POST-RIFT TECTONIC SUBSIDENCE AND PALAEO-WATER DEPTHS IN THE NORTHERN CARNARVON BASIN, WESTERN AUSTRALIA

Abstract

The subsidence history of the Northern Carnarvon Basin has been dominated by simple thermal sag following the creation of the Exmouth, Barrow and Dampier Sub-basins by Early to Middle Jurassic rifting. This conclusion follows from the recognition of vitrinite reflectance suppression, which removes the need for recent heating events, and from the use of seismic stratigraphy, rather than only palynology and micro-palaeontology, to determine palaeo-water depths.

The simple thermal-sag model, related to Jurassic rifting, accounts for the post-rift sedimentary architecture of the Northern Carnarvon Basin, especially in areas of sediment starvation. It also has implications for the timing of hydrocarbon generation and the reconstruction of migration pathways. This work has re-emphasised the theoretical possibility of determining palaeo-water depths by adjusting one-dimensional basin models to fit simple thermal sag tectonic subsidence curves.

Miocene uplift, in the order of several hundred metres, has caused local basin inversion, accentuated some preexisting structures and re-activated some faults causing hydrocarbon remigration, but has otherwise not affected the thermal history of the sediments.