Publication Name: The Sedimentary Basins of WA
Authors: R.P. Iasky, A.J. Mory, K.A. Blundell & K.A.R. Ghori
Publication Volume: 3
Date Published: December 2002
Number of Pages: 36
Reference Type: Book Section
Abstract:
The Peedamullah Shelf and adjacent Onslow Terrace, on the southeastern margin of the Northern Carnarvon Basin, are an established petroleum province containing the Tubridgi Gas field. Isotopic and molecular data indicate biodegradation of both oil and gas in the region. Geochemical analyses of oil samples in the area indicate a pre-Jurassic source, whereas the gas is probably sourced from the shallow Cretaceous section.During rifting episodes in the Carboniferous to Jurassic, the Flinders Fault System on the western margin and the
Sholl Fault on the northeast margin controlled the evolution of the area. In the Jurassic the Peedamullah Shelf remained elevated, while a thick succession was deposited to the northwest. During Late Jurassic to earliest Cretaceous rifting, a thin section of the Barrow Group delta onlapped older formations in the Onslow Terrace and adjacent parts of the Peedamullah Shel? After the Early Neocomian breakup of Gondwana, transgressive units of the marine Wmning Group were deposited with no detectable angularity over the Barrow Group. Late Cretaceous extensional faulting in the area is more subdued than to the west in the Barrow Subbasin. Mid-Miocene transpression reactivated major faults, producing economically attractive structures in the Barrow
Sub-basin and Onslow Terrace. However, the effects of this event are minor on the Peedamullah Shelf southeast of the Flinders Fault System.
The most prospective plays on the Peedamullah Shelf are pre-breakup unconformity fault or anticlinal traps of latest Jurassic or older age. Traps in which Palaeowic strata are truncated by the breakup unconformity and sealed by the Muderong Shale have not been extensively tested. Similarly, mid-Miocene anticlines, present largely within the Onslow Terrace, deserve further attention. It is also possible that oil has been displaced from the Onslow Terrace into other midMiocene anticlines on the Peedamullah Shelf.