Major and trace element concentrations of sediments from the IODP Exp302 sites

We analyzed a suite of sediment samples recovered in the central Arctic Ocean for major, trace, and rare earth elements in order to assess changes in terrigenous source material throughout the Cenozoic. The terrigenous component consists of two end-members. Input from a shale-like composition dominates bulk sediments, especially those deposited during the Paleocene and since the Miocene, and may represent sediment supply from the eastern Laptev Sea. Therefore, even though the environment and transport mechanisms may have varied from ice free to ice dominated, sequences of the early Paleogene and later Neogene appear to have been influenced by a single major terrigenous source. This suggests similar transport capabilities and trajectories for both ocean and drift currents through significant parts of the Cenozoic. Influence from a more mafic source appears to be more important through the early Eocene to the middle Miocene and most likely represents material from the western Laptev Sea or Kara Sea. Thus, Eocene major changes in surface water productivity appear broadly synchronous with those in terrigenous provenance. A combination of regional sea level variations, local shelf processes, and transport mechanisms are among the more probable causes for the observed source changes. Although the assignment of sources using chemistry presently is constrained by a lack of data from certain regions (e.g., eastern Siberian Sea) our results generally agree with inferences based on mineralogy or radiogenic isotopes and shed further light on long-term reconstructions of the central Arctic Ocean.

Magnetostratigraphy of ODP Leg 207 sediments

Ocean Drilling Program (ODP) Sites 1257-1261 recovered thick sections of Upper Cretaceous-Eocene oceanic sediments on Demerara Rise off the east coast of Surinam and French Guiana, South America. Paleomagnetic and rock magnetic measurements of ~800 minicores established a high-resolution composite magnetostratigraphy spanning most of the Maastrichtian-Eocene. Magnetic behavior during demagnetization varied among lithologies, but thermal demagnetization steps >200°C were generally successful in removing present-day normal polarity overprints and a downward overprint induced during the ODP coring process. Characteristic remanent magnetizations and associated polarity interpretations were generally assigned to directions observed at 200°-400°C, and the associated polarity interpretations were partially based on whether the characteristic direction was aligned or apparently opposite to the low-temperature "north-directed" overprint. Biostratigraphy and polarity patterns constrained assignment of polarity chrons. The composite sections have a complete polarity record of Chrons C18n (middle Eocene)-C34n (Late Cretaceous).

Chemistry of upper Eocene microtektites

Late Eocene microtektites and crystal-bearing microkrystites extracted from DSDP and ODP cores from the Atlantic, Pacific, and Indian oceans have been analyzed to address their provenance. A new analysis of Nd and Sr isotopic compositions confirms previous work and the assignment of the uppermost microtektite layer to the North American tektites, which are associated with the 35.5 Ma, 85 km diameter Chesapeake impact structure of Virginia, USA. Extensive major element and Nd and Sr isotopic analyses of the microkrystites from the lowermost layer were obtained. The melanocratic microkrystites from Sites 216 and 462 in the Indian and Pacific oceans possess major element chemistries, Sr and Nd isotopic signatures and Sm-Nd, T CHUR, model ages similar to those of tagamite melt rocks in the Popigai impact structure. They also possess Rb-Sr, T UR, model ages that are younger than the tagamite TCHUR ages by up to ~1 Ga, which require a process, as yet undefined, of Rb/Sr enrichment. These melanocratic microkrystites are consistent with a provenance from the 35.7 Ma, 100 km diameter Popigai impact structure of Siberia, Russia, while ruling out other contemporaneous structures as a source. Melanocratic microkrystites from other sites and leucocratic microkrystites from all sites possess a wide range of isotopic compositions (epsilon (143Nd) values of -16 to -27.7 and epsilon (87Sr) values of 4.1-354.0), making the association with Popigai tagamites less clear. These microkrystites may have been derived by the melting of target rocks of mixed composition, which were ejected without homogenization. Dark glass and felsic inclusions extracted from Popigai tagamites possess epsilon (143Nd) and epsilon (87Sr) values of -26.7 to -27.8 and 374.7 and 432.4, respectively, and T CHUR and T UR model ages of 1640-1870 Ma and 240-1830 Ma, respectively, which require the preservation of initially present heterogeneity in the source materials. The leucocratic microkrystites possess diverse isotopic compositions that may reflect the melting of supra-basement sedimentary rocks from Popigai, or early basement melts that were ejected prior to homogenization of the Popigai tagamites. The ejection of melt rocks with chemistries consistent with a basement provenance, rather than the surface ~1 km of sedimentary cover rocks, atypically indicates a non-surficial source to some of the ejecta. Microkrystites from two adjacent biozones possess statistically indistinguishable major element compositions, suggesting they have a single source. The occurrence of microkrystites derived from a single impact event, but in different biozones, can be explained by: (1) diachronous biozone boundaries; (2) post-accumulation sedimentary reworking; or (3) erroneous biozonation.

Early to middle Miocene radiolarian stratigraphy of the Kerguelen Plateau, Southern Ocean

Early to middle Miocene radiolarian assemblages were examined at three sites (747, 748, and 751) that were cored during Ocean Drilling Program Leg 120 south of the present polar frontal zone on the Kerguelen Plateau (Indian sector of the Southern Ocean). The radiolarian biostratigraphic study relies on a radiolarian zonation recently developed on Leg 113 materials in the Atlantic sector of the Southern Ocean, which is correlated with the geomagnetic time scale. New radiolarian biostratigraphic data also considering the established geomagnetic polarity record were used to improve and emend the age calibration of some lower Miocene radiolarian zones and a redefined middle Miocene radiolarian zonation is proposed. Based on these results, a revised age assignment of the lower Miocene sections drilled at Leg 113 Sites 689 and 690 is proposed.

Geochemistry of abyssal oceanic magmas

Massive, nearly holocrystalline dolerites from DSDP Hole 417D contain from 0.5 to 1.5% of granophyric patches composed mainly of Na-plagioclase and quartz. These patches are compositionally similar to other crystalline silicic rocks from oceanic spreading centers and differ from rarer abyssal silicic glasses. Crystalline varieties with SiO2 > 60 wt.% generally have Na/K >10, whereas silicic glasses have Na/K in the range 3-6. While crystal fractionation readily accounts for the Na2O and K2O contents of abyssal silicic glasses, both the 417D granophyres and other crystalline abyssal silicic rocks have much lower K2O than that predicted by any reasonable crystal-liquid fractionation model. We propose that high-temperature vapor phase transport is responsible for removal of potassium during late-stage crystallization of these rocks. This allows for the formation of cogenetic silicic glassy and crystalline rocks with greatly different Na/K ratios. These observations and interpretations lead to a more confident assignment of high Na/K silicic rocks of oceanic and ophiolitic environments to a cogenetic origin with basaltic oceanic crust.

XRF iron (Fe) counts of ODP Hole 171-1050A and 171-1051A

Upper Paleocene to lower Eocene sediments drilled at Ocean Drilling Program (ODP) Site 1051 (Blake Nose, off Florida) display well-defined orbital cycles, a detailed magnetic stratigraphy, and a suite of planktonic foraminiferal datums. We derived a cyclostratigraphy by using spectral analysis of high-resolution records of elemental concentrations obtained by an X-ray fluorescence (XRF) Core Scanner. XRF counts of iron serve as a proxy for the relative amount of terrestrial material. Sliding-window spectral analysis, bandpass filtering, and direct counting of precession and obliquity cycles yield minimum durations for magnetic polarity chrons C22 to C26 (~49 to ~61 Ma), calculations of sediment accumulation rates, as well as constraints on the timing of biostratigraphic and climatological events in the vicinity of the Initial Eocene Thermal Maximum (IETM). Durations of polarity chrons as represented in sediments drilled at Site 1051 were estimated using a conservative assignment of 41 k.y. for obliquity cycles and 21 k.y. for precession cycles. Combined polarity chrons C26r and C26n span 3.61 m.y., and chron C25r spans 1.07 m.y. Polarity chron C24r is estimated as 2.877 m.y. The interpretation of polarity chron C24n is ambiguous, but its duration is probably <1.23 m.y. Polarity chron C23r spans 0.53 m.y., chron C23n is 0.74 m.y., and chron C22r is 0.9 m.y. Spectral analysis through this interval indicates that spectral peaks shift through time and are related to changes in sedimentation rate in Site 1051. The sedimentation rates dramatically increased ~200 k.y. after the IETM and remained high for most of chron C24r.

Carbonate minerals, uranium and thorium concentration and U-Th ages of sediments from ODP Leg 166 sites

We have performed U-Th isotope analyses on pure aragonite samples from the upper sections of Leg 166 cores to assign each aragonite-rich sediment package to the correct sea-level highstand. The uppermost sediment package from each of the four sites investigated (Sites 1003, 1005, 1006, and 1007) yielded a Holocene U-Th age. Sediment packages from deeper in the cores have suffered diagenesis. This diagenesis consists of significant U loss (up to 40%) in the site nearest the platform (Site 1005), slight U gain in sites further from the platform, and continuous loss of pure 234U caused by alpha recoil at all sites. The difference in diagenesis between the sites can be explained by the different fluid-flow histories they have experienced. Site 1005 is sufficiently close to the platform to have probably experienced a change in flow direction whenever the banks have flooded or become exposed. Other sites have probably experienced continuous flow into the sediment. Although diagenesis prevents assignment of accurate ages, it is sufficiently systematic that it can be corrected for and each aragonite-rich package assigned to a unique highstand interval. Site 1005 has sediment packages from highstands associated with marine isotope Stages 1, 5, 7, 9, and 11. Site 1006 is similar, except that the Stage 7 highstand is missing, at least in Hole 1006A. Site 1003 has sediment only from Stage 1 and 11 highstands within the U-Th age range. And Site 1007 has sediment only from the stage 1 highstand. This information will allow the construction of better age models for these sites. No high-aragonite sediments are seen for Stage 3 or Substages 5a and 5c. Unless rather unusual erosion has occurred, this indicates that the banks did not flood during these periods. If true, this would require the sea level for Substages 5a and 5c to have remained at least ~10 m lower than today.

NMR spectrum of lindgomycin from a Marine Fungus of the Lindgomycetaceae

An unusual polyketide with a new carbon skeleton, lindgomycin (1), and the recently described ascosetin (2) were extracted from mycelia and culture broth of different Lindgomycetaceae strains, which were isolated from a sponge of the Kiel Fjord in the Baltic Sea (Germany) and from the Antarctic. Their structures were established by spectroscopic means. In the new polyketide, two distinct domains, a bicyclic hydrocarbon and a tetramic acid, are connected by a bridging carbonyl. The tetramic acid substructure of compound 1 was proved to possess a unique 5-benzylpyrrolidine-2,4-dione unit. The combination of 5-benzylpyrrolidine-2,4-dione of compound 1 in its tetramic acid half and 3-methylbut-3-enoic acid pendant in its decalin half allow the assignment of a new carbon skeleton. The new compound 1 and ascosetin showed antibiotic activities with IC50 value of 5.1 (±0.2) µM and 3.2 (±0.4) µM, respectively, against methicillin-resistant Staphylococcus aureus.

Os isotope record of ODP Site 159-959

The known temporal relationship between the benthic foraminiferal d18O record and the marine Os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the West African margin Ocean Drilling Program (ODP) Site 959. Although organic-rich sediments require significant corrections for in situ decay of 187Re to 187Os, these results demonstrate the utility of the marine Os isotope record for chemostratigraphic correlation of organic-rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences. Revision of the ODP Site 959 chronology shifts the age assignment of an interval of biosiliceous, organic-rich sediment deposition from the Oligocene to the late Eocene and earliest Oligocene, likely culminating with the first major glaciation of the Oligocene (Oi1). We speculate that enhanced organic carbon burial over much of the West African margin may have contributed to drawdown of atmospheric carbon dioxide before and during the Oi1 event and suggest that Os isotope chemostratigraphy provides a valuable tool for further exploring this possibility.