Survey of pollen and spores in DSDP Holes 96-618 and 619

A preliminary palynological survey of 118 samples from the Mississippi Fan (Sites 615, 616, and 620) and from 2 intraslope basins (Sites 619 and 618) shows pollen in all samples. Reworked pollen is generally abundant, forming over 50% of the sum of pollen and reworked pollen. Concentration of nonreworked pollen is usually low (on the order of tens to hundreds of pollen grains per cubic centimeter wet sediment). Conifers, primarily Pinus, Picea, and Tsuga, dominate Pleistocene marine pollen spectra; significant percentages of Quercus are present in Holocene sediments and in sediments deposited during oxygen-isotope Stage 5.

Interstitial water chemistry, Deep Sea Drilling Project, Leg 96

On Leg 96 of the Deep Sea Drilling Project (DSDP), holes were drilled in Orca and Pigmy basins on the northern Gulf of Mexico continental slope and on the Mississippi Fan. The holes on the fan encountered interbedded sand, silt, and mud deposited extremely rapidly, most during late Wisconsin glacial time. Pore-water chemistry in these holes is variable, but does not follow lithologic changes in any simple way. Both Ca and SO4 are enriched in the pore water of many samples from the fan. Two sites drilled in the prominent central channel of the middle fan show rapid SO4 reduction with depth, whereas two nearby sites in overbank deposits show no sulfate reduction for 300 m. Calcium concentration decreases as SO4 is depleted and Li follows the same pattern. Strontium, which like Li, is enriched in samples enriched in Ca, does not decrease with SO4 and Ca. Potassium in the pore water decreases with depth at almost all sites. Sulfate reduction was active at the two basin sites and, as on the fan, this resulted in calcium carbonate precipitation and a lowering of pore water Ca, Mg, and Li. The Orca Basin site was drilled through a brine pool of 258? salinity. Pore-water salinity decreases smoothly with depth to 50 m and remains well above normal seawater values to the bottom of the hole at about 90 m. This suggests constant sedimentation under anoxic hypersaline conditions for at least the last 50,000 yr.