(Table 1) Mineral composition at DSDP Leg 64 Holes

Mineral composition and compounds of sediments from the Guaymas Basin.

(Table 1) Minerals of bulk sediment at DSDP Holes 64-480 and 64-481

This paper provides a brief, descriptive, sedimentological background for the chapters on hydraulic piston core Site 480 in this symposium, and supplements data given in the site chapter for Sites 479-480 (this volume, Pt. 1). Sediments are composed primarily of planktonic diatoms, with minor numbers of silicoflagellates, radiolarians, and varying amounts of both benthic and planktonic foraminifers, along with a large terrigenous component of olive brown, silty clay. The section contains meter-thick intervals of finely laminated facies alternating with nonlaminated zones. A few paleoenvironmental events are documented within the generally uniform sequence by sporadic occurrences of thin turbidites, phosphatic concretions, fish debris concentrations, an ash layer, and a thin layer of diagenetic dolomite. The distribution of nonlaminated and laminated zones is attributed to fluctuations of bottom-water oxygen content caused by variations in circulation, fertility, and productivity. Homogeneous sections are interpreted as coinciding with cooler climatic periods, whereas laminated sections seem to correspond to upwelling conditions during drier periods.

Organic chemistry of sediments from the Tyrrhenian Sea

Thirty sediment samples from Tortonian to Pleistocene age of five ODP locations (Holes 650A, 651A, and 652A, and Sites 654 and 655) in the Marsili Basin, Vavilov Basin, and Sardinia Margin (Tyrrhenian Sea) were studied by organic geochemical methods including total organic carbon determination, Rock-Eval pyrolysis, bitumen extraction, pyrolysis-gas chromatography, and organic petrography. Six organic facies, including open ocean anoxia with variable terrestrial input, oxic open ocean, oxic tidal flat, mildly oxic lagoon, and anoxic lacustrine algal-bacterial mat environments, have been recognized in these sediments. The sediments below 500 m in Sardinia Margin are mature for significant hydrocarbon generation. Possible mature source-rock (Type I and IIB/III kerogen) and migrated bitumen occur in the deeper part of the section in Vavilov Basin and Sardinia Margin sediments. Sporadic sapropel formation observed in the studied Pliocene-Pleistocene sediment section is probably controlled by organic productivity due to nutrient supply by the rivers and terrestrial input associated with open ocean anoxia or anoxia caused by the material balance between rate of organic matter supplied by turbidites and organic matter consumption. Pliocene and Pleistocene sapropels are mostly immature and lie within Type II-III (precisely as IIA-IIB and IIB source rocks) kerogen maturation path.