Late Eocene–early Miocene evolution of the southern Australian subtropical front: a marine palynological approach

Abstract. Improvements in our capability to reconstruct ancient surface-ocean conditions based on organic-walled dinoflagellate cyst (dinocyst) assemblages from the Southern Ocean provide an opportunity better establish past position, strength and oceanography of subtropical front (STF). Here, we aim late Eocene early Miocene (37–20 Ma) depositional palaeoceanographic history STF context evolving Tasmanian Gateway as well potential influence Antarctic circumpolar flow intense waxing waning ice. We approach this by combining information seismic lines (revisiting existing data generating new marine palynological Drilling Program (ODP) Hole 1168A) western continental slope. apply improved taxonomic insights palaeoecological models sea surface palaeoenvironmental evolution. Late Eocene–early Oligocene (37–30.5 show a progressive transition dominant terrestrial palynomorphs inner-neritic dinocyst taxa cysts produced heterotrophic dinoflagellates predominantly outer-neritic/oceanic autotrophic taxa. This reflects deepening margin, interpretation supported investigations. The dominance species like Spiniferites spp. Operculodinium relatively oligotrophic conditions, those regions north modern-day STF. increased abundance earliest Nematosphaeropsis labyrinthus, typical for modern subantarctic zone (frontal) indicates cooling and/or closer proximity site . absence major shifts contrasts with other records region suggests that small changes oceanographic occurred during Oligocene. Despite southerly (63–55? S) location Site 1168, rather stable reflect continued proto-Leeuwin Current along southern Australian coast Australia drift northward. “warm” at ODP compared cold Integrated (IODP) U1356, testify establishment pronounced latitudinal temperature gradient Ocean.