STRATIGRAPHIC MODELLING OF THE GIPPSLAND BASIN

Abstract

The Gippsland Basin is an asymmetric graben which initially formed during the break-up of Australia and Antarctica in the Early Cretaceous. During continental rifting the basin was filled by volcano-clastics of the Strzelecki Group. The overlying alluvial sediments of the Golden Beach Group represent a second phase of rift fill associated with the Tasman Sea rift. Following continental break-up in the Campanian, the Latrobe Group was deposited as a transgressive sequence of marine and coastal plain sediments. Thermal subsidence from the Oligocene to Recent was accompanied by the deposition of marine marls and limestones of the Lakes Entrance Formation and Gippsland Limestone.

A north-south cross-section through the basin, based on regional seismic data and nine exploration wells, has been used to study the tectonic, thermal and basin-fill history. A detailed basin subsidence history based on a crustal rifting model was constructed, constrained by stratigraphic data and palaeo-water depth estimates at well locations. The history of sedimentation was then modelled by a Shell proprietary package, using the subsidence history and published eustatic sea level variations. This numerical model is based on a forward time-stepping scheme using semi-empirical algorithms to define the facies deposited. The gross basin architecture of the Gippsland Basin is successfully reproduced by the model. In addition the model details the timing and extent of marine incursions in the Golden Beach Group and the eustatic control on facies patterns in the Latrobe Group.

The method has potential for predicting the sedimentary facies in undrilled parts of the Gippsland Basin and in frontier areas in general.