Major and rare earth element composition of ODP Site 191-1179 sediments, northwest Pacific

Depth profiles of major element and rare earth element (REE) abundances in sediment samples (mainly siliceous ooze and clay) recovered from Holes 1179B and 1179C at Site 1179, Ocean Drilling Program Leg 191 (41.4°N, 159.6°E) were determined. The oxidation states of Mn and Ce were determined by X-ray absorption near-edge structure. Some geochemical indicators were tested, including the MnO/TiO2 ratios, a bivariate diagram of La/Ce vs. Al2O3/(Al2O3+Fe2O3), and other discrimination diagrams. The oxidation state of Mn is reduced Mn(II) in the depth profile below 0.60 meters below seafloor (mbsf), which is consistent with relatively low and high abundances of Mn in the sediments and pore waters, respectively. It is possible that the diagenetic effect on the oxidation state and abundance of Mn makes it difficult for the MnO/TiO2 ratio to reflect the depositional environment. The normalized ratio of La and Ce does not change very much with depth, suggesting that the diagenetic effect does not affect the REE signature in the sediments. On the diagram of La/Ce vs. Al2O3/(Al2O3+Fe2O3), the sediments studied here plot at the boundary of the pelagic and continental margin fields. This suggests that continental material has contributed to the sediment to some degree, even though Site 1179 is in a pelagic region of the northwestern Pacific Ocean, >1600 km from Japan.

Geochemistry, physical properties, diatom abundance and datums of ODP Site 186-1150 and Hole 186-1151A

Detection of climate response to orbital forcing during Cenozoic long-term global cooling is a key to understanding the behavior of Earth's icehouse climate. Sedimentary rhythm, which is a rhythmic or cyclic variation in the sequence of sediments and sedimentary rocks, is useful for quantitative reconstruction of Earth's evolution during geological time. In this study, we attempt to (1) identify sources of natural gamma ray (NGR) emissions of core recovered during Ocean Drilling Program (ODP) Leg 186 by analyses of physical properties, major element concentrations, diatom abundances, and total organic carbon contents, (2) integrate whole-core NGR intensity of recovered core with wireline logging NGR measurements in order to construct a continuous sedimentary sequence, and (3) discuss changes in the NGR signal in the time domain. This attempt gives us preliminary information to discuss climate stability in relation to orbital forcing thorough geologic time. NGR values are obtained mainly by indirectly measuring the amount of terrigenous minerals including potassium and related elements in the sediments. NGR intensity is also affected by high porosity, which in these sediments was related to the amount of diatom valves. NGR signals might be a proxy of the intensity of the East Asian monsoon off Sanriku. A continuous sedimentary record was constructed by integration of the whole-core NGR intensity measured in sediments obtained from the drilled holes with that measured directly in the borehole by wireline logging, then using a stratigraphic age model to convert to a time series covering 1.3-9.7 Ma with a short break at ~5 Ma. High sedimentation rate (H) stages were identified in the sequence, related to intervals of low-amplitude precession and eccentricity variations. The transition of the dominant periodicities through the four H stages may correlate to major shifts in the climate system, including the onset of major Northern Hemisphere glaciation, the initial stage of the East Asian monsoon intensification, and the onset of the East Asian monsoon with uplift of the Himalayas and the Tibetan Plateau.

Nannofossil biostratigraphy of ODP Site 210-1276 sediments

Ocean Drilling Program (ODP) Leg 210 is one of very few deep-sea legs drilled along the eastern Canadian continental margin. Most other drilling on this margin has been carried out by the petroleum industry on the shallow-water regions of the Scotian shelf and the Grand Banks (see Doeven, 1983, for nannofossil studies). Deep Sea Drilling Project (DSDP) Leg 12 Site 111 and ODP Leg 105 Site 647 were drilled in the general vicinity of Leg 210 but recovered no appreciable Lower Cretaceous (Albian-Cenomanian) sediments. Site 111 yielded indurated limestones dated tentatively as late Albian-early Cenomanian, whereas Site 647 encountered no Albian-Cenomanian sediments. Two sites (Sites 1276 and 1277) were drilled during Leg 210 in the Newfoundland Basin with the primary objective of recovering basement rocks to elucidate the rifting history of the North Atlantic Basin. The location for Leg 210 was selected because it is conjugate to the Iberia margin, which was drilled extensively during DSDP/ODP Legs 47B, 103, 149, and 173. A secondary but equally important objective was to recover the overlying sediments with the purpose of studying the postrift sedimentation history of this margin.