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.

Cretaceous and Paleogene calcareous nannofossils from ODP Leg 123

Two of five holes drilled at two separate sites during Leg 123 of the Ocean Drilling Program intersected thick and relatively complete sections of Upper Cretaceous-Paleogene nannofossiliferous sediments. Although dominated by turbidite deposition in the upper part, Hole 765C contains a thick and relatively complete Albian-Oligocene section, including a particularly thick Aptian interval, with abundant and fairly well-preserved nannofossils. Several unconformities are confidently interpreted in this section that span much of the Santonian, late Campanian, Maestrichtian, late Eocene, and early Oligocene. Hole 766A contains a thick and relatively complete Albian-lower Eocene section having generally abundant and well-preserved nannofossils. Several unconformities also have been identified in this section that span much of the Coniacian, early Campanian, Maestrichtian, and late Eocene through early Pliocene. The chronostratigraphic position and length of all these unconformities may have considerable significance for reconstructing the sedimentary history and for interpreting the paleoceanography of this region. A particularly thick section of upper Paleocene-lower Eocene sediments, including a complete record across the Paleocene/Eocene boundary, also was cored in Hole 766A that contains abundant and diverse nannofossil assemblages. Although assemblages from this section were correlated successfully using a standard low-latitude zonation, difficulties were encountered that reduced biostratigraphic resolution. Several lines of evidence suggest a mid-latitude position for Site 766 during this time, including (1) high assemblage diversity characteristic of mid-latitude zones of upwelling and (2) absence of certain ecologically controlled markers found only in low latitudes.

Geochemistry at DSDP Leg 75 Holes

Samples of sediments and rocks collected at DSDP Sites 530 and 532 were analyzed for 44 major, minor, and trace elements for the following purposes: (1) to document the downhole variability in geochemistry within and between lithologic units; (2) to document trace-element enrichment, if any, in Cretaceous organic-carbon-rich black shales at Site 530; (3) to document trace-element enrichment, if any, in Neogene organic-carbon-rich sediments at Site 532; (4) to document trace-element enrichment, if any, in red claystone above basalt basement at Site 530 that might be attributed to hydrothermal activity or weathering of basalt. Results of the geochemical analyses showed that there are no significant enrichments of elements in the organic-carbon-rich sediments at Site 532, but a number of elements, notably Cd, Co, Cr, Cu, Mo, Ni, Pb, V, and Zn, are enriched in the Cretaceous black shales. These elements have different concentration gradients within the black-shale section, however, which suggests that there was differential mobility of trace elements during diagenesis of interbedded more-oxidized and less-oxidized sediments. There is little or no enrichment of elements from hydrothermal activity in the red claystone immediately overlying basalt basement at Site 530, but slight enrichments of several elements in the lowest meter of sediment may be related to subsea weathering of basalt

Geochemistry at DSDP Leg 74 Holes

Clay mineralogical and inorganic geochemical data from the Campanian to the Pleistocene provide information bearing on the evolution of both continental and marine paleoenvironments in the Walvis Ridge area. (1) Alteration processes of basalts occurred under subaerial conditions during the Campanian and Maestrichtian and were virtually absent in deeper marine environments. (2) Strong tectonic effects were present during the Campanian and persisted until the early Eocene. (3) Subsidence of this part of the Walvis Ridge became important during the late Maestrichtian and continued into the Paleocene and Eocene. (4) The influence of global climatic cooling was evident from the late Eocene on. (5) Modification of oceanic circulation and the increasing influence of surface and deep water masses on the sedimentation characterized the Cenozoic.

Geochemistry, isotopic ratios and mineral composition of samples from ODP Leg 163 sites

Thirty-five samples from the drill core of the three Leg 163 sites (Sites 988, 989, and 990) off the southeast coast of Greenland were analyzed for 27 major, minor, and trace elements by X-ray fluorescence (XRF) and for 25 trace elements, including 14 rare-earth elements (REEs), by an inductively coupled plasma source mass spectrometer (ICP/MS). Sr- and Nd-isotope data are reported for seven samples and oxygen-isotope data are reported for 19 plagioclase separates. In addition, a reconnaissance survey of the composition of the main mineral phases, plagioclase, pyroxene, and oxides was determined on an electron microprobe to provide the basic information required for petrogenetic modeling. Olivine pseudomorphs are present in many of the samples, but in no case was an olivine grain found that was fresh enough to give a reliable analysis. The chemical and isotopic data recorded here were determined to provide a comparison with the larger data sets acquired by the Edinburgh, Copenhagen, and Leicester laboratories from both Legs 152 and 163 drill cores. This will permit a detailed comparison of the North Atlantic flood basalt province as a whole with the better known Columbia River, Deccan, and Karoo continental flood basalt provinces, for which substantial chemical data sets are already available at Washington State University.

Age models, accumulation rates, sand and carbonates at DSDP Leg 74 holes

Accumulation rates for the five sites drilled during Leg 74 of the Glomar Challenger are presented on a common timescale based on calibration of datum levels to paleomagnetic records in Leg 74 sediments for the Paleogene, and a new compilation by Berggren et al. (1985), for the Neogene, and using the seafloor-spreading magnetic anomaly timescale of Kent (1985). We present data on accumulation of total sediment, of foraminifers, of the noncarbonate portion, and of fish teeth that give a history of productivity, winnowing, carbonate dissolution, and nonbiogenic input to what was then a part of the South Atlantic at about 30 deg S.

Isotopic composition of interstitial fluids and origin of methane at DSDP Leg 84 Holes

CH4 and CO2 species in pore fluids from slope sediments off Guatemala show extreme 13C-enrichment (d13C of -41 and +38 per mil, respectively) compared with the typical degree of 13C-enrichment in pore fluids of DSDP sediments (d13C of - 60 and + 10 per mil). These unusual isotopic compositions are believed to result from microbial decomposition of organic matter, and possibly from additional isotopic fractionation associated with the formation of gas hydrates. In addition to the isotopic fractionation displayed by CH4 and CO2, the pore water exhibits a systematic increase in d18O with decrease in chlorinity. As against seawater d18O values of 0 and chlorinity of 19 per mil, the water collected from decomposed gas hydrate from Hole 570 had a d18O of + 3.0 per mil and chlorinity of 9.5 per mil. The isotopic compositions of pore-fluid constituents change gradually with depth in Hole 568 and discontinuously with depth in Hole 570.

Interstitial water d13C and sediment geochemistry of ODP Leg 166 sites

A review of interstitial water samples collected from Sites 1003-1007 of the Bahamas Transect along with a shore-based analysis of oxygen and carbon isotopes, minor and trace elements, and sediment chemistry are presented. Results indicate that the pore-fluid profiles in the upper 100 meters below seafloor (mbsf) are marked by shifts between 20 and 40 mbsf that are thought to be caused by changes in sediment reactivity, sedimentation rates, and the influence of strong bottom currents that have been active since the late Pliocene. Pore-fluid profiles in the lower Pliocene-Miocene sequences are dominated by diffusion and do not show significant evidence of subsurface advective flow. Deeper interstitial waters are believed to be the in situ fluids that have evolved through interaction with sediments and diffusion. Pore-fluid chemistry is strongly influenced by carbonate recrystallization processes. Increases in pore-fluid Cl- and Na+ with depth are interpreted to result mainly from carbonate remineralization reactions that are most active near the platform margin. A lateral gradient in detrital clay content observed along the transect, leads to an overall lower carbonate reactivity, and enhances preservation of metastable aragonite further away from the platform margin. Later stage burial diagenesis occurs at slow rates and is limited by the supply of reactive elements through diffusion.

Planktonic foraminiferal stratigraphy of sediments from ODP Leg 173 sites

Planktonic foraminifers recovered from five sites drilled off western Portugal during Ocean Drilling Program Leg 173 are documented. Hole 1065A yielded planktonic foraminifers from Miocene sediments in Sections 173-1065A-1R-1 through 6R-2. Hole 1067A penetrated middle Eocene sediments containing planktonic foraminifers in Section 173-1067A-1R-1 through Lower Eocene planktonic foraminiferal horizons to Section 12R-CC. Hole 1068A yielded planktonic foraminiferal assemblages from middle Eocene sediments at Section 173-1068A-1R-1 to Maastrichtian sediments at Section 173-1068A-15R-3, whereas Hole 1069A contained middle Eocene taxa in Section 173-1069A-1R-1 through Campanian/Maastrichtian forms in Section 173-1069A-15R-2. All of the planktonic foraminifers recovered from these sites are of poor to moderately good preservation and are variable in abundance. Hole 1070A yielded only six planktonic foraminifers, with the assemblages being dominated by benthic foraminifers and fish teeth. The co-occurrence of other microfossil groups, including benthic foraminifers, are only briefly discussed here. The lower Miocene biosiliceous facies recorded in Hole 1065A is considered to be coeval with a similar facies found in onshore sections farther to the east, in southern Spain.