Basin Modelling and Geothermal Evolution of the Exmouth-North Carnarvon and Browse Basins, Australia: Insights from a New Integrated Crustal Scale Study

Abstract

Long offset (10 km), long record length (18 s) seismic reflection data acquired and processed during 2012–13 across the Australian NW Margin was interpreted in conjunction with reprocessed seismic refraction, standard seismic reflection, gravity, magnetic, well and IODP borehole data. Moho has been interpreted for the first time from the reflection data and comparisons made with estimates from refraction seismic data, gravity data and isostatic modelling. Whilst there is broad agreement in the results there can also be distinct differences, illustrated by the Browse Basin (BB) and Exmouth-North Carnarvon Basin (ENC). For example, isostatic modelling predicts a shallower Moho compared to the seismic observations in the BB, whilst they are in better agreement in the ENC. This difference is likely the result of interpretation uncertainty for the basement in the BB. In general though, crustal thickness in the ENC is predicted to be much thinner (~6–12 km) than the adjacent BB (~8–22 km), whereas sediment thickness is much greater in ENC (up to ~18 km) than BB (up to ~10 km). Despite these gross differences the well data shows that geothermal gradients across both basins are typical for a normal passive margin, generally around ~ 30°C/km, which requires traditional models for heat flux from the mantle, crust and sediment to be revisited. Radiogenic heat production from sediments and changes in thermal conductivity related to low-grade metamorphism seem to have more impact on heat flow in basins such as the ENC where highly attenuated crust provides a minor amount of heat input. In order to help explain the observed present day geothermal gradients and predict their evolution through geological time, the various data sets have been interpreted and compared to understand basin fill, architecture, seismic velocities and implied densities. Regional map-based and 3D basin models have been constructed, based on the integrated data sets, in order to predict the geothermal evolution of the area from the Permian to the present, incorporating deposition, lithology and compaction, uplift, erosion, paleobathymetry and paleoclimate. The resulting models have been calibrated to wells and provide a margin-scale tool for petroleum prediction.

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