ALBERT

Description: Voluminous, subaerial magmatism resulted in the formation of extensive seaward-dipping reflector sequences (SDRS) along the Paleogene Southeast Greenland rifted margin. Drilling during Leg 163 recovered basalts from the SDRS at 66ºN (Site 988) and 63ºN (Sites 989 and 990). The basalt from Site 988 is light rare-earth-element (REE) enriched (La(n)/Yb(n) = 3.4), with epsilon-Nd(t=60) = 5.3, 87Sr/86Sr = 0.7034, and 206Pb/204Pb = 17.98. It is similar to tholeiites recovered from the Irminger Basin during Leg 49 and to light-REE-enriched tholeiites from Iceland. Drilling at Site 989, the innermost of the sites on the 63ºN transect, was proposed to extend recovery of the earliest part of the SDRS initiated during Leg 152. These basalts are, however, younger than those from Site 917 and are compositionally similar to basalts from the more seaward Sites 990 and 915. Many of the basalts from Sites 989 and 990 show evidence of contamination by continental crust (e.g., epsilon-Nd(t=60) extends down to -3.7, 206Pb/204Pb extends down to 15.1). We suggest that the contaminant is a mixture of Archean granulite and amphibolite and that the most contaminated basalts have assimilated ~5% of crust. Uncontaminated basalts are isotopically similar to basalts from Site 918, on the main body of the SDRS, and are light-REE depleted. Consistent with previous models of the development of this margin, we show that at the time of formation of the basalts from Sites 989 and 990 (1) melting was at relatively shallow levels in a fully-fledged rift zone; (2) fragments of continental crust were present in the lithosphere above the zones of melt generation; and (3) the sublithospheric mantle was dominated by a depleted Icelandic plume component.

Description: The following data paper summarizes diatom biostratigraphic data from sediments drilled in the Costa Rica accretionary wedge during Ocean Drilling Program Leg 170. Quaternary through lower Miocene diatom zones characteristic of the equatorial Pacific region are recognized in the reference section, Site 1039, which was drilled on the downgoing Cocos plate. At Sites 1040-1043, where the recovered silty clay units are primarily wedge and apron sediments that overlie the underthrust sections, diatoms are generally low in abundance, and complete zonation of the cores was not possible above the décollement surface.

Description: Phospholipid fatty acids were measured in samples of 60°-130°C sediment taken from three holes at Site 1036 (Ocean Drilling Program Leg 169) to determine microbial community structure and possible community replacement at high temperatures. Five of six samples had similar concentrations of phospholipid fatty acids (2-6 pmol/g dry weight of sediment), and biomass estimates from these measurements compare favorably with direct microscopic counts, lending support to previous microscopic measures of deep sedimentary biomass. Very long-chain phospholipid fatty acids (21 to 30 carbons) were detected in the sediment and were up to half the total phospholipid fatty acid measured; they appear to increase in abundance with temperature, but their significance is not known. Community composition from lipid analysis showed that samples contained standard eubacterial membrane lipids but no detectable archaeal lipids, though archaea would be expected to dominate the samples at high temperatures. Cluster analysis of Middle Valley phospholipid fatty acid compositions shows that lipids in Middle Valley sediment samples are similar to each other at all temperatures, with the exception of very long-chain fatty acids. The data neither support nor deny a shift to a high-temperature microbial community in hot cores, so at the present time we cannot draw conclusions about whether the microbes observed in these hot sediments are active.

Description: Sulfide mineral major and trace element analyses were performed on more than 50 polished slabs representing mineralization from three seafloor hydrothermal massive sulfide deposits. Samples from the Bent Hill and ODP Mound massive sulfide deposits, both on the Juan de Fuca Ridge, can be contrasted with samples from the Trans-Atlantic Geotraverse (TAG) hydrothermal mound on the Mid-Atlantic Ridge. The massive sulfide at Bent Hill is predominantly pyrite and pyrrhotite, with increasing amounts of copper-bearing sulfide minerals at the base of the massive sulfide body and through the stockwork to an interval 200 m below seafloor that hosts high copper mineralization (Deep Copper Zone). ODP Mound contains much more abundant sphalerite and copper-bearing sulfides as compared to either Bent Hill or TAG, which are predominantly pyrite with much less abundant chalcopyrite. Copper-bearing sulfides from the Deep Copper Zone beneath Bent Hill and the lowest sampled interval of ODP Mound are petrographically and chemically similar, but distinct from copper-bearing minerals higher in either sequence.

Description: Sequences of late Pliocene to Holocene sediment lap onto juvenile igneous crust within 20 km of the Juan de Fuca Ridge in northwestern Cascadia Basin, Pacific Ocean. The detrital modes of turbidite sands do not vary significantly within or among sites drilled during Leg 168 of the Ocean Drilling Program. Average values of total quartz, total feldspar, and unstable lithic fragments are Q = 35, F = 35, and L = 30. Average values of monocrystalline quartz, plagioclase, and K-feldspar are Qm = 46, P = 49, and K = 5, and the average detrital modes of polycrystalline quartz, volcanic-rock fragments, and sedimentary-rock plus metamorphic-rock fragments are Qp = 16, Lv = 43, and Lsm = 41. Likely source areas include the Olympic Peninsula and Vancouver Island; sediment transport was focused primarily through the Strait of Juan de Fuca, Juan de Fuca Channel, Vancouver Valley, and Nitinat Valley. Relative abundance of clay minerals (〈2-µm-size fraction) fluctuate erratically with depth, stratigraphic age, and sediment type (mud vs. turbidite matrix). Mineral abundance in mud samples are 0%-35% smectite (mean = 8%), 18%-59% illite (mean = 40%), and 29%-78% chlorite + kaolinite (mean = 52%). We attribute the relatively low content of smectite to rapid mechanical weathering of polymictic source terrains, with little or no input of volcanic detritus from the Columbia River. The scatter in clay mineralogy probably was caused by converging of surface currents, turbidity currents, and near-bottom nepheloid clouds from several directions, as well as subtle changes in glacial vs. interglacial weathering products.

Description: Ocean Drilling Program Site 1002 in the Cariaco Basin was drilled in the final two days of Leg 165 with only a short transit remaining to the final port of San Juan, Puerto Rico. Because of severe time constraints, cores from only the first of the three long replicate holes (Hole 1002C) were opened at sea for visual description, and the shipboard sampling was restricted to the biostratigraphic examination of core catchers. The limited sampling and general scarcity of biostratigraphic datums within the late Quaternary interval covered by this greatly expanded hemipelagic sequence resulted in a very poorly defined age model for Site 1002 as reported in the Leg 165 Initial Reports volume of the Proceedings of the Ocean Drilling Program. Here, we present for the first time a new integrated stratigraphy for Site 1002 based on the standard of late Quaternary oxygen-isotope variations linked to a suite of refined biostratigraphic datums. These new data show that the sediment sequence recovered by Leg 165 in the Cariaco Basin is continuous and spans the time interval from 0 to ~580 ka, with a basal age roughly twice as old as initially suspected from the tentative shipboard identification of a single biostratigraphic datum. Lithologic subunits recognized at Site 1002 are here tied into this new stratigraphic framework, and temporal variations in major sediment components are reported. The biogenic carbonate, opal, and organic carbon contents of sediments in the Cariaco Basin tend to be high during interglacials, whereas the terrigenous contents of the sediments increase during glacials. Glacioeustatic variations in sea level are likely to exert a dominant control on these first-order variations in lithology, with glacial surface productivity and the nutrient content of waters in the Cariaco Basin affected by shoaling glacial sill depths, and glacial terrigenous inputs affected by narrowing of the inner shelf and increased proximity of direct riverine sources during sea-level lowstands.

Description: We used paleomagnetic results from Sites 998, 999, 1000, and 1001 to estimate the paleolatitude of the Caribbean region over the past 80 m.y. The data include remanence measurements of split-core sections (typically 1.5 m long) and discrete samples (6-12 cm**3 in volume) from volcanic and sedimentary rocks. From these, we computed 15 new paleolatitude estimates for Sites 999 and 1001 on the Caribbean plate and three new paleolatitude estimates for Site 998 on the Cayman Rise, currently on the southern North American plate. One estimate from Site 1001 is based on 230 measurements made along split-core sections of basalt after demagnetization of 20-25 mT. The other 17 estimates are based on principal component analysis of demagnetization data from 438 discrete paleomagnetic samples from sedimentary units. Where necessary, the 18 new paleolatitude estimates are corrected for a polarity ambiguity bias that occurs when averaging paleomagnetic data from drill cores that have shallow inclinations and are not azimuthally oriented. We also investigated the contribution of additional biases that may arise from a compaction-related inclination error, which could affect the sedimentary units, though not the basalt units. Several lines of evidence, including the lack of a correlation between porosity (or water content) and inclination, indicate that the inclination error is small, if present at all. The results from Sites 999 and 1001 indicate that the Caribbean plate was 5°-15° south of its current position at ~80 Ma, possibly placing it directly over the equator in the Late Cretaceous. Although the data do not preclude changes in the rate of northward motion over the past 80 m.y., they are consistent with a constant northward progression at a rate of 18 km/m.y. Given the uncertainties in the data, rates of northward motion could be as low as 8 km/m.y. or as high as 22 km/m.y. These results are compatible with several existing models for the evolution of the Caribbean plate, including those that have the Caribbean plate originating in the Pacific Ocean west of subduction zones active in the Central American region during the Cretaceous, and those that have the Caribbean plate originating within the Central American region, though more than 1000 km west of its current position relative to North and South America.

Description: The isotopic characteristics of CH4 (d13C values range from -101.3 per mil to -61.1 per mil PDB, and dD values range from -256 per mil to -136 per mil SMOW) collected during Ocean Drilling Program (ODP) Leg 164 indicate that the CH4 was produced by microbial CO2 reduction and that there is not a significant contribution of thermogenic CH4 to the sampled sediment gas from the Blake Ridge. The isotopic values of CO2 (d13C range -20.6 per mil to +1.24 per mil PDB) and dissolved inorganic carbon (DIC; d13C range -37.7 per mil to +10.8 per mil PDB) have parallel profiles with depth, but with an offset of 12.5 per mil. Distinct downhole variations in the carbon isotopic composition of CH4 and CO2 cannot be explained by closed-system fractionation where the CO2 is solely derived from the locally available sedimentary organic matter (d13C -2.0 per mil ± 1.4 per mil PDB) and the CH4 is derived from CO2 reduction. The observed isotopic profiles reflect the combined effects of upwards gas migration and decreased microbial activity with depth.

Description: About 13 m of Cretaceous, tholeiitic basalt, ranging from normal (N-MORB) to transitional (T-MORB) mid-ocean-ridge basalts, was recovered at Ocean Drilling Program Site 843 west of the island of Hawaii. These moderately fractionated, aphyric lavas are probably representative of the oceanic basement on which the Hawaiian Islands were built. Whole-rock samples from parts of the cores exhibiting only slight, low-temperature, seawater alteration were analyzed for major element, trace element, and isotopic composition. The basalts are characterized by enrichment in the high field strength elements relative to N-MORB, by a distinct positive Eu anomaly, and by Ba/Nb and La/Nb ratios that are much lower than those of other crustal or mantle-derived rocks, but their isotope ratios are similar to those of present-day N-MORB from the East Pacific Rise. Hole 843A lavas are isotopically indistinguishable from Hole 843B lavas and are probably derived from the same source at a lower degree of partial melting, as indicated by lower Y/Nb and Zr/Nb ratios and by higher concentrations of light and middle rare earth elements and other incompatible elements relative to Hole 843B lavas. Petrographic and trace-element evidence indicates that the Eu anomaly was the result of neither plagioclase assimilation nor seawater alteration. The Eu anomaly and the enrichments in Ta, Nb, and possibly U and K relative to N-MORB apparently are characteristic of the mantle source. Age-corrected Nd and Sr isotopic ratios indicate that the source for the lavas recovered at ODP Site 843 was similar to the source for Southeast Pacific MORB. An enriched component within the Cretaceous mantle source of these basalts is suggested by their initial 208Pb/204Pb-206Pb/204Pb and epsilon-Nd-206Pb/204Pb ratios. The Sr-Pb isotopic trend of Hawaiian post-shield and post-erosional lavas cannot be explained by assimilation of oceanic crust with the isotopic composition of the Site 843 basalts.

Description: Sediment spectral reflectance measurements were generated aboard the JOIDES Resolution during Ocean Drilling Program Leg 162 shipboard operations. The large size of the raw data set (over 1.3 gigabytes) and limited computer hard disk storage space precluded detailed analysis of the data at sea, although broad band averages were used as aids in developing splices and determining lithologic boundaries. This data report describes the methods used to collect these data and their shipboard and postcruise processing. These initial results provide the basis for further postcruise research.