Sediment cycling on the Marion Plateau since the Miocene

The Middle Miocene represents one of the warmest intervals in Earth’s recent geological history. Understanding the climate dynamics of this period can provide valuable insight into how the climate system may respond to future anthropogenic forcing. The study of tropical regions during the Miocene is particularly important, because these environments are underrepresented in climate records. Since the Miocene, Australia’s climate has undergone substantial changes driven by the northward drift of the continent, its collision with Southeast Asia, and the associated reorganisation of oceanic circulation around the Maritime Continent. Northern tropical Australia is presently influenced by a monsoonal system that forms part of the broader Asian Monsoon; however, the Australian Monsoon remains poorly understood, particularly with respect to its onset and variability. Investigating monsoon dynamics across different climatic states in this region may therefore improve our understanding of how large-scale circulation patterns could evolve under anthropogenically driven climate change. As a result of persistent arid conditions and lack of tectonic subsidence, evidence of fluvial and lacustrine activity has been destroyed, meaning terrestrial records of palaeoclimatic change in Australia are sparse. This study focuses on a marine core: Ocean Drilling Program (ODP) Hole 1195B on the Marion Plateau. Hole 1195B preserves an erosional and oceanographic record extending back to ~21 Ma and provides an opportunity to examine links between climate variability and continental weathering since the Middle Miocene.

This study employs XRF core scanning, GDGT biomarker analysis, and elemental analysis using ICP-OES. The results indicate that the highest delivery of clastic material to the Marion Plateau occurred during the Miocene Climatic Optimum (~17 Ma), coinciding with peak sea surface temperatures. The most pronounced cooling is observed between 11 and 9 Ma and was accompanied by significant changes in sediment input to the site. These changes were likely associated with shifts in Coral Sea circulation, potentially reflecting a strengthening of the East Australian Current. Notably, this regional response occurs ~2 Myr after the global cooling event observed elsewhere at ~13 Ma, suggesting that tropical climate systems may respond independently, or with some delay, in comparison to global climate perturbations. This highlights the importance of understanding climate dynamics in the tropics when considering potential future responses to anthropogenic climate change.