Reverse structures in accommodation zone and early compartmentalization of extensional system, Laminaria High (NW shelf, Australia)

Abstract

The sediments dynamics and structural development associated with the Late Jurassic rifting phase represent the key factors on the accumulation of hydrocarbon in the Timor Sea. On the Laminaria High (Bonaparte Basin) the main Oxfordian–Kimmeridgian E–W fault system forms structural traps where several discoveries have been made. Recent 3D seismic analysis has been performed based on a combination of classic structural analysis, structure-sensitive seismic attributes (grid-based, surface-based, full-volume) and meta-attribute computations. The analysis has revealed secondary reverse structures associated with the main E–W fabric and prone to act as secondary hydrocarbon traps and/or as migration barriers. The main E–W fault system consists of a complex series of sub-parallel faults that connect via relay ramps or accommodation zones. One of these zones is associated with a transverse anticline resulting from the development of a positive flower structure. The model presented in this article and supported by the interpretation of the seismic data demonstrates that the flower structure developed in an extensional setting. The formation of such a reverse structure can be related to the propagation process of the main E–W fault plane which grows by addition of secondary en-echelon tip faults. Isopach analysis and displacement pattern suggest that a zone of differential displacement occurs between two segments of the main fault plane, inducing local strike-slip movements able to form transpressional uplift associated with restraining bend. This structure related to a rotation of the stress field compartmentalises the early development of the adjacent graben and then controls the distribution of the syn-rift Frigate Fm (Oxfordian–Kimmeridgian).