Publication Name: The Sedimentary Basins of WA
Authors: A. R. Yasin and R. P. Iasky
Publication Volume: 2
Date Published: December 1998
Number of Pages: 29
Reference Type: Book Section
Abstract:
Five main tectonic phases are recorded as unconformities in the ?Ordovician-Tertiary succession of the Peedamullah Shelf: Lower-Middle Devonian rifting, Upper Carboniferous rift rejuvenation, Upper Jurassic breakup movements, Neocomian and Lower Middle Miocene tectonism. The most significant events were Upper Jurassic breakup and Miocene tectonism: the former faulted and folded the ?OrdovicianJurassic succession; the latter enhanced anticlinal features such as the Thbridgi anticline.The shelf contains four terraces (Marilla, Onslow, Cane River, and Candace) bounded by north-northeasterly trending en echelon faults. The Onslow Terrace is located updip from the main Barrow Subbasin hydrocarbon accumulations, which lie along a northeastern trend. The Thbridgi Gas Field, on the Onslow Terrace, is the most southwestern hydrocarbon accumulation found along this trend. Two other northeasterly trends along the Cane River and Candace terraces could exist, with the former possibly extending into the Barrow Sub-basin.
Mesozoic source rocks in the Barrow sub-basin probably supplied hydrocarbons across the basin bounding faults into structurally higher Mesozoic, and older, reservoirs on the shelf. Lower Triassic and older strata on the shelf are generally mature and possibly contributed to the hydrocarbon accumulations. Possible traps in the Peedamullah Shelf include Lower Cretaceous sandstones within Miocene anticlines, truncation pinchouts below the Breakup. Unconformity sealed by the Muderong Shale, Triassic and older sandstones in fold and fault traps, negative topographic features at the base of the Locker Shale and Lyons Group, and ?reefs in the Devonian
carbonates.