Miocene dissolution facies and microfacies at Northwest Atlantic Deep Sea Drilling Project Site 93-603

Depth fluctuations of the lysocline and calcite compensation depth (CCD) through time were investigated at Deep Sea Drilling Project Site 603, Leg 93. The CCD fell during the middle Miocene at the onset of the Western Boundary Undercurrent, correlated with seismic Horizon X. Subsequently deposited units show fluctuations of the dissolution curve. Major changes in dissolution facies correspond with lithologic boundaries.

Geochemistry and petrography of organic matter at DSDP Site 93-603

A series of 22 sediment samples of Cretaceous and Cenozoic age from DSDP Holes 603, 603B, and 603C at the continental rise off the northeastern American coast near Cape Hatteras was investigated by organic geochemical methods including organic carbon determination, Rock-Eval pyrolysis, gas chromatography and combined gas chromatography/mass spectrometry of extractable hydrocarbons, and kerogen microscopy. An abundance of terrigenous organic matter, including larger coal particles (almost exclusively consisting of huminite/vitrinite macerals), is the dominant characteristic of the organofacies types at Site 603. Marine organic matter, mostly structurally degraded and in the form of fecal pellets, was preserved in the Valanginian laminated marls and in Cenomanian black claystone turbidites. Long-chain nalkanes reflect the terrigenous imprint in the nonaromatic hydrocarbon fractions, whereas a second maximum at lower carbon numbers in most cases is caused by the presence of more mature recycled organic matter. Abundant isoprenoid and steroid hydrocarbons were found in sediments containing mainly marine organic matter, whereas hopanoids reflect the ubiquitous microbial activity. The organic matter in the Site 603 sediments, in so far as it is not recycled, is thermally immature.

Paleocene-Eocene calcareous nannofossils of onshore wells from the Coastal Plain of New Jersey and Maryland, USA

Paleogene calcareous nannofossils from split spoon cores recovered from five wells along the Coastal Plain of New Jersey and Maryland have been analyzed in order to provide onshore information complementary to that derived from the offshore DSDP Site 605 (upper continental rise off New Jersey). Hiatuses are more numerous and of greater extent in the onshore sections, but the major ones correlate well with those noted in the offshore section. At one site at least (Leggett Well), sedimentation may well have been continuous across the Cretaceous/Tertiary boundary, as it is believed to have been at DSDP Site 605. These various correlations are discussed elsewhere in a companion paper (Olsson and Wise, this volume). Important differences in nannofossil assemblages are noted between the onshore (shelf paleoenvironment) and offshore (slope-rise paleoenvironment) sections. Lithostromation simplex, not present offshore, is consistently present onshore and seems to be confined to the Eocene shelf sediments of this region. The same relationship holds for the zonal marker, Rhabdosphaera gladius Locker. The Rhomboaster-Tribrachiatus plexus is more diverse and better preserved in the onshore sections, where the lowermost Eocene Zone CP9 is well represented. Differential preservation is postulated to account for two morphotypes of Tribrachiatus bramlettei (Brönnimann and Stradner). Type A is represented at DSDP Site 605 by individuals with short, stubby arms, but these forms are not present in the equivalent onshore sections. There they are replaced by the Type B morphotypes, which exhibit a similar basic construction but possess much longer, more delicate arms.

Sediment descriptions, stage, calcium carbonate, organic carbon, delta 13C and geolipids at DSDP Hole 93-603B

Organic matter contents of black shales from the Cretaceous Hatteras and Blake-Bahama formations have been compared to those from surrounding organic-poor strata using C/N ratios, d13C values, and distributions of extractable and nonsolvent-extractable, long-chain hydrocarbons, acids, and alcohols. The proportion of marine and land-derived organic matter varies considerably among all samples, although terrigenous components generally dominate. Most black shales are hydrocarbon-poor relative to their organic-carbon concentrations. Deposition of the black shales in Hole 603B evidently occurred through turbiditic relocation from shallower landward sites and rapid reburial at this outer continental rise location under generally oxygenated bottom-water conditions.