Archive for the East Australian Current: carbonate contourite depositional system on the Marion Plateau, Northeast Australia

Abstract

The modern East Australian Current (EAC) sweeps across the Marion Plateau, forming a widespread contourite depositional system. The history of the EAC is recorded in the contourite drifts that have evolved through time as topographic, sea level, and oceanographic changes have influenced the current flow. During the Miocene, five isolated carbonate platforms on the Marion Plateau formed obstacles for the EAC, leading to the development of a complex contourite drift system in which drift types and non-depositional/erosional features transition laterally and temporally because of continuously evolving platform-current interactions. The significant topographic changes are caused by two episodes of platform drowning in the Middle and Late Miocene. We reinterpreted 2D seismic, well, and core data from ODP Legs 133 and 194 and updated the ages of the seismic sequences. The updated ages enable the reconstruction of the evolution of the EAC since the Miocene. The influence of the EAC in the study area began at 13.5 Ma, with five significant phases of change identified by shifts in contourite drifts' geometry and thickness. During the first phase (13.5 Ma – 11 Ma), strong currents carried sediment across platforms and deposited as periplatform drifts (Marion Drift B6), previously identified as a lowstand platform. In Phase 2 (11 Ma – 7 Ma), strong EAC caused the formation of Marion Drift C, characterized by thick, confined, and elongated mounded drifts separated by the wide moats and a marginal valley along the drowned Northern Marion Platform. At 7.5 Ma, a major re-arrangement of the contourite depositional system documents the influence of EAC across the drowned platforms. The subsequent Marion Drift D smoothed out some of the antecedent topography. However, the Marion Reef and Southern Marion Platform still presented obstacles to the EAC, leading to the deposition of multi-crested drifts. Phase 4 (5.7 Ma – 3.3 Ma) is marked by decreased sedimentation rates, possibly due to sea level fall at Mi-7 and the restriction of the Indonesian Throughflow. The youngest and currently active depositional phase began at around 3.3 Ma with a change in drift geometry from multi-crested to elongated mounded, coinciding with the onset of the Northern Hemisphere Glaciation and further reduction of the Indonesian Throughflow.