HR: 0800h
AN: PP11A-0556    [Abstracts]
TI: The Nature of the $\delta$$^{13}$C of Periplatform Sediments: Implications for stratigraphy
AU: * Swart, P K
EM: pswart@rsmas.miami.edu
AF: University of Miami, MGG/RSMAS,4600 Rickenbacker Causeway, Miami, Fl 33149 United States
AU: Eberli, G P
EM: geberli@rsmas.miami.edu
AF: University of Miami, MGG/RSMAS,4600 Rickenbacker Causeway, Miami, Fl 33149 United States
AU: Katz, D
EM: dkatz@rsmas.miami.edu
AF: University of Miami, MGG/RSMAS,4600 Rickenbacker Causeway, Miami, Fl 33149 United States
AB: The carbon isotopic composition ($\delta$$^{13}$C) of bulk carbonates, obtained from a transect of sites drilled through platform and periplatform sediments of Holocene to Early Miocene age, have been compared to ascertain whether changes in the $\delta$$^{13}$C can be correlated between sediments of equivalent ages and whether such changes can be related to global changes in the $\delta$$^{13}$C of the dissolved inorganic carbon in the oceans over this time period. Five of the sites were drilled during Leg 166 of the Ocean Drilling Project (1003-1007) in a transect ranging from five km to 25 km away from the platform margin and penetrating sediments of Holocene to Oligocene age that are contained in 17 depositional sequences (A-Q). Two shallow water sites, Clino and Unda were situated on a extension of the same transect on Great Bahama Bank in a water depth of 10-15 m. With the exception of Unda and Clino, the $\delta$$^{13}$C of the carbonates range in isotopic composition from +5% in the younger sequences to +1% in the Early Miocene. In each of the sites the $\delta$$^{13}$C is strongly positively correlated with the percentage of aragonite. As a consequence the $\delta$$^{13}$C of sequences A through F is strongly correlated, reflecting the decreasing amount of aragonite with increasing depth. In the two platform sites, the $\delta$$^{13}$C is significantly more negative in the younger portions of the cores as a result of the influences of meteoric diagenesis during repeated exposure during the Pleistocene. Although the $\delta$$^{13}$C of the individual sequences can be correlated in most instances between the ODP holes, the changes are not related to global changes in the 13C of the oceans which in contrast to the $\delta$$^{13}$C of the platform sediments become isotopically more negative towards the present day. Instead the $\delta$$^{13}$C appears to be related to varying contributions from $\delta$$^{13}$C rich bank-top sediments. While the results from this study may not be universally applicable to all carbonates associated with shallow water platforms formed throughout geological time, they certainly cast a note of caution that apparently related changes in the carbon isotopic composition can be caused by mechanisms other than global changes in the carbon cycle.
DE: 4806 Carbon cycling
DE: 4870 Stable isotopes
DE: 4267 Paleoceanography
DE: 1040 Isotopic composition/chemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting