Publication Name: The Sedimentary Basins of WA
Authors: AGSO North West Shelf Study Group
Publication Volume: 1
Date Published: July 1994
Number of Pages: 28
Reference Type: Book Section
Abstract:
The Australian Geological Survey Organisation has recently acquired a unique grid of regional, deep-seismic data across all of the major structural elements of the North West Shelf. Interpretation of a set of 'dip' profiles across the northern Carnarvon, offshore Canning, Browse, and Bonaparte basins reveals that all the basins have been influenced by the same tectonic events, alttiough different elements have responded differently to the prevailing regional stress field.The critical events with respect to basin formation and development of their petroleum systems are interpreted
to have been in the Late Devonian-Early Carboniferous, mid-Carboniferous-Early Permian, and Late Triassic Early
Jurassic.
Approximately northeast-oriented upper and lower crustal extension in the Late Devonian-Early Carboniferous produced the intra-cratonic Fitzroy Trough and Petrel Sub-basin, which were linked by complex accommodation zones to both the southeast (Halls Creek Mobile Zone) and northwest ('North West Shelf Megashear'). Periodic reactivation of the North West Shelf Megashear has been critical in determining the fabric of the continental margin and the distribution of the petroleum systems. In the mid-Carboniferous to Early Permian, a major episode of extension and thinning, largely in the lower crust/upper mantle, commenced to the northwest of the megashear, giving rise to the Westralian Superbasin. The thinning is interpreted to have been on a north-northwesterly or northerly azimuth. An important consequence of the style and magnitude of thinning is that the North West Shelf sediments do not show characteristic syn-rift geometries, but are dominated mainly by sag-style deposits in the Permo-Triassic.
The major event with implications for petroleum generation and entrapment took place in the Late Triassic/Early Jurassic, and involved transpressional reactivation which created the mid- to Late Jurassic source rock depocentres, and uplifted adjacent blocks such as the Rankin Platform.