Organic geochemistry of ODP Leg 107 sediments

The Rock-Eval pyrolysis of rock samples and the elemental analysis of kerogens show clear differences between Messinian black shales and Pliocene-Pleistocene sapropels recovered during ODP Leg 107. The Messinian black shales are characterized by a large variety of compositions which probably reflects a great diversity of depositional and diagenetic paleoenvironments. In contrast, the Pliocene-Pleistocene sapropels, occurring as discrete layers in nannofossil oozes barren of organic carbon, constitute a rather homogeneous group in terms of organic content. A considerable contribution of terrestrial organic matter in the sapropels could mean that an identical phenomenon of terrestrial input has been periodically reproduced in the basin. The maturity and the nature of the organic matter are discussed with respect to anomalous values recorded for Tmax parameter

(Table 1) Organic geochemistry of sediments recovered from DSDP Leg 65 Holes

Pliocene-Pleistocene marls, muds, and hemipelagic clays with some beds of silt and sand were recovered on Leg 65 near the crest of the East Pacific Rise at the mouth of the Gulf of California. The organic matter in the sediments is mainly of marine origin for the upper Pleistocene sediments (0-0.61 m.y.), while the lower Pleistocene deposits (0.61- 1.80 m.y.) are characterized by continental organic matter except near the bottom of the sediment section in Hole 483A, where marine organic matter was found. The sediments belong to an early stage of geochemical evolution, except in Hole 482D, where hydrothermal effects are invoked to explain the maturity of the organic matter above the basement

(Table 1) Carbon content and petroleum potential at DSDP Hole 73-520

At the end of the Leg 73 cruise, at Site 520, a thick upper Miocene facies of laminated diatomite was discovered. It was hypothesized that the sediment was derived from nutrient-rich waters in a young Cenozoic anoxic basin in the open Atlantic Ocean near the Mid-Atlantic Ridge