--> Abstract: Glacial/Interglacial Sedimentological Changes During the Mid-Pleistocene at Bjorn Drift, ODP Site 984, Leg 162, by S. O'Connell, C. Venherm, J. Minicucci, E. Arnold, and C.Knowlton; #90937 (1998).

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Abstract: Glacial/Interglacial Sedimentological Changes During the Mid-Pleistocene at Bjorn Drift, ODP Site 984, Leg 162

O'CONNELL, SUZANNE, CLAUDIA VENHERM, and JENNA MINICUCCI, Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459, U.S.A.; EVE ARNOLD and CHRIS KNOWLTON, Graduate School of Oceanography, University of Rhode Island, Kingston, RI, 02881

Summary

Six sedimentological parameters, % bulk carbonate, clay mineralogy, fine silt mineralogy, % sortable silt, sortable silt mean size, and % sand (>63 µm), were examined at ODP Site 984 on Bjorn Drift in the North Atlantic to investigate paleoceanographic changes during Isotope Stages 39-43. This time period, between approximately 1.36 and 1.26 ma, is near the end of the period of time dominated 40,000 year obliquity cycle.

These analyses show complex sedimentary patterns, suggesting multiple influences on sediment deposition and preservation. However, the clearest glacial/interglacial signal is present in the mean size and the percent of the sortable silt (10-63 µm). These are proxy indicators of current strength (McCave et al., 1994). With the exception of Stage 39/40, both sortable silt parameters begin to increase near the end of glacial stages (Figure 1). The increase continues into the next interglacial stage where a maximum in current strength is reached before the maximum interglacial. This suggests that changes in bottom current strength, in particular North Atlantic Intermediate Water, lead the temperature and ice volume changes recorded in the d18O isotope signal for both warming and cooling. The strength of intermediate water circulation increases before warming begins and decreases before cooling commences. The disrupted signal at Isotope Stage 39/40 may be linked to climatic and circulation changes near the end of the obliquity-dominated climatic cycles.

Other measured parameters do not show as clear glacial/interglacial signatures and suggest complex and varying source areas. Percent carbonate, highest during Isotope Stage 43, shows no clear, glacial/interglacial signal (Figure 1). Clay mineralogy (<2µm), is dominated by smectite and also shows no consistent glacial/interglacial trends. Fine silt (2-20µm) mineralogy shows higher abundance of kaolinite, chlorite and quartz during interglacials. Overall sand abundance is low (<10%)

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah