Underappreciated Cenozoic Tectonism Along the Southern Australian Margin and Influences on Hydrocarbon Prospectivity

Abstract

Thermal history reconstruction (THR) principally incorporating apatite fission track analysis (AFTA) low temperature thermochronology combined with vitrinite reflectance data has revealed a number of episodes of Cenozoic tectonism involving km-scale burial and subsequent uplift and erosion along the southern Australian margin, from the Gippsland Basin in the east to the Eyre Sub-Basin in the west (no results are currently available from offshore wells west of Jerboa-1). The Cenozoic events constrained by THR in shelf areas of these offshore basins correlate closely with long-known unconformities in the outcropping stratigraphic section, and show a remarkable consistency in timing in areas separated by several 1000's of km. What is less appreciated, however, is that many of these unconformities mark the occurrence of former additional burial by km-scale additional section that was subsequently removed by uplift and erosion before deposition of the overlying preserved sequences. This evolution contrasts starkly with the conventional assumption based on their low-angle nature that these unconformities represent periods of little or no additional burial. Key Cenozoic events are recognised in the Late Miocene-Pliocene, Oligocene, Mid-Eocene and Paleocene. The magnitude and timing of these events have clear implications for trap formation and breach, cessation of hydrocarbon generation as a result of cooling due to uplift and erosion, and sediment supply to deep-water basins offshore. Examples include cooling as result of ~1.5 km of uplift and erosion beginning in the Eocene-Oligocene at Jerboa-1 in the Eyre Sub-basin and at Potoroo-1 in the Ceduna Sub-basin and at least 0.5 km of post-Early Eocene uplift and erosion at Echidna-1 in Duntroon Basin, areas bounding the deep water basins of the Great Australian Bight. One km or more of Eocene-Oligocene uplift and erosion has occurred in and around the Polda Trough offshore and extending to the Eyre Peninsula with similar amounts removed at this time across Kangaroo Island and the Fleurieu Peninsula. In the western Otway Basin, ~1.5 km of Late Paleocene to mid-Eocene uplift and erosion occurred at Morum-1 and numerous other wells along the offshore shelf with ~1 km of Late Miocene uplift and erosion at Nerita-1 in the eastern Otway Basin. Regional km-scale post-Early Eocene uplift and erosion characterises the onshore and offshore shelves in and around the Gippsland Basin.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015