Palaeobathymetric Interpretations using Foraminiferal Data from the North-west Continental Shelf off Western Australia, IODP Expedition 356

Abstract

In 2015, Integrated Ocean Discovery Program Expedition 356 drilled along the passive margin off the West Australian coast to investigate the history of the Indonesian Throughflow (ITF) and its integral role in the development of global thermohaline circulation and climate. Throughout the expedition, a suite of foraminiferal analyses were employed wherein planktic specimens revealed biostratigraphy, and an incredibly diverse benthic fauna (~ 260 species) was used to reveal palaeo- water depth, palaeobathymetric settings and variable conditions at the sediment-water interface. Benthic foraminiferal biofacies are particularly sensitive to changes in environmental conditions, have a rapid turnover and are ideal proxies for monitoring physical and chemical changes in marine environments. When this information is combined with lithostratigraphic and other microfossil data, a robust understanding of past environments can be reconstructed. Stretching from the Northern Carnarvon Basin up to the Roebuck Basin, several distinct biofacies were isolated at sites U1461-U1464 that reveal an array of marine settings and events that span from the Miocene to the Pleistocene. These features include water depths ranging from shallow reefs (Larger Benthic Foraminifera) to bathyal depths (~ 1000 m), the appearance of key indicator species for both the Leeuwin Current and the West Pacific Warm Pool, and episodes of downslope sediment transport. Here we present the main isolated biofacies, their associated lithofacies and their implications for reconstructing fluctuating sea-level, thermohaline circulation and sediment transport in a changing marine landscape.