Sedimentological study of deltaic evolution using 3D seismic data

Category Sedimentology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Gracia-Garay, Claire; Weber, Philippe J.N.; Stampfli, Gerard M.
Holding Date 08 October 2008

Timor Sea is a province that extends over 2400km along the North West margin of Australia. The North West Shelf is a geographic term applying to the offshore and marginal basin areas. We focused our study on the Browse Basin that has a complex geodynamic history. This margin developed in the Carboniferous to Early Permian as a response to a north-northwest extension due to the separation of Sibumasu from Gondwana (Neotethys opening). It was followed by the Jurassic opening of the Argo abyssal plain. A new extension phase affected the area (Australia-Antarctica rifting), then local inversion took place in the Eocene related to the Argo mid-ocean ridge subduction under Indonesia, preceding the Indonesia-Australia collision. The Browse Basin has a Proterozoic basement that was uplifted during the Argo Abyssal Plain Rifting (Middle Jurassic) and hence has been strongly eroded, indeed the Palaeozoic to Triassic sequences are missing.
The initiation of seafloor spreading during the early Cretaceous induced a large scale thermal subsidence, marked by the Jurassic infill of the valleys. Our current understanding of sedimentological processes of the Browse Basin is based on geometrical structures observed on 2D and 3D seismic data (Cornea Area), acquired by the Australian Geological Survey, and the interpretation has been calibrated with well data provided by Shell. The interpretation of the complete sedimentary sequences allowed us to develop a sismo-stratigraphical model of the region. A detailed cartography of the erosional surface, located between the Jurassic and Cretaceous sequence of the Browse basin, shows the presence of a major paleorelief (500 to 800 m) related to the rift shoulder. Paleo-valleys and characteristic drainage patterns demonstrate the continental origin of this relief. The valley infill is likely made of continental deposits (sandstone) passing to fluvio-deltaic deposits (sandstone-claystone) to shallow marine (claystone-siltstone-sandstone) and open marine depositional environments. A 3D modelling of this infill of paleo-valleys as well as of deltaic fans, and their evolution in space and time was built up. This basin presents deltaic fans that may be potential hydrocarbon traps, due to organic-rich matter brought by the fluviatile networks. In this case, however the high-relief basement is partially to completely devoid of seal. The thin sealing unit and poor reservoir quality due to high porosity justifies the lack of hydrocarbon. However, the deltaic province in the Cornea Area includes some key features for the understanding of the sedimentological settings in the North-West Shelf of Australia.