HR: 16:40h
AN: PP42D-03    [PDF]
TI: Orbital Cycles, Climate, and Diagenesis Mimic Methane Releases: Results from a High Resolution Study of OAE2, New Jersey Coastal Plain
AU: * Wright, J D
EM: jdwright@rci.rutgers.edu
AF: Rutgers University, Dept of Geological Sciences 610 Taylor Road, Piscataway, NJ 08854 United States
AU: Cramer, B S
EM: benjamin@dges.tohoku.ac.jp
AF: Tohoku University, Aoba, Aramaki, Institute of Geology and Paleontology, Sendai, NJ 980-8578 Japan
AU: Miller, K G
EM: kgmt@rci.rutgers.edu
AF: Rutgers University, Dept of Geological Sciences 610 Taylor Road, Piscataway, NJ 08854 United States
AU: Katz, M E
EM: mimikatz@rci.rutgers.edu
AF: Rutgers University, Dept of Geological Sciences 610 Taylor Road, Piscataway, NJ 08854 United States
AB: The Cenomanian-Turonian (Upper Cretaceous) section from Bass River State Park, New Jersey contains a 15 m thick interval representing Ocean Anoxic Event (OAE2). Our high resolution (~5cm) bulk sediment inorganic stable isotope record, can be used to define OAE2 at Bass River. The down-hole gamma log shows well-developed cycles throughout the OAE2 interval that we interpret as short eccentricity cycles, providing a chronology for the OAE2 event. Assuming a 95 kyr eccentricity cycle and that OAE2 at Bass River is defined the interval of high $\delta$$^{13}$C values, the duration of this event was $\sim$700$\pm$100 kyr. The dominant eccentricity forcing in the Bass River OAE2 record suggests that a monsoonal circulation controlled the regional and global carbon cycles as evidenced by sedimentary organic carbon and $\delta$$^{13}$C, respectively. Our results show a series of negative $\delta$$^{13}$C excursions, that are typically on the order of 3 to 5 per mil, but in two instances the excursions were $>$20 per mil. We initially interpreted these excursions as reflecting methane releases from gas hydrates. Closer examination shows that the $\delta$$^{13}$C excursions were produced by seafloor diagenesis in the presence of elevated organic carbon levels. These transients are characterized by: 1) the lack of a corresponding decrease in organic carbon $\delta$$^{13}$C values; 2) calcite infilling of foraminiferal shells; and 3) increased $%$CaCO$_{3}$. The $\delta$$^1$$^3$C value of the authigenic CaCO$_{3}$ is $\sim$-25 per mil, indicating that reducing organic-rich sediments supplied much of the CO$_{2}$. We argue that increases in organic carbon flux raised alkalinity (through sulfate reduction) and resulted in authigenic precipitation of CaCO$_{3}$ at Bass River. In our model, negative $\delta$$^{13}$C excursions are the result of seafloor diagenesis that is forced by climate rather than from the dissociation of methane hydrate.
DE: 4267 Paleoceanography
DE: 4805 Biogeochemical cycles (1615)
DE: 4870 Stable isotopes
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting