A sequence stratigraphic interpretation of the eastern Gippsland Basin

Abstract

The Latrobe stratigraphic section subcropping the 'Top Coarse Clastics Unconformity' in the eastern Gippsland Basin consists of three depositional sequences of Maastrichtian to Palaeocene age. A Lower Palaeocene sequence illustrates the sedimentological and seismic relationships typical of these sequences. It has been further subdivided into three seismically mappable depositional units. Unit C is a 40 m basal sandstone section characterised seismically by high frequency sigmoidal clinoforms. It is interpreted to represent lowstand fan deposition prior to a marine transgression. Unit B consists of a 50 m argillaceous siltstone overlain by a 70 m coarsening upward sandstone section, characterised seismically by high frequency and high amplitude sigmoidal reflections. It is the product of marine transgression and subsequent highstand progradation. Unit A consists of a thin argillaceous siltstone overlain by a coarsening upwards sandstone deposited during a minor transgression and continued progradation. Unit A also consists of interbedded sands, shales and coals producing parallel, often high amplitude reflections. Deposition of this facies occurred in a coastal plain environment behind the prograding shoreline. The mapping of these seismic facies allow prediction of stratigraphy and reservoir and seal quality in an area of little well control, the deep water part of the Gippsland Basin. Stratigraphic pinchout plays of Unit B shoreface sandstones prograding into offshore siltstones and claystones and Unit C lowstand fan sandstones into Unit B offshore siltstones and claystones are also identified.