HR: 13:40h
AN: PP23C-01    [Abstracts]
TI: An Alternative Mechanism for Producing Global Changes in the Carbon Isotopic Composition of Platform Derived Sediments
AU: * Swart, P K
EM: pswart@rsmas.miami.edu
AF: University of Miami, MGG/RSMAS University of Miami 4600 Rickenbacker Causeway, Miami, FL 33149, United States
AB: The stable carbon isotopic composition of the skeletons of carbonate organisms and sediments has been widely used not only in order to derive information upon the burial of organic material throughout the geological record, but also for correlative purposes. While the preferred type of material for analysis in sediments younger than ~ 200 Ma are microfossils derived from oceanic sediments, in older deposits one is forced to use the δ¹³C of bulk sediments deposited on and surrounding carbonate platforms. Such sediments are often problematic as a result of diagenesis and the fact that they are derived from a variety of different sources which have differing δ¹³C values. This can lead to the correlation of the δ¹³C in age equivalent strata prograding from a carbonate platform. A notable example of this is shown in the Bahamas which show good correlations between individual sequences, but little correlation to global carbon curves derived from planktonic and benthonic foraminifera. In order to assess whether similar phenomenon are present surrounding other carbonate edifices over the same time period, the δ¹³C was measured in Holocene to Miocene aged material from cores taken off the Maldives (Ocean Drilling Program Site 716), the Queensland Plateau (Site 817), the Great Barrier Reef (Sites 821 and 822), and the Great Australian Bight (Site 1126). All these sites showed similar patterns in the δ¹³C values of the bulk sediments compared to the Bahamas between the present day and the middle Miocene and no correlation with the global δ¹³C curve. It is suggested that the synchronous variations in the δ¹³C values in sediments of equivalent age are related to variations in sea level which flood the platform, allowing the production of carbonate sediments with positive δ¹³C values. These sediments become admixed into pelagic sediments producing an apparent global signal. These results have obvious implications on the use of δ¹³C records in carbonate derived sediments to interpret the paleocarbon cycle in that widespread changes in the δ¹³C cannot be used as evidence that variations are related to the burial and oxidation of organic material.
DE: 1051 Sedimentary geochemistry
DE: 4806 Carbon cycling (0428)
DE: 4825 Geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting