Inherited morphobathymetric controls over contourite drift deposition: a case study from the late Cenozoic Mentelle Basin, Australia

Abstract

Deep-sea sedimentary deposits are important archives of the geologic past that preserve the records of past environmental changes in earth’s ocean. The detailed analysis of deep-sea sedimentary archives, in particular of contourite drifts, can help elucidate past changes in ocean circulation and the stratigraphic evolution of continental margins. However, the bathymetric profile of an oceanic basin can shape and modify the architecture of contourite drifts via the interaction between down-slope and along-slope processes. The identification of local bathymetric influence on depositional architectures is therefore important to help decipher local versus regional influences on deep-sea sedimentary signatures. Seismic data from Mentelle Basin in the southeast Indian Ocean integrated with deep-sea core data reveal a calcareous-siliciclastic mixed contourite-turbidite system developed during the late Cenozoic, starting in the middle Miocene. Current winnowing led to the formation of regional hiatuses, ferromanganese crusts, and siliciclastic lag deposits. The main locus of sediment deposition occurred on the shallower parts of the basin, whereas sediment preservation remained low in the deeper areas. Seismic analysis shows that inherited topography influenced the architecture of contourite deposits within the basin, with elongate-mounded and sheeted drifts forming preferentially at shallower depths on the continental slope and the Naturaliste Plateau, while channel incision occurred in the deepest parts of the basin. These results suggest that the intensification of current transport occurred preferentially within the deeper and spatially constrained parts of the basin, whereas current deflection around the slope and plateau enhanced drift deposition and preservation at shallower depths. Therefore, the basin topography at the time of deposition controlled the distribution of deep-sea deposits and drift morphologies within the mixed contourite-turbidite system in the Mentelle Basin.