(Table 1) Composition of paraffin hydrocarbons at DSDP Site 56-434

Geochemical investigation of 18 samples of sediments from Site 434 involved determining the content of organic carbon, of bitumoid A (The chloroform A-chl and alcohol-benzene A-alb extracts) and its various fractions, and of individual hydrocarbons as well as the structural group composition of resins. We identified certain samples that differed sharply from the rest by their increased bitumen content and relatively low molecular hydrocarbons and by the fact that their resinous components were more neutral and aliphatic in composition. The distribution of bitumoid and its components seems to reflect migration processes in operation during the early stages of the transformation of organic matter.

(Table 1) Sediment descriptions and age at DSDP Legs 5 and 63 Holes

Sediments from immediately above basalt basement and from between sections of basalt recovered from Deep Sea Drilling Project Legs 5 and 63 were analyzed by atomic absorption spectroscopy for Mg, Al, Si, Ca, Mn, Fe, Co, Ni, Cu, Zn, and Ba. All of these sediments showed enrichment in Fe and Mn over values typical of detritus supplied to the northeastern Pacific Ocean. X-ray diffractometry and differential chemical leaching indicate that up to 50% of the sediment, by weight, is in amorphous phases and that these phases are rich in Mn, Co, Cu, Ni, and Zn. Multivariate statistical analysis and normative partitioning of the chemical data indicate that much of the excess Fe and other transition elements in the sediment originate from hydrothermal sources.

(Table 1) Geochemistry of ash layers at DSDP Leg 57 Holes

The study of the main characteristics of ash layers in Leg 57 cores shows that they are suitable for an analysis of the effect on eruptive activity of their distribution. We found (1) sediment recovery good and ash layers numerous; (2) sedimentary environment generally free from terrigenous clastic material; (3) reworking limited; (4) volcanic glass very acidic, ranging from rhyolitic to rhyodacitic composition; and (5) alteration and diagenesis negligible above the lower Miocene. The curves of explosive volcanic activity in Holes 438, 439, and 440 display two stages of high activity: an early one around 16 m.y. and a late one starting 5 m.y. B.P., both stages being separated by an upper Miocene quiescence. Detail in these results is limited by the chemical composition of the glass and accounts only for trends in explosive acid volcanism. Nevertheless, results are roughly in agreement with other data from the Northwest Pacific, although some discrepancies in the correlation of intensity of the episodes occur. The data from Leg 57 support the hypothesis of synchronous pulses in explosive volcanism.