ABSTRACT: Problems and Ambiguities of Thermal Maturity Modeling: Examples from Eastern Australian Sedimentary Basins

MIDDLETON, MICHAEL F., West Australian Geophysics and Environmental Research, Perth, Western Australia, Australia, and NIGEL J. RUSSELL, CSIRO Division of Exploration Geoscience, North Ryde (Sydney), New South Wales, Australia

Basin modeling software (BASINMOD {TM}) is used to illustrate some problems and ambiguities associated with thermal maturity modeling. Model sensitivity to various modeling options, e.g., linear vs. exponential compaction correction, steady state vs. transient heat flow calculation of paleotemperatures, heating duration at, or near, the maximum paleotemperature, etc., is discussed. Vitrinite depth/reflectance profiles are calculated using a Lawrence Livermore National Laboratory (LLNL)-derived kinetic modeling algorithm in preference to the Lopatin/Waples TTI method.

Examples are taken from coal and petroleum exploration boreholes in Permian-Triassic/Mesozoic rocks of the Bowen-Surat, Clarence-Moreton and Sydney-Gunnedah basins of Eastern Australia. In the Bowen-Surat basin, which is located some distance west of the eastern continental margin, our modeling addresses relative contributions of tectonic thickening (tilting, folding and overthrusting) associated with thin skinned thrust tectonics, local high-level Early Cretaceous igneous intrusive activity and the thickness of the Jurassic-Cretaceous (Surat basin) cover. In the eastern parts of the Clarence-Moreton and Sydney-Gunnedah Basins, which are located adjacent to the Late Cretaceous Tasman Sea seafloor spreading center, our modeling takes account of a possible heat flow anomaly associated w th thermal doming prior to rifting. Available apatite fission track analysis (AFTA) data are used to constrain our modeling.

While matching observed and calculated vitrinite depth/reflectance profiles does not provide unique solutions, it narrows down the range of possible solutions, many of which may be eliminated as geologically improbable. It also provides a means of testing the plausibility of unconventional solutions.

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