ABSTRACT: Gumprecht

Sasha Gumprecht
Department of Earth Sciences, Royal Holloway, University of London, Egham Hill, Egham TW20 0EX, U.K.

Tectono­-Stratigraphic Evolution of the Centaur 3D Survey, Exmouth Plateau, North West Shelf Australia

Global 3D Seismic Studies (GCSSEPM) (GRBCC, Room 310ABC)
Monday, September 21, 2015, 4:35 pm

This project illustrates the tectono-­stratigraphic evolution of the Exmouth Plateau, a deepwater sub­basin within the Northern Carnarvon Basin. The project was completed by fully interpreting the Centaur survey, a recently acquired 3D seismic dataset located in the northwestern part of the plateau. The investigation involved detailed qualitative and quantitative seismic analysis of structural and stratigraphic elements that were then assessed on their impact to the hydrocarbon potential of the area. The Centaur provided spectacular imaging of north-northeast and northeastern trending, highly-segmented. rift border faults that comprise the main graben­forming boundaries formed between the Late Triassic and Early Cretaceous, as a consequence of rifting of Greater India from Australia. The rifted fault blocks were affected by subsequent tectonic uplift associated with ridge push, then degradation, creating rounded eroded footwall block crests and redeposited hanging-wall block strata up to 50 m thick. Continued extension and displacement of the rift­border faults created long, obliquely-trending, intra­graben faults that intersected the rift­border faults’ hanging-wall blocks. Extensional fault­propagation folding helped create 1–3 km wide, asymmetric depocenter synclines in the hanging-wall blocks of the rift­border faults, while uplifting and rotating footwall block strata eastwards. Since the beginning of the passive margin phase in the Late Cretaceous, the plateau has been subjected to minor episodic fault reactivation, subsidence, and slumping, including Neogene inversion producing a localized anticlinal structure within the southern margin of the survey. The timing of formation is supported by mass­transport flows away from the uplifted area and onlapping of sediments onto the structural high.

Seismic facies analysis of the Triassic strata has shown a multitude of stratigraphic elements, including deltaic channel systems, sheeted sand bodies, igneous intrusions and hydrothermal vent complexes. Amplitude extractions have identified potential structural traps in tilted Triassic fault blocks, as well as potential stratigraphic traps in intra­Triassic channels and sandbodies.
Strong evidence suggests that the overall structural evolution of the rift­border faults was influenced by the reactivation of pre­existing Early Triassic structures. These include (1) existence of fault­propagation folding of Triassic rift­border faults, (2) along strike variations in geometry and orientation of rift faults, and (3) the appearance of faults propagating upwards obliquely through Lower Triassic strata. Unlike the traditional orthogonal extensional models of rifting that creates long, linear rift patterns, the structural geometry is comparable to offset or oblique rifting analog models; where the rift-­border faults are short, highly ­segmented and curved, containing long intra­graben faults that are formed perpendicular to the direction of extension to create numerous asymmetric hanging-wall block depocenters.

The results of the project suggest various structural and stratigraphic elements that provide varying levels of risk and reward in the Triassic prospective play targets for petroleum exploration. While the Triassic strata provide potential hydrocarbon targets, fault reactivation (since the mass­transport complexes of the Cretaceous and Tertiary) and fluid escape features (of the Top Triassic) pose a threat in the way of seal quality of trapped hydrocarbons and slope stability for drilling infrastructure.