STRUCTURAL INHERITANCE, STRESS ROTATION, OVERPRINTING AND COMPRESSIONAL REACTIVATION IN THE GIPPSLAND BASIN—TUNA 3D SEISMIC DATASET

Abstract

In the Tuna area, Turonian rifting between Australia and the Lord Howe Rise produced extensive irregular NE–SE to ENE–WSW trending Emperor Subgroup depocentres by oblique reactivation of inherited Early Cretaceous Strzelecki Group and Palaeozoic basement fault geometries. Santonian Tasman seafloor spreading rotated the stress vectors clockwise so that NE–SW Emperor Subgroup syn-rift depocentres were abandoned and more easterly trends were reactivated. This developed the Proto-Rosedale Fault across the northern margin as a complex series of branching fault splays with reactivated ENE–WSW trending segments and new east– west hard linkages. In the Late Cretaceous, extension vectors rotated a further 45o clockwise sympathetic to NW–SE trending Tasman Sea mid oceanic ridges. ENE– WSW trending splays of the Proto-Rosedale Fault became abandoned and overprinted by new Maastrichtian NW–SE trending segments perpendicular to the NE–SW stress field. By the Paleocene these segments had linked, displaying en echelon geometries above the obliquely reactivated Proto-Rosedale Fault. Tasman seafloor spreading and fault-controlled subsidence in Gippsland had finished by the Early Eocene. Extension was punctuated by Coniacian-Santonian, Eocene and Oligocene compressive pulses that inverted abandoned splays of the Proto-Rosedale Fault forming the Tuna faulted anticline oil and gas traps.

The Santonian-Campanian Proto-Rosedale Fault and other similarly oriented structures are promising fairways for deep exploration. Attractive reservoir targets include stacked braided fluvial channel sands of the Golden Beach Subgroup deposited along NE–SW to ENE–WSW trending segments of the Proto-Rosedale Fault. Anticlinal traps developed during multiple Cretaceous and Tertiary compressive phases. Campanian dykes, sills and flows are prevalent in the Golden Beach section and offer the potential for effective seal as seen in the Kipper field.