Concentration and isotope composition of sulphur in sediments and pore water at DSDP Leg 70 Holes

Data obtained while investigating the mounds area near the Galapagos Spreading Center demonstrate the direct influence of solutions derived from the interaction of seawater and young oceanic crust on the sedimentary cover. Investigation of metalliferous sediments from the mid-oceanic ridges, the Galapagos mounds, and the FAMOUS-area zone formations have shown that this influence and the resulting products are dependent on composition, temperature, and conditions of solution input. The study of sulfur in upwardly migrating solutions and the interaction of these solutions with sediments is of great interest. Investigations of different types of hydrothermally derived formations (Edmond, et al., 1979; Spiess et al., 1980; Styrt et al., 1981; Rosanova 1976; Grinenko et al., 1978) have shown the significant role of sulfur-bearing minerals in deposits formed from hightemperature solutions. In contrast, the addition of hydrothermal sulfur is negligible in those metalliferous sediments that precipitated as a result of the interaction between the solutions and open seawater (Bonatti et al., 1972, 1976; Gordeev et al., 1979; Migdisov, Bogdanov, et al., 1979). For example, sulfides are absent in clearly oxidized metalliferous sediments from the East Pacific Rise (EPR). Barite sulfur from these sediments is identical with seawater sulfate sulfur in isotope composition (Grinenko et al., 1978). Gurvich and Bogdanov (1977) have suggested that barium from EPR metalliferous sediments results completely from biological activity and from the components of ocean waters. Edmond et al. (1979) report that low-temperature springs from the Galapagos Rift axis contain two types of solutions: those with and those without H2S.

Geochemical characterizations of the Cretaceous formations at DSDP Holes 93-603B and 11-105

Geochemical characterizations of the Cretaceous formations at Site 603 are quite comparable with those at Site 105. In the Blake-Bahama and the Hatteras formations, the petroleum potential is medium (<5 kg HC/t of rock) to very low (<0.5 kg HC/t of rock), and the organic matter is mainly of type III origin, that is, terrestrial. At the top of the Hatteras Formation, there is a condensed series, which chiefly contains organic matter of type II origin, with up to 20 wt.% total organic carbon content in Core 603B-34 and 25 wt.% in Core 105-9. This accumulation corresponds to the Cenomanian/Turonian boundary event. An examination of dinoflagellates in the kerogen concentration assigns dates to the samples studied by organic geochemistry. The Cenomanian and Turonian age of the organic-matter-rich black claystones indicates a low rate of sedimentation, about 1 m/Ma. Furthermore, the occurrence of type II organic matter indicates an anoxic environment with insufficient oxygen renewal to oxidize the sinking hemipelagic organic matter. This organic enrichment is not related to local phenomena but to sedimentation over an extended area, because deposits are well known in various areas with different paleodepths in the North Atlantic.