247 by James B. Jago1, James G. Gehling2, John R. Paterson3, Glenn A. Brock4 and Wenlong Zang5 Cambrian stratigraphy and biostratigraphy of the Flinders Ranges and the north coast of Kangaroo Island, South Australia 1 School of Natural and Built Environments, University of South Australia, Mawson Lakes, SA 5095, Australia. E-mail: [email protected] 2 South Australian Museum, North Terrace, Adelaide, SA 5000, Australia. E-mail: [email protected] 3 Division of Earth Sciences, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia. Email: [email protected] 4 Department of Biological Sciences, Macquarie University, NSW 2109, Australia. E-mail: [email protected] 5 Oroya Mining Ltd, Suite 3, 72 Canning Highway, Victoria Park, WA 6100, Australia. E-mail: [email protected] The lower Cambrian sediments of the Flinders unconformably on Neoproterozoic rocks, probably reflecting the Ranges, South Australia can be divided into three influence of the late Ediacaran Petermann Orogeny of Central Australia. Cambrian deposition was strongly influenced by regional sequence sets. They rest unconformably on the Ediacaran tectonism, starting with rifting and finishing with the 514–490 Ma succession. Sequence set C– 1 comprises lower clastic units Delamerian Orogeny. The following information is based on Zang et overlain by a carbonate dominated marine succession al., (2004, 2006). More detailed descriptions and interpretation of that shows marked lateral and vertical facies changes. individual stratigraphic units are found in Gravestock (1995). Figure Sequence sets C– 2 and C– 3 together comprise a largely 2 summarises the Cambrian stratigraphic relationships of the Arrowie and Stansbury basins. The Cambrian of the N coast of Kangaroo Island clastic dominated succession of marginal marine to non- is treated separately. marine sediments with subordinate shallow marine carbonates. Sequence set C– 1 is richly fossiliferous at Cambrian succession in the Arrowie Basin some levels with biostratigraphy established for Gravestock (1995) divided the Cambrian of South Australia into trilobites, archaeocyaths, brachiopods, small shelly four sequence sets, C– 1, C– 2, C– 3 and C– 4. Set C– 4, from the Warburton fossils, acritarchs and molluscs. The Emu Bay Shale Basin, is not considered herein. The lowest Cambrian sequence,C– 1.0, Lagerstätte (Cambrian Series 2) from the north coast of Uratanna Formation, has limited outcrop in the northern Flinders Kangaroo Island occurs within a clastic-rich shelf Ranges. It comprises channel deposits overlain by prodeltaic and succession dominated by conglomerate and sandstone. deltaic siltstones and sandstones and was deposited in valleys cut into the Ediacaran Rawnsley Quartzite. Where the Uratanna The fossil content is dominated by trilobites in terms of Formation is absent, the Parachilna Formation disconformably overlies relative abundance and currently over 50 taxa are known the Rawnsley Quartzite (Gravestock, 1995); where both the Uratanna including, Anomalocaris, the bivalved arthropods Isoxys and the Parachilna Formations are missing, the younger Hawker Group and Tuzoia, the nektaspids Emucaris and Kangacaris, carbonates directly overlie the Ediacaran sediments. Mount and McDonald (1992) suggested that the change from the clastic the megacheiran Oestokerkus amongst a variety of other dominated Ediacaran, Uratanna and Parachilna successions indicated arthropods. Other common taxa include palaeoscolecid a decrease in clastic sediment supply due to drowning of source areas worms, Myoscolex, sponges, hyoliths, brachiopods, a in central and southern Australia. vetulicolian and several other enigmatic forms. The Sequence C– 1.1 (Parachilna Formation, Woodendinna Dolomite, oldest known well preserved complex arthropod eyes lower Wilkawillina Limestone) contains an unconformity that divides the sequence into subsequences C– 1.1A and C– 1.1B; the unconformity occur in this biota. does not extend beyond the shelf edge. The Parachilna Formation comprises transgressive upwards fining sandstones and siltstones with During the Cambrian, Australia was near the equator and in the minor carbonates. The basal sandstones are strongly bioturbated with tropical carbonate development zone (Brock et al., 2000, Jago et al., abundant Diplocraterion in places. The maximum of this initial 2006). In South Australia, Cambrian sediments occur in the Stansbury, Cambrian transgression was reached at the top of C– 1.1A Arrowie, Warburton and eastern Officer basins (Figure 1). In the (c. Tommotian) with deposition of the Woodendinna Dolomite that Stansbury and Arrowie basins, Cambrian sediments rest comprises oolitic, stromatolitic, dolomitic shale with desiccation Episodes Vol. 35, no. 1 248 Nepabunna Siltstone) that intertongue 135° 131° 133° 137° 139° 129° 141° with limestones of the Mernmerna Formation. MUSGRAVE PROVINCE Sequence C– 1.3 commences with the Marla WARBURTON Bunkers Sandstone, which in the Bunkers BASIN Oodnadatta Graben comprises up to 300 m of cross bedded, quartz sandstone, but elsewhere 28° it is mainly either quite thin or missing; EASTERN however, in the Donkey Bore Syncline, OFFICER Coober Pedy BASIN to the NE, it comprises deeper water basin floor fan deposits (Reilly and Lang, 2003). GAWLER The distinctive khaki Oraparinna Shale 30° represents a transgressive unit; in the Roxby Downs Leigh Creek BENAGERIE MS AN RIDGE eastern Nepabunna Trough the Oraparinna ARROWIE BASIN DB Shale intertongues with fine to medium STUART BG SHELF grained feldspathic sandstones of the Narina Greywacke (Gravestock, 1995). In DR 32° places, the Oraparinna Shale abuts reef CRATON Hawker Port Augusta complexes of the upper Wilkawillina Limestone (Clark, 1990). The dark silty 0 100 200 km ? limestones of the upper Mernmerna ? ? Formation comprise the main transgressive unit beyond the shelf edge. 34° The upper Wilkawillina Limestone and the Port Lincoln Yorke Peninsula Moorowie Formation both contain ADELAIDE archaeocyath-rich reef and biohermal Fleurieu Peninsula STANSBURY complexes. These include some of the EB BASIN earliest known corals (e.g., Fuller and NT Kangaroo Island 36° Qld ? Jenkins, 2007) and were deposited during ? ? WA ? the worldwide Botoman transgression SA (Gravestock and Shergold, 2001). NSW ? Concealed margins of Gawler Craton Above the Hawker Group in the Vic Flinders Ranges there is much less lateral Western margin of Stuart Shelf ? 38° and vertical lithological variation. Tas ? 204067-081 Sequence C– 2 was deposited during the world wide Toyonian regression Figure 1 Cambrian basins of South Australia (after Jago et al., 2006). AN, Angepena-Nepabunna (Gravestock and Shergold, 2001); it area; BG, Bunkers Graben; DB, Donkey Bore Syncline; DR, Druid Range; EB, Emu Bay; MS, comprises the dominantly iron-rich red Mt Scott Range. Billy Creek Formation deltaic sandstones cracks and halite casts plus abundant quartz sand horizons (Haslett, and siltstones (Moore, 1980) and the overlying shallow marine 1975). Sequence C– 1.1B commences with the lower Wilkawillina carbonates of the Wirrealpa Limestone (Youngs, 1977). In the Mt Limestone representing an Atdabanian shelf limestone that shows Scott Range area, the Aroona Creek Limestone is equivalent to the marked lateral facies changes and passes basinwards (eastwards) into Wirrealpa Limestone. the Wirrapowie Limestone which contains the oldest known Gravestock (1995) suggested that Sequence C– 3 comprises the archaeocyaths and trilobites in Australia. On shelf areas, the clastic dominated Lake Frome Group, although it could be argued Woodendinna Dolomite is overlain disconformably by the lower that sequences C– 2 and C– 3 are a single clastic dominated succession Wilkawillina Limestone; basinwards there is no corresponding break briefly interrupted by the Wirrealpa Limestone. The lowest within the Wirrapowie Limestone. member of the Lake Frome Group is the Moodlatana Formation that Sequences C– 1.1 and C– 1.2 are separated by the Flinders comprises marginal marine shale, siltstone (including evaporite casts Unconformity (James and Gravestock, 1990) with the lower and abundant trace fossils) and cross bedded sandstones with two or Wilkawillina Limestone disconformably overlain by either the middle three thin carbonate units near the top, one of which contains the Wilkawillina Limestone (platform carbonates) or the Mernmerna youngest known Cambrian trilobites in the Flinders Ranges. Formation (dark slope facies carbonates and calcareous siltstones). The conformably overlying Balcoracana Formation comprises a There are numerous lateral and vertical facies changes (Daily, shallow to marginal marine cyclic succession of shallowing upwards 1976). The limestone shows considerable thickness variations packages of red mudstones with abundant trilobite tracks that pass with 100–500 m in many sections, up to 800 m in the Bunkers up into thin horizons of stromatolitic carbonates. The Pantapinna Graben (Clark, 1990) and over 2,500 m in the Nepabunna Trough Sandstone comprises mainly planar to trough cross bedded fine to (Gravestock, 1995). In the northern Flinders Ranges, in the Angepena– medium grained sandstones with minor siltstone and shale; much of Nepabunna area, there are two siltstone units (Midwerta Shale, the Pantapinna is probably of marginal marine to fluvial origin, March 2012 249 although there is some open marine influence. The Grindstone Range reported the youngest known archaeocyath fauna in Australia