Structure and stratigraphy of the Sherbrook Supersequence: 3-D seismic analysis of growth faults in the Outer Otway Basin

Abstract

Prominent growth faulting and sediment bypass influenced the thickness of Sherbrook Supersequence sediments south of the Mussel Fault Zone in the Voluta Trough. This study quantifies the geometry and kinematics of faults and sediment dispersal in the deep-water province of the Otway Basin, offshore Victoria. A 3D seismic reflection survey was used to investigate the geometries and origin of complex linked growth fault arrays present within the Upper Cretaceous Sherbrook Supersequence in the Voluta Trough area. Five horizons and 46 faults were mapped within the confines of the OS2-3D seismic reflection survey which encompasses a 773 km² area along the present-day shelf edge in the central Otway Basin, Victoria. The resulting geological framework consists of two NW striking listric hard-linked fault arrays, as well as two NNE striking fault arrays that are crosscut by the identified NW striking fault arrays. Isopach maps of four Upper Cretaceous stratal units indicate growth of all studied faults has controlled distribution of sediments temporally throughout the study area since the Turonian or earlier. Episodes of growth faulting created scoop shaped hanging-wall depocentres and caused SW-SE basinward thickening of stratal units. Isolated hanging-wall depocentres coalesced to form large combined depocentres in subsequent strata. Growth faults overlying basement faults underwent multiple separate phases of displacement and may have been activated preferentially. Cumulative displacement of major NW-SE striking fault arrays increases SE along strike, where growth strata reach thicknesses >1500 m. Lateral throw variations along strike of fault arrays imply fault arrays once consisted of individual faults that grew independently prior to linkage. Throw variations along depth of faults reveals up to 722 m of throw present within Turonian-Santonian and age strata, and suggests faults nucleated in response to an Upper Cretaceous phase of rifting proposed by previous studies of the Otway Basin. Differential compaction of sediment above basement-related topography may be an important factor influencing fault distribution within the study area.