INVESTIGATION OF WHETHER OLIGOCENE CARBONATE SEDIMENTS FROM ODP LEG 115 SITE 709, INDIAN OCEAN RECORD AN ENVIRONMENTAL RESPONSE TO AFRO-ARABIAN FLOOD BASALT VOLCANISM

There has been much speculation on the global environmental impact of large igneous provinces. For example, within the oceans, the volcanism is often associated with the development of widespead oxygen-poor conditions, but the mechanism(s) by which the volcanism affects the environment are uncertain. The Oligocene (~30 Ma) Afro-Arabian province (Yemen-Ethiopia) provides a unique situation to investigate these changes because distal silicic ash layers occur within a continuous marine carbonate section in Ocean Drilling Program (ODP) cores in the Indian Ocean. These ash layers can be correlated to specific well-dated eruptive units onshore and therefore have the potential to demonstrate synchronicity between the volcanism and sedimentary records of environmental change. We are analyzing trace elements (including redox-sensitive elements and REE) and Pb isotope variations within this carbonate sequence to evaluate whether any changes in ocean chemistry are recorded in the composition of the sediments that can be demonstrated to be synchronous with specific events (e.g. initiation of flood basalt eruptions, onset of large-volume silicic ignimbrite eruptions). Increased continental weathering or input of volcanic-derived material will both potentially cause changes in ocean chemistry. The initial component of this study is setting up a suitable analytical procedure for ICP-MS trace element analysis of the carbonate fraction of the sediments. Based on previous studies, we are currently evaluating different acids and molarities as the best means to dissolve carbonate without leaching other components present in the sediments, including visible examination of the residues. At the meeting, we aim to present comprehensive trace element profiles through the sedimentary sequence at ODP Leg 115 Site 709 on the Madingley Rise to see if the Afro-Arabian volcanism is associated with any changes in ocean chemistry.