10. GEOCHEMISTRY AND CARBONATE PETROLOGY OF SELECTED SEDIMENT SAMPLES FROM DEEP SEA DRILLING PROJECT LEG 54, EASTERN PACIFIC

Thirty selected samples of pelagic and hydrothermal sediments retrieved on DSDP Leg 54 were chemically analyzed for major and minor oxide concentrations. Additionally, 11 samples of lithified carbonate sediments were petrologically studied. The pelagic sediments, which are described as foraminiferal bio-micrite, were found to be generally higher in Fe and Zn, similar in Co content, and lower in Cu content, than the average Pacific pelagic sediments. Mineralogically, these samples are composed principally of calcite with minor amounts of quartz and clays. Hydrothermal sediments from Site 424 are divisible into three classes: (1) silica-rich, iron-poor smectites; (2) silica-poor, iron-rich mixtures of smectites and oxides; and (3) silica-poor, iron-rich mate-rials, comprising mainly amorphous manganese oxides. Thus, two chemically distinct hydrothermal phases are recognizable: Class 1, iron-rich smectites, and Class 3, Mn-rich oxides and oxyhydroxides. Dolomite and pyrite were identified in X-ray diffraction studies of samples from Site 427