New 3D seismic imaging of Late Cretaceous extrusive volcanics in the deep-water Gippsland Basin: implications and insights for paleo-depositional environments and petroleum systems

Abstract

The presence of Late Cretaceous volcanics has been well documented within the marginal areas of the Gippsland Basin, Australia. A new basin-scale 3D seismic survey recently acquired by CGG, has expanded 3D data coverage, and revealed the presence of previously unseen depositional features and extensive intrusive and extrusive volcanic complexes in the deep-water areas. A well-preserved and previously undetected extrusive volcanic edifice has been identified in the deep-water area at the crest of a large basement high and correlated with Emperor–Golden Beach Subgroup successions. These large basement structures and faults compartmentalise the deep-water areas of the Gippsland Basin and exert a structural control and focal mechanism for vertical migration and upwelling of basaltic volcanics. The volcanic features discussed herein are characteristic of early-rift, intra-cratonic tectonic settings and are the first of their kind to be imaged in the deep-water areas of the basin. Depositional features that have been identified in association with the extrusive volcanics, exhibit seismic characteristics consistent with massive, very fine-grained facies. The presence of these features, which can be correlated with the early opening of the Tasman Sea provide important clues into paleo-depositional environments with implications for source rock development in the deep-water areas.