Preliminary Eocene-Oligocene magnetostratigraphy of ODP Hole 711A from the western Indian Ocean

Ocean Drilling Program (ODP) Site 711, which is located in the western equatorial Indian Ocean near the Seychelles Archipelago on Madingley Rise, is an important site for studying Eocene-Oligocene climatic evolution. We are studying the impact of Neo-Tethyan gateway closure on Indian Ocean currents and circulation to further understand global climate changes during the switch from greenhouse to icehouse conditions. Lower Eocene-to-lower Oligocene strata recovered within Hole 711-A (Cores 711A-14X to 25X) primarily consist of clay-bearing nannofossil oozes/chalks, radiolarian-bearing nannofossil oozes, and radiolarian oozes. We have developed a high-resolution magnetostratigraphic record and have constructed a new integrated age model. Our results confirm published results from the lower Oligocene section of the hole and extend the existing polarity record down into the lower Eocene. Correlation of the polarity pattern to the geomagnetic polarity timescale provides a record from subchron C12n (early Oligocene) to C22r (early Eocene). Environmental magnetic records spanning the same interval have also been developed for Hole 711A. The integrated records indicate that the magnetic mineral assemblage is dominated by low-coercivity minerals, probably magnetite and/or titanomagnetite. Magnetic parameters also indicate significant variations in the concentration of magnetic minerals at 185 meters below seafloor (mbsf) and 197 mbsf, which are most likely related to carbonate dissolution during the Middle Eocene Climate Optimum (MECO) and during another event in the middle Eocene. Overall, these new results from Hole 711A have important implications for identifying and dating global climate change events, and for reconstructing CCD history at this site.