ABSTRACT: The Proterozoic Centralian Superbasin: A Frontier Petroleum Province

WALTER, M. R., J. J. VEEVERS, C. R. CALVER. K. GREY, and D. HILYARD, School of Earth Sciences, Macquarie University, Australia

In Neoproterozoic times 2 million sq km of Australia was occupied by a single depositional system, the Centralian Superbasin. This was disrupted 580-600Ma ago by a central uplift, and then dismembered by late Paleozoic tectonism to form numerous basins, including the Amadeus, Georgina, Ngalia, Officer and Savory. Recognition of the integrity of the original depositional system allows the stratigraphy of relatively well known areas to be extrapolated to predict that of those that are poorly known. Acritarch biostratigraphy and isotope chemostratigraphy, in conjunction with conventional lithostratigraphy and sequence analysis, allow a preliminary paleogeographic reconstruction.

Crustal sagging around 800Ma initiated the superbasin with deposition of hundreds of meters of marine and fluvial sands. These form a uniform sheet over much of the superbasin, wedging out against granitic basement in the northeast (Georgina Basin) and apparently thickening greatly in the west (Savory Basin). An overlying kilometer of marine and lacustrine carbonates, evaporites and fine siliciclastics completes the first major depositional sequence (1). Faulting during and after deposition of sequence 1 localized subsequent Sturtian glacigene sediments and overlying marine shales and carbonates (sequence 2).

Sequence 3 begins with renewed glacial sedimentation (Marinoan), perhaps about 600610Ma ago. This glaciation may have been global, and post-glacial transgression was extensive, depositing turbiditic and pelagic sands and shales over most of the superbasin. A carbonate-evaporite unit caps the sequence. In the latest Proterozoic marine sands and silts (sequence 4) were widespread, and continental flood basalts were erupted, following compression in the Officer Basin and southern Amadeus Basin. Sequence 5 (Cambrian) commences with more deposition of marine sands and silts, followed by carbonates and evaporites.

A significant gas show was discovered in the Proterozoic of the Amadeus Basin in 1963. This was shortly after the first major petroleum discoveries in the Neoproterozoic and Cambrian of the Siberian Platform, where subsequently at least 50 oil and gas fields and major discoveries including giants were proven in a succession closely comparable with that of the Cenhalian Superbasin. Comparison with prospects of similar age in Siberia, Oman and China suggests many plays, mostly untested. The Dingo gas discovered in sequence 4 of the Amadeus Basin may be the first to be developed in the Neoproterozoic of the Centralian Superbasin.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)