HR: 0800h
AN: B21A-1022    [Abstracts]
TI: Mapping Ocean Biological Productivity During Mid-Cretaceous Ocean Anoxic Events
AU: * Yan, K K
EM: kyan@stanford.edu
AF: Adina Paytan, Department of Geological and Environmental Sciences Stanford University , Stanford, CA 94305-211 United States
AB: Several events of widespread shallow deposition of organic-carbon-rich marine sediments (black shales), referred to as Oceanic Anoxic Events or OAEs, occurred in the middle of the Cretaceous, about 125-80 million years ago. The increased burial rates during these OAEs have been attributed to two different mechanisms: a) the ocean stagnation model, where external physical processes like temperature, evaporation, and continent configuration, cause stable vertical stratification; b) the high productivity model, where internal biogeochemical processes in the ocean create lower oxygen levels due to extensive use of oxygen by ocean organisms. However, there is still debate as to which one of these mechanisms was the major cause for the oceanic anoxia. I will use marine barite accumulation rates in three deep-sea cores that span the mid-Cretaceous time intervals of the Cenomanian-Turonian (OAE 2, 94 Ma) and the Aptian-Albian (OAE 1a, 120 Ma) to reconstruct export production in the open ocean and find a probable cause for these OAEs. Marine barite has been associated with decaying organic matter for a long time. Barite accumulation responds only to organic matter fluxes out of the euphotic zone. Thus, it can serve as a superior proxy for productivity when compared to organic carbon accumulation. My samples come from Leg 198 in the Ocean Drilling Program. All are located on the Shatsky Rise in the Central Pacific Ocean. The shallow sediment burial depth results in very little diagenetic alteration. Using ocean drilling cores with good age control and relatively high sedimentation rates from this oceanic basin will enable me to examine possible variability between different oceanic regimes that have been studied in the past. In addition, I will use high resolution sampling to construct the temporal and spatial distribution of export production during these two periods of wide spread anoxia.
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
SC: Biogeosciences [B]
MN: Fall Meeting 2005