Dating the Northwest Shelf of Australia Since the Pliocene

Abstract

Abstract Accurate dating of marine sediments is essential to reconstruct past changes in oceanography and climate. Benthic foraminiferal oxygen isotope series from such sediments record long‐term changes in global ice volume and deep‐water temperature. They are commonly used in the Plio‐Pleistocene to correlate deep ocean records and to construct age models. However, continental margin settings often display much higher sedimentation rates due to variations in regional depositional setting and local input of sediment. Here, it is necessary to create a regional multi‐site framework to allow precise dating of strata. We create such a high‐resolution regional framework to determine the ages of events for the Northwest Shelf (NWS) of Australia, which was cored by International Ocean Discovery Program (IODP) Expedition 356. We employ benthic foraminiferal oxygen and carbon isotopes to construct an astronomically‐tuned age model for IODP Site U1463 (5.16–1.69 Ma). The age model is applied to the IODP Site U1463 downhole‐logging natural gamma radiation (NGR) depth‐series, which was then correlated to NGR depth‐series of several IODP sites and industry wells in the area. This approach allows assigning ages to regional seismic reflectors and the timing of key climate‐related siliciclastic phases in a predominantly carbonate‐rich sequence, like the late Miocene‐Pliocene Bare Formation. This age model is also used to chronologically calibrate planktonic foraminiferal biostratigraphic datums showing that the Indonesian Throughflow (ITF) had shoaled enough in the early Pliocene to act as biogeographical barrier between the Pacific and Indian Ocean.

Keywords

• benthic foraminiferal isotopes
• downhole wireline logging
• NW‐Australia
• planktonic foraminiferal biostratigraphy
• seismic network