Comparison of the Crustal Scale Architecture and Basin Fill of the Exmouth-North Carnarvon Basin with the Browse Basin, Australia: New Insights from Deep Reflection and Refraction Seismic Data, Gravity and Magnetic Data

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. The integration of the data enabled a new understanding of the crustal architecture and basin fill, which varies dramatically along the margin. The Exmouth Plateau is characterized by a Moho typically at ~22–26 km, crustal thickness of ~6–12 km and a sediment thickness of ~16–18 km. The crust here is interpreted to be highly extended, thinned, and potentially intruded. The crust is overlain by Permian marine, carbonate and igneous lithologies which are likely to be deeply metamorphosed. The overlying Triassic-Jurassic section is a thick post-rift to syn-rift section characterised by major regressive and transgressive cycles. Multiphase extensional fault domains are generally decoupled from basement structures. The Cretaceous-Cenozoic section is a progradational marine mudstone and carbonate wedge developed during rift to drift transition. Break-up magmatism has locally caused dyke and sill injection, with jack-up structures. The outboard area is characterised by crustal blocks which failed to separate during Gondwana break-up. The inboard North Carnarvon area is characterised by much thicker Jurassic syn-rift, with evidence of older compressional faults being reactivated in extension, i.e. structural inheritance and basement control are more important. The Browse Basin is characterised by a Moho typically at ~20–24 km, crustal thickness of ~8–22 km and a sediment thickness of ~4–10 km. It is possible to identify deeper Paleozoic rift structures which are later reactivated both in transtensional and transpressional phases. While the stratigraphy of the Triassic section is similar in facies it is relatively thin in comparison with the Exmouth Plateau. Thicker sediment deposition occurred during the Jurassic, due to an increased sediment influx after a compressional ‘Fitzroy Event’ in Northern Australia. As with the area to the south, the Cretaceous-Cenozoic is dominated by a passive margin development of marine mudstone and carbonate wedges.

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