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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
2010. The American Association of Petroleum Geologists. All rights reserved.
DOI:10.1306/01051009120
Extensional
fault
segmentation and linkages, Bonaparte Basin, outer North West Shelf, Australia
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E. Frankowicz,1 K. R. McClay2
1Fault
Dynamics Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom; [email protected]
2Fault
Dynamics Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom
ABSTRACT
A detailed structural analysis of the Zone of Cooperation A-2 (ZOCA-2) three-dimensional (3-D) seismic survey on the outer northwestern edge of the Sahul Platform, northern Bonaparte Basin, outer North West Shelf, Australia, has identified three major populations of extensional faults. From oldest to youngest, these are (1) Jurassic north-south–trending extensional synrift faults, (2) Jurassic–Cretaceous east-west– to east-northeast–west-southwest–trending extensional faults, and (3) Neogene to present-day northeast-southwest–striking, right-stepping en-echelon faults. Seismic attribute analyses combined with fault
-displacement analyses have illustrated the initial segmentation of all of the
fault
systems and characterized both the horizontal and vertical linkages formed by soft-linkage relay structures.
The strongly segmented Neogene to present-day northeast-southwest–striking faults are interpreted to be a result of Neogene reactivation of underlying zones of weakness generated by preexisting east-northeast–trending Jurassic to Early Cretaceous faults. The Neogene to present-day northwest-southeast–directed extension was oblique to the underlying zones of weakness and thus formed characteristic strongly segmented en-echelon fault
arrays.
The Jurassic to Early Cretaceous extensional faults together with the overlying northeast-southwest–striking Neogene to present-day fault
systems form a pseudoconjugate
fault
system separated by a Cretaceous sequence that acted as a decoupling horizon. Within this Cretaceous interval, which is characterized by polygonal
fault
systems, vertically segmented, isolated, and overlapping extensional
fault
arrays form a zone of soft linkage between the underlying Jurassic to Early Cretaceous rift faults and the overlying Neogene to present-day
fault
systems.
This study shows that extension oblique to preexisting deeper fault
systems produces en-echelon segmented extensional faults in the overlying sequences. Such en-echelon segmentation does not indicate major strike-slip deformation. The results of this research have implications for understanding the distribution, segmentation, linkages, and ages of extensional faults in many other rift basins as well as for the northern Bonaparte Basin. In addition, the complex 3-D linkage patterns shown in this study have significant implications for understanding
trap
geometries and
fault
-seal characteristics in other extensionally faulted basins.
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