Abstract Sedimentary features characteristic of ice-rafting are present in the Bunyeroo Formation (Wilpena Group) of the Adelaide Geosyncline and in the coeval Dey Dey Mudstone (Ungoolya Group) of the eastern Officer Basin (Figs 66.1 & 66.2), providing evidence of a mid-Ediacaran glacial climate in South Australia. The Acraman asteroid impact, a negative shift in marine δ 13 C, and a major acritarch turnover coincided with this frigid epoch.

Abstract The record of two Neoproterozoic glaciations in South Australia has been known for about a century. The earlier glaciation, of Sturtian age, is represented by the Yudnamutana Subgroup and is characterized by widespread diamictites with both intrabasinal and extrabasinal clasts, some locally faceted and striated. Associated facies include shallow-water sandstone, bedded and laminated siltstone with lonestones and dropstones, and sedimentary ironstones (mainly ferruginous siltstone and diamictite). Proximal settings adjacent to the Curnamona Province display massive basement-derived conglomerate and gigantic basement megaclasts (up to hundreds of metres across). Sturtian glaciogenic sediments of the Yudnamutana Subgroup unconformably overlie a variety of older rock units, including crystalline basement near basin margins and uppermost Burra Group sediments in the depocentre, and were deposited both in shallow marine shelf environments and in tectonically active rift basins encircling the Curnamona Province, with corresponding increases in total thickness from 100–300 m to more than 5 km. Recent U–Pb zircon SHRIMP dating of a thin volcaniclastic layer indicates that the waning stages of the Sturtian glaciation occurred at c. 660 Ma. Unlike the deposits of the younger Elatina glaciation, the Yudnamutana Subgroup has so far not yielded reliable palaeomagnetic data.

Abstract Deposits of the late Cryogenian Elatina glaciation constitute the Yerelina Subgroup in the Adelaide Geosyncline region, South Australia. They have a maximum thickness of c . 1500 m, cover 200 000 km 2 , and include the following facies: basal boulder diamictite with penetrative glaciotectonites affecting preglacial beds; widespread massive and stratified diamictites containing faceted and striated clasts, some derived from nearby emergent diapiric islands and others of extrabasinal provenance; laminated siltstone and mudstone with dropstones; tidalites and widespread glaciofluvial, deltaic to marine-shelf sandstones; a regolith of frost-shattered quartzite breccia up to 20 m thick that contains primary sand wedges 3+ m deep and other large-scale periglacial forms; and an aeolian sand sheet covering 25 000 km 2 and containing primary sand wedges near its base. These deposits mark a spectrum of settings ranging from permafrost regolith and periglacial aeolian on the cratonic platform (Stuart Shelf) in the present west, through glaciofluvial, marginal-marine and inner marine-shelf in the central parts of the Adelaide Geosyncline, to outer marine-shelf in sub-basins in the present SE and north. The Elatina glaciation has not been dated directly, and only maximum and minimum age limits of c . 640 and 580 Ma, respectively, are indicated. Palaeomagnetic data for red beds from the Elatina Formation (Fm.) and associated strata indicate deposition of the Yerelina Subgroup within 10° of the palaeoequator. The Yerelina Subgroup is unconformably to disconformably overlain by the dolomitic Nuccaleena Fm., which in most places is the lowest unit of the Wilpena Group and marks Early Ediacaran marine transgression. Supplementary material Photographs are available at http://www.geolsoc.org.uk/SUP18481 .

Abstract In mid-1979, a stratigraphic well drilled by the South Australian Department of Mines and Energy (SADME), Byilkaoora-1, encountered shows of aromatic-naphthenic and naphthenic oils while coring Cambrian carbonates in the northeastern Officer basin, South Australia. The oils occupy vugs and partly healed fractures in an alkaline playa-lake sequence of algal-plate dolomite mudstone, dolomite mudstone with Magadi-type chert, and organic-rich dolomitic argillaceous mudstone containing calcite pseudomorphs of sodium carbonate-bicarbonate minerals, notably trona and shortite. Oil-source-rock correlations confirm that the oils originated within those facies drilled. The Byilkaoora oils are thus the first reported examples of nonmarine Cambrian petroleum. They are unusually rich in the C 15 -C 25 and C 30 acyclic isoprenoid alkanes, except where severely biodegraded. Sterane and hopane distributions indicate that the oils were expelled from marginally mature source rocks. On the southeastern flank of the Officer basin, micritic carbonates deposited in a marine-sabkha environment are marginally mature to mature and have good oil-source potential, although minor staining is the only evidence of oil generation and migration in these rocks. The primary organic facies of the Officer basin carbonates determines whether they are oil or gas prone. Kerogen in the oil-prone carbonates is either Type I (deposited in an alkaline playa–lacustrine environment) or Type II (deposited in a marine-sabkha or lacustrine environment). Marine lagoonal carbonates contain gas-prone Type III kerogen derived from algal (including cyanobacterial) mucilage. Petrographically, the major components of the oil-prone kerogens are lamellar alginite and bituminite. Likely precursors include the lipids of cyanobacteria (blue-green algae) and various heterotrophic bacteria. The sesterterpanes and squalane present in high concentrations in the Byilkaoora oils and their source rocks may be biological markers of halophilic and/or methanogenic archaebacteria.