Geochemistry and petrographic characters at DSDP Leg 58 Holes

Refractive index and chemical composition were determined for glass shards contained in more than 100 tephra layers in DSDP Leg 58 sediment cores collected in the Shikoku Basin, North Philippine Sea. The refractive index is consistent with chemical composition. Refractive index and total iron show a linear relationship. Tephra in Pleistocene and Pliocene sediments is mostly rhyolitic and dacitic (non-alkali), whereas tephra in the Miocene shows wide composition variations in the eastern part of the basin. Basaltic tephra is recognized in Miocene sediments at Sites 443 and 444, but not at Site 442, west of the other two sites. This indicates that the basaltic tephra came from eruption relatively close to those drill sites (perhaps the Kinan Seamounts and the Shichito-Iwo Jima volcanic arc), although the exact source has not been identified.

Wet-bulk densities, mean atomic weights, effective porosities, grain densities, and compressional-wave velocities at DSDP Leg 58 Holes

The effects of water saturation and open pore space on the seismic velocities of crystalline rocks are extremely important when comparing laboratory data to in situ geophysical observations (e.g., Dortman and Magid, 1969; Nur and Simmons, 1969; Christensen and Salisbury, 1975). The existence of fractured rocks, flow breccias and drained pillows in oceanic crustal layer 2a, for instance, may appreciably reduce seismic velocities in that layer (Hyndman, 1976). Laboratory data assessing the influence of porosity and water saturation on seismic velocities of oceanic crustal rocks would certainly aid interpretation of marine geophysical data. Igneous rocks recovered during Leg 58 of the Deep Sea Drilling Project, in the Shikoku Basin and Daito Basin in the North Philippine Sea, are extremely vesicular, as evidenced by shipboard measurements of porosities, which range from 0 to 30 per cent (see reports on Sites 442, 443, 444, and 446, this volume). Samples with this range of porosities afford an excellent opportunity to examine the influence of porosity and water saturation on seismic velocities of oceanic basalts. This paper presents compressional-wave velocities to confining pressures of 1.5 kbars for water-saturated and air-dried basalt samples from the North Philippine Sea. Samples used in this study are from sites 442, 443 and 444 in the Shikoku Basin and Site 446 in the Daito Basin. Excellent negative correlation between porosity and compressional-wave velocity demonstrates that waterfilled pore space can significantly reduce compressionalwave velocities in porous basalts. Velocities measured in air-dried samples indicate that the velocity difference between dry samples and saturated samples is small for porosities exceeding 10 per cent, and very large for lower porosities.

Geochemistry of carbon at DSDP Legs 58 and 59 Holes

I obtained 68 quarter sections of cores from the JOIDES Organic Geochemistry Panel for studying type, distribution, and stages of organic diagenesis of sedimentary organic matter in the West Philippine and Parece Vela basins and Mariana Trough area (Figure 1). The present chapter compares (1) 11 geochemical parameters used to determine organic source and its stage of genesis within the 9 site locations in this study area and (2) compares these 11 with the same parameters reported from Leg 56, outer trench slope of the Japan Trench, and Leg 60, Mariana Trough and Trench (Schorno, in press a, b). Even though these sediments are considered pelagic, the organic content in most of the core sections appears to be hemipelagic. The sedimentary organic matter in these cores is believed to be in an early stage of diagenesis. Both conclusions are based primarily on the fl-alkane distribution within the organic matter. This particular parameter, I note later, has a major weakness. As Hunt (Hunt, 1979) and I (in press b) observed, marine organisms synthesize /z-alkanes with distributions containing neither odd nor even preferences. Thus those sediments that did contain w-alkane distributions with OEP near 1, suggesting a late stage of catagenesis, may in actuality be immature marine sediments.

(Table 1) Description and tetrapyrrole-pigment yield at DSDP Leg 58 Holes

Nineteen core samples from the Shikoku Basin and the Daito Ridge and Basin province of the northwest Philippine Sea, obtained from DSDP Leg 58, were examined for products of chlorophyll diagenesis; we aimed at gaining a better understanding of the very early diagenetic history of sedimentary chlorophyll. We choose samples which, a priori, would allow isolation of tetrapyrrole pigments characteristic of (destructive) diagenesis modes. Studies of Japan Trench sediments (Louda et al., 1980; Baker and Louda, 1980) showed well the interplay of two main diagenesis schemes: anoxic preservation and oxic destruction. The results reported herein are a product of a preliminary investigation on sediments of scant organic matter content, which yielded limited tetrapyrrole pigment.

Petrological parameters of sands and sandstones from DSDP and ODP holes in arc-related areas

Detrital modes for 524 deep-marine sand and sandstone samples recovered on circum-Pacific, Caribbean, and Mediterranean legs of the Deep Sea Drilling Project and the Ocean Drilling Program form the basis for an actualistic model for arc-related provenance. This model refines the Dickinson and Suczek (1979) and Dickinson and others (1983) models and can be used to interpret the provenance/tectonic history of ancient arc-related sedimentary sequences. Four provenance groups are defined using QFL, QmKP, LmLvLs, and LvfLvmiLvl ternary plots of site means: (1) intraoceanic arc and remnant arc, (2) continental arc, (3) triple junction, and (4) strike-slip-continental arc. Intraoceanic- and remnant-arc sands are poor in quartz (mean QFL%Q < 5) and rich in lithics (QFL%L > 75); they are predominantly composed of plagioclase feldspar and volcanic lithic fragments. Continental-arc sand can be more quartzofeldspathic than the intraoceanic- and remnant-arc sand (mean QFL%Q values as much as 10, mean QFL%F values as much as 65, and mean QmKP%Qm as much as 20) and has more variable lithic populations, with minor metamorphic and sedimentary components. The triple-junction and strike-slip-continental groups compositionally overlap; both are more quartzofeldspathic than the other groups and show highly variable lithic proportions, but the strike-slip-continental group is more quartzose. Modal compositions of the triple junction group roughly correlate with the QFL transitional-arc field of Dickinson and others (1983), whereas the strike-slip-continental group approximately correlates with their dissected-arc field.

Chemical composition of bottom sediments and rocks from DSDP Holes 3-14 through 64-477

Data on analyses of chemical composition of DSDP samples of bottom sediments and rocks carried out in P.P. Shirshov Institute of Oceanology are reported. Basal sediments and sedimentary rocks prevail in the sample set.