(Table 2) Facies and grain-size description for Mississippi Fan sediments of DSDP Leg 96

Eight lithologic facies recognized in the Mississippi Fan sediments drilled during DSDP Leg 96 are defined on the basis of lithology, sedimentary structures, composition, and texture. Of these, the calcareous biogenic sediments are of minor importance, volumetrically, as compared with the dominant resedimented terrigenous facies. Clay, mud, and silt are the most abundant sediments at all the sites drilled, with some sand and gravel in the midfan channel fill and an abundance of sand on the lower fan. Facies distribution and vertical sequences reflect the importance of sediment type and supply in controlling fan development. Sea-level changes and diapiric activity have also played an important role. Clay and sand fraction mineralogy closely mirror the dominant sediment source, namely, the Mississippi River system and adjacent continental shelf. Local and regional variation in composition on the fan mostly reflects facies differences.

Geochemistry of interstitial waters of DSDP Leg 96 sites

Interstitial water studies were done at 9 of the 11 sites visited in the Mississippi Fan and Orca and Pigmy Basins during DSDP Leg 96. High concentrations of sulfate were observed at Mississippi Fan Sites 616, 617, 620, and 623. The maximum sulfate value of 38.8 mM, recorded at Site 617, is the highest ever found in DSDP sediments. Hypersaline interstitial water was observed at Site 618 in Orca Basin. Concentration ratios of salinity to chlorinity and to sodium in interstitial waters are similar to those of Orca Basin bottom water, suggesting that the chemistry of interstitial water is affected by the dissolution of buried salt.

Pyrolyzable carbon, temperature maximum, production index and lithology for DSDP Leg 96 holes

Sediments from Deep Sea Drilling Project Sites 615, 617, 618, 619, and 620-623 were subjected to pyrolysis. The sediments are immature with respect to petroleum generation as determined by production index values of less than 0.1 and Tmax values of 460-480°C. The amount of pyrolyzable organic matter was moderately low as compared to typical petroleum source rocks. The immature organic matter present does not appear to contain a significant proportion of woody material as shown by the low gas-generating potential. Typical overbank sediments from Sites 617 and 620 generally show higher P2 values (500-800 µg hydrocarbon per g dry weight sediment) than typical channel-fill sediments from Sites 621 and 622 (P2 = 450-560 µg/g). Tmax for both types of sediment remained very constant (462-468 °C) with a slight elevation (+ 15°C) occurring in samples containing lignite. The highest P2 values occurred in sections described as turbidites. Very low P2 values (about 50 µg/g) occurred in sands. P2 values for shallower sections of basin Sites 618 and 619 tended to be higher (900-1000 µg/g) and decreased in deeper, more terrigenous sections of Site 619. Preliminary experiments indicate that microbiological degradation of sediment organic matter causes a decrease in P2. Pyrolyzable organic matter from lower fan Site 623 appears to increase with depth in two different sediment sequences (40-85 and 95-125 m sub-bottom). Organic matter type, as shown by pyrolysis capillary gas chromatography (GC) patterns, was generally the same throughout the well, with much more scatter occurring in the deepest sections (130-155 m sub-bottom). One major and two minor organic matter types could be recognized in both fan and basin sites drilled on Leg 96.