38. ORGANIC MATTER IN PERU UPWELLING SEDIMENTS—ANALYSIS BY PYROLYSIS, PYROLYSIS-GAS CHROMATOGRAPHY, AND PYROLYSIS-GAS CHROMATOGRAPHY MASS SPECTROMETRY1

Significant variations in the nature and content of total carbon and total organic carbon (TOC) in closely spaced near-surface samples from Sites 681, 686, and 683 are accompanied by changes in pyrolysis parameters. All TOC, pyrolyzable carbon values (P2), and hydrogen index (HI) values (e.g., P2 normalized to TOC) were found to be significantly higher in Hole 681A sediments, compared with those from Sites 686 and 683. Samples from Hole 681A contained almost no carbonate. Tmax values (e.g., maximum temperature of P2 evolution) generally were highest for Site 683 sediments, possibly indicating a greater influx of more reworked or terrigenous organic matter at this site, which is situated on the slope, at the edge or outside of today's upwelling area. TOC and pyrolysis (P2) values correlated in closely spaced near-surface samples from Hole 681A (correlation coefficient, r = 0.78), with correlation decreasing for Holes 686A (r = 0.5) and 683A (r = 0.22). On the basis of comparison with data from surface cores obtained by Woods Hole Oceanographic Institution, we postulate that the lack of correlation of P2 and organic carbon values in several Site 683 intervals may indicate that these intervals contain more terrigenous or more reworked marine organic carbon. Pl values showed poor correlation with TOC values at all three sites. Variations in Pl values, which generally fall in the immature range of 0.04 to 0.08, are thought to show the relative amounts of in-situ marine biogenic (rather than petrogenic) influence