HR: 1340h
AN: PP33A-1553    [Abstracts]
TI: Detrital Carbonate (Heinrich-type) Layers During Glacial Stages of the Brunhes Chronozone at IODP Site 1308 (re-occupation of DSDP Site 609)
AU: * Hodell, D A
EM: hodell@ufl.edu
AF: University of Florida Department of Geological Sciences, PO Box 112120, Gainesville, FL 32611 United States
AU: Romero, O E
EM: oromero@uni-bremen.de
AF: University of Bremen Research Center for Ocean Margins, PO Box 33 04 40, Bremen, 28334 Germany
AU: Roehl, U
EM: uroehl@rcom-bremen.de
AF: University of Bremen Research Center for Ocean Margins, PO Box 33 04 40, Bremen, 28334 Germany
AU: Channell, J E
EM: jetc@ufl.edu
AF: University of Florida Department of Geological Sciences, PO Box 112120, Gainesville, FL 32611 United States
AB: Heinrich Events in the north Atlantic are marked by their low abundance of foraminifera (biogenic carbonate) and high concentration of detrital carbonate derived from Paleozoic limestones in the region of Hudson Strait. Although Heinrich events have been well documented for the last glacial period, less is known about whether similar events occurred during older glacial periods. During IODP Expedition 303, Site 1308 was drilled at the same location as DSDP Site 609, which is an important reference section for detrital (Heinrich-type) layers and their correlation to Greenland ice cores over the last climate cycle. Using the Avaatech XRF core scanner at the University of Bremen, we measured the full suite of elements between Al and Ba (e.g., Al, Si, P, S, K, Ca, Ti, Mn, Fe, Sr, Ba) at 1-cm resolution in the upper 50 m of the spliced composite section of Site 1308, corresponding to the last 780 kyrs (i.e., Brunhes Chronozone). We found that the Ca/Sr ratio is an excellent proxy for detrital carbonate layers. Because the Sr/Ca partition coefficient is much greater for biogenic carbonate than inorganic (detrital) carbonate, detrital carbonate events are clearly identified by peaks in Ca/Sr. At Site 1308, four distinct Ca/Sr peaks occurred during the last glacial period corresponding to Heinrich Events 2, 3, 4, and 5. These four layers were originally described by Heinrich (1988) as ''cemented marls'' and each is also marked by an increase in sediment bulk density measured by gamma ray attenuation. Similar detrital carbonate layers, identified by peaks in Ca/Sr and density, also occurred during Marine Isotope Stages (MIS) 8 (three events), 10 (one large event near Termination IV and another smaller event), 12 (1 event just before Termination V), and 16 (two large events). No events were recognized in glacial MIS 6 or any of the interglacial stages. Initial analysis indicates that detrital carbonates tend to occur late in the glacial cycle just prior to terminations when ice volume is near its maximum. On the basis of density data alone, detrital carbonate events did not occur prior to MIS 16 at Site 1308 and are thus limited to periods of large ice volumes associated with the '100-k world' in the latest Pleistocene. We conclude that Ca/Sr ratios provide an excellent proxy for the rapid, non-destructive recognition of detrital carbonate layers (i.e., Heinrich-like events) in North Atlantic sediments. Detailed geochemical analysis is needed to verify the source areas of these older detrital carbonate events.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4901 Abrupt/rapid climate change (1605)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005