Bulk geochemistry, mass change and alteration intensity of basalts from ODP Leg 187 sites and survey dredges

Shipboard studies during Ocean Drilling Program Leg 187 (Australian Antarctic Discordance, AAD) suggested that there was no discernible coincidence between the interpreted age of rocks recovered and the intensity of alteration observed. Samples from the oldest sites occupied appeared to exhibit the least overall effects of alteration, and the intensity of alteration varied from site to site. Previous investigations of low-temperature alteration in oceanic basement samples have been restricted by the myopic perspective provided by single drill holes or dredge collections. Combining core samples from Leg 187 and dredge samples from the AAD collection at Oregon State University (USA) offers the unique opportunity to investigate mineral and bulk chemical changes attending alteration of basalt over a range of ages from 0 to 28 Ma. Results of this research indicate that there is a general increase in the intensity of alteration as the basalts age and mosve off axis, but that this relationship is somewhat veiled by the dominating control on alteration intensity dictated by variations in permeability.

(Table T2) Relative signal intensity of intact polar lipids in sediments from ODP Sites 207-1257 and 207-1258

We report results from the analysis of intact polar lipids (IPLs) in sediments from Ocean Drilling Program Sites 1257 and 1258. IPLs, constituting the cell membranes of living organisms, were detected in organic-lean sediments but not in underlying organic-rich black shales. Microbial activity in organic-lean sediments is likely due to sulfate-dependent oxidation of methane whereas difficulties detecting IPLs in black shales are interpreted to result from unfavorable signal-to-noise ratios due to low cell concentrations in combination with extremely high analytical noise created by uncharacterized organic matrix. IPLs found are consistent with a low-diversity community of archaea and bacteria. The concentrations of IPLs are more than one order of magnitude lower than those in Neogene deep subsurface sediments at the Peruvian margin, suggestive of significantly lower cell concentrations in Demerara Rise. This finding is consistent with inferred low rates of subsurface microbial activity.