Abstract Many Neoproterozoic successions contain viable hydrocarbon source rocks, even though they were deposited before most extant life forms evolved. Eukaryotic microalgae, bacteria, chlorophyte micoalgae, marine pelagophyte algae and dinoflagellates may have contributed organic matter. Major global-scale glaciations, which are commonly attributed to a ‘snowball’ or ‘slushball’ Earth scenario, or deposited under a ‘zipper rift’ scenario, are believed to have played an important role in the deposition of hydrocarbon source rocks during the mid- Neoproterozoic (Cryogenian). Phases of Cryogenian deglaciation may have culminated in the deposition of high total organic carbon shales and ‘cap carbonates’ in restricted anoxic basins, which may have been carved by ice sheets themselves or, alternatively, formed as restricted extensional half graben as Rodinia began to fragment. One example of these organically enriched deglacial sediments comprises shales and dolostones deposited following the Sturtian glaciation in the Centralian Superbasin of Australia, an amalgam of basins that extends almost continent-wide across Australia. Data from the Marmot MMDD-1 drill core on the Stuart Shelf in the southern part of the Centralian Superbasin, together with previously published data on organic enrichment in the Amadeus Basin in the central part of the Centralian Superbasin, suggest that the deposition of organically enriched shales was widespread during the Sturtian deglaciation.

Abstract The Bitter Springs Formation constitutes the upper part of Supersequence 1, an 830 Ma carbonate succession deposited in the intracratonic Centralian Superbasin. The Superbasin covered 2 million km 2 of the Australian continent during Neoproterozoic times. We have integrated new carbon, oxygen, sulfur, and strontium isotopic information, and new biomarker information, with existing results, to test and extend previous studies of the formation. The Gillen Member of the Bitter Springs Formation was deposited in a marine environment. The evidence for this interpretation includes isotopes of strontium, carbon, and sulfur, and biomarkers. 87 Sr/ 86 Sr ratios in the Gillen Member are comparable to the lowest ever recorded from the Shaler Supergroup of Canada, of similar age. These low strontium isotopic ratios are associated with comparable secular change in seawater δ 13 O carb . Steroidal hydrocarbon biomarker assemblages, seawater δ 34 S sulfate values, and low δ 34 S pyrite values further indicate a marine origin. The lower part of the Loves Creek Member (Units 1 and 2) was also deposited in a marine environment. Facies-independent secular change in seawater δ 13 O carb and low 87 Sr/ 86 Sr ratios are comparable to those in the upper Shaler Supergroup of Canada. Seawater δ 34 S sulfate , values, low δ 34 S pyrite , and evidence for algal biomarkers are also consistent with marine deposition. The upper part of the Loves Creek Member (Unit 3), and lower part of Unit 2, is nonmarine. Rare pyrite, heavy δ 34 S pyrite , abundant irregularly branched C 25 and C 30 isoprenoids from methanogens, and abundant pseudomorphs after halite indicate carbonate precipitation in sulfate-poor hypersaline lakes. Heavy and variable δ 13 S carb and δ 18 O indicate that continental groundwater brines, which were low in dissolved carbonate, drained into the lakes. Evaporation of the lake waters increased the concentration of dissolved carbonate, and increased still more the δ 18 O values, and may have had a small positive effect on δ 13 C carb . Dolomitization of the continental redbeds occurred by the evaporative reflux of groundwater. Cyanobacteria formed mats on the lake margins, where they were quickly silicified. Domical and irregular stromatolites formed within the lakes. The occasional presence of C 30 desmethyl steranes and 4-methylsteranes in the lower parts of Unit 3 indicates that either there were marine incursions or that marine algae were transported to the lakes, possibly by winds. Nonmarine Neoproterozoic algae may have synthesized these sterols.

Abstract Cryogenian correlation in Australia is based on an extensive data set from the Centralian Superbasin and Adelaide Rift Complex and integrates biostratigraphy and isotope chemostratigraphy to provide a three-dimensional interpretation based on outcrop and drill holes. Studies are ongoing, but newer data are consistent with the distributions discussed here. From the chemostratigraphic and biostratigraphic viewpoint, the first appearance of the acritarch Cerebrosphaera buickii , coupled with a large negative isotope excursion at c. 800 Ma, supported by the first appearance of the stromatolite Baicalia burra , seems to have potential for boundary placement. It is widely recognized across Australia and seems to have potential globally.

Abstract This review covers global uppermost Neoproterozoic–Cambrian petroleum systems using published information and the results of studies undertaken by the Geological Survey of Western Australia (GSWA) on the Neoproterozoic Officer Basin. Both production and hydrocarbon (HC) shows sourced from, and reservoired in, uppermost Neoproterozoic–Cambrian successions occur worldwide, and these provide ample incentive for continuing exploration for these older petroleum systems. However, the risks of charge volume, timing of generation–migration v. trap formation and preservation of accumulation are significantly higher than in conventional Phanerozoic petroleum systems. Therefore, the location and assessment of preserved HC accumulations in such old petroleum systems presents a significant exploration challenge. Organic-rich metamorphosed Proterozoic successions of SE Greenland, the Ukrainian Krivoy Roy Series, the Canadian Upper Huronian Series and the oil shales of the Russian Onega Basin are known as the world's oldest overmature petroleum source rocks. The oldest live oil has been recovered from the McArthur Basin of Australia ( c . 1.4 Ga; Ga is 10 9 years), followed by the Nonesuch oil of Michigan. Numerous other petroleum shows have been reported from Australia, Canada, China, India, Morocco, Mauritania, Mali, Oman, Pakistan, Venezuela and the USA. These demonstrate that generation and migration of Proterozoic petroleum has occurred worldwide. The Siberian Lena–Tunguska province, the Russian Volga–Ural region and the Middle Eastern south Oman petroleum fields exemplify the productive potential of uppermost Neoproterozoic–Cambrian successions, where petroleum generation, migration and trapping were either late in the geological history (Palaeozoic–Mesozoic, Oman) or where accumulations have been preserved beneath highly effective super-seals (Lena–Tunguska). The total resource potential of the Lena–Tunguska petroleum province is estimated to be 2000 Mbbl (million barrels) oil and 83 Tcf (trillion cubic feet) gas. The equivalent proven and probable reserves derived from Neoproterozoic–Early Cambrian source rocks and trapped in Late Neoproterozoic (Ediacaran), Palaeozoic and Mesozoic reservoirs in Oman are at least 12 bbbl (billion barrels) of oil and an undetermined volume of gas. The recovery of 12 Mcf (million cubic feet) of Precambrian gas from the Ooraminna-1 well in the Amadeus Basin in 1963, together with the occurrence of numerous HC shows within the Australian Centralian Superbasin, triggered the initial exploration for Proterozoic hydrocarbons in Australia. This included exploration in the Neoproterozoic Officer Basin, which is reviewed in this paper as a case study. Minor oil shows and numerous bitumen occurrences have been reported from the 24 petroleum exploration wells drilled in the Officer Basin to date, indicating the existence of a Neoproterozoic petroleum system. However, the potential of the Neoproterozoic petroleum system in the vast underexplored Officer Basin, with its sparse well control, remains unverified, but may be significant, as may that of many other ‘Infracambrian’ basins around the world.

Abstract The geological record of intraplate deformation in central Australia implies that past tectonic activity (basin formation, deformation and erosion) has modulated the response of the lithosphere during subsequent tectonic activity. In particular, there is a correspondence between the localization of deformation during intraplate orogeny and the presence of thick sedimentary successions in the preserved remnants of a formerly widespread intracratonic basin. This behaviour can be understood as a kind of ‘tectonic feedback’, effected by the long-term thermal and mechanical consequences of changes in the distribution of heat producing elements induced by earlier tectonism. From a geochemical point of view, one of the most dramatic effects of intraplate orogeny in central Australia has been the exposure, in the cores of the orogens, of deep crustal rocks largely depleted in the heat producing elements. The geochemical structuring of the crust associated with the erosion of the heat-producing upper crust resulted in long-term cooling of the deep crust and upper mantle with associated lithospheric strengthening. This is illustrated here by mapping the consequences of deformation and associated tectonic responses onto the h−q c plane, where h is the characteristic length-scale for heat production distribution, and q c is the total crustal heat production. Because rates of intraplate deformation in central Australia appear to be much slower than that typical of plate margin orogens, it is possible that the ongoing geochemical structuring of the crust has played an important role in terminating intraplate orogeny in central Australia by providing a ‘thermal lock’. The diagnostic geophysical signature of this lock may be the extraordinary gravity anomalies of the central Australian intraplate orogens.