O'CONNELL, SUZANNE and CLAUDIA VENHERM
Dept E&ES, Wesleyan University, Middletown CT 06459

Abstract: Evidence for Short Cooling Intervals During Early Interglacials in the Mid-Pleistocene

Feni Drift, carbonate-rich North Atlantic drift east of Rockall Bank was drilled during ODP Leg 162 at Sites 980 and 981. Site 981 recovered a complete Pleistocene section with sedimentation rates of approximately 4-6 cm/kyr. Whole core magnetic susceptibility records, and discrete carbonate and grain-size measurements on an approximately 200-kyr section with 5 glacial-interglacial cycles were analyzed. Higher magnetic susceptibility is equated with increased terrigeneous input and glacial conditions. Higher carbonate percentage is equated with warmer, interglacial conditions. Coarser size of the mean sortable silt (10-63 micron fraction) is equated with stronger bottom currents. Sedimentation rates are tuned to 41 kyr, by setting the lowest magnetic susceptibility value as the maximum glacial for each cycle. Within a cycle sedimentation rates are held constant.

Carbonate and magnetic susceptibility vary roughly in phase. And in all but the upper most cycle bottom current strength begins to increase during the early glacial, reaching a maximum during the early interglacial.

In all cycles, preceding the maximum carbonate value (maximum interglacial), there is a cooling interval of less than 6-kyr duration. The magnitude of the change varies from about 2% to about 12% carbonate and commonly coincides with a change in bottom current strength. We suggest that these intervals may be similar to Younger Dryas type events.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas