PRELIMINARY RESULTS FROM PLIOCENE SEDIMENTS (ODP SITE 697), JANE BASIN, ANTARCTICA AND CIRCUM-ANTARCTIC WELL LOGS SHOW A STRONG OBLIQUITY SIGNAL

Antarctic Pliocene ice behavior as recorded at ODP Site 697 (3480 m water depth) at the distal tip of the Antarctic Peninsula is investigated using both non-invasive measurements and measurements on sediment samples. Non-invasive techniques include high resolution color measurements (CIE L*a*b color), magnetic susceptibility, and XRF elemental counts, both made on split sediment cores. These measurements represent a straightforward, inexpensive, and non-destructive method of determining composition. Sediment color is created by a combination of the chemical composition, redox conditions, and the biological, lithological, and depositional characteristics of the environment in which the sediment was deposited. The color data correlate with split-core scanned XRF determined Fe/Ti ratios. Wavelet analysis on CIE L*a*b* color from Site 697 allow us to identify 20, 40, and 100, Milankovitch periodicities, with 40-kyr (obliquity) dominating. Similar analysis will be performed on multi-proxy ANDRILL well logs within conformable sequences and we anticipate a strong obliquity signal there.

Sediment analyses include weight percent ice rafted detritus (IRD), percent biolsilica and diatom identification. IRD is identified as sediment with a diameter > 63 microns, and ranges from < 1 to 22% by dry weight, with the highest percentages in the early and middle Pliocene. Weight % biosilica ranges from 1 to 13%. Diatoms, radiolarians, and silicoflagelates comprise the biolsilica. Prior to ~ 3.3 myr, both high IRD and high biosilica occur at the same time. After ~3.3 myr, IRD remains low (<4%), but biosilica is generally high, suggesting warmer and ice free conditions which allowed biosiliceous organisims to flourish in a realtively ice-free environment.