Gross Seismic Facies Mapping of the Cretaceous: Browse Basin, North West Shelf
Honours Degree 2010
University of Adelaide
Gross seismic facies mapping within a seismic stratigraphic framework has been conducted over the Cretaceous section of an extensive area of interest of the Browse Basin spanning the Caswell Subbasin and the northern extent of the Barcoo Sub-basin. Seismic facies were mapped over a coarse grid of 2D seismic lines tying key wells used in the study. Mapping was conducted between intervals defined by key seismic horizons provided by Woodside; KV_MAM, MAM_KA, KA_KC and KC_T. From this, an interpretation of the occurrence and distribution of lithofacies has been made by integrating seismic data and well data with the objective that they will be used as input parameters in thermal maturation basin modeling studies. Calibration of observed seismic facies with well data has revealed a good correlation between the two, both within intervals and between intervals. Additionally, seismic facies maps in conjunction with interpretative biostratigraphy data have been used to generate gross depositional environment maps within the defined area of interest.
Seismic facies mapping and the subsequent generation of gross lithology maps and gross palaeogeographical environment maps have revealed several changes through the evolution of the Browse Basin during the Cretaceous within the defined area of interest. During the Early Cretaceous, the basin was in a period of marine transgression and claystone deposition dominated. Extensive polygonal fault networks occur on shallowly dipping slope settings through the intervals KV_MAM, MAM_KA and KA_KC and are associated with claystone. Coarse grained sediments were restricted to the Yampi Shelf and Prudhoe Terrace. The KA sequence boundary marks the onset of increased carbonate deposition into the basin which continues through to the T sequence boundary. The system becomes more complex past the KC sequence boundary and the shelf morphology changes from a shallowly dipping ramp to a more defined shelf, slope basinal setting, interpreted to be a result of progradational wedges forming in response to increased sediment supply. Additionally, the strata above the KC sequence boundary become more sand prone. Seismic facies mapping of channels, ponded turbities and submarine fans illustrates mechanisms for sand deposition into basinal settings during lowstand events, where fluvial systems incised the underlying shelf and deposited unconfined submarine fans and ponded turbidites.