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Regional Geohistory Of The Northern Carnarvon Basin: North West Shelf, Western Australia.

Kaiko, Alexander

Honours Degree, 1992

University of Adelaide

Abstract

The regional geohistory of the Northern Carnarvon Basin was derived from geohistory plots of 15 wells produced using the geohistory computer software package Bury 5.42.

The study area was divided into three sub-areas; the Dampier Sub-basin, the Barrow Sub-basin - Rankin Trend and the Southern Exmouth Plateau-Exmouth / Barrow Sub-basin. Four to six wells located on the major tectonic elements (shelf, trough, platform and plateau) representing a NW / SE transect across the area were used to determine the geohistories of the sub-areas.

Regional subsidence related to intracratonic sag in the Triassic had ceased along the eastern shelf by the Jurassic with the area becoming a relative high. Along the Rankin Trend regional subsidence was ended with the formation of an intrabasin arch at the end of the Triassic. Both these areas remained as highs until the Early Cretaceous when regional subsidence recommenced. The Northern Exmouth Plateau continued to subside until the Mid Jurassic before it also became a stable area. Rift related subsidence occurred in the troughs from the Early Cretaceous and continued until rifting was aborted in the Neocomian.

On the Southern Exmouth Plateau, a period of rapid subsidence occurred in the Early Cretaceous with deposition of Barrow Group sediments prior to onset of regional slow subsidence to Recent. From the end of Cretaceous time rapid dounwarp along the Exmouth Plateau and in the southern Barrow and Exmouth Sub-basins occurred which corresponds to Timor Sea subduction and isostatic subsidence of the Exmouth Plateau due to oceanic crustal cooling.

Within the Northern Carnarvon Basin, the source rocks that have been identified to be mature are the Locker Shale on the shelf and plateau, the Dingo Claystone in the trough areas. The Muderong Shale remains immature throughout the majority of the study area and only becomes early mature on the western margins of the Barrow Trough and Dampier Trough.

Along the shelf and shelf / trough margin maturity history analysis has modelled the Locker Shale as entering the maturity window in the Early Jurassic However, on the Exmouth Plateau it did not begin to be mature until the Early Cretaceous.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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