HR: 0800h
AN: PP51B-0595    [Abstracts]
TI: Distinguishing Between Pelagic and Allochthonous Deposition in High-Resolution Records of Aptian-Albian Oceanic Anoxic Events at Deep Sea Drilling Project Site 398, North Atlantic Ocean
AU: * Kaldahl, S M
EM: soviet@adelphia.net
AF: Elizabeth City State University, Department of Geological Environmental and Marine Sciences, Elizabeth City, NC 27909 United States
AU: Bralower, T J
EM: bralower@geosc.psu.edu
AF: Pennsylvania State University, Department of Geosciences, University Park, PA 16802 United States
AU: Montanez, I P
EM: montanez@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Osleger, D A
EM: osleger@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AB: A high-resolution and expanded record of Oceanic Anoxic Events (OAE) in the early Aptian (OAE1a; 120 Ma) and latest Aptian-early Albian (OAE1b; 112Ma) were recovered at Deep Sea Drilling Project Site 398 on Vigo Seamount in the North Atlantic Ocean. The OAEs are recognized by minor increases in organic carbon content (up to 2.5 wt % TOC) and characteristic carbon isotopic variations including a short-term 4-5 per mil shift to negative values followed by a longer term 2-3 per mil shift to more positive values. The Aptian and Albian section contains abundant intercalated coarse siltstone and sandstone horizons often with inclined lamination. These horizons indicate that hemipelagic sedimentation at Site 398 was interrupted periodically by deposition by turbidity currents. Although we generally avoided sampling coarse-grained intervals, the purpose of this investigation is to determine whether there is a relationship between mode of deposition and TOC and δ¹³C_org. A spectral grain-size instrument (Malvern Mastersizer) provided continuous grain size distributions between 0.5 and 900 microns. Abundance of calcareous nannofossils determined from smear slides was used to monitor variations in the pelagic component of the sediment. Grain size and nannofossil abundance show no significant relationships with TOC and δ¹³C_org over short-term intervals as well as across the OAEs. This indicates that the high-resolution Aptian-Albian δ¹³C_org and TOC records at Site 398 are hemipelagic signals and are not influenced by redeposition in turbidity currents. In addition, the lack of significant relationship between grain size and TOC suggests that mineral surface area has little effect on organic richness at this location.
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4901 Abrupt/rapid climate change (1605)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005