flinders Ranges, and very fine-grained dolomitic sandstones to siltstones in more northerly areas. DISCUSSION: DEPOSITIONAL ENVIRONMENT Deposition of this facies association occurred in a very shallow basin in which all areas except perhaps the northeastern Willouran Ranges were periodically subjected to periods of exposure. The depositional basin may have consisted of shallow perennial and smaller ephemeral lagoons or lakes separated by exposed mudflats. Occurrences of shallow water facies throughout indicate low palaeoslopes, hence small variations in water level would have resulted in flooding or exposure of extensive areas. Normal tidal processes are unlikely to have been effective, however water level changes could have occurred due to wind tides or sediment build-ups, or more regionally as a resiilt of climatic changes or basin subsidence. The close association of dolomite and magnesite e.g. interlaminated dolomite and magnesite, dolomite matrix in intraclastic magnesite, and magnesite intraclasts as nuclei to dolomite ooids and oncoids; and the preservation of primary depositional textures, indicate that dolomite and magnesite, or closely related minerals, were present at the sediment surface and hence were essentially primary. The widespread and at times very thick nature of the dolomite-magnesite sequence, the absence of limestone and the uncommon occurrence of sulphates, appears to preclude deposition in a marine basin, while the widespread uniformity of facies indicates a relatively similar chemistry throughout the basin. Mg^"*", Ca^"*" and HCO3- are likely to have been the dominant ions within the basin waters. A Mg/Ca ratio in excess of one would have favoured dolomite deposition, while evaporative concentration and elevation . of this ratio as a result of dolomite deposition caused the evolution of"waters suitable for the precipitation of magnesite or possibly hydrated magnesium carbonates.

~ 19 -

BASEMENT BLOCKS IN UMBERATANA GROUP - QLARY R. G. Wiltshire School of Applied Geology, S.A. Institute of Technology, Adelaide, SA Within the Umberatana Group in the MacDonald Corridor north of Olary there are several blocks of Willyama Complex which have previously been interpreted as basement inliers (Campana and King, 1958 and Pitt, 1971), however, field evidence suggests that they may be icerafted blocks deposited from icebergs during the Sturtian glaciation. The Willyama Complex blocks consist of granite, gneiss and migmatite and have approximately elliptical shapes with sizes ranging from 50m X lOOm to 200m x 800m. The blocks lie in the upper part of the Pualco Tillite (Sturtian glacial sequence and lower part of the overlying Benda Siltstone and have their long axes parallel to bedding. The contacts of the blocks with the enclosing sedimentary rocks are concordant but unconformable and in places thin (1 to 2m) conglomerates are developed along the contacts. Facing in the surrounding sedimentary rocks is consistently to the east on both sides of the basement blocks. Campana and King (1958) interpreted one of these blocks as the core of an anticline with an overturned western limb. This is contrary to the facing evidence and also the blocks do not occur at the base of the Adelaidean sequence. Pitt (1971) suggested that the blocks were fault bound inliers but there is no evidence of major faulting at or near the contacts of the blocks. Forbes and Pitt (1980) interpreted some of the blocks as coarse granite clast conglomerate, but some of these have continuous outcrop of massive granite.

The evidence supporting the interpretation that the blocks were icerafted during the Sturtian glaciation are: (i)

the stratigraphic position of the blocks in the Pualco Tillite and Benda Siltstone, both of which contain dropstones

(ii)

the constant facing of the enclosing sedimentary rocks across the blocks

(iii)

the lack of faulting adjacent to the blocks

(iv)

the gradation from dropstones 20cm across through erratics 2m across to blocks 200m and 800 m across.

References: Campana, B., and King, D., 1958: Regional geology and mineral resources of the Olary Province. 5. Aust.^ Geol. Surv.^ Bull. 34. Forbes, 6.G., and Pitt, G.M., 1980:

Geology of the Olary Region.

S. Aust. Dept. Mines and Energy Ept. Bk. 80/161 (unpubl.). Pitt, G.M., 1971:

Geology of the MacDonald Corridor, Olary Province.

S. Aust. Geol. Supv.y Q. Geol. Notes^ 39^ 3-7.

STURTIAN GLACIATION, IRONSTONE DEPOSITION PENECONTEMPORANEOUS FAULH N3, NORTHERN YEDNALUE ANTICLINE, CENTRAL FLINDERS RAN3ES, SOUTH AUSTRAUA by G . Circostal, D. New2 and V.A. Gostin 3 1.Utah Development Co., Blackwood, S.A. 2.Exploration Logging Co. Ltd., Adelaide, S.A. 3.Geology Department, University of Adelaide, S.A. The Sturtian sequence rests on a major unconformity cut across a tilted and faulted sequence of Burra Group dolomites, siltstones and quartzites. Sturtian sediments thicken over a distance of 12km from a few tens of metres in the southwest to 1600 metres in the northeast, and form the southwestern edge of a deep Sturtian sedimentary basin with most of the sediment apparently being derived from the west. The earliest Sturtian deposits of the Pualco Formation ("Tillite") consist mainly of siltstones, some sandstones and lenticular diamictites containing striated clasts. These glacigene diamictites increase in abundance towards the western source. This was succeeded by a probable lacustrine environment which gave rise to mixed chemical and clastic, iron-rich and siliceous sediments of the Holowilena Ironstone. Penecontemporaneous erosion and redeposition formed various calcareous and ferruginous sandstones with jasper and other fragments indicating early selective lithification. In the west, basinward downfaulting along preexisting faults was accompanied by removal of sediments, and preservation of a small syncline of Pualco Formation deposits against a fault, while in the east, deposition continued with a conformable sequence of the Wilyerpa Formation. Minor faulting persisted during deposition of the lower part of the Wilyerpa Formation when ferruginous, dolomitic siliceous silt matrix diamictites were deposited by mass flow mechanisms down the palaeoslope. These diamictites wedge-out eastwards and are replaced by laminated siltstones, some graded sandstones, and rare conglomerates. The major part of the Wilyerpa Formation consists of laminated siltstones with varying proportions of ice-rafted megaclasts. Some massive sandstones were deposited probably by mass flow mechanisms. A 90 metre long sandstone dyke originating in the Pualco Formation passes upward into the basal Wilyerpa Formation, showing that part of the early Sturtian sequence was still unlithified, and that only a short time interval was involved in the local unconformities. The Wilyerpa Formation wedges out south-westward against the basin edge where it is unconformably overlain by shales of the widespread Tapley Hill Formation, whereas in the east, a conformable sequence is present. ALl tectonic activity had apparently ceased in the area during the deposition of the Tapley Hill Formation.

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TECTONIC DEVELOPMENT OF THE ADELAIDE FOLD BELT A.J. Parker South Australian Department of Mines and Energy, P.O. Box 151, Eastwood, S.A., 5063. INTRODUCTION Excluding the Pandurra Formation of the Gawler Craton, the tectonic development of the Adelaide Fold Belt/Geosyncline and its adjoining platform regions spans an interval of some 600 million years. Three broad stages of tectonic development can be identified: an early stage involving intracontinental graben and/or half-graben formation associated with local basic volcanism; a later stage involving epeirogenic uplift and downwarping on a passive continental margin; and a final orogenic stage leading to the formation of the Adelaide Fold Belt as we now know it. EARLY DEVELOPMENT In the past the Pandurra Formation has been considered as the earliest Adelaidean cover unit on the Stuart Shelf (Mason et al., 1978). The Pandurra Formation is confined to a 120 km wide, graben-like depression running NW from the Pt. Augusta region and flanked to the SW and NE by Early to Middle Proterozoic basement squences. Facies changes occur across NW trending faults and the thickest sequences appear to be in NWSE trending troughs oblique to structural trends in the Adelaide Fold Belt. West of Pt. Augusta the Pandurra Formation is unconformably overlain by the Backy Point Beds and Beda Volcanics. Fanning et al. (in press) now record an age ca 1420 Ma for Pandurra Formation silts tones and they regard this figure as a maximum though likely estimate for the date of deposition of those silstones. Considering a ca 1100 Ma age for the early Adelaidean Beda Volcanics (Rutland et al., 1981), and in view of unconformable relationships in the Pt. Augusta region, the Pandurra Formation must be regarded as preAdelaidean although it may represent an older aulacogen indirectly related to the early development of the geosyncline. Intruding Pandurra Formation in the Lake Gairdner region is a swarm of NW-SE trending mafic dykes informally known as the Gairdner Dyke Swarm. Some of these dykes are closely associated with or intrude along bounding faults of Pandurra graben. This suggests that the dyke intrusion may have been related to the same tensional environment that first formed the graben. However, since the dykes are probably ca 1050 ± 50 Ma old (unpubl. Amdel Rept. GS4986/83) they are apparently much younger than the Pandurra Formation. Mason et al. (1978) implied that the dykes were feeders to upper flows in the Beda Volcanics and certainly the preliminary dating supports this. Rowlands et al. (1980, p«55) suggest that the basal Adelaidean sequence, the Callanna Group, was "formed in playa lake or prograding sabkha complexes, that formed in a series of yoked half-grabens". Furthermore, along with Preiss (in Rutland et al., 1981) and von der Borch (1980) they suggest that the sequence formed within an intracontinental rift system in a tectonic, climatic, and geochemical setting analogous to the present-day East African Rift Valley.

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Von der Borch also suggested that the intersection of three major gravity "ridges" near Mt. Painter represents an ancient triple junction possibly initiated by a mantle plume. He inferred that the gravity "ridges" represent ancient spreading axes in the Adelaide palaeorift system, analogous to the North American mid-continental rift system. The coincidence of the Wooltana Volcanics with gravity highs in the Mt. Painter region supports this observation but the Beda Volcanics NW of Pt. Augusta appear to be the product of a separate NW trending axis coincident with the Gairdner Dyke Swarm. LATER DEVELOPMENT A major change in the tectonic development of the Adelaide Geosyncllne occurred following Willouran deposition. The Torrens Hinge Zone which had very little effect on the early development, became an Important tectonic structure during depositon of the Burra Group and appears to have been a significant tectonic feature during subsequent sedimentation. For example, a gravity "trough" which coincides with thick accumulation of Torrensian and Sturtian sediments along the western margins of the Flinders Ranges is bound to the west by the Torrens Hinge Zone. The change in tectonic setting is also reflected by evidence throughout the central Flinders Ranges, Willouran Ranges and Mt. Lofty Ranges for mild deformation prior to both Torrensian and Sturtian depositon. Many anticlinal cores in the central Flinders were emergent at least during the early Sturtian, blockfaulting and/or thrusting was clearly important (e.g. in the Willyama Block), and low angle unconformities such as at Chintapanna in the Willouran Ranges clearly indicate mild, pre-Sturtian tectonism. The Burra Group was certainly affected by this mild tectonism but not as severely as the Callanna Group. In the central Flinders Ranges and Willouran Ranges disrupted Callanna sediments occur in a number of tectonic structures which have been variously described as thrust complexes (Sprigg, 1949), diapirs (Webb, 1960; Dalgarno and Johnson, 1968), syn-sedimentary slump breccias (Murrell, 1977), and tectonic decollements (Burns et al., 1977). One such structure occurs at Rischbieth Well in the Willouran Ranges (Figure 1) • Within the Rischbieth structure, intense folding and brecciation of the Callanna Group sediments has deformed them into a barely recognisable sequence of qu^rtzites, sandy dolomites, and slaty shales. The sequence is often overturned, disrupted by breccia zones, faults and thrusts, and is locally intruded by semi-circular, albitic, monzonite-syenite-diorite plugs. The marked contrast in structural complexity between the Callanna and Burra Groups suggests either early folding preceeding deposition of the Burra Group, disharmonic folding in the cores of antlclinoria, or megaslumping of the Callanna Group. Murrell (1977) believed that the contrast in structural complexity was due to early deformation of the Callanna Group and that it represented either mega-slumping or Musgravian deformation. Furthermore, he along with Rowlands and Warrin (1979) attributed apparent thinning and fades changes within Burra sediments along the margins of the Rischbieth structure to stratigraphic thinning; that is, suggesting that the Rischbieth structure was an emergent horst uplifted and deeply eroded

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FIG. 1

Post~Torrensian (? Delamerian) fold

/ RIS< lllh

Fault/thrust. Sedimentary facing Lamprophyric diorite (age uncertain) Albitic granite

(age uncertain)

^ ^

BURRA GROUP (Undifferentiated) Pre—Torrensian fold_X*^ CALLANNA GROUP (sequence uncertain) Quartzite Dolomite Slate Cu prospect

RISCHBIETH STRUCTURAL COMPLEX

KILOMETRES Dm. G.B.

83-561 SADME

prior to or early during Torrenslan deposition. referred to this horst as the "Tarltonla Uplands".

Rowlands and Warrln

In many places (e*g. the Bungarlder Fault)» the contact between the core complex and Burra sediments Is now tectonic rather than stratlgraphlc and local folding of Burra sediments Immediately adjacent to the core complex suggests modification of the boundary during subsequent deformation. Also, some of the apparent thinning can be attributed to tectonic extension since there are abundant quartz-filled tenslonal veins perpendicular to bedding. However, the apparent lack of deformation of stromatolites makes It hard to attribute all the thinning to a deformatlonal event. Furthermore, post-Torrenslan (?Delamerlan) folds readily Identified In the Burra Group surrounding the Rlschbleth structural complex can be seen to overprint early formed, very tight to Isoclinal folds and thrusts within the core complex. Therefore It is suggested that a period of folding and thrusting occurred prior to or early during deposition of the Burra Group. It is envisaged that the isoclinal folds and thrusts were shallowly inclined at depth but that they were steeper (easterly dipping) near the surface. They are analogous to steep thrust structures in the Wi'llyama Block and suggest a westerly directed thrusting leading to shallow onlap of Burra sediments from the east but deeper, more active sedimentation in front of the thrust complex to the west. The age of the albitic, monzonite-syenite-diorite suite in the Rlschbleth area is not known. The margins of the plug like bodies have been locally brecciated and the plugs often occur in the cores of postTorrensian anticlines which would suggest that they were intruded either prior to or during that fold event. In the Peake and Denison Ranges monzonites intrude Burra Group sediments (Ambrose et al., 1981) and have been dated by K-Ar on hornblende at ca 490 Ma although there is one apparently spurious K-Ar, biotite age of 680 Ma. Models and interpretations proposed for other megabreccia zones, particularly those in the central Flinders, are as varied as the rocks themselves. Internal fabrics within some zones indicate early, syndepositional deformation in the form of folding, faulting and/or thrusting. Furthermore, mapping of sedimentary fades variations in adjacent sediments demonstrates that many of the megabreccia zones were emergent at various times during the Adelaidean and Cambrian. Faulting also influenced sedimentation but while many faults may have been initiated during sedimentation most were reactivated during the Delamerian such phat sedimentary fades relationships are no longer clear. The most obvious syn-sedimentary fault structures are those that now define a ENE trend through the central Flinders. These formed during Marlnoan-early Cambrian time and are particularly strong along the NE trending gravity "ridge" suggesting that that ridge may have been a major horst or a complex of horsts and graben active during the late Adelaidean. DELAMERIAN DEFORMATION Regional folding of the Adelaide System has largely been attributed to the Cambro-Ordovician Delamerian Orogeny. The effects of this deformation are widespread throughout the Adelaide Fold Belt east of the Torrens Hinge Zone but are not evident on the Stuart Shelf. Folding, faulting, regional metamorphism, local brecciation, and intrusion of granites around the Fleurieu Arc are all products of the orogeny.

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lt is now clear that the Delamerian Orogeny was a multi-phase orogeny. Several workers on the Kanmantoo Group have identified at least two phases of Delamerian folding with the first phase representing the peak metamorphism and emplacement of the Encounter Bay Granites (Milnes et al., 1977). The pervasive schistosity developed during D, was subsequently folded and crenulated on all scales, locally with the production of differentiated crenulation cleavages (Marlow and Etheridge, 1977; Flint and Grady, 1979). Pre-S^ metamorphism has been demonstrated in many areas (Fleming and Offler, 1968; Flint and Grady, 1979) and was probably associated with granite intrusion immediately preceeding or early during D ^ Most of the structural work describing the Delamerian Orogeny has been concentrated in the southern regions. However Bell (1978) describes the development of slaty cleavage (Sj^) in the Nackara Arc region and Berry et al. (1978) identify two phases of Delamerian folding in the Olary region. Regional metamorphism accompanied Delamerian folding and while peak metamorphic conditions were attained around D^ time, there was considerable recrystallization during D2 and D3 events. Consequently geochronological dates from low grade Adelaidean metasediments throughout the fold belt give early Ordovician ages corresponding to the later phases of the Delamerian Orogeny (Milnes et al., 1977). In recent years some attention has been given to the sigmoidal shape of the Fleurieu and Inner Nackara Arcs. Simple shearing has been postulated for the development of N-S axial trends in the Mt. Lofty Ranges and southern Flinders Ranges (Coward, 1976) however (as noted by Rutland et al., 1981), the inferred ductile shear zone does not continue into the Stuart Shelf region. Glen et al. (1976) and Mancktelow (1981) have argued that older basement blocks - the Gawler Craton to the west and the Willyama Block to the northeast - have played a more significant role in the development of the arcuate fold belt than did a major crustal shear zone. Glen et al. suggest a local component of simple shear in the Mt. Lofty - southern Flinders region but point out that this is a consequence of crustal shortening directed from the SE against a relatively rigid basement block, viz. the Gawler Craton. The deep sedimentary trough in this southern Flinders region (coincident with the gravity "trough") may be a zone of crustal weakness which has accommodated greater strain than those areas such as the eastern portions of the Nackara Arc which could be underlain by shallower basement. REFERENCES Ambrose, G.J., Flint, R.B. and Webb, A.W., 1981. Precambrian and Palaeozoic geology of the Peake and Denison Ranges. Geol. Surv. S. Aust., Bull. 50. Bell, T.H., 1978. The development of slaty cleavage across the Nackara Arc of the Adelaide Geosyncline. Tectonophysics, 51:171-201. Berry, R.F., Flint, R.B. and Grady, A.E., 1978. Deformation history of the Outalpa area and its application to the Olary Province, South Australia. R. Soc. S. Aust., Trans., 102:43-54. Burns, K.L., Stephansson, 0. and White, A.J.R., 1977. The Flinders Ranges breccias of South Australia - diapirs or decollement? Geol. Soc. Lond., J., 134:363-84. Coward, M.P., 1976. Large scale Palaeozoic shear zone in Australia and present extension to the Antarctic Ridge. Nature, 259:648-9.

Dalgarno, C.R. and Johnson, J.E., 1968. Diapiric structures and late Precambrian-Early Cambrian sedimentation in the Flinders Ranges, South Australia. J ^ Braunstein, J . and O'Brien, G.D. (eds.), Diapirism and diapirs: a symposium. Am. Assoc. Petrol. Geol., ^ m . , 8:301-14. Fanning, C.M., Flint, R.B. and Preiss, W.V., in press. Geochronology of the Pandurra Formation. Geol. Surv. S. Aust., Q . geol. Notes. Fleming, P.D. and Offler, R . , 1968. Pre-tectonic metamorphic crystallization in the M t . Lofty Ranges, South Australia. Geol. Mag., 105:356-9. Flint, D.J. and Grady, A.E., 1979. Structural geology of Kanmantoo Group metasediments between West Bay and Breakneck River, Kangaroo Island. R . Soc. S. Aust., Trans., 103:45-56. Glen, R.A., Laing, W.P., Parker, A.J. and Rutland, R.W.R., 1977. Tectonic relationships between the Proterozoic Gawler and Willyama orogenic domains, Australia. Geol. Soc. Aust., J., 24:125-50. Mancktelow, N.S., 1981. Variation in fold axis geometry and slaty cleavage microfabric associated with a major fold arc, Fleurieu Peninsula, South Australia. Geol. Soc. Aust., J . , 28:1-12. Marlow, P.S. and Etheridge, M.A., 1977. Development of a layered crenulation cleavage in mica schists of the Kanmantoo Group near Macclesfield, South Australia. Geol. Soc. Am., Bull., 88:873-82. Mason, M.G., Thomson, B.P. and Tonkin, D.G., 1978. Regional stratigraphy of the Beda Volcanics, Backy Point Beds and Pandurra Formation on the southern Stuart Shelf, South Australia. Geol. Surv. S. Aust., Q . geol. Notes, 66:1-9. Milnes, A.R., Compston, W . and Daily, B., 1977. Pre- to syn-tectonic emplacement of early Palaeozoic granites in southeastern South Australia. Geol. Soc. Aust., J . , 24:86-106. Murrell, B., 1977. Stratigraphy and tectonics across the Torrens Hinge Zone between Andamooka and Marree, South Australia. Ph.D. thesis. University of Adelaide (unpubl.). Rowlands, N.J. and Warin, O.N., 1979. Stratiform copper in cyclic sediments of the late Proterozoic Burra Group, Willouran Ranges, South Australia. Soc. Geol. Belg., Ann., 102:549-65. Rowlands, N.J., Blight, P.G., Jarvis, D.M. and von der Borch, C.C., 1980. Sabkha and playa environments in late Proterozoic grabens, Willouran Ranges, South Australia. Geol. Soc. Aust., , 27:55-68. Rutland, R.W.R., Parker, A.J., Pitt, G.M., Preiss, W.V. and Murrell, B., 1981. The Precambrian of South Australia. J ^ Hunter, D.R. (ed.), Precambrian of the Southern Hemisphere. Developments in Precambrian Geology, 2:309-60. Sprigg, R.C., 1949. Thrust structures of the Witchelina area. South Australia. R. Soc. S. Aust., Trans., 73:40-7. von der Borch, C.C.^ 1980. Evolution o F late Proterozoic to early Palaeozoic Adelaide foldbelt, Australia: comparisons with post-Permian rifts and passive margins. Tectonophysics, 70:115-34. W e b b , B.P., 1960. Diapiric structures in the Flinders Ranges, South Australia. Aust. J . Sci., 22:9.

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THE L E I G H CREEK--FREELING H E I G H T S S T R U C T U R A L

CORRIDOR

E.S.T. O'DriscoIl Western Mining Corporation., Adelaide. S.A. I n v e s t i g a t i o n s of the r e g i o n a l s t r u c t u r a l p a t t e r n of the A d e l a i d e G e o s y n c l i n e have shown the p r e s e n c e of a n u m b e r of c o n t i n u o u s linear zones of s t r u c t u r a l d i s t u r b a n c e w h i c h cross through the body of the g e o s y n cline and e x t e n d into the s u r r o u n d i n g d o m a i n s . They a p p e a r to be s y s t e m a t i c , and their e f f e c t s are seen as linear d i s c o n t i n u i t i e s or " b r e a k s " in the p a t t e r n s of i n t e g r a t e d data d r a w n v a r i o u s l y from g r a v i m e t r i c s , a e r o m a g n e t i c s , t o p o g r a p h y , g e o l o g y , a i r - p h o t o g r a p h y and L a n d s a t i m a g e r y . Since these linear d i s c o n t i n u i t i e s appear to be p r e f e r e n t i a l l y a s s o c i a t e d w i t h u n u s u a l rock t y p e s , s t r a t i g r a p h i c a n o m a l i e s and m i n e r a l d e p o s i t s of d i f f e r e n t a g e s , they are c o n s i d e r e d to r e p r e s e n t a n c i e n t f o u n d a t i o n a l f e a t u r e s of the A d e l a i d e G e o s y n c l i n e w h i c h have been i n t e r m i t t e n t l y r e a c t i v a t e d t h r o u g h o u t its g e o l o g i c history. One such c o r r i d o r o b s e r v e d in a L a n d s a t l i n e a m e n t study of n o r t h e a s t e r n South A u s t r a l i a and n o r t h - w e s t e r n New South W a l e s c r o s s e s the n o r t h e r n end of the A d e l a i d e G e o s y n c l i n e in an e a s t - n o r t h e a s t e r l y d i r e c t i o n through the v i c i n i t y of M o u n t P a i n t e r . It is a p p r o x i m a t e l y 18 km w i d e , and e x t e n d s for a p p r o x i m a t e l y 150 km a c r o s s the g e o s y n c l i n e .

GEOSYNCLINE BOUNDARY

F i g . 1 . Plot of L a n d s a t h i g h - f r e q u e n c y l i n e a m e n t s over n o r t h e a s t e r n South A u s t r a l i a , i n d i c a t i n g the p o s i t i o n of the L e i g h C r e e k - F r e e l i n g H e i g h t s s t r u c t u r a l c o r r i d o r ( L C - F H ) b e t w e e n the p a i r e d a r r o w s .

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coinciding with the axial trend of the broad anticlinal zone along the linear northern flank of the Gammon Ranges. It is here named "the Leigh Creek-Freeling Heights structural corridor" (LC-FH in Fig. 1), in terms of two well-known geographic features which correspond to its position within the boundaries of the geosyncline. This part figured appears, however, to be only a segment of a much longer regional feature previously recognised as corresponding to an alignment of granite culminations and structural highs extending for some hundreds of kilometres from Eyre Peninsula through Mount Painter and Tibooburra, and on into Queensland through the Eulo and Neebine Ridges (O'Driscoll, 1968). In the east this trend is associated with Devonian and younger granitic intrusions., and in the Freeling Heights area the corridor includes the high level British Empire Granite and all occurrences of the young intrusive suite of sodic bodies within the Adelaidean, such as Tourmaline Hill, The Pinnacles, Sitting Bull, etc. The LC-FH Corridor is not readily apparent from inspection of the Copley 1:250,000 Geological Map. However, when the path of the corridor is laid on the map, it is seen to be the locus of a number of singular geological features, some of which are contained within its central precincts, some maximised where they lie in its path, and others disposed along its margins. It is noteworthy that the group of uranium occurrences at Mount Painter and the neighbouring Beverley deposit are located within the corridor. The Mount Painter Inlier is the only horst of Mid and Early Proterozoic rocks in the Flinders Ranges, and its structural setting in relation to the corridor, at the intersection with the Paralana Fault, invites close study. The margin of the basement in the Hamilton Creek area, near Freeling Heights, is determined by ENE-oriented growth faulting which controlled the Adelaidean unconformity. This is almost coincident with the northern border of the LC-FH corridor. Within the basement in this area, and also south of Mount Painter, two concentrations of amphibolite dykes, occur underneath the Adelaidean unconformity, correspond respectively to the north and south limits of the corridor, and reflect localised stress. The local thickenings of the Humanity Seat Formation and Wooltana Volcanics along the southern margin of the corridor are also notable, as is the position of the later developed structural complexity and overthrusting of the basement along ESE trends in the vicinity of Arkaroola. The corridor trend appears to mark a profound change in late Adelaidean stratigraphy in certain areas. Thus it generally defines a south to north shelf-to-basin transition for the Sturtian and Marinoan with angular unconformities in several localities. A submarine fault escarpment near Mt. Warren Hastings occurs some 4 km south of the corridor in the late Sturtian. Diamictite in the Marinoan glacials does not occur south of the corridor, whilst the shelf facies of the Wilpena Group, including the ABC Range Quartzite, is confined to the region to the south. The only known submarine canyons in the Wonoka Formation of the North Flinders Ranges, at Patsy Springs and Fortress Hill, are respectively on the immediate south and north of the corridor, suggesting some causative relationship during Ediacaran time. Also near Mount Scott a contemporaneous fault paralleling the southern margin of the corridor is associated with conglomerates in the Pound Sub Gp. and also facies changes in the Cambrian (Gravestock, D.I., this volume).

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On the Stuart Shelf the projection of the LC~FH Corridor coincides with an inferred graben extending ENE from Woomera in which there is relative thickening of the Pandurra Formation. Embayments in the distribution pattern of the Tapley Hill Formation and Whyalla Sandstone in the area between Woomera and Andamooka Island suggest that a localised trough here may coincide with the corridor, which also broadly defines the southern limit of distribution of Cambrian limestones. The coal basins of the Leigh Creek Field represent a unique occurrence of Triassic in the North Flinders Ranges. Aligned along a North-South trend, they lie wholly within the 18 km width of the corridor path, and apparently reflect the intersection of the corridor with another deep basement structure crossing through it. Refinement of geological observations and interpretations in areas of well-studied facies relationships and contemporaneous structures, such as those of the Adelaide Geosyncline, may offer a fundamental explanation for observed pattern discontinuities in regional data of the kind exemplified by the broad LC-FH Corridor seen in the Landsat lineament study. REFERENCES von der Borch, C.C., 1980. Evolution of Late Proterozoic to Early Palaeozoic Adelaide Foldbelt, Australia: Comparison with postPermian Rifts and Passive Margins. Tectonophysics, 70, p.115-134. Coats, R.P. and Blissett, A.H., 1971. Regional and Economic Geology of the Mount Painter Province. Bull. Geol. Surv. S. Austral., 43, p.1-426. O'Driscoll, E.S., 1968. Notes on the structure of the Broken Hill lode and its tectonic setting. Proc Aust. Inst. Min. Met. Annual Conf., 1968, p.87-102.

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DIAPIRS AND DIAPIRISM IN THE ADELAIDE

'GEOSYNCLINE'

SOUTH AUSTRALIA^^ T.J. Mount Delhi Petroleum Pty. Ltd., Adelaide Approximately 180 diapirs define a 500 km belt coincident with the Flinders-Mount Lofty Ranges. New observations on these structures are prefaced by reviews of the concept of diapirism in general and of the history and regional geological setting of the province - the Adelaide 'Geosyncline'. The proposed model for diapirism in the 'Geosyncline' is based on a detailed map of the Arkaba Diapir. Primary control of diapir distribution in the trough can be related to fracture patterns in the pre-source-bed rocks. Outcrop of diapiric material is distinctive over a wide area, and may be accentuated by patterns of vegetation. Weathering is deep and intense but cap-rock or solution megabreccias are absent. Typical forms are very complex, varying from massifs, domes, dykes, and plugs; shapes that have been controlled by host-rock anisotropy, notably patterns of fracture. Diapir/host-rock contacts are invariably abrupt and coincide with planes of weakness in the host. The contacts, despite sculpting and quarrying by invading diapiric material, can often be matched in 'continental drift' type reconstructions across the cores. Host strata are rarely brecciated or upturned against a diapir, illustrating the passive nature of the intrusions. Where such deformation occurs, it usually pre-dates diapirism and is due to faulting. Permitted intrusion under local extension in the cover, plausibly induced by regional compression, is implied. Alteration of host rock adjacent to contacts is absent but for minor dolomitization in certain zones. The intrusive material is an intensely mixed chaotic breccia but one which includes many well rounded and subspherical xenoclasts, from kilometres across to the finest dust. The size spectrum appears to obey Rosin's Law of Crushing. The breccias, but for rare basement and hostrock xenoclasts, involve a restricted and characteristic range of shallow-marine lithologies including terrigenous clastics, carbonates (especially dolostones), and saline evaporites. This suite may well be assigned to the Callanna Beds of Late Precambrian age. Petrographic studies have revealed a suite of metamorphic minerals, notably carbonate, chlorite, clay, felspar, haematite, magnesioriebeckite, quartz, stiIpnomelane, and talc, developed in the core rocks. All mineral components may reasonably have been derived by simple processes entirely from rocks of the type that comprise typical xenoclasts. Many reactions involved dedolomitization and/or saline evaporites. A low pressure, hypersaline, aqueous, oxidative metamorphic environment (zeolite facies) is indicated; replete with CO2, opensystem, and low temperature (150^0 - 250°C - 300^C). Affinities are with natural hydrothermal and geothermal systems. Igneous rocks with a wide range of ages occur in the cores and include both intrusive and extrusive types, mainly basic to intermediate in

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character. They are essentially xenoclastic but include some in situ post-diapiric intrusions. The occurrence of igneous rock is fortuitous and non-essential to diapirism. Typical breccias have a banded fabric and other features such as the shaping, disruption, mixing, and alignment of xenoclasts that must be attributed to flow. Movement was slow, rather passive, and plug-like, described by non-Newtonian, Andradean law. Mobility of the source material, rather than factors such as density, was paramount to diapirism. The mobility is explained by the former presence of saline evaporites in the interstices of the breccias and by appeal to the concepts of dilatancy, fluidization, and rheidity. The over-burden was relatively brittle, its weight the prime driving force to the intrusions. Emplacement was at least partly syn-tectonic, linked to pulses of deformation of the cover, as well as to basement evolution in the 'Geosyncline'. Decollement at the source layer is implied. The host was not explosively breached in the manner of a diatreme; the diapirs are not carbonatites. Although further problems have been outlined, a study of diapirs in the Flinders-Mount Lofty Ranges has clarified many aspects of the global theory. The essence of the new observations is embodied in a proposed classification of intrusions that includes diapirs.

-'^Reference; Mount, T.J., 1975.

Diapirs and Diapirism in the Adelaide 'Geosyncline', South Australia. Unpub. thesis (PhD), Univ. Adelaide, 1975.

- 34 -

MARINQAN MUD ISLANDS, MOUNT FROME, S. AUST. R. Dalgarno Seltrust Mining Corporation, Adelaide Mud islands and shale diapirs are features of rapidly deposited slope sequences which occur at the toe of depositional wedges in response to gravitational loading on older, water-saturated basinal sediments. In modern deltas these features have dimensions of the order of several square kilometres and involve transport of large blocks of semi-consolidated deposits from lower in the sedimentary pile. Rates of uplift have been measured at many metres per year but marine action tends to rapidly erode the unconsolidated mud matrix surrounding the larger blocks, wearing them down to wave base and resulting in shoals and mud islands of low relief. East of Wirrealpa, on the PARACHILNA Sheet Area, unconformable onlap of the Wonoka Formation on the eastern flank of the Frome Anticline, and evidence of intrusion of the core breccias suggest geometry similar to a mud island emergent during the late Marinoan (Ediacaran of Gostin and Jenkins, 1983). The Wonoka Formation of the Flinders Ranges is the carbonate sequence which follows the maroon basinal shales of the Bunyeroo Formation, and underlies the Pound Subgroup. Gostin and Jenkins redefine the base of the Wonoka Formation at the Wearing Dolomite and suggest that the overlying terrigenous turbidites indicate a phase of tectonic instability and rapid subsidence which initiated downcutting of submarine canyons. The later part of the Formation represents carbonate shoals and lagoonal flats which were transgressed by prograding deltaic and littoral deposits of the Bonney Sandstone (Pound Subgroup). The unconformity beneath the Wonoka Formation at Mt. Frome is preserved only along the eastern flank of the breccia core whereas the west flank is locally overturned with clear exposure of breccias intruding the earlier Brachina Formation. Sea floor topography apparently first developed prior to deposition of carbonates in the Wonoka Formation as there are pebbly grits and cobble lenses and also prominent slump rolls in underlying red and maroon silts near the Mt. Frome barytes pit. The contact between overturned west-facing siltstones and the carbonateclastic breccia is well exposed in a north-facing cliff of Bendieuta Creek 1 km farther south. It is a steep east-dipping contact between breccias and partly bleached, much faulted siltstones. Flame-like tongues of the breccia in the siltstone are consistent with an intrusive relationship. Flowage banding is developed in the breccia which comprises clasts of sedimentary rocks from metric to centimetric dimensions close to the contact, but includes large rafts of earlier Adelaidean units within the core of the structure. One of the most prominent ridges in the central part of the breccia mass is some 500 metres long and comprises a dislocated block of Sturtian glacial sediments which includes diamictite facies with granite boulders. Other features are consistent with the model of a "bald cap" diapiric dome forming a 'mud island' during deposition of the Wilpena Group with blocks of earlier Adelaidean sediments incorporated in disrupted, overpressured clastic breccias in the intrusive core.

- 35 -

Along the exposed unconformity zone, which extends S-N some 2 km minor faults with throws of 3-lOmetres result in local thickness and facies changes, indicating syndepositional movement during deposition of the Bonney Sandstone. Well rounded pebbles suggest reworking of resistant lithologies from the core in a high energy wave environment. The onlapping Wonoka Formation is overlain by an incomplete sequence of the Pound Subgroup and Early Cambrian Hawker Group carbonates in which several further pebble and cobble beds occur, indicating episodic emergence. Post Wonoka Formation intrusion of the breccias is apparent in several localities along the east side of the structure. Intersections of deep basement faults appear to determine the location of this and similar structures which in many cases developed as complex diapiric intrusions during Palaeozoic folding. The controlling mechanism of initial formation appears to have been unequal loading of sediments and ductility differences arising from confined formation waters in older units of the Adelaidean. Sudden relief of pressure due to fault movement may contribute to deformation as a result of dewatering of partly lithified sediments. Interpreted rheomorphic phenomena are common near country rock contacts and the degree of mixing of clasts from different levels in the stratigraphic sequence supports the concept of flowage of the breccia masses. Thus in the case of the Beltana Diapir, which had a similar history to the Frome Diapir, a large fault block of Cambrian fossi1 iferous sediments is preserved within the structure, in close proximity to early Adelaidean sediments and also blocks of granite and stressed amphibolite, which were presumably plucked from the pre-Adelaidean basement

It is suggested that the concept of shale diapirs emergent during deposition and resulting in "mud islands" accounts for the extensive megabreccias envisaged as regolith material by certain workers. REFERENCES Gostin V.A. and Jenkins R.J.F. Sedimentation of the Early Ediacaran, Flinders Ranges, South Australia. GSA Abstract Series No. 9, 1983; pp 196, 197. IDEALIZED ROCK RELATIONSHIPS FOR THE LATE ADELAIDEAN NORTH FLINDERS RANGES

Hawker Gp Wilpena Gp

Umberatana Gp

Burra Gp ^^Callanna Gp

- 36 -

ENORAMA DIAPIR CONTACT RELATIONSHIPS J.H. Cann, I.F, Clark, B.J. Cook and W.G. Shackleton Salisbury Campus of S.A.C.A.E., Salisbury East, S.A. 5109

Three different contact relationships of the Enorama diapir are suggested: Contact type 1 Along the northern part of the western boundary of the Enorama diapir, a distinctive yellow dolomite, the uppermost horizon of the Etina Formation, unconformably overlies the diapiric breccia. This unconformable relationship was recognised by Dalgarno and Johnson (1968). Ascending the sequence, which dips steeply westwards, diapiric breccia is overlain by yellow dolomite, conglomeratic at base, and shale. Sections across the boundary, which are revealed in several creek beds, are described below. Locality A In sections exposed several hundred metres south of Dedman's Hut dolerite outcrops within the diapiric breccia adjacent to the boundary. The overlying material is composed of large angular dolerite clasts in a matrix of massive yellow dolomite. Many clasts exhibit a jig-saw like fit (fig 1). The relative proportion of clasts decreases up sequence, giving way to a massive yellow dolomite. Overlying shales dip steeply westwards.

Fig 1. Sketch of exposed pavement at locality A. Dolerite fragments (stippled) are embedded in a matrix of massive yellow dolomite (unshaded).

It is considered that the dolerite was essentially untransported, the clasts representing an in situ, sub-aerial, weathered surface prior to marine transgression. Carbonate sedimentation infilled gaping joints in the submerged outcrops. Nearer Dedman's Hut, a similar, but less obvious relationship exists between quartzite diapiric ''rafts" and quartzite clasts at the base of the dolomite. Locality B About 3 km SSE of Dedman's Hut the dolomite outcrops in a major tributary of Enorama Creek. At this locality the diapiric breccia consists of fragmented red and green shales. This material is overlain by conglomeratic dolomite, the lower surface of which shows erosion scours into the breccia. The contact is variably sandy to pebbly with

INDEX TO ADJOINING SHEETS Showing MagncKc 0«clmat<on

SOURCE '

P A R A C H I L N A SHEET

1:250,000

GEOLOGICAL SURVEY OF SOUTH A U S T R A L I A DEPARTMENT OF MINES A D E L A I D E

KILOMETRES 0

- 38 -

fragments of the underlying shale occurring as imbricate clasts. Larger clasts include dolerite and quartzite. Above the conglomeratic base, the dolomite becomes sandy and finely bedded with soft sediment deformation structures. The overlying shale dips 85® E, but small scale scour and fill and cross bedding structures in the sandy dolomite confirm that the sequence is facing westwards. The northern western margin of the Enorama diapir can therefore be interpreted as a surface of sub-aerial exposure. This surface contributed clasts of distinctive lithology to the intraformational sediments which formed after marine transgression. Contact type 2; Locality C In the vicinity of Dedman's Hut the total width of diapiric breccia exposed in the creek bed is about 100 m. The breccia consists of fragmented red shale with a "raft" of yellow, banded dolomite containing gypsum pseudomorphs. At the eastern boundary of this exposure the breccia physically overlies a pink limestone which is in part massive, in part silty to sandy and in part conglomeratic (fig 2). Larger clast Hthologies include dolerite, basalt, quartzite, yellow dolomite with gypsum pseudomorphs and massive limestone intraclasts. Sand grains are predominantly of quartz, well rounded and uniformly sorted. The limestone beds dip westwards at about 30°. Scour and fill structures confirm westwards facing. The overall colour of the limestone, and the clast lithologies suggests that sub-aerial diapiric breccia was a provenance for the sediment. Sandy textures favour a near-shore, shallow water, marine environment where conditions permitted accumulation of carbonate muds. Boulder sized fragments of the limestone are enclosed in the overlying breccia, seemingly a stratigraphic paradox. The relationship is illustrated in fig 2. Fig 2 Sketch of creek section near Dedman's Hut.

Pink sandy limestone, regionally conformable westwards dipping. Brecciated red shale (diapir). Dolerite clasts.

Possible explanations for the emplacement of the breccia over the limestone include a late pulse of diapirism, low angle thrust faulting or gravity slumping. Contact type 5; Locality D The northern-most boundary of the Enorama diapir is complex. Diapiric breccia and the steeply westwards dipping Etina Formation limestones appear to ihterdigitate. "Rafts" of dolomite, quartzite and basic igneous rocks outcrop prominently. In places an unconformable relationship similar to that of the western boundary can be inferred. There is also considerable outcrop data which may be considered evidence for faulting.

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MARINQAN AND EDIACARAN TYPE SECTIONS IN THE CONTEXT OF TECTONIC CYCLES IN THE ADELAIDE GEOSYNCLINE, Richard J.F. Jenkins & Victor A. Gostin Department of Geology and Mineralogy, University of Adelaide, S,A. Recent proposals for the recognition of stratotypes for international chronostratigraphic units within the late Precambrian of the Adelaide fold-belt 1|2,5 pose questions as to the validity, significance and boundaries of earlier recognised time-rock divisions, such as the Sturtian ^ and Marinoan Studies of the type development of the Marinoan 6,7 have been generally neglected since the pre-requisite stratigraphic framework necessary for geological mapping emphasized a different major lithostratigraohic subdivision comprising the Umberatana and Wilpena Groups Upward extension of the Marinoan in the Flinders Ranges evidently reflected an erroneous correlation between quartzites at the top of the type section and the Pound Quartzite 8. The formal erection of an 'Ediacaran System' in the Flinders Ranges 1 implies that the Marinoan should be restricted to the rock interval represented in its type section and equivalents of the Bunyeroo Formation sequential above the same rocks in the Willunga Escarpment 10. on the other hand the "Ediacarian System" of Q o u d and Glaessner 2 overlaps known correlatives of the type Marinoan (Fig, 1). The Marinoan stratotype succeeds ooidal dolostones and laminates with teepee structures comprising the top of the Brighton Limestone• The basal ~ 3 4 0 m of the succession 6 comprises thin, alternate beds of greenish and red-brown siltstone with ubiquitous intraclasts of the brown siltstone in the lower part, and mudcracks common throughout. Flaggy, silty sandstones ( ~ 6 0 m) continue this shallow-water regimen, which passes into arkosic carbonates, blue-grey limestones and minor conglomerates (Marino Arkose ^ 5 5 m), with associated steep crossbedding sets also suggestive of tidal deposition. There is a TYPE AREA Ref. 5 CAMBRIAN

FLINDERS

RANGES

GENERAL ^

8 CAMBRIAN I II I II I

TTrnrmrrr POUND

MARINOAN

EPOCH

W O N O K A

FM. FM.

RANGE

5<< 2hmOco < >QCO LU

QTZ.

BRACHINA

FM.

NUCCALEENA

FM.

ELATINA

FM.

STURTIAN

BRIGHTON LST. &

1 1.18,19, This CAMBRIAN EDIACARAN SYSTEM JWILLUNGA ESCARP. TYPE SECT.

U-

WILLOCHRA FM. & EQUIVALENT

STURTIAN

CAMBRIAN

QTZ.

B U N Y E R O O ABC

MARINOAN

GLAESSNER IN P R E S S

EQUIV.

MARINOAN MARINOAN

POUND

FM.

SUBGROUP

WONOKA FM. (AMEND.) BUNYEROO ABC

FM.

RANGE

BRACHINA

SILT.M

BRIGHTON

Figure 1. C o r r e l a t i o n c h a r t showing s e v e r a l c u r r e n t u s a g e s of the M a r i n o a n , E d i a c a r a n and E d i a c a r i a n .

QTZ.

SUBGROUP

^ SEACLIFF SS.M. Ireynflla WILLOCHRA

STURTIAN

Paper

URATANNA

rTrrrrTTTTTTTTT

iiiiiii

ELATINA

SUBGROUP

LST. &

EQUIV.

- 40 -

sharp boundary with overlying dark coloured, laminated siltstones which grade upwards into carbonate-rich, bluish, intercalated thin siltstones and sandstones C^60 m); this is the oldest part of the succession represented in the sea-cliffs at Marino. In this interval deposition was initially below wave base; there is an upward progression through minor turbidites (A,D,E Bouma divisions), storm beds and sub-tidal crossbed sets. A minor disconformity originally developed on a soft substrate marks the base of a thin (^12 m), but persistent interval of minor conglomerates, arkosic, ripple-bedded sandstones and sandy limestone. A sharp change above to laminated siltstones m) with some starved ripples (contourites) again suggests deposition below wave base; one brief shallowing event is indicated by a thin sandstone with ripple bedding and heavy mineral laminae. There is a passage through thin bedded siltstones and sandstones into overlying massive dolomitic sandstones (-^30 m) which commonly show convoluted bedding indicating slumping. A gradation into crossbedded sands with pebbly bands records rapid shallowing immediately below the interval of reddish diamictites ( ~ 4 0 m ) comprising the Reynella Siltstone Member 7. jhe latter includes pebbles of porphyry and a variety of gravel sized clasts. Numerous ripple-bedded intervals suggest deposition in shallow water; one level shows varve-like bedding. There can be no doubt that the Reynella Siltstone Member corresponds to a major part of the Elatina glacial cycle in the Flinders Ranges. Several thin, laminated dolomites occur in association with the Seacliff Sandstone Member^ (~'90 m); comparison with rocks in the Quorn area suggests that the upper dolomitic interval above the sandstones corresponds to the Nuccaleena Dolomite. The upper half of the Marinoan type section comprises a thick interval of turbidites and storm beds (^690 m), and succeeding intercalated siltstones and quartzites (~350 m). Rocks of the Ediacaran System are known only from the Flinders Ranges. While there seems to be continuous deposition between the Bunyeroo Formation and Wonoka Formation (amended H ) at the type section, Bunyeroo Gorge, a disconformity occurs at the base of the Wonoka Formation in most areas. The basal interval of the Wonoka Formation commonly comprises a thin intraclastic dolomite bed. East of the Stirrup Iron Range this boundary is similarly represented and is located a few tens of metres stratigraphically above a suite of several dolomite beds within the Bunyeroo Formation. Relationships between more or less quiet basinal sediments and turbidites (intercalated calcareous siltstones and sandstones or •flysch') within the greater part of the Wonoka Formation are variable and clearly reflect local settings. Submarine fans seem to have prograded northeastward in the vicinity of the Heysen Range. Variable current directions characterise the submarine canyon complex which forms the site of Waukarie Creek, south of Quorn. In this area several transects of canyons showing up to 800 m relief are exposed in steeply dipping limbs of folds. Comment on other facies within the Ediacaran is developed elsewhere 1,2,11,12,13,14. TECTONIC CYCLES The late Precambrian and Cambrian sediments of the Adelaide fold-belt can be reinterpreted in terms of the model of geosynclinal cyclicity outlined by Hsu 15 (Fig.2).

- 41 -

LITHOSTRATIGRAPHY

CHRONOSTRATIGRAPHY

ORDOVICIAN LU

FLINDERS —

RANGES

ADELAIDE

? -L GRINDSTONE RANGE SS.

MIDDLETON S S . PETREL COVE FM. BALOUIDDER FM.

OCL LU -J Q Q

REGION

CE D

T A P A N A P P A FM. TALISKER CALC-SILT.

DC ••

M O O D L A T A N A FM. YORKE PEN. WIRREALPA LST. & NTH. KANGAROO B I L L Y C R E E K FM. BLAND

< O

r T T r m r n T T T T f - ? CARRICKALINGA HEAD NARINA FORMATION GREYWACKE HEATHERDALE SHALE ORAPARINNA SH.

DC < LU

DC ^ LU Q-

PARARA LST. WILKAWILLINA L S T AJAX LST. P A R A C H I L N A FM. URATANNA FM.

BACKSTAIRS P A S S A G E FM-

FORK TREE LST. S E L L I C K HILL FM. WANGKONDA FM.

TECTONOSEDIMENTARY CYCLES REGIONAL DELAMERIAN METAMORPHISM PLUTONISM OROGENY 'MOLASSE^

— pCI UJ Q

'FLYSCH'

2 <

'EUXINIC KANGAROOIAN 'MOLASSE'

MOVEMENT

BASINAL

D <

-J

'EUXINIC'

Q <

PRE-GEOSYNCLINAL

MT. T E R R I B L E FM.

x n n m n : ^

Z< DC <

Q . Z Q.

RAWNSLEY QTZ.

Oco a.

BONNEY S S .

O <

POST-GEOSYNCLINAL

^rrrrmTT

DUTTONIAN

'MOLASSE'

MOVEMENT WONOKA FM.

Q LU

jUl

tt Z<

i^ iCC O o $ CO

o z E<

B U N Y E R O O FM. > ABC ^ ^ 7 ^ RANGE QTZ.

'FLYSCH* B U N Y E R O O FM.

WARPING 'EUXINIC

ABC RANGE QTZ. & EQUIV.

'MOLASSE'

E L A T I N A FM.

prvMPMAV SEAC.IFF SS.M. SiLT. M.

WILLOCHRA SUBGROUP a. Q. D O QC O <

i5 s0 < OQ CO

Q < tr D hco

BRIGHTON LST.

T A P L E Y HILL

FORMATION

T T T r r n r r APPILA TILLITE \ WILYERPA FM. 5 a-

z < Q z

BENDA SILTSTONE BRAEMAR IRONSTONE PUALCO

D <

WARPING

EXTENSIVE BASIN 'EUXINIC

STURT TILLITE

G L A C I A L S AND TURBIDITES

QC D Q

WARPING

< O

LOCAL DEEP TROUGHS

TILLITE

TTTTTTT-ml F i g u r e 2.-

EUSTATIC CYCLES

GLACIALS BASINAL

'TINDELPINA M.V.

K < tr lU Q] s D

TURBIDITES

Z < LU

< z

SIGNIFICANT

FOLDING

T e c t o n o - s e d i m e t a r y c y c l e s in the A d e l a i d e G e o s y n c l l n e . N a m e s u s e d a r e of a b o r i g i n a l t r i b e s w h i c h i n h a b i t e d a r e a s w h e r e c y c l e s a r e well d i s p l a y e d , with the e x c e p t i o n of A D J N A . K u j a n i for "hill*. A r b i t a r y v e r t i c a l

s e a le.

- 42 ~

The 2800 m thick Wilyerpa Formation of the Sturtian of the Bibliando Dome comprises mainly turbidites. The same unit extends through the Nackara Ark to the Olary region lA, we suggest that phases of rapid subsidence which occurred during Sturtian time were related to compressive tectonics manifest by syndepositional faulting, and responsible for activating diapirism lA, with local translocation of incompetent salt-rich strata of the Callanna Beds. Pn interesting comparison can be made with the Damara Orogen of southwest Africa, where a thick sequence of late Precambrian glacials (Chuos Formation) is succeeded by large thicknesses of turbidites and volcanics (Khomas S u b g r o u p , 7 7 5 Ma) which apparently underwent polycyclic deformation and metamorphism starting at about 750 Ma 16. In the local province, the formation of an extensive starved basin (Tapley Hill Formation), which was initially euxinic (Tindelpina Shale Member), heralded the start of the next tectono-sedimentary cycle. Sedimentation was below storm wave base. The related phase of compressive tectonism lead to broad upwarping of localised parts of the basin, with shallow-water carbonates (Brighton Limestone and equivalents 17) deposited on the highs. Diapirism was reactivated 14 in the cores of developing folds. The rocks of the greater part of the Marinoan record progressive subsidence. This trend was early punctuated by several episodes of abrupt shallowing which may have resulted from eustatic lowering of sea level related to distant glaciations. Cycles of shallowing in the mid-Marinoan almost certainly relate to glacio-eustatic phenomena, with deposition of arkosic outwash fans and complexes of multiple diamictites. The late Marinoan was characterised by a long interval of basinal sedimentation. The •molasse' phase of this cycle is represented by the ABC Range Quartzite, with tidally deposited sands and red silts. Its thickest developments were in troughs localised in the present region of the southern Flinders Ranges and probably parts of the Adelaide Hills; an extensive apron covered much of the Stuart Shelf. Abrupt transgression or subsidence with widespread deposition of laminated silts (Bunyeroo Formation) in a starved basin characterised the start of the following cycle, which is principally represented by the rocks of the Ediacaran System 11>18. jhe history of repeated tectono-sedimentary cycles in the local Precambrian broadly parallels the polycyclic tectonic events evidenced in late Precambrian orogens extending the length of Africa and represented in parts of the Americas and Europe 19. These events evidently record collision orogenies between various plates during the closure of a major Precambrian seaway. The Cambrian of the Flinders Ranges 20 shows at least one tectonic cycle. The greater part of the Hawker Group and the equivalent portion of the Normanville Group in the south of the fold-belt constitute a 'pre-geosynclinal' episode. The Narina Greywacke needs restudy and could represent a basinal facies broadly equivalent to the Carrickalinga Head Formation. 'Molasse' phases include the Billy Creek Formation, Wirrealpa Limestone and Lake Frome Group, and equivalents of part of this sequence are present on Yorke Peninsula. The fossiliferous rocks on the north coast of Kangaroo Island 21 comprise a spectacular 'molasse' considered to have developed in response to the Kangarooian movement 20. Knowledge of facies within the sedimentary prism represented by the Kanmantoo Group is incomplete. The prism evidently includes several euxinic intervals and certainly contains

- 43 -

thick developments of classical turbidites (e.g. Balquidder and Petrel Cove Formations) which probably comprise parts of submarine fan complexes 22. Ttie flat-bedded and cross-bedded Middleton Sandstone seems to have been deposited in an energetic shelf environment and may represent the start of a 'molasse' phase; its deposition predated granite intrusion at 50A + 8 to A95 + 6 MB 23 and regional metamorphism. Uplift and development of nappe tectonics in various parts of the Damara belt occurred at ~ 5 2 0 - 500 Ma, and a strong thermal event with basement mobilization and formation of dome structures, together with emplacement of granites, spanned the time interval from 510 - 455 Ma 16. Qearly the tectonic event reflected in the 'Delamerian' orogeny also profoundly affected part of the crust of Africa. The traditional time-rock and lithostratigraphic divisions of the Adelaide fold-belt provide the primary basis for intraregional correlation and geological mapping. Their placement in respect of broader tectono-sedimentary cycles emphasizes fundamental similarities between the history of this geosyncline and tectonised belts of similar age on other continents, and offers a basis for coarse correlation. As the Marinoan sensu stricto comprises the greater part of one such cycle, we advocate its continued recognition as a time-rock division.

REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Jenkins, R.J.F., 1931. Trans. R. Soc. South Aust. 105: 179-194. Qoud, P. & Glaessner, M.F., 1982. Science 2rrT 783-792. Harland, W.B., Cox. A.V., Qewellyn, P.G., Pickton, C.A.G., Smith, A.G. & Walters, R., 1982. "A geologic time scale". (Cambridge University Press : Cambridge) x^i + 131 pp. Howchin, W., 1918. "The Geology of South Australia". (Government Printer: Adelaide) xvi + 543 pp. Mawson, D. & Sprigg, R.C., 1950. Aust. J. Sci. 13: 69-72. Sprigg, R.C., 1942. Trans R. Soc. South Aust. 66: 185-214. Thomson, B.P., 1966. Quart, geol. Notes, geol. Surv. 5. Aust. 20: 7-9. Thomson, B.P., Coats, R.P., Dalgarno, C.R., Forbes, B.G., Johnson, J.E. 4 Mirams, R.C., 1964. Quart, geol. Notes, geol. Surv. S. Aust. 9: 1-19. Preiss, W.V., 1982. Trans R. Soc. South Aust. 106: a-83. Hoiwitz, R.C. 1960. Eel. Geol. Helv. 53 : 211-263. Gostin, V.A. & Jenkins, R.J.F., 1983. Sixth Aust. Geol. Conv. Canberra 1983. Geol. Soc. Aust. Abstr. Ser. 9: 196-197. Von der Borch, C.C., Smit, R. & Grady, A.E., 1982. Bull. Am. Ass. Petrol. Geol. 66, 332-347. Jenkins, R.J.F., Ford, C.H. & Gehling, J.G., 1983. J. geol. Soc. Aust. 29:101-119. Preiss, W.V., Rutland, R.W.R., & Murrell, B., 19a. ^ H u n t e r D.R., (ed.) "Precambri^n of the Southern Hemisphere". (Elsevier : Amsterdam) pp.327-360 (and included references therein). Hsu, K.J., 1982. ^ Hsu, K.J. (ed.) "Mountain Building Processes". (Academic Press: London) pp.3-12. Kroner, A., 1982. Am. J. Sci. 282: 1471-1507. Preiss, W.V., 1973. J. geoTT Soc. Aust. 19: 501-532.

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18 19 20

22 23

Jenkins, R.J.F., 1983. Sixth Aust. Geol. Conv. Canberra 1983. Geol. Soc. Pust.flbstr.Ser. 9: 233-234. Jenkins, R.J.F., 1983. Geol. Mag, (in press). Daily, B., 1976. In Thomson, B.P., Daily, B., Coats, R.P. & Forbes, B.G. ~"Late Precambrian and Cambrian geology of the Adelaide 'Geosyncline' and Stuart Shelf, South Australia". 25th International Geol. Congress Excursion Guide No. 33A. (Progress Press: Canberra) pp.15 - 19. Daily, B., Milnes, A.R., Twidale, C.R. & Bourne, J.A., 1979. In Tyler, M.J., Twidale, C.R. & Ling, J.K. (eds) "Natural History of Kangaroo Island". (Royal Society of SOIJOT Australia: Adelaide) pp. 1-38. Flint, D.J., 1968. Trans. R. Soc. S. Aust. 102: 203-222. Milnes, A.R., Compston, W. & Daily, B., 1977. J. geol. Soc. Aust. 24:87-106 [dates cited from this work corrected to current decay constants].

~ 45 ~

FOSSIL PERIGLACIAL STRUCTURES IN THE CATTLE GRID MINE, MOUNT GUNSON D.G. Tonkin^ & G.E. Williams^ k S R Limited, A.M. & C. Division, P.O. Box 259, Glenside, S.A. 5065 ^BHP Exploration Department, G.P.O. Box 1818, Adelaide, S.A. 5001 The Cattle Grid copper mine on the central Stuart Shelf is situated on the Pernatty culmination, an inlier of the mid-Proterozoic(?) Pandurra Formation onlapped by formations of the late Proterozoic Umberatana and Wilpena groups. The Pandurra Formation comprises medium to very coarse grained, poorly sorted, cross-bedded, red lithic sandstone and minor mudstone lenses of probable braided stream origin. At the mine site the flat-lying Pandurra Formation is disconformably overlain by the Whyalla Sandstone, a sequence of medium to very coarse grained, moderately well sorted, quartzose sandstone displaying very large-scale cross-bedding. The Whyalla Sandstone is equivalent to the Marinoan glaciogenic rocks of the Adelaide Geosyncline (Preiss, 1979), and in view of its coarse, locally pebbly character, the occurrence of broad channel forms, and its unimodal palaeocurrent directions, is best interpreted as a glaciofluvial deposit (Williams, 1983). The Pandurra Formation is silicified to a depth of about 150 m on the Pernatty culmination; this silicification may be related to a palaeoweathering episode, possibly of Sturtian age. The Cattle Grid orebody is tabular-shaped, measuring 1,500 x 700 m in plan and averaging 4.5 m thick. Mineralization consists of fracture and interclast filling of copper sulphides in fractured bedrock and sedimentary breccia of the Pandurra Formation (Fig. la) at its contact with the overlying Whyalla Sandstone. The breccia profile at Cattle Grid, termed the Cattle Grid Breccia, comprises several transitional horizons. Typically, the uppermost horizon consists of irregular and biscuit-shaped angular fragments of quartzite (silicified Pandurra Formation) usually 2 to 10 cm across, randomly oriented in a sandy matrix similar in texture to the Whyalla Sandstone. The contact with the Whyalla Sandstone is indistinct in many places. This uppermost breccia grades downward into in situ brecciated Pandurra Formation with only a minor matrix of sandstone, in which a preferred orientation of clasts reflects the original bedding of the quartzite. In most places the in situ breccia is separated from underlying strongly jointed bedrock by a mudstone horizon 10 20 cm thick, within the Pandurra Formation. The mudstone usually shows internal disruption and appears to have acted as a horizontal slip plane or decollement surface. As the degree and extent of brecciation at Cattle Grid appears to control the grade of copper, the origin of the host breccia has economic significance. Brecciation clearly was related to the unconformity at the top of the Pandurra Formation, and several explanations for its origin were advanced, viz: brittle fracturing due to differential movement between the Pandurra Formation and the Whyalla Sandstone; hydraulic fracturing through shock loading of mineralizing pore fluids; minor local faulting; accumulation of scree or talus; preservation of a "normal" palaeo-weathering profile; and deposition of glacial debris. Preservation of a palaeoregolith was the most widely accepted explanation, although opinions differed as to whether normal weathering

- 46

alone could account for the breccias. The involvement of glacial processes was suspected before the discovery of Cattle Grid; D.J.CIappison and D.G. Tonkin suggested in 1967 that closed depressions in the Pandurra palaeosurface were sculptured by glacial activity, possibly during the Sturtian glaciation. The initial observation and interpretation of fossil periglacial forms was made by G.E. Williams following a visit to Cattle Grid in January 1981. In the southern face of the pit a wedge of fine clayey sandstone about 1 m long extended downward beneath the Whyalla Sandstone into the Cattle Grid Breccia (Fig. lb); the crudely bedded breccia was turned upward adjacent to the wedge. This structure was recognized as either an ice-wedge cast, which Washburn (1980, p. 115) considers to be "among the few acceptable criteria for former permafrost", or a sandstone wedge such as form under more arid conditions in Antarctic dry valleys today. Several additional sandstone wedges were identified at that time and during a subsequent visit to the mine in February 1981. The recognition and interpretation of sandstone wedges was critical to the interpretation of a palaeopermafrost environment. The evidence from the other periglacial features present within the Cattle Grid Breccia, such as strongly brecciated rock, antiforms, reverse faults, and involutions (Fig. la, c-e) would be equivocal without the diagnostic presence of these wedges. However, once the wedges are accepted as periglacial in origin, the other features become supporting evidence which adds up to a coherent and convincing interpretation. Subsequently, M. Busbridge carried out a study of the Cattle Grid mine as part of Honors Degree research in 1981. Busbridge identified numerous sandstone wedges and other structures that could be attributed to a permafrost environment. Tonkin (1982) reviewed the structural features observed at Cattle Grid and the case for a palaeopermafrost origin.

Figure 1:

Structures within the Cattle Grid Breccia attributable to periglacial action.

Strongly brecciated Pandurra Formation, with copper (dark) as fracture and interclast filling.

sulphides

Sandstone wedge about 1 m long at contact between horizontally bedded Whyalla Sandstone and crudely bedded Cattle Grid Breccia. The bedding in the breccia is turned upward adjacent to the wedge.

Antiform in crudely bedded Cattle Grid Breccia, penetrated by a sandstone wedge.

Diagram showing an asymmetric antiform developed within the Cattle Grid Breccia and fractured Pandurra Formation, cut by a reverse fault.

Involution of sandstone and massive breccia within crudely bedded breccia and fractured quartzite.

- 47 -

FIG.1

- 48 -

Most of the sandstone wedges identified were about 1 m deep and comprised fine to medium grained sandstone with a texture very similar to the Whyalla Sandstone. They occurred in the top of the Cattle Grid Breccia immediately below the Whyalla Sandstone. The wedges typically showed a vertical lamination or fabric, indicating lateral accretion of the wedges rather than replacement of melted ice wedges. By comparison with modern periglacial structures, the wedges imply a strongly seasonal climate, with summer expansion and thaw and winter contraction of the upper part of the permafrost under harsh periglacial conditions, The preservation of the Cattle Grid Breccia was accomplished through its rapid burial by glaciofluvial outwash of the Whyalla Sandstone. The emerging palaeogeographic picture is of an ice sheet on the Shelf to the northwest of Mount Gunson, bordered by a periglacial belt containing permafrost and outwash sands in the vicinity of Cattle Grid, passing southeastward into a region of deltaic and glaciolacustrine deposition (Williams, 1983). REFERENCES BUSBRIDGE, M., 1981:

An analysis of the sedimentary host rocks to mineralization at the Cattlegrid orebody, Mt. Gunson. Honours Thesis, Univ. of Adelaide, November, 1981.

PREISS, W.V., 1979:

Adelaidean sedimentation: The Adelaide Geosyncline and Stuart Shelf. Dept. Mines Energy, S.Aust., Rep. Bk. 79/24.

TONKIN, D.G. 1982:

The Cattlegrid Breccia: A summary of observations and interpretations and the case for a palaeopermafrost origin. CSR Limited Exploration Group report EMR 129/82. Dept. Mines Energy, S.Aust., Envelope no. 3703.

WASHBURN, A.L., 1980:

Geocryology. A Survey of Periglacial Processes and Environments. Wiley, New York, 406 pp.

WILLIAMS, G.E. 1981:

Origin of the Cattlegrid copper deposit, Mt. Gunson, S.A. BHP Exploration Dept., Internal memorandum, February 1981.

WILLIAMS, G.E. 1983:

Cyclic lamination in the late Precambrian Elatina Formation and its palaeoclimatic significance. This volume, p.

- 49 -

THE SIGNIFICANCE OF HUMMOCKY CROSS-STRATIFICATION IN THE LATE PRECAMBRIAN BRACHINA SUBGROUP, HALLETT COVE, SOUTH AUSTRALIA.

I.A. Dyson

Delhi Petroleum Pty. Ltd., 33 King William Street, Adelaide, S.A.

The recognition of storms as an important sedimentation mechanism has increased markedly in the last few years. Storms transport sediment and generate sedimentary structures in rocks deposited in shallow subtidal to open shelf environments. A distinctive type of low angle cross-stratification, named hummocky cross-stratification by Harms and others (1975) in SEPM Short Course 2, is now recognised as a common sedimentary structure in many ancient storm deposits. The late Precambrian Brachina Subgroup is a sequence of shale, siltstone and sandstone which crops out in the Adelaide Geosyncline of South Australia. At the base of the sequence in the study area are interbedded shales and sandstones, interpreted as turbidites, with sole marks indicating flow to the southeast. Sandstones with hummocky cross-stratification (HCS) occur in the upper part of this turbidite sequence. Palaeocurrent directions obtained from the base of these sandstones are identical to those of the underlying turbidites. The HCS consists of very low angle (2-10 degrees) curved to undulating laminae in sets which can be convex-up or concave-up. It is the convex-up stratification that defines the hummocks. The laminae are parallel over the hummocks, but are slightly asymptotic with respect to the lower surface of the troughs. Sets range from about 2-20 cm thick, with wavelengths 1-5 m and amplitudes generally less than 50 cm. The dimensions of HCS increase with increasing bed thickness, sand content and grain size. The sandstones coarsen up section. They also increase in abundance and thickness upward. Higher in the section, interbedded mudstones are absent and the successive sandstones are amalgamated. In thin sandstone beds (<20 cm) only parallel lamination and no HCS occur. Occasionally, some of these beds are displayed as lenticular sandstones isolated within shale. The sharp bases of the sandstone beds are flat overlain by parallel lamination, gently undulating or deeply scoured. Oriented sole marks, typically flute marks and other scours, are common with occasional tool marks and gutter casts. The tops of the hummocky cross-stratification often show ripple cross-lamination. This is commonly of the near- syrametrical wave ripple type. Interference and flat-topped ripples also occur. Well developed parting lineation is displayed on bedding surfaces underlying the ripples. In plan view, the swales and hummocks are broadly circular. However, a few examples are observed where the swales and hummocks are elliptical. This elongation is approximately perpendicular to the interpreted palaeoshoreline. The crests of near- sjomnetrical wave ripples are oblique or parallel to the major axis of the ellipse.

- 50 -

The appearance of HCS suggests shallowing from a turbidity currentdominated environment to an environment at storm wave base. HCS sole marks are identical to turbidite sole marks, suggesting that deposition of HCS was influenced by the same palaeoslope. That is, they were emplaced by density currents and are the upslope equivalent of the turbidite facies. Once the turbidite was deposited, it was reworked into HCS by storm surges. The occurrence of wave ripples on top of many hummocky cross-stratified sandstones suggests that these beds were formed at or above storm wave base but below fairweather wave base. The absence of fair-weather current structures supports this interpretation. Also, the only wave ripples in the sequence lie directly above the HCS. It seems that parting lineation, frequently displayed on the bedding surface below wave ripples, is indicative of upper flow regime conditions and is transitional between the deposition of HCS and subsequent formation of wave ripples. HCS is therefore attributed to a flow greater than that needed to produce ripples. The observed HCS to parting lineation to wave ripple sequence indicates a decreasing flow rate during deposition. A rapid flow rate is also indicated by the erosional bases of HCS. Rapid deposition is indicated by the sharp bases of hummocky cross-stratified sandstones. The flat bases of many beds implies reworking of sand already on the bed. This interpretation is supported by the occurrence of thin sandstone lenses isolated within shale. The abundance of HCS and wave ripples suggests this was a wave-dominated environment. The elliptical nature of some HCS in plan view suggests that it was the result of two interfering processes; an unidirectional current emplaced the sand (a turbidite) which was modified by storm waves with crests oblique or parallel to the direction of the unidirectional current. The implication of turbidites overlain by HCS is that basinal depths have shallowed by sediment progradation and aggradation from below storm wave base (turbidites) to above storm wave base but below fairweather wave base (HCS). For the Brachina Subgroup at Hallett Cove, the environment of deposition is interpreted as a storm- dominated shallow marine area with a southeastward slope into a deeper turbidite basin.

- 51 -

SUBMARINE

CANYONS - WILPENA

GROUP

C.C. von der Borch and A.E. Grady School of Earth Sciences, The Flinders University of South Australia, Bedford Park, South Australia, 5042.

A series of major erosional incisions, i n f i l l e d by sediments of the Wonoka Formation, cut the progradational basin-slope facies sediments of the Brachina Formation, in the central and northern Flinders Ranges. These large incisions, measuring of the order of several kilometres in width and up to 1.8 kilometres deep, are interpreted to represent submarine canyons eroded by subaqueous processes which were dominated by catastrophic turbidity current flow. Canyon i n i t i a t i o n is considered to have been triggered by a relative fall in sealevel to a level below the pre-existing shelf edge. This allowed sands and gravels of fluvial origin to have direct access to a relatively steep basin slope. The series of east-west trending incisions, which is exposed in the Umberatana region of the northern Flinders Ranges, is interpreted to represent the western extremity of a tightly meandering gorge-like canyon, set on a north-facing palaeoslope. This canyon appears to have developed within the upper fan portion of the basin slope. Palaeocurrent vectors determined from measurements on flute casts at bases of turbidite sandstone beds within the canyon f i l l provide evidence for the meandering nature of this canyon system. The asymmetric occurrence of major diamictite units and thalweg channel sandstones, invariably biased towards north walls of the eastwest trending meanders, provides evidence that the high-ener^ turbidity currents that flowed down-canyon tended to behave in a "roller-coastering" fashion, preferentially seeking outer bends of pre-eroded meanders of the primary gorge,and thus emplacing diamictites (wall slumps) and levee sands along the locus of maximum flow energy. Recent research being carried out by other workers on modern deep sea fancanyon systems, particularly the Amazon and Mississippi Fans, demonstrates that the middle fan regions are characterized by highly sinuous channel-levee systems. This suggests that low density turbitity currents typical of mid-fan regions result in a geomorphic end product which closely resembles that of subareal fluvial meandering streams on low gradient coastal plains. Evidence for such meandering has not been discovered to date in sediments of the late Proterozoic canyon f i l l of the Wonoka Formation. However this implies that these ancient examples may have been developed on slopes steeper than those studied in the Amazon and Mississippi regions, and perhaps were in a more proximal situation with respect to the major basin slope and sediment source area. In such a case turbidity currents could be expected to have been more energetic, thus producing the observed roller-coastering phenomenon.

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THE EDIACARA MEMBER : A SHALLOWING UPWARD SUBMARINE FAN SEQUENCE, WITHIN THE POUND SUBGROUP J.G. GEHLING SOUTH AUSTRALIAN COLLEGE OF ADVANCED EDUCATION MAGILL The Ediacara Member of the ..ate Precambrian (Ediacaran) Pound Subgroup includes all fossils of the well known Ediacara assemblage. The Member, which occurs low in the Rawnsley Quartzite, is herein enlarged to include thick comformablti cycles of massive sandstones, siltstones, and fossil bearing thin to medium bedded sandstones, passing up into white crossbedded quartzites. This package of beds fills a significant erosional unconformity which, in the central Flinders Ranges, cuts down some 300 metres through the underlying shallow water sandstones of the Rawnsley Quartzite into the Bonney Sandstone. While the remainder of the Rawnsley Quartzite is demonstrably of shallow marine shelf origin, the Ediacara Member exhibits characteristics of mass flow and deposition below wave base. The palaeoenvironmental interpretation of Jenkins et al. (1983) was based on the upper part of the Ediacara Member from the western flank of the ranges. A systematic study of complete sections of the Pound Subgroup in the central Flinders Ranges has made the interpretation of the Ediacara Member as a barrier-lagoon tidal complex quite untenable. In the type section for the Ediacaran System at Bunyeroo Gorge (Jenkins, 1981), the Ediacara Member begins 85 metres above the base of the Rawnsley Quartzite. Pink and white sandstones with crossbedding and disrupted lamination are characteristic of the Rawnsley Quartzite both above and below the Ediacara Member. In Bunyeroo Gorge the Member is 60 metres thick, and consists of a sequence of siltstones, laminated fine sandstones, silty parted sandstones with fossil horizons and finally, crossbedded quartzites. The sharply erosional base can be followed south where it cuts down through the lower part of the Rawnsley Quartzite and bottoms in the Bonney Sandstone along the eastern wall of Wilpena Pound, where the sequence from the base of the Member to the highest fossil beds exceeds 300 metres. Equivalent thick sequences occur in the Chace, Druid and Elder Ranges and north of Brachina Gorge in the Heysen Range. An isopach map of the Ediacara Member suggests the filling of NW-SE trending valleys, incised into the underlying sediments. These 2-8 km wide valleys are similar in scale to modern submarine valleys described by Tilbary and Fraser (1981) from the Ceduna Terrace of South Australia. The southern margin of one of these Ediacaran valleys is best viewed just north of Rawnsley Bluff in Wilpena Pound. The valley fill sequence comprises basal massive channel fill sandstones locally packed with shale and sandstone clasts, massive amalgamated sandstones, khaki and maroon coloured siltstones and fine grained sandstones, passing up into wavy, silty parted sandstones and ending in white crossbedded quartzite. Massive sands in Chace Range sections often show dish structures, indicating dewatering. Climbing ripples occur near the top of metre thick beds. Thick sets of these sandstones pass laterally into thinly bedded turbidites in the south eastern sections, which are interpreted as distal, judging from palaeocurrent indicators. In the Elder Range and Wilpena Pound the massive sands lens into monotonously laminated, thick sequences of

- 53 -

siltstone. Where either the massive sands or well bedded sands sharply succeed thick silts, sandstone load structures are common, including detached balls from 1 to 10 metres in diameter. The foundering of sand into thixotropic silts suggests rapid deposition and insufficient opportunity for dewatering. Channel filling conglomeratic sandstones and the overlying amalgamated sets represent Walker's (1980) "resedimented coarse-clastic family". They were formed by sand dominated grain flow, as mid-fan channelized deposits. Laterally and vertically hemipelagic siltstones fill abandoned channels and interdistributary regions. Shallowing up to storm-wave base is marked by the passage into streaky sandstones and then lenticular to wavy bedded sandstones interleaved with siltstones. Here animals of the Ediacara assemblage were entombed,where they lived or had settled, by storm-surge sands. The bed surface distribution of fossils and the style of trace fossils suggest that these off-shore silty substrates were inhabited by benthic feeders. Bed forms suggest mantelling by sand and later reworking by waning storm waves. Sub-aqueous shrinkage cracks occur, but no sun desiccation cracks have been demonstrated. All sections through the Ediacara Member comprise at least the shelf sequence of white crossbedded sandstones which gradually succeed the coarsening upward cycle of siltstones and fossiliferous sandstones. In the thickest sections, the Member involves up to three incomplete cycles of this shallowing up sequence, above the submarine fan complex of proximal turbidite sandstones and pelagic siltstones. Previous studies (Jenkins et al., 1983 and W a d e , 1970) had largely been confined to measured sections where only the upper, subtidal shelf sequence was preserved on the valley shoulders. This upper part of the member, which includes the fossil horizons, represents the culmination of a major cycle of sedimentation. The Ediacara Member appears to be absent from sections of the Pound Subgroup examined in the north eastern Flinders Ranges. In these extremely thick sections, the only evidence of this major sedimentary event is a thin red clayey sandstone unit bearing desiccation cracks, occurring low in the Rawnsley Quartzite. While the Subgroup in this region has not been systematically studied, it seems that during the time of Ediacara Member deposition, this region was either exposed or subject to an erosional hiatus. Two possible explanations for the erosional event which interrupted Rawnsley sedimentation are presented: 1.

a rapid eustatic fall in sea level with consequent subaerial valley erosion into the shelf, followed by a rapid rise in sea level.

a subaqueous valley incision initiated by down faulting of the basin southeast of an arcuate hinge running NE-SW, parallel to the Druid and Chace Ranges.

In view of the growing evidence of synsedimentary tectonic events within the Adelaide Geosyncline, the latter, tectonic hypothesis must be considered more plausible.

- 54 -

The Ediacara Member represents the last of a nuitiber of major shallowing up cycles in the Wilpena Group. There is now increasing evidence of a more dynamic tectonic setting for the Adelaide Geosyncline, where sedimentation was not always in delicate balance with subsidence, as has previously been proposed.

REFERENCES Jenkins, R.J.F., 1981: The concept of an 'Ediacaran Period' and its stratigraphic significance in Australia. R. Soc. S. Aust., Trans., 105, 179-194. Jenkins, R.J.F., Ford, C.H. and Gehling, J.G., 1983 : The Ediacara Member of the Rawnsley Quartzite : the context of the Ediacara assemblage (late Precambrian, Flinders Ranges). Geol. Soc. Aust. J., 30, 101-119. Tilbury, L.A. and Eraser, A.R., 1981. Submarine valleys on the Ceduna Terrace off South Australia. Bureau Min. Res., J. Aust. Geol. Geophys., 6, 259-264. Wade, M. 1970 : The stratigraphic distribution of the Ediacara fauna in Australia. R. Soc. S. Aust., Trans., 94, 87-104. Walker, R.G., 1978 : Deep-water sandstone facies and ancient submarine fans : models for exploration for stratigraphic traps. Am. Assoc. Petrol. Geol. Bull., 62, 932-966.

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LOWER CAMBRIAN SYNDEPOSITIONAL TECTONICS AT WIRREALPA, S.A, P.G. Haslett BHP Minerals, Adelaide, S.A. At Wirrealpa, Cambrian-age sequences are exposed around an area of probable Call anna Bed equivalents and widespread breccias and megabreccias. This central zone of Proterozoic rocks has previously been considered to be of diapiric origin, having been intruded as a plastic breccia mass carrying blocks of Callannalithologies from depth to their present position. The contacts between the Cambrian sequences and the Adelaidean lithologies of the core are complex and variable. Detailed mapping has confirmed that a NW-SE trending breccia "limb" north of Old Wirrealpa Spring represents a narrow zone of active syndepositional tectonism in Lower Cambrian times. Across this "limb" major changes in sedimentary facies, thickness and diagenetic alteration can be demonstrated in time equivalent carbonate and clastic sequences in the Lower Cambrian. Sequences NE of the "limb" have generally been deposited in deeper water environments, are thicker, and show lateral facies changes from ill-sorted non-carbonate megabreccias adjacent to the "limb" passing gradationally into better sorted, more carbonate-rich and finer grained sequences distally. The equivalent age sequences to the SW of the "limb" are massive shallow water platform carbonates overlying poorly bedded clastic breccias. Extensive erosion and karst development has occurred in response to periodic uplift and exposure of this sequence prior to the middle Lower Cambrian. Many of the areas of breccia/megabreccia previously considered to be of intrusive diapiric origin can be shown to be of Cambrian age and of sedimentary origin. Clearly there has been significant uplift and exposure of Callanna-type sequences in the Lower Cambrian, particularly across relatively narrow hinge zones like the one referred to above. Repeated syndepositional movements have caused very complex facies relationships in nearby contemporaneous sediments, as well as complex structural relationships in underlying Cambrian breccias and older sequences. There is little evidence of substantial nearby exposure of Adelaidean sequences at Wirrealpa after the middle Lower Cambrian although minor pebble beds indicative of local instability are still present in the Middle Cambrian Billy Creek Formation. Thick lithic sandstones of the Narinna Greywacke at Wirrealpa also reflect more distal exposure of polymict sources in the general area in the Lower Cambrian. A precise understanding of the nature of the Cambrian syndepositional tectonism is difficult to achieve. As indicated above, diapirism has been postulated as one possible mechanism by which older sequences have been emplaced at the Cambrian depositional surface. High angle block faulting, with associated talus breccia deposition also bears consideration, as does Lower Cambrian low-angle thrusting.

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The Cambrian/Proterozoic contact relationships should be of considerable significance in any attempt to determine the nature of t h i s tectonism. The Delamerian folding and later f a u l t i n g , along with the generally poor exposure, has meant that a study of these contacts has not yet presented any clear-cut answer. Very l i t t l e d r i l l - h o l e data i s available to clearly determine the nature and orientation, at depth, of the contacts. Limited mapping carried out at t h i s stage within exposed areas of Call anna Bed sequences suggests that very s i g n i f i c a n t portions are generally intact, and present a folded and faulted but quite mappable entity. Hypotheses about the nature of the Cambrian syndepositional tectonism will need to take account of the apparent continuity and order of the Call anna sequences in proposing a mechanism for their emplacement at such high levels in the stratigraphy.

HYPOTHETICAL CROSS SECTION - WIRREALPA Triaggy

dark

mlcrltlc

limestones

(PARARA

LIHESTONEj

Datum i s the top of D a i l y ' s Faunal Assemblage 2.

FACIES CHANGES AND ARCHAEOCYATHID DISTRIBUTION IN EARLY CAMBRIAN CARBONATES, FLINDERS RANGES, SOUTH AUSTRALIA D.I. Gravestock South Australian Department of Mines and Energy, Adelaide SA The vertical and lateral distribution of species of Archaeocyatha are traced in the Wilkawillina Limestone at Wilkawillina Gorge, central Flinders Ranges, and in the Ajax Limestone, Mt. Scott Range, ih km northwest of the classic Ajax Mine locality. Only Faunal Assemblages I and II of Daily (1956) are considered; these however, contain 69 species of Archaeocyatha, most of them new. The study areas are restricted to the vicinity of the Wilkawillina Limestone type section (Daily, 1956), and a 5 km strike length in the central Mt. Scott Range. Archaeocyatha in Faunal Assemblage I became established as an Early Cambrian sea transgressed marginal-marine carbonates (ooid grainstones and packstones, fenestral mudstones, ?algal boundstones) at Wilkawillina Gorge. A similar transgression is presumed for dolomitized equivalents in the Mt. Scott Range. There, ooid grainstones and stromatolite boundstones are overlain by dolomitized bioclastic limestone in which few species can be determined. Many of the first Archaeocyatha at Wilkawillina Gorge are in growth position, frequently surrounded by Renalcis^ but elsewhere are fragmented. They are all rapidly overlain by unfossiliferous ooid grainstones, but most reappear on return to stable marine conditions. Not one of the first ik species occurs above Faunal Assemblage I. Faunal Assemblage II is divided into Lower and Upper parts based on the stratigraphic ranges of diagnostic archaeocyathan species (Gravestock, in press). At Wilkawillina Gorge, Lower and Upper Faunal Assemblage II occur in packstones and grainstones, frequently crossbedded, suggesting moderate to high-energy shallow marine environments. Species are moderately diverse and uniformly laterally distributed, most are found in all h measured stratigraphic sections. Upper Assemblage II is truncated by a widespread disconformity. In the Mt. Scott Range, Lower Assemblage II occurs in packstones (high species diversity, alga Epiphyton rare), wackestones (low-mod. species diversity, Epiphyton common) and mudstones (Archaeocyatha rare and reworked, Epiphyton absent, Chanoelloria and hyolithids common). Mapped facies associations suggest (where outcrop permits) that biostromal accumulations in moderate to high energy environments pass laterally and vertically into low energy, possibly deeper marine environments with Archaeocyatha in growth position but not in bioherms. Upper Assemblage II occurs principally in packstones (moderate species diversity) with subordinate wackestones (low species diversity, sparse occurrence). The uppermost wackestones are dominated by other small shelly fossils from which the Assemblage II-III boundary can be determined. There is no evidence of a disconformity. The facies dependance of archaeocyathid species distribution requires elucidation before an effective biostratigraphic zonation can be achieved.

- 58 -

Nevertheless, separation of Lower and Upper Faunal Assemblage II has been accomplished at species level with Archaeocyatha, and preliminary studies indicate that the succession of other shelly fossils (brachiopods, gastropods, tommotiids and others) changes at the chosen LowerUpper Assemblage II boundary. Where carbonate facies elsewhere are impoverished in Archaeocyatha, such shelly fossils (usually phosphatic or phosphatised) will aid biostratigraphic correlation. Correlation with Archaeocyatha-bearing carbonate sequences in the USSR is currently possible at generic level. Carbonate facies indicative of unrestricted shallow marine shelf environments are favoured to yield diagnostic genera with wide geographic distributions. REFERENCES DAILY, B., 1956: The Cambrian in South Australia; in El sistema Camhviooy su palaeogeographia y el-prohlemade su base. Rep. Internat. geol. Congr. 20th, Mexico 1956, 2, 91-1^7. GRAVESTOCK, D.I., 198U: Archaeocyatha from the lower parts of the Lower Cambrian carbonate sequence in South Australia. Mem. Ass. Australas. Palaeontols^ (in press).

MFTALLOGFNY OF THF ADFLAIDF GFOSYNCLINF STUART SHFLF COPPFR PRQVINCF Ian B. Lambert, T.H. Donnelly, J. Knutson, H. Ftminan Baas Becking Laboratory, Canberra, ACT. The Adelaide Geosyncline and Stuart Shelf contain late Proterozoic (Adelaidean) strata which accumulated on middle Proterozoic and older basement in four major cycles of predominantly shallow-water sedimentation. Basement rocks of various ages contain hydrothermal copper (uranium) mineralization. Late Proterozoic carbonaceous strata contain widespread, largely biogenic pyrite and local concentrations of isotopically similar Cu-Fe sulfides in all but the uppermost cycle. The copper minerals partly rim and/or replace pyrite in the relatively pristine mineralization on the Stuart Shelf. The mean 6 S values increase progressively with decreasing age of the Adelaidean units,a trend most readily interpreted in terms of deposition in intracratonic basins with restricted or no access to ocean water. Alternatively, these may have been major global tectonic processes which resulted in very major 34s-enrichment of ocean water during the late Proterozoic. The most likely metal sources for the Adelaidean mineralization are metal-enriched basement rocks, basal clastics and basic igneous rocks, and it is envisaged that these were leached by brines which ascended via permeable strata and structures to deposit their metals at moderately low temperatures in anoxic sedimentary environments. Copper introducrion or remobilization continued after early diagenesis in most cases, and there are some examples of totally epigenetic deposits. Sulfide-carbonate veinlets are particularly common in the copper deposits of the Geosyncline and these appear to have formed from their host strata both by sediment dewatering and low-grade metamorphic processes. The potential for major buried copper mineralization in the Adelaidean strata is indicated by the widespread occurrence of generally small copper deposits, and by age and lithological similarities with the African Copperbelt. The largest deposits are most likely to be found in the Adelaide Geosyncline near basement palaeohighs, in sequences of pyritic, carbonaceous siltstones, red beds and stromatolitic and evaporitic strata. There is obviously also good potential for additional important hydrothermal copper (uranium, gold, RFF) mineralization in the basement rocks of this province, most likely near major ancient fault systems, in rocks that have been subjected to Fe-, Si, K-, CO3- metasomatism. The chances of there being major mineralization in the Adelaidean sequence of the Stuart

Shelf is considered to be relatively low. This assessment is based on the long period of weathering and erosion which occurred between the formation of the b a s a l clastics and basic v o l c a n i c s , and the earliest preserved reducing strata (Tapley H i l l Formation). During this period there is likely to have been considerable flushing of metals from the s y s t e m . It is noteworthy, that deposits of different ages in this province lie on lineaments p a r a l l e l to the Torrens Hinge Zone, as exemplified by WallarooM o o n t a , M y a l l C r e e k , Mount Gunson and Roxby Downs on the Stuart S h e l f . This probably reflects the influence of major basement structures on the Adelaidean sequence.

ADEIAIDEAN SEDIMENTS OF IHE P I M E AND DENISON RANGES R.B. Flint South Australian Department Mines and Energy P.O. Box 151, Eastwood 5063 The Peake and Denison Ranges consist of four Precambrian inli^s surrounded by Palaeozoic and Mesozoic sediments of the Arckaringa and Eromanga Basins. Adelaidean sedimentation occurred in a northwesterly extension of the Adelaide Geosyncline, approxirrately midway between the Willouran Ranges and the southeastern Musgrave Block. A great thickness of dominantly paralic sediments were deposited in a steadily subsiding fault-bounded trough. Sequences represented include Callanna Group, Burra Group and Umberatana Group (Ambrose et al., 1981; Rutland et al., 1981). Initial rifting of the geosyncline resulted in deposition of the Callanna Group consisting of thin, basal conglomeratic sandstones and red mudstones, stromatolitic and oolitic dolomites, and basic volcanics (Cadlareena Volcanics). The latter unit is >750 m thick and consists dominantly amygdaloidal basalts and coarsergrained dolerites with minor pyroclastics. Igneous textures are preserved, however the volcanics have been extensively altered; present mineralogy being albitic plagioclase, orthoclase, chlorite, actinolite, epidote, calcite, hematite and quartz. Faulting and diapirism caused extensive disruption of the Callanna Group sequence above the Cadlareena Volcanics. The upper lithologies consist of thin-bedded sandstones (often^ with mudcracks, ripple-marks and halite casts on shale laminae), flaggy, buff dolomites, dolomitic siltstones, shales, sandstones and arkoses. Gypsum pseudomorphs, halite casts and cauliflower cherts are common. These cyclic, hypersaline sand-shale-carbonate sediments were deposited in a rifted, intracratonic basin (Rowlands et al., 1980) and their ijnmense thickness (min. 5500 m £ i ^ . 17 000 m) attests to considerable subsidence during deposition. Continued basinal subsidence and paralic sedimentation during the Torrensian period produced over 10 000 m of Burra Group sediments; a thicker and more arenaceous sequence than elsewhere in the geosyncline. Dominant rock types are orthoquartzites and sandy siltstones (with clay-galls and ripple-marks) of the Itoxmt M^garet Quartzite, and dolomites (conglomeratic and stromatolitic) and arenites of the Skillogalee Dolomite. Other lithologies include black cherts, magnesite conglomerates and microfossiliferous, stromatolitic dolomites. Sturtian-Marinoan sediments of the Umberatana Group disconform^ly overlie the Burra Group. The glacial Calthorinna Tillite consists of 650 m of diamictites (with striated erratics), conglomeratic dolomites, and arenites. A marine transgression followed the glacial phase with deposition of laminated silty shales and dolomitic siltstones (Tapley Hill Formation). The sequence is

capped by regressive marine carbonates which are overlain by reddish-brown to green siltstones and shales, sandstones and dolomites (Willochra Subgroup). Neither the upper boundary of the unit nor younger Adelaidean sediments are exposed. Diapirism has affected all Adelaidean units to form two styles of megabreccia: broad, irregularly shaped zones of disruption containing disorientated, rafted blocks of varying size and lithology within a carbonate matrix. Bedding within "tiie blocks is often highly contorted, and the blocks which include rafts of Ordovician monzonites-syenites can be up to several kilometres across. narrow bands of carbonate breccia intruded as sills, plugs or dykes along Delamerian faults and anticlinal hinge zones. AMBROSE, G.J., FLINT, R.B. and WEBB, A.W., 1981. Precambrian and Palaeozoic geology of the Peake and Denison Ranges. Bull, geol. Surv. S. Aust., 50. ROWLANDS, N.J., BLIGHT, P.G., JARVIS, D.M. and VON DER BORCH, C.C., 1980. Sabkha and playa environments in late Proterozoic grabens, Willouran Ranges, South Australia. J. geol. Soc. Aust., 27: 55-68. RUTLAND, R.W.R., PARKER, A.J., PITT, G.M., PREISS, W.V. and MURRELL, B., 1981. The Precambrian of South Australia. In: Hunter, D.R. (Ed). Precambrian of the Southern Hemisphere. Elsevier, Amsterdam, pp 309-360.

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LARGE SCALE S L U M P I N G IN THE U M B E R A T A N A G R O U P , W I L L Q U R A N

RANGES

R . P . Coats and R . D a l g a r n o D u r i n g r e g i o n a l m a p p i n g for the SA G e o l o g i c a l Survey in the 1960's one of u s , (RPC) n o t e d e x t e n s i v e e x a m p l e s of s e d i m e n t a r y b r e c c i a in large scale e r o s i o n a l scours at the base of the A m b e r o o n a F o r m a t i o n in the W i l l o u r a n R a n g e s . H e l i c o p t e r sampling for A n a c o n d a A u s t Inc. in 1 9 6 6 , t o g e t h e r w i t h field v i s i t s for SADME in 1980 gave o p p o r t u n i t y for rapid e x a m i n a t i o n and p h o t o g r a p h y by R . D . M a p p i n g for thesis p r e s e n t a t i o n by M u r r e l l ( 1 9 7 7 ) p r o v i d e d a record of a series of these slumps in a s t r u c t u r a l b a s i n near the i n t e r s e c t i o n of the B u n g a r i d e r and South Hill Faults. The U m b e r a t a n a G r o u p in the W i l l o u r a n R a n g e s is m a r k e d by u n c o n f o r m i t y r e p r e s e n t i n g early or p r e - S t u r t i a n fault b l o c k m o v e m e n t s on the series of s t r u c t u r e s p a r a l l e l i n g the N o r w e s t F a u l t . A n g u l a r t r u n c a t i o n of the Burra G r o u p by the S t u r t i a n g l a c i a l s o c c u r s locally a d j a c e n t to faults in the three s y n c l i n e s p r e s e r v e d b e t w e e n the South H i l l Fault and W i l l o u r a n Hill in the s o u t h e a s t corner of C U R D I M U R K A 1 : 2 5 0 , 0 0 0 sheet ( u n p u b ) . The p a l a e o g e o g r a p h y of the S t u r t i a n in the n o r t h e r n F l i n d e r s R a n g e s w o u l d imply both e a s t e r n and w e s t e r n sources for the S t u r t i a n g l a c i o c o m p l e x e s w i t h a deeper w a t e r facies d o m i n a n t in the axial trough of the C O P L E Y Sheet a r e a . T h u s in the e a s t e r n part of the W i l l o u r a n R a n g e s and e x t e n d i n g to M t . Burr a r e a , there is little true tillite due to a d o m i n a n c e of the W i l y e r p a F m . f a c i e s . The T a p l e y H i l l F o r m a t i o n in the W i l l o u r a n R a n g e area is m i l d l y transg r e s s i v e , p r o b a b l y r e f l e c t i n g rising sea level f o l l o w i n g m e l t i n g of the S t u r t i a n ice s h e e t s . L o c a l u n c o n f o r m i t y o c c u r s along the east flank of the W i l l o u r a n R a n g e from ' W i t c h e l i n a ' to north of B r e a d e n Hill w h e r e it is a s s o c i a t e d w i t h n u m e r o u s c o n g l o m e r a t e l e n s e s . The f o r m a t i o n is t y p i c a l l y finely laminated shale and s i l t s t o n e , c a l c a r e o u s and d a r k or b l a c k , w i t h thin laminated d o l o m i t e s in the lower p a r t . The o v e r l y i n g A m b e r o o n a F o r m a t i o n , w h i c h is s i m i l a r l y l a m i n a t e d , is g r e e n and g r e y - g r e e n in c o l o u r and it does not d e v e l o p a c a r b o n a c e o u s c h a r a c t e r . M a p p i n g d i f f i c u l t y b e t w e e n these f o r m a t i o n s in the n o r t h e r n F l i n d e r s R a n g e s r e f l e c t s the early p r o b l e m s in d e f i n i n g the S t u r t i a n M a r i n o a n b o u n d a r y in the a b s e n c e of the B r i g h t o n L i m e s t o n e e q u i v a l e n t w i t h i n the g e o s y n c l i n a l t r o u g h . The b r o a d zone of slumps in the A m b e r o o n a F o r m a t i o n of the W i l l o u r a n R a n g e s a p p e a r s to d i s p l a y only low angle d i s c o r d a n c e w i t h u n d e r l y i n g u n i t s . N o r t h w e s t of W e s t M o u n t Hut to b e y o n d M t . N o r ' W e s t on the w e s t e r n side of the W i l l o u r a n R a n g e s , the A m b e r o o n a F o r m a t i o n e r o d e s the T a p l e y H i l l F o r m a t i o n in a broad scour a p p r o x i m a t e l y 15km in w i d t h . L o c a l l y near M t N o r ' W e s t i t s e l f , the A m b e r o o n a Slump rests on the u p p e r part of the S t u r t i a n g l a c i a l s . D i r e c t i o n a l s t r u c t u r e s o b s e r v e d in this area indicate an e a s t e r l y t r e n d of slump t r a n s p o r t . The f e a t u r e r e s e m b l e s b r o a d slumps and scour f e a t u r e s on low angle slopes off the p r e s e n t delta area of the M i s s i s s i p p i . In the three s y n c l i n e s of M a r i n o a n p r e s e r v e d w i t h i n the W i l l o u r a n R a n g e s , ( v i z . a d j a c e n t to the South Hill F a u l t ; in the K i n g s t o n Dam synclinal s t r u c t u r e ; in the faulted r e p e t i t i o n to the n o r t h a l o n g M i r r a C r e e k ) m u l t i p l e slump units occur over several h u n d r e d m e t r e s v e r t i c a l l y in

the basal part, of the Amberoona Formation. Near the South Hill Fault some 5km south of Chintapanna Dam, six major debris slumps are recorded by Murrell (op. cit.) eroding to the level of the Tindelpina Shale Member of the Tapley Hill Fm. Beyond the Bungarider Fault only 4km farther east, near Kingston Dam, the Amberoona Slump comprises a major breccia unit, tens of metres in thickness, with blocks to metric size of Tindelpina Member, til lite and Burra Gp. carbonates. The deposits here 1ie on a base level of quartzites of the Burra Group (Bungarider Fm). Farther north beyond Kingston Dam along the west flank of the syncline there is slight angular discordance with further downcutting by the debris deposits which rest on progressively older units of the Burra Group. In the keel and along the northern flank of this Kingston Dam structure, parallel to Upper Wattle Creek, up to 20 individual debris deposits of the Amberoona Slump rest on a residual of basal Tapley Hill Fm and the Sturtian glacials. The latter have local high angle unconformity with the Burra Group adjacent to a diapiric body which invades the fault zone between this and the Mirra Creek syncline to the north. This structure has a similar high angle unconformity between the Sturtian glacials and the Burra Group adjacent to the fault which truncates its eastern limb. The most easterly record of disturbance in the Amberoona Formation is in the vicinity of North Well on the Willouran Creek (MARREE), and extending north and south some lOkms along strike. (Forbes, p e r s . c o m m . ) Evidence for such slope instability in the west near the Torrens Hinge Zone is afforded by disconformity between Amberoona Fm. and Sturtian til lite near Lake Pid1eeominna. The Amberoona slumps may thees have been triggered by seismic activity in unconsolidated sediments, generated by movements on the fundamental NW to N-S faults such as the Torrens Hinge Zone, Bungarider and East Willouran Faults. REFERENCE Murrell, B., 1977. Stratigraphy and tectonics across the Torrens Hinge Zone between Andamooka and Marree, South Australia. Univ. of Adel. PhD Thesis (unpublished).

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CYCLIC LAMINATION IN THE LATE PRECAMBRIAN ELATINA FORMATION AND ITS PALAEOCLIMATIC SIGNIFICANCE G . E . Williams

BHP Exploration Department, G.P.O. Box 1818, ADELAIDE, S.A. 5001

Cyclic lamination is conspicuous within a 10-m thick member of the late Precambrian Elatina Formation at Pichi Richi Pass in the southern Flinders Ranges. There the Elatina Formation comprises mainly red brown siltstones and fine sandstones with a total thickness of 30-60 m (Dalgarno et al., 1968; Preiss, 1979). The formation is interpreted as a distal, glacio1acustrine-deltaic sequence of western provenance deposited on a western 'shelf of the Adelaide Geosyncline during the Marinoan glaciation. Correlative glaciofluvial outwash deposits (Whyalla Sandstone) occur on the shelf 100-150 km northwest of Pichi Richi Pass; palaeocurrents in the Whyalla Sandstone are generally directed to the SE or SSE, suggesting the former presence of an ice sheet on the low-relief cratonic region to the northwest. A palaeogeographi c sketch-map of the region is shown in Figure 1. The cyclic lamination in the Elatina Formation is characterized by the regular repetition of dark red brown, clayey-hematitic bands spaced 216 mm apart that bound groups of paler, usually graded, silty to finesandy laminae. The clayey bands typically are 0.1-0.5 mm thick and the clastic laminae 0.1-2.5 mm thick. The lamination is essentially planar and laterally persistent over several hundreds of metres within the limits of outcrop. Examination of thin sections indicates that, on average, about 11 clastic laminae occur in each group or 'cycle' between successive clayey bands. The thickness of clastic laminae varies systematically within each cycle, attaining a maximum near the cycle centre. Moreover, through systematic variation in the thickness of such cycles, longer rhythms of 2, ca. 13 and ca. 26 cycles (representing, respectively, means of ca. 22, 145 and 290 clastic laminae) are evident. The clastic, usually graded laminae are best attributed to deposition by density (turbidity) currents in a proglacial or periglacial lake (Williams, 1981). The non-random variation in the thickness of such laminae and the envisaged environment of deposition together provide good evidence that the laminae record non-random spring or summer meltwater floods and are, therefore, annual deposits or 'varves'. The occurrence on the outwash plain of periglacial sand-wedge structures in the upper part of a Marinoan permafrost horizon (see Tonkin & Williams, this volume, and Fig. 1) similar to wedges that form through repeated seasonal expansion and contraction of the upper part of permafrost in modern periglacial regions provides independent evidence of a strongly seasonal Marinoan glacial climate in South Australia. The relative thinness of the varves in the Elatina Formation is explained by their deposition in a distal, relatively deep portion of an extensive (30+ km) lake situated some 150 km from the source of the glacial meltwaters (Fig. 1).

6 6

As the thickness of clastic varves at a particular site may vary with the relative warmth of summers, the regular variation in thickness of varves of the Elatina Formation suggests the cyclic waxing and waning of summer temperatures with a mean period near 11 years. It follows that the clayey bands bounding each cycle of ca, 11 summer laminae were deposited during the coldest portion of the climatic spectrum; they probably record a very severe winter every 11 or so years when the distal, deepest portions of the lake froze over. By the above interpretation of the lamination, the Elatina Formation records strong climatic periods of ca. 11 , 22, 145 and 290 years. It is intriguing that the 11- and 22-year rhythms equate with modern sunspot periods, and the ca. 145- and 290-year cycles with solar and climatic periods for the past several millennia as indicated by tree-ring studies (Williams, 1981, 1983). The evidence strongly suggests, therefore, that solar activity similar to that of today existed at least ca. 680 m.y. ago and markedly influenced the glacial climate in South Australia at that time. Such great stability of the solar activity cycle is consistent with modern solar and stellar theory. Ancient annually-layered rocks therefore should be seen as potential solar observatories that may provide valuable information to solar physics and solar terrestrial science.

References DALGARNO, C.R., JOHNSON, J.E., FORBES, B.G. & THOMSON, B.P., 1968: Port Augusta 1:250,000 Geol. Map Sheet, Geol. Surv. S. Aust., Adelaide. PREISS, W.V., 1979: and Stuart Shelf.

Adelaidean sedimentation: The Adelaide Geosyncline Dept. Mines Energy, S.Aust., Rep. Bk. 79/24.

TONKIN, D.G. & WILLIAMS, G.E., 1983: Fossil periglacial structures in the Cattlegrid Mine, Mount Gunson. This volume, p. WILLIAMS, G.E., 1981: Sunspot periods in the late Precambrian glacial climate and solar-planetary relations. Nature, 291, 624-628. WILLIAMS, G.E., 1983: Precambrian varves and sunspot cycles. In Weather and Climate Responses to Solar Variations, Colorado Assoc. Univ. Press, Boulder, 519-533.

I39*E

I3«'E

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KILOMETRES

•30*S

ICE SHEET

STRUCTURES OUTWASHv PLAIN

DELTAS

VARVE CYCLES ' ^ i r A z i IN DISTAL LAKE

— 33*S

Figure 1: Palaeogeographic sketch-map of north-central South Australia during the Marinoan glaciation ca. 680 m.y. ago, showing: the approximate position of the ice sheet on the western, cratonic shelf; the outwash plain and generalized palaeocurrent directions for the glaciofluvial Whyalla Sandstone; the location of the periglacial permafrost structures at Mount Gunson; and the periglacial lake within which the Elatina Formation was deposited. The triangle marks the location of the varve cycles in Pichi Richi Pass.

EVIDENCE OF EVAPORITE MINERALS IN THE LATE PRECAMBRIAN BRACHINA SUBGROUP, HALLETT C O V E , SOUTH AUSTRALIA

I . A . Dyson

and C . C . von der Borch

^Delhi Petroleum P t y . L t d . , 33 King William Street, A d e l a i d e , S.A., 5000 School of Earth S c i e n c e s , Flinders University of South A u s t r a l i a , Sturt R o a d , Bedford P a r k , S.A. 5042 The former presence of evaporite minerals within the late Precambrian Brachina Subgroup, Hallett C o v e , is inferred from the identification of botryoidal quartz nodules which have formed by the replacement of early diagenetic sulphates. The Brachina Subgroup is a sequence of s h a l e , siltstone and sandstone which crops out in the Adelaide Geosyncline of South A u s t r a l i a . Storm-induced resedimentation processes are thought to have been responsible for much of the sedimentation in the study area at Hallett C o v e . Thick cross-bedded sandstones, occurring in the top half of the sequence, are host to the quartz n o d u l e s . A storm-induced sedimentary structure, swaley cross-stratification, is strongly associated with these s e d i m e n t s . The nodules are roughly circular in plan and are flattened parallel to b e d d i n g . They v a r y from about 0.5-1.5 cms in d i a m e t e r , with the lower surface more flattened. Internally, the nodules are composed of chalcedonic quartz which occur isolated or in aggregates. Isolated cryst a l s , infilled with chalcedonic q u a r t z , are equant or prismatic and display extensive boundary corrosion and length-slow optical character. Interfacial angles of some six sided euhedra are the same as those of gypsum crystals elongated parallel to the c crystallographic axis. Aggregates of chalcedonic quartz with a radial crystal habit also display corrosion effects and length-slow optical c h a r a c t e r . The chalcedonic quartz is interpreted as filling voids created by dissolution of sulphate c r y s t a l s . The presence of nodules parallel to bedding indicates that at least during d i a g e n e s i s , the sandstone was in the capillary zone above the water table where evaporative concentration and upward capillary draw would proceed simultaneously with greatest e f f i c i e n c y . This explains why nodule formation is restricted to sandy z o n e s . The better sorted the sandstone, the greater the density of n o d u l e s , suggesting original permeability was a major control on nodule growth s i t e s . The assemblage of primary and diagenetic structures we have observed indicates largely clastic deposition between wave base and strand line possibly in a marine setting. This environment was subject to brine concentration by e v a p o r a t i o n , to periodic e x p o s u r e , storm flooding, e r o s i o n , and transportation and deposition by storm waves and curre n t s . The evidence for intermittent exposure is flat pebble conglomerates and mud c r a c k s . The flat pebble conglomerates are mud-crack polygons ripped up by particularly strong currents and transported a short distance before d e p o s i t i o n . Evidence for current action is found in the cross-bedded sandstones. The occurrence of swaley crossstratification within the sequence has been interpreted as a stormi n d u c e d s t r u c t u r e f o r m e d a b o v e f a i r w e a t h e r w a v e b a s e ( D y s o n and o t h e r s , in prep.).

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As the shoreline prograded. the intertidal sandflat was left stranded in the supratidal zone, giving rise to a coastal sabkha. Beneath the sabkha surface, diagenetic growth of gypsum occurred within the porous tidal flat sandy sediments above the shallow groundwater table. References Dyson. I.A., von der Borch, C.C., and Gostin, V.A., in prep: Hummocky cross- stratification in the late Precambrian Brachina Subgroup at Hallett Cove, South Australia.

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EDIACARAN EXTENSIONAL FAULTS, MT. FROME R. Dalgarno Seltrust Mining Corporation, Adelaide Unconformity exposed along the east flank of the Mt. Frome Diapir has been mapped in outline but detailed stratigraphic and sedimentological studies should be pursued. The region presents an opportunity to study details of progressive unconformable onlap of the Ediacaran sequence from Black Oak Well in the south, continuously for 5 km to the north. The Wonoka Formation is overlapped with slight angular discordance by the Bonney Sandstone in two areas 1 km N and 3-4 km NNW of Black Oak Well. The total Precambrian sequence is locally reduced to less than 100 m thickness and shows considerable variation along strike. Basal conglomerates of the Bonney Sandstone resting on the diapir illustrate penecontemporaneous extensional faulting which is illustrated by the poster. Growth faults range in throw from a few metres to the order of 100 metres with bedding plane splays resulting in zero displacement within the overlying Cambrian limestone sequence. Alligned clasts within the breccia body below the unconformity are consistentwith either later viscous flow or penecontemporaneous decollement planes which would have permitted the low angle, rotational detachments of the cover. Pull-apart features observed are prograded by the Bonney Sandstone resulting in lenses of conglomerate which thicken into the faults and display ductile rollovers and flexural folds characteristic of growth structures. Some brittle deformation involves rupture of the basal conglomerate lenses by breccia. Detailed studies may reveal that this represents ductile piercement by a "mud diapir" following synsedimentary faulting.

PLAN VIEW SHOWING GROWTH FAULTS NEAR MT. FROME

N Cambrian iimtttone Bonnty Sondtton«

Scale

hlOCXX)

500 m (approx)

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STURTIAN AND CAMBRIAN GROWTH FAULTS, ORAPARINNA

DIAPIR

R. Dalgarno Seltrust Mining Corporation, Adelaide The O r a p a r i n n a D i a p i r is located c e n t r a l l y on the P A R A C H I L N A 1:250 000 Sheet A r e a and is a d o m a l c u l m i n a t i o n on a p r o m i n e n t s t r u c t u r a l trend e x t e n d i n g t h r o u g h B l i n m a n Dome and the O r a t u n g a D i a p i r and h a v i n g as its s o u t h e r n e x p r e s s i o n a small c i r c u l a r d i a p i r i c dome east of W i l p e n a P o u n d . The O r a p a r i n n a s t r u c t u r e is a s y m m e t r i c a l w i t h S t u r t i a n t i l l i t e ( H o l o w i l e n a I r o n s t o n e ) as the o l d e s t unit p r e s e n t on p a r t s of the e a s t e r n f l a n k , s t e e p l y d i p p i n g to the east or o v e r t u r n e d a d j a c e n t to the c o r e and w i t h late S t u r t i a n or e a r l i e s t M a r i n o a n h a v i n g similar r e l a t i o n s h i p s on the w e s t e r n l i m b . Dips farther away from the core (in the M a r i n o a n , E d i a c a r a n and C a m b r i a n s e q u e n c e s of the B r a c h i n a and M t . B i l l y C r e e k s ) m o d e r a t e to the order of 30 . I n t r u s i v e r e l a t i o n ships by b r e c c i a s of the core a f f e c t all s t r a t i g r a p h i c u n i t s of the S t u r t i a n and t h e r e is e v i d e n c e of at least three s i g n i f i c a n t s y n d e p o s i t i o n a l faults w h i c h i l l u s t r a t e p e r i o d i c g r o w t h of the structure d u r i n g late A d e l a i d e a n and C a m b r i a n t i m e . 1. 2. 3.

A p p e a l i n a F a u l t - a c t i v e during d e p o s i t o n of the T a p l e y H i l l F m . (Sturtian) E n o r a m a g r o w t h s t r u c t u r e s - Etina Fm ( S t u r t i a n - M a r i n o a n ) B u n k e r s F a u l t - s o u t h e r n b o u n d i n g fault of the E a r l y C a m b r i a n syndepositional graben.

The A p p e a l i n a F a u l t is located on the s o u t h w e s t m a r g i n of the O r a p a r i n n a D i a p i r w h e r e it e x t e n d s from the A p p e a l i n a Cu M i n e in a n o r t h e r l y dire c t i o n in the T a p l e y H i l l F o r m a t i o n . It is a d j a c e n t to the m a r g i n of the O r a p a r i n n a D i a p i r some 500 m e a s t e r l y of L i n k e ' s B a r y t e s w o r k i n g s . T r a c i n g the s t r u c t u r e n o r t h w a r d s , c o n g l o m e r a t i c u n i t s a p p e a r d o w n s e c t i o n w i t h i n c r e a s i n g f r e q u e n c y on the e a s t e r n (downthrown) side of the fault u n t i l c o n t a c t w i t h the s o u t h e r n m a r g i n of the d i a p i r is r e a c h e d . Here c o n g l o m e r a t e s up to 1 m in t h i c k n e s s w i t h small b o u l d e r s , p o s s i b l y rew o r k e d from the S t u r t i a n g l a c i a l s , a l t e r n a t e w i t h finely l a m i n a t e d g r a p h i t i c shales t y p i c a l of the T i n d e l p i n a S h a l e M e m b e r . It is i n f e r r e d that r e p e a t e d u p l i f t of the core r e s u l t e d in a p e n e c o n t e m p o r a n e o u s fault w h i c h gave rise to the r h y t h m i c a l t e r n a t i o n of slump c o n g l o m e r a t e s and l a m i n a t e d shale w h i c h are d e v e l o p e d t h r o u g h a p p r o x i m a t e l y 100 m of the section. M a r g i n a l u p t u r n i n g to v e r t i c a l dip at the b a s e of the s e q u e n c e and i r r e g u l a r i n t r u s i v e m a s s e s of c a r b o n a t e b r e c c i a s , t o g e t h e r w i t h s t o p e d b l o c k s of T a p l e y H i l l F o r m a t i o n w i t h i n the s o u t h w e s t c o r n e r of the diapir, a t t e s t to post S t u r t i a n i n t r u s i o n of the b r e c c i a s . A series of g r o w t h s t r u c t u r e s occur in the Etina F o r m a t i o n 1 - 4 km N W of the O r a p a r i n n a A s b e s t o s M i n e on the w e s t e r n flank of the E n o r a m a D i a p i r . O n l a p of s u c c e s s i v e c o n g l o m e r a t e b a n d s and b a s i n w a r d t h i c k e n i n g of shales and l i m e s t o n e s has p r o d u c e d the t y p i c a l d r a p e and o v e r s t e p p i n g e f f e c t a s s o c i a t e d w i t h s y n d e p o s i t i o n a l f a u l t s . The u p p e r m o s t c o n g l o m e r a t i c unit o v e r l a p s the f a u l t s in the n o r t h and rests u n c o n f o r m a b l y on the d i a p i r . T h i c k e n i n g a c r o s s the s t r u c t u r e s is of the o r d e r of 10 f o l d , from 50 m of c o n g l o m e r a t i c and sandy d o l o m i t e in the n o r t h to a p p r o x i m a t e l y 500 m of c o n g l o m e r a t e , c r o s s - b e d d e d s a n d s t o n e and sandy l i m e s t o n e i n t e r b e d d e d w i t h s h a l e s , w i t h i n a k i l o m e t r e to the s o u t h . P h a s e s of r e l a t i v e fault s t a b i l i t y are r e p r e s e n t e d by the shale

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Units, up to 50m thick, which are interbedded with conglomerates adjacent to the structures. Detail of the Bakker Creek area near the asbestos mine is recorded by Cann et al (1981) whose mapping indicates that breccias truncate the older part of the sequence. The above growth structures coincide with the margin of the diapir to the immediate northwest of the Bakker Creek area and they apparently represent rotational faults with decollement along the unconformity. The Bunkers Graben owes its origin to rise of the Oraparinna Diapir during Ediacaran and Early Cambrian which is indicated by local absence of the Rawnsley Quartzite and by the pattern of growth faults forming the Graben. Facies/thickness variations and the biostromal bank developed adjacent to the southern bounding fault indicate that subsidence on this structure occurred synchronously with deposition of the Hawker Group. Thickness variation for the Early Cambrian across the fault has not been measured in detail but is of the order of hundreds of metres. The Bunkers Fault itself extends from the Sturtian of the Loves Mine area near the Oraparinna Diapir easterly to the Billy Creek Formation but evidence for movement during deposition is restricted to the Early Cambrian. An interesting facet of sedimentation close to the fault is the presence in the uppermost unit of the carbonate bank (Edeowie Member) of relic layers of the order of 5cm with a fibrous radiating or coxcomb character interpreted as replaced evaporites. Halite casts and mud cracks occur in the overlying red shales of the Billy Creek Fm. The three structures described above record a history of periodic fault movement during sedimentation about the Oraparinna structure which extended over a period of some 250 million years. REFERENCES Cann J.H., Clark, I.F., Fanning, C.M., 1981: Geology of the Bakker Creek Walking Trail - Oraparinna.(SADME Plan 81-917). Dalgarno, C.R. & Johnson, J.E., 1968: Diapiric structures and Late Precambrian-Early Cambrian sedimentation in the Flinders Ranges, South Australia. Am. Assoc. Pet. Geol., Mem., 8, 301-14.

R«f«r«nce points (Cann ft Ai this volum«)

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MOUNT PAINTER BRECCIAS J.F. Drexel and R.B. Major South Australian Department of Mines and Energy The Mount Painter Block, in the northern Flinders Ranges of South Australia, is about 550 km north of Adelaide. The lower to middle Proterozoic Mount Painter Complex basement is composed of metasedimentary gneisses and schists (Radium Creek Metamorphics), granites and amphibolite dykes. The Complex was folded and metamorphosed prior to deposition of the upper Proterozoic Adelaidean System. The Complex and Adelaidean sediments were folded and metamorphosed by the Cambro-Ordovician Delamerian Orogeny (Thomson, 1969) and intruded by pegmatites (460 m.y.-Compston, 1966). Large volumes of breccia occur along a broad wedge-shaped northeasterly trending zone from Radium Ridge to Hematite Valley, a distance of 20 km. The breccias are of several types and origins. The most abundant are massive granitic breccias which resulted from pervasive fracturing of the crystalline basement by hydrothermal fluids. Included in this type are small irregular and discontinuous pods of clastic sediments and uranium-bearing hematitic layers and dykes that show both sedimentary and intrusive characteristics. Numerous linear and generally northeasterly trending fault breccias cut through the basement, and many merge into the margins of the massive granitic breccias. Potash metasomation affected the basement prior to and during the early phases of brecciation and has completely replaced the original rock in some areas. The best examples of potash metasomation are found within fault breccias where they merge with the massive granitic breccias. The faults were presumably fluid feeders to the massively brecciated areas. All varieties of breccia are found overlain or intruded quartz-hematite rocks of the Mount Gee unit.

Age of Brecciation Estimation of the age of massive brecciation is based on the following data: . the breccias, and particularly the included pods of fine to mediumgrained sediment, show no evidence of metamorphism by the Delamerian Orogeny which affected other rocks on and around the Mount Painter Block . a dyke-like body of hematitic breccia within granitic breccia contains clasts of pegmatite which has been equated to the 460 my Arkaroola Pegmatite (Lambert et al., 1982) . monazite from the hematitic breccia has been dated (U/ Pb method) at 440±50 my (Pidgeon, 1979) . samarskite from the hematitic breccia has been dated (U/Pb method) at 400±50 my (Kleeman, 1946).

The evidence indicates that the main phase of hydrothermal activity and brecciation probably occurred in the upper Ordoviclan. Relatively passive hematite-quartz-uraninite fluids were emplaced along more porous zones of the granitic breccias during and after their formation. The occurrence of a kaolinised palaeosurface on basement below the quartz-hematite Mount Gee unit on Mount Gee and Mount Painter suggests that a second period of hydrothermal-hot spring activity may have occurred as recently as the Tertiary, REFERENCES Compston, W., Crawford, A.R. and Bofinger, V.M., 1966. A radiometric estimate of the duration of sedimentation in the Adelaide Geosyncline, South Australia. J. geol. Soc. Aust., 13(l):229-276. Kleeman,

A.W., 1946. An age determination on samarskite Painter, South Australia. Trans. R. Soc. 70(1):175-177.

Lambert,

I.B., Drexel, J.F., Donnelly, T.H. and Knutson, J., Origin of breccias in the Mount Painter area, Australia. J. geol. Soc. Aust., 29:115-125.

Pidgeon,

R.T., 1979. Letter dated DM.601/74, Vol. 2 (unpub.)

October,

from Mount S. Aust.,

1982. South

S.A.D.M.E.,

1979.

Thomson, B.P., 1969. The Delamerian Orogeny. In; L.W. Parkin (Ed), Handbook of South Australian Geology, p.106-108. South Australian Geological Survey. STREITBERG

• PROSPECT

••••.A- ' ^ ^ ' M T WARD ^ ^

ST zc^r:

THE ARMCH/Vlffr+

f +

•»•

•

I C'

^ t—t

\ * - -J

BILLS FOLLY ^PROSPECT

— ^ t

Painter ^ m ^

M l t f ^ V A HEIGH^F

PRO^EC GUM^EE

PROSPECT

13^1'

ORDOVICIAN T T i y i m o u n t GEE u n i t : »Layered

quartz-hematite;

Geological boundary: hematite

breccia

Observed Approxinnate or inferred

MASSIVE GRANITIC BRECCIA: Breccias

of predomiriarytly

local

———

clasts

Gneissosity/Schistosity

"YOUNGER GRANITE SUITE ". Undifferentiated

microcUne-quartz

granitoid:

pegmatite

PROTEROZOIC

BASEMENT; Undifferentiated

granite of the

Faults and fault breccia

OLDER GRANITE SUITE"

and metasediments of the RADIUM CREEK METAMORPHICS

Uranium workings: X P4

Painter

X EP4

East Painter

-75-

30015'-

ORDOVICIAN breccias »nd Mt Gee unit ORbOVICIAN " younger granite suite" Late PROTEROZOIC strata of Adelaide Geosyncllne ¥ Ml ^ '

Middle PROTEROZOIC "Older granite Suite" Early-Middle PROTEROZOIC Radium Creek Metamorphics

Geological sketch map, Mount Painter Inlicr.

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MYLONITIZATION AND THE FORMATION OF THE ECONOMIC KYANITE/SILLIMANITE, KAOLINIZED SILLIMANITE AND BRITTLE MICA DEPOSITS NEAR WILLIAMSTOWN, SOUTH AUSTRALIA C.H.H. Conor Seltrust Mining Corporation, Adelaide Near Wi11iamstown, 55km north northeast of Adelaide, are unique aluminous deposits of kyanite, sillimanite, kaolinized sillimanite, brittle micas (muscovite, paragonite, margarite), and kaolinitic clay. These deposits are the only kyanite/si 11imanite deposits being mined in Australia. Williamstown is located on a major north northwesterly trending, transcontinental lineament. The lineament is coincident with an axis of maximum strain associated with which is the isograd containing some of the most intense Delamerian metamorphism and deformation. An inlier of Barossa Complex, pre-Adelaidean, metamorphic basement is part faulted and part folded upwards as an anticlinal core, and is onlapped by Burra Group, Aldgate Sandstone which grades upwards, through Skillogallee Dolomite equivalent into Woolshed Flat Shale. The western limit of the inlier is locus of an extensive tectonic zone which is considered to have been intensely deformed by phyllonitization, a process similar to mylonitization. Parts of the Woolshed Flat Shale, Aldgate Sandstone and Barossa Complex are affected. At least nine metamorphic/deformational stages are deduced which together have given rise to the economic aluminous deposits by shearinduced base leaching. The sequence of events is as follows : 00 0 D1 D2

D3 D4 D5

M6 D7

Barossa Complex Basement Adelaidean, Burra Group, sedimentation Regional Metamorphism, fine grained-graphitic-biotite-K-sparplagioclase-quartz schists, sedimentary layering retained. Coarse grained biotite-sillimanite-garnet-plagioclase-quartz schists and gneisses, sedimentary layering obliterated. Pegmat ites. Flaser kyanite-sillimanite-quartz gneisses. Subvertical and subhorizontal mesofolds. Anastomosing schistosity, sillimanite, muscovite, vermiculite. Steeply inclined mesofolds. Geniculate folding, steep northerly axes. SILLIMANITE ORE. Kyanite-quartz veins post-date. Loss of K and Na into parts of the Woolshed Flat Shale as pyritic albitites and microclinites. Hydro-thermal addition of water. Kaolinitization. Kaolinized sillimanite. KAOSIL ORE. Phyllonites (Muscovite shears, Ringenbergs 1975). Muscovite, paragonite, margarite, sillimanite, kyanite, corundum, rutile, quartz. Reverse faults. Kaolinite, talc, pyrite. WARREN REFRACTORY SHALE/BOND CLAY ORE. Phyllonites and fine grained Woolshed Flat Shale folded, geniculate to transposed isoclinal, subhorizontal axes.

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Reverse faults folded, gentle geniculate, subhorizontal axes.

From D2 onwards deformation/metamorphism is localised and related to shear, all elements except A1 are mobile (e.g. Na, K, Ga, Fe); loss results in formation of kyanite, sillimanite, kaolinite,; addition results in formation of brittle micas, albitite, microcUnites. The aluminous deposits are contained by a mass of coarse grained schists and gneisses along strike from and occupying the stratigraphic position of the lower Woolshed Flat Shale. Whether the deposits are derived from alteration of Barossa Complex rocks or the Adelaidean sediments is contentious.

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MIGMATITE FORMATION IN RELATION TO S T R U C T U R A L

HISTORY

OF THE P A L M E R A R E A : EVIDENCE FOR THE EARLY ONSET A N D LATER P E R S I S T E N C E OF PARTIAL MELT C O N D I T I O N S IN THE M T . LOFTY R A N G E S , SOUTH A U S T R A L I A . P . D . Fleming & A . J . R . White D e p a r t m e n t of Geology^ La Trobe University^ B u n d o o r a , V i c t o r i a , 3083 M i g m a t i t e s in the Palmer a r e a , located within the high grade core of the M t . Lofty Ranges m e t a m o r p h i c b e l t , are considered to have formed by partial melting of quartzofeldspathic schists and g n e i s s e s , rather than by m e t a m o r p h i c segregation as p r e v i o u s l y suggested (White, 1 9 6 6 a ) . Large and small-scale tectonic structures indicate that the Kanmantoo G r o u p rocks of the area have undergone three main d e f o r m a t i o n s , D , , Dj and D ^ . The structures have styles and o r i e n t a t i o n s that are similar to those of corresponding g e n e r a t i o n s of structures in a number of other areas of the eastern M t . Lofty Ranges (eg. Offler & F l e m i n g , 1968; M i l l s , 1973). D^ folds are g e n e r a l l y tight or isoclinal with penetrative axial plane s c h i s t o s i t y . D^ and D^ folds deform this s c h i s t o s i t y and b e d d i n g , producing c r e n u l a t i o n s , a n d , in the case of D ^ , an axial plane crenulation c l e a v a g e . D2 folds have axiai traces that c o m m o n l y trend n o r t h - n o r t h - w e s t . D^ folds o v e r p r i n t D^ s t r u c t u r e s and have axial traces that afe generally nortTi-west trending. The macroscopic structures b r o a d l y delineated in the Palmer area by White (1966b) are here considered to m a i n l y reflect Dj g e o m e t r y with local interference by D^ f o l d s . On a small-scale, migmatite veins show a variety of relationships to the tectonic s t r u c t u r e s . For e x a m p l e , some veins are tightly folded by f o l d s , and are cut by their axial plane schistosity; other veins cross-cut the s c h i s t o s i t y but are deformed by D folds; still others form parallel to the axial planes of D ^ f o l d s . It is concluded that m i g m a t i t e vein formation commenced before D , folding had s i g n i f i c a n t l y deformed the r o c k s , and that partial m e l t c o n d i t i o n s were maintained during and after D^^ and were still in force during and/or after D ^ . The early onset of partial melting is c o n s i s t e n t with previous evidence that thermal activity in the M t . Lofty Ranges m e t a m o r p h i c belt began before penetrative d e f o r m a t i o n (e.g. Fleming & O f f l e r , 1 9 6 8 ) . It perhaps reflects a

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continuation of the unusual thermal activity that has been suggested as having been important in the earliest stages of the tectonic and sedimentary history of the Adelaide Orogenic Belt (cf. von der Borch, 1980). The persistence of partial melt conditions to around D^ time contrasts with other areas away from the high grade core of the Ranges. In these D- was not accompanied by high grade metamorphism. One explanation is that this reflects the contraction of isotherms back towards the high grade core as Delamerian regional metamorphic activity waned. REFERENCES Pretectonic metamorphic FLEMING, P.D. and OFFLER, R., 1968: Lofty Ranges, South crystallization in the Mt Australia. Geo1. Mag.^ 10 5, 356-359. MILLS,

K.J., 1973: The structural geology of the Warren National Park and the western portion of the Mount Crawford State Forest, South Australia. R. Soc. S. Aust. , Trans. , 97 , 281-315.

OFFLER,

A synthesis of folding R. and FLEMING, P.D., 1968: and metamorphism in the Mt. Lofty Ranges, South Australia. Geol. Soc. A u s t J JL 15, 245-266.

VON DER BORCH, C.C., 1980: Evolution of Late Proterozoic to Early Proterozoic Adelaide foldbelt, Australia: comparisons with post-Permian rifts and passive margins. Tectgnophysics, 70, 115-134. WHITE, A.J.R., 1966a: Genesis of migmatites from the Palmer region of South Australia. Chem. Geol,, 1, 165-200. WHITE, A.J.R., 1966b: Petrology and structure of the Rathjen Palmer region. South Granitic Gneiss of the Australia. Geol, Soc. Aust.^ J., 13, 147-489.

STURTIAN SUBMARINE ESCARPMENT OR DELAMERIAN DECOLLEMENT? by Dy I.P. L.f. Youles Youies P.O. Box 172, Hahndorf, S.A. 5245 Coats, in the description of the Regional Geology of the Mount Painter Province, (Coats and Blissett, 1971), interpreted abrupt thinning of the Balcanoona Formation in the vicinity of Oodnaminta Hut as the result of a marine escarpment. Discordances are explained as basin directed slumps in the Yankaninna Siltstone Member which he considers laps on to the carbonates of the Balcanoona Formation along the line of the scarp. Also, "The submarine scarp subsequently formed the locus for fault movement which dislocated the overlying succession". An alternative interpretation is that the fault is a tectonic feature of the Delamerian Orogeny. In a photogeological interpretation, the author defined a complex fault pattern dominated by major thrusts or decollements within the Umberatana and Burra Groups. The 'escarpment' referred to is interpreted as a cross-fault, where the Balcanoona Formation has been piled up against the Yankaninna Siltstone Member by movement on the decollement within the Tapley Hill Formation. In detail, this decollement has vertical and horizontal components making an average dip parallel to bedding. The Balcanoona carbonates are horizontally thrust over the Tapley Hill Formation slates, which have been rotated to near vertical with dislocated blocks adjacent to the decollement plane. These and similar major thrusts occur in and at the contact zone of the Adelaidean sequence around the Mt. Painter basement block; they are thought by the author to be related to movement of that block southwestwards into the Adelaidean sequence during the Delamerian Orogeny, (Youles 1978). REFERENCES Coats, R.P. & Blissett, A.H. 1971 : Regional and Economic Geology of the Mt. Painter Province, S. Aust. Geol. Surv., Bull., 43. Youles, I.P. 1978 : Comparison of Olympic Dam copper-uranium deposit and Mt. Painter uranium deposits, S. Aust. Dept. Mines & Energy, Rep. Bk. 78/85.

^ t

TO: CHIEF GEOLOGIST

PROFORMA

REGIONAL GEOLOGY B R A N C H ADELAIDE GEOSYNCLINE M A N U A L

SADME, P.O. BOX 151,

R E C O R D OF SIGNIFICANT LOCALITIES

EASTWOOD. S.A.

G E N E R A L DESCRIPTION OF F E A T U R E :

LOCALITY: CO-ORDS:

1:250,000 SHEET:

CO-ORDS:

1:100,000 SHEET: AERIAL PHOTOGRAPH -

SHEET: PHOTO NOS:

SURVEY: H E L D BY: DESCRIPTION OF L O C A T I O N A N D A C C E S S : DETAILS: ORIGINATOR: ADDRESS: REFERENCE: S T R A T I G R A P H I C UNITS, ETC.:

P H O T O G R A P H OR S K E T C H - VIEW

° DIP

FACINGS

A F F I X PHOTO OR F I G U R E H E R E Features may include documented photos, maps, overlays or aerial views of type sections,

unconformities,

structures

notable

exposures.

Sedimentary

structures, contacts or typical and unusual lithologies, etc., photographs and location of cores, elc. The object is a concise tabulation and pictorial catalogue of the Adelaide Geosyncline,

its

synsedimentary

structures,

internal

unconformities

and

structures. Assistance from all interested in the geology of the province is invited

with the object of ultimate publication by the South Australian Division of the Geological Society of Australia.

N E G No.

TRANSPARENCY REF.

FILE