HR: 0800h
AN: PP51D-1354    [Abstracts]
TI: Orbital forced sea level fluctuations during the Middle Eocene (ODP site 1172, East Tasman Plateau)
AU: * Warnaar, J
EM: J.Warnaar@bio.uu.nl
AF: Utrecht University, Budapestlaan 4, Utrecht, 3584CD Netherlands
AU: Stickley, C
EM: cathy@earth.cf.ac.uk
AF: Cardiff University, P.O. Box 914, Cardiff, CF10 3YE United Kingdom
AU: Jovane, L
EM: jovane@ingv.it
AF: Instituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Roma, 00143 Italy
AU: Roehl, U
EM: uroehl@marum.de
AF: Bremen University, Postfach 33 04 40, Bremen, 28334 Germany
AU: Brinkhuis, H
EM: H.Brinkhuis@bio.uu.nl
AF: Utrecht University, Budapestlaan 4, Utrecht, 3584CD Netherlands
AU: Visscher, H
EM: H.Visscher@bio.uu.nl
AF: Utrecht University, Budapestlaan 4, Utrecht, 3584CD Netherlands
AB: Ocean Drilling Program leg 189 was undertaken to test and refine the hypothesis (by Kennett et al., 1975), that the reconfiguration of continents around Antarctica (e.g.: the opening of the Tasmanian Gateway and Drake passage) led to the onset of the Antarctic Circumpolar Current that, in turn, would cause thermal isolation and hence cooling of Antarctica. This would possibly even cause global cooling, as suggested by the 33.3 Ma Oi1 event. The cores of leg 189, site 1172 on the eastern side of the Tasmanian Gateway provided a nearly complete succession of Eocene and Oligocene sediments. Cyclostratigraphic analysis based on XRF derived Ca and Fe records indicates distinct Milankovitch cyclicity between 40 and 36 Ma. (R”hl et al, in press). In the core-section representing magnetochron 18n-1n, the Ca record shows precession cycles in combination with obliquity, suggested to reflect sea level fluctuations (R”hl et al, in press). New datasets include microfossil data (organic-walled dinoflagellate cysts, pollen/spores and diatoms), loss-on-ignition measurements, magnetic data (environmental magnetics - ARM). Here, we aim to further investigate the proposed relationship between astronomical forcing and sea-level fluctuations. Additionally, we aim to obtain insight in the palaeoecology of the distinct endemic circum-Antarctic late Middle to Late Eocene dinoflagellate cyst assemblages. Results corroborate the concept that the cyclicity recorded by Ca and Fe measurements is the result of sea-level fluctuations. This implies that during late Middle Eocene times, astronomical forcing has modulated sea level - most likely through Antarctic ice buildup and meltdown. In turn, this would indicate the presence of significant, though probably modest, ice masses already ~40 Ma ago, well before the onset of the Antarctic Circumpolar Current. Kennett, J. P., R. E. Houtz, et al. (1975). Development of the circum-Antarctic current. Science 186: 144-147. R”hl, U.; H. Brinkhuis, C.E. Stickley, M. Fuller, S.A. Schellenberg, G. Wefer, G. Williams, Cyclostratigraphy of Middle and Late Eocene sediments from the East Tasman Plateau (site 1172), in press.
DE: 4855 Plankton
DE: 4267 Paleoceanography
DE: 3005 Geomagnetism (1550)
DE: 0400 Biogeosciences
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting