(Table 1) Stabile isotopes at DSDP Leg 55 Holes

Deep sea drilling on four seamounts in the Emperor Seamount chain revealed that Paleogene shallow-water carbonate sediments of the "bryozoan-algal" facies crown the basalt edifices. According to the biofacies model of Schlanger and Konishi (1966, 1975), this bryozoan- algal assemblage suggests that the seamounts formed in cooler, more northerly waters than those presently occupied by the island of Hawaii; i.e., the paleolatitudes of formation were greater than 20 °N. Moving southward toward the youngest member of the seamount chain, a facies gradient indicative of warmer waters was observed. This gradient is interpreted as a reflection of a northward shift in isotherms during the time span in which the seamounts were progressively formed (Savin et al., 1975). On all seamounts, sedimentation at the drilling sites occurred in a high-energy environment with water depths of approximately 20 meters. Early-stage carbonate diagenesis began in the phreatic zone in the presence of meteoric water, but proceeded after subsidence of the seamounts into intermediate sea waters, where the bulk, stable isotopic composition was determined. The subsidence into intermediate waters was rapid, and permitted establishment of an isotopic equilibrium which, like the facies gradient, reflects the northward shift in isotherms during the Paleogene. Calcite and zeolite cements comprise the later-stage diagenesis, and originated from solutions arising from the hydrolysis of the underlying basalt. In conclusion, the results of this study of the shallow-water carbonate sediments are not inconsistent with a paleolatitude of formation for Suiko Seamount (Site 433) of 26.9 ±3.5 °N, as determined by paleomagnetic measurements (Kono, 1980).

Late Cenozoic silicoflagellate biostratigraphy, relative paleotemperature, and distribution of various genera and morphologic subgroups with remarks on noteworthy occurrences at DSDP Leg 86 Holes

A quantitative study of late Cenozoic silicoflagellates from the northwestern Pacific sites of Deep Sea Drilling Project Leg 86 shows a relative paleotemperature (Ts) gradient with lowest values (Ts = 30) in the north. Some new ecostratigraphic relations for the region are indicated, such as the last common occurrence of Dictyocha brevispina at 2.6 - 3.0 m.y. ago during a cool interval. Elements of North Pacific and low-latitude biostratigraphic zonations can be identified, but the mixing of cool- and warm-indicator taxa prompted the definition of the new Miocene Mesocena hexalitha Subzone and Pliocene Distephanus jimlingii Subzone. Scanning-electron microscope study of Leg 86 silicoflagellates was done to determine whether various types of skeletal surface texture are temperature dependent. To conduct the study we organized a new surface-texture descriptive code, which characterizes the apical structure/basal ring/spine sequence using new definitions of the terms crenulate (C), linear (L), nodular (N), reticulate (R), and smooth (S). One new silicoflagellate genus, Caryocha Bukry et Monechi, n. gen., is described and several new combinations are made.

Molecular properties of gases of ODP Leg 204 sites

The recognition of finely disseminated gas hydrate in deep marine sediments heavily depends on various indirect techniques because this mineral quickly decomposes upon recovery from in situ pressure and temperature conditions. Here, we discuss molecular properties of closely spaced gas voids (formed as a result of core recovery) and gas hydrates from an area of relatively low gas flux at the flanks of the southern Hydrate Ridge offshore Oregon (ODP Sites 1244, 1245 and 1247). Within the gas hydrate occurrence zone (GHOZ), the concentration of ethane (C2) and propane (C3) in adjacent gas voids shows large variability. Sampled gas hydrates are enriched in C2 relative to void gases but do not contain C3. We suggest that the observed variations in the composition of void gases is a result of molecular fractionation during crystallization of structure I gas hydrate that contains C2 but excludes C3 from its crystal lattice. This hypothesis is used to identify discrete intervals of finely disseminated gas hydrate in cored sediments. Variations in gas composition help better constrain gas hydrate distribution near the top of the GHOZ along with variations in pore water chemistry and core temperature. Sediments near the base of the gas hydrate stability zone are relatively enriched in C2+ hydrocarbon gases. Complex and poorly understood geological and geochemical processes in these deeper sediments make the identification of gas hydrate based on molecular properties of void gases more ambiguous. The proposed technique appears to be a useful tool to better understand the distribution of gas hydrate in marine sediments and ultimately the role of gas hydrate in the global carbon cycle.