Resolving lithostratigraphic complexities in the Crayfish Group, Otway Basin using chemostratigraphy
Betina Bendall A D , Anne Forbes B and Tony Hill CA South Australia Department for Energy and Mining (SA-DEM), GPO Box 320, Adelaide, SA 5001, Australia.
B Chemostrat Australia Pty Ltd, 1131 Hay Street, West Perth, WA 6005, Australia.
C Email: hilburt@bigpond.com
D Corresponding author. Email: Betina.Bendall@sa.gov.au
The APPEA Journal 61(2) 588-593 https://doi.org/10.1071/AJ20114
Accepted: 23 February 2021 Published: 2 July 2021
Abstract
The Otway Basin comprises a significant part of the eastern Australian Southern Rift System, a divergent passive continental margin formed during the Cretaceous separation of the Australian and Antarctic continents. Early rifting activity resulted in the development of many half grabens within the Otway Basin, which are largely infilled by sediments of the Casterton Formation and Crayfish Group. Despite over 20 years of exploration and hydrocarbon production from these units however, their lithostratigraphic characterisation and nomenclature remain ambiguous, with structural complexity and prevalent lateral facies changes leading to confusion in their basin-wide correlation. Deposited in a largely non-marine, fluvial/lacustrine environment, repeating cycles of sandstones and shales of the Crayfish Group can be difficult to resolve using petrology, palynology and wireline log data. The use of chemostratigraphy is favoured as an investigative tool in this situation since changes in provenance, lithic composition, facies, weathering and diagenesis are reflected in the mineralogy of the sediments, resulting in variations in their inorganic geochemistry. Uniform sedimentary successions can thus potentially be differentiated into unique sequences and packages based on their characteristic geochemistry, aiding in the resolution of complex structural relationships and facies changes. In this study, we present new inorganic geochemistry data for four key wells in the South Australian (SA) Penola Trough and interpret the geochemistry data consistent with, and building on, the chemostratigraphic schema of Forbes et al. to demonstrate its utility and robustness. We then undertake inter-well wireline log correlations across the SA Penola Trough using the wells with chemostratigraphic data as controls.
Keywords: Crayfish Group, Otway Basin, Penola Trough, Chemostratigraphy, Katnook Sandstone, Pretty Hill Formation, Sawpit Sandstone, McEachern Sandstone, hydrocarbon reservoirs.
Betina Bendall has a BSc (Hons) and PhD in geology from the School of Earth and Environmental Sciences at the University of Adelaide and a PGrad Dip in environmental management from Charles Sturt University. She currently holds the position of chief geoscientist in the Energy Resources Division in the South Australia Department for Energy and Mining and has previously worked in the minerals and geothermal industries in Australia and the petroleum industry in the United Arab Emirates. |
Anne Forbes has a BA (Hons) and MSc from the University of Cambridge in natural science and a PhD from the Open University in volcanology, where she studied the interaction of lava flows with ice and water. She joined Chemostrat Australia in January 2014 and has since undertaken chemostratigraphy studies in most of Australia’s principle petroleum producing basins. She is a member of PESA and the Geological Society of London. |
Tony Hill graduated with a BSc in applied geology from the Royal Melbourne Institute of Technology in 1980. From 1982 to 2020, he worked extensively in a number of petroleum basins across Australia and also worked in the fields of hydrogeology and geothermal energy within the South Australian Government. In 2021, he plans to work as a consultant. |
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