Oblique Rift System in Caswell Sub-basin, Browse Basin (NW Shelf, Australia): Insights from 3-D Seismic Interpretation and Structural Modeling

Wu, Long; Kluth, Charles F.; Trudgill, Bruce D.

The Caswell Sub-basin forms the northern part of the Browse Basin in Northwest shelf of Australia, holding considerable, but still unproduced hydrocarbon resources. Detailed structural analysis on three-dimensional (3-D) seismic surveys was performed and a 3-D geometry model is constructed to study the rifting system in Caswell Sub-basin.

An angular unconformity, formed in the Callovian as continental break-up occurred and significant regional block faulting took place along the NW Shelf of Australia, is the oldest and deepest horizon that could be well constrained and regionally mapped. This surface also serves as the boundary between pre-Callovian rift system and Late Jurassic to Cenozoic post-rift package. Three rifting features have been identified on this surface and in vertical sections: 1) A NE-SW-trending, NW-dipping border fault that defines the rift margin of the basin and reveals segmentation and variation along strike. The northeast section is featured by high topographic relief with a large single normal fault seated beneath; towards the southwest, the topographic relief gradually decreases and the linear feature is segmented and dimmed by 2). 2) A series of NEE-SWW-trending grabens and horsts sub-parallel to the border fault. These structures developed on the northwest side of border fault reveal left-stepping en echelon features and curve into the rift margin. 3) In the outer sub-basin, an E-W trending structural grain, 35-40° oblique to border fault, is represented by tilted rift blocks, bounded by north-dipping normal faults.

Integrated with 3-D normal fault linkage analysis and comparisons with physical modeling results, we suggest that these three features could fit into an oblique rifting model. In this model, the general rift axis is parallel to the NE-SW border fault whose orientation is mainly controlled by the underlying basement structural fabric; a N-S extension vector is indicated by the E-W trending structures which could be interpreted as major intra-rift fault segments; this is also supported by the group of left-stepping horsts and grabens that segments the rift margin and accommodates the lateral extension.

This study has implications for understanding the distribution, segmentation, and linkages of extensional fault system in Caswell Sub-basin, as well as other basins along the NW Shelf of Australia. In addition, it has potential impact on hydrocarbon exploration strategies in deep-water, data-sparse area of Browse basin.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013