Oceanographic and Biotic Changes in Australia During Cretaceous Oceanic Anoxic Events

During the Mesozoic, Earth experienced a rare series of abrupt and short-lived episodes of Ocean Anoxic Events (OAEs), characterised by severe global warming and possibly triggered by volcanic degassing of CO2. Despite their importance for understanding the Earth-ocean-atmosphere system, the environmental impacts and causal mechanisms of OAEs have yet to be fully resolved, and are particularly poorly understood in the southern hemisphere where records are extremely limited. One of the largest such events, OAE2 at the Cenomanian-Turonian boundary (~94 Ma), has been associated with volcanism, abrupt warming, an increased hydrological cycle, nutrient supply to the oceans, high productivity, and mass extinctions in marine biota. This project aims to reconstruct palaeoceanography and vegetation of southwest Australia before, during and after OAE2 for the first time, with exclusive access to new core material collected during International Ocean Discovery Program (IODP) Expedition 369.

The aims of this project are to investigate both the short and long term impacts of global climate change on Cretaceous palaeoceanography, palaeoclimate and biotic evolution of southwest Australia. The student will reconstruct changes during the Cretaceous with a specific focus on OAE2 using sedimentary organic geochemistry GDGTs, including the TEX86 sea surface temperature proxy. Data from southern high latitudes is currently lacking (Jenkyns et al. 2012), so this project will test the extent of OAE2 high latitude warming and look for evidence of short term changes, such as the "Plenus cold event" that occurs within OAE2 in the northern hemisphere (Zheng et al. 2013). Local changes in productivity will be reconstructed using dinoflagellate cyst assemblages, to investigate oceanic upwelling and terrigenous nutrient delivery over OAE2 and the longer term Cretaceous. The project will also assess regional vegetation changes linked to the hydrological cycle by generating pollen grain and spore records over the late Cretaceous, and in high resolution over OAE2. Pristine new sediment cores recently collected during IODP Expedition 369 offshore SW Australia (Hobbs et al. 2016) are ideal for organic geochemical and palynological analyses as they are thermally immature and have a low burial depth.