Authors / CoAuthors
Czarnota, K.
Abstract
This study was aimed at testing whether the regional tectonostratigraphic history established for Australia's premier hydrocarbon province, the North Carnarvon Basin, is applicable to the less well endowed, western Exmouth Sub-basin on its southern margin. This was achieved through the first systematic analysis of the structural architecture of the basin utilising 3D seismic and potential field data. Analysis focused on the Late Triassic to present basin history which highlighted some significant departures from the established tectonostratigraphic paradigm. The results indicate rifting occurred in two separate events. The first occurred under an east-west paleostress field and developed north striking faults controlled by Phanerozoic and Carbonifer to Permian pre-rift structures. This phase of basin development climaxed in the Callovian which resulted in the development of a significantly under filled basin and the deposition of anoxic petroleum source rocks. The first phase of rifting ceased in the Oxfordian and was followed by post-rift subsidence and later, previously unrecognised, Oxfordian to Tithonian south directed inversion localised above Proterozoic basement west-northwest oriented structures. This inversion event occurred under a detached stress filed which resulted in the formation of doubly plunging fault propagation anticline above south directed thrusts which terminated at a depth of 5-6 km. accompanied by contemporaneous extension along north to north-northeast striking fault segments in the upper most crust. Inversion ceased at the base of the Cretaceous and was followed by the second phase of rifting this time under west-northwest extension which resulted in rift fault system reorganisation and new normal fault growth. Rifting terminated at the onset of nearby Valanginian sea floor spreading. Post-rift thermal subsidence followed punctuated by variably directed periods of basin inversion over the last 130 Myrs. This long phase of inversion was enabled by an abnormally thick pre-rift lithosphere which took a long time to cool following rifting and hence could accommodated shortening over this long time span. A consideration of this thick lithosphere in hydrocarbon charge modelling in the Exmouth Sub-basin may lead to a change in the prevailing view that the main hydrocarbon charge occurred before the deposition of the regional seal, thereby making this apparently less well endowed basin more prospective for future exploration. A new understanding of the tectonstratigraphic evolution of the area has also highlighted new petroleum plays in previously un recognised structures some of which have been unaffected by Valanginian fresh water flushing and hence may contain non-biodegraded hydrocarbons.
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document
eCat Id
69704
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Keywords
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- GA PublicationProfessional Opinion
- ( Theme )
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- structural geology
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- AU-WA
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2009-01-01T00:00:00
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geoscientificInformation
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Professional Opinion 2009/15
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[-22.0, -21.0, 113.0, 114.0]
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