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M. Kastner

Publications and source records attributed to M. Kastner.

5 recordsLinked to original sources
USGS2008

Methane hydrate formation in turbidite sediments of northern Cascadia, IODP Expedition 311

Expedition 311 of the Integrated Ocean Drilling Program (IODP) to northern Cascadia recovered gas-hydrate bearing sediments along a SW-NE transect from the first ridge of the accretionary margin to the eastward limit of gas-hydrate stability. In this study we contrast the gas gas-hydrate distribution from two sites drilled ~ 8??km apart in different tectonic settings. At Site U1325, drilled on a depositional basin with nearly horizontal sedimentary sequences, the gas-hydrate distribution shows a trend of increasing saturation toward the base of gas-hydrate stability, consistent with several model simulations in the literature. Site U1326 was drilled on an uplifted ridge characterized by faulting, which has likely experienced some mass wasting events. Here the gas hydrate does not show a clear depth-distribution trend, the highest gas-hydrate saturation occurs well within the gas-hydrate stability zone at the shallow depth of ~ 49??mbsf. Sediments at both sites are characterized by abundant coarse-grained (sand) layers up to 23??cm in thickness, and are interspaced within fine-grained (clay and silty clay) detrital sediments. The gas-hydrate distribution is punctuated by localized depth intervals of high gas-hydrate saturation, which preferentially occur in the coarse-grained horizons and occupy up to 60% of the pore space at Site U1325 and > 80% at Site U1326. Detailed analyses of contiguous samples of different lithologies show that when enough methane is present, about 90% of the variance in gas-hydrate saturation can be explained by the sand (> 63????m) content of the sediments. The variability in gas-hydrate occupancy of sandy horizons at Site U1326 reflects an insufficient methane supply to the sediment section between 190 and 245??mbsf. ?? 2008 Elsevier B.V.

Earth and Planetary Science Letters↗
USGS1998

Chemistry, isotopic composition, and origin of a methane-hydrogen sulfide hydrate at the Cascadia subduction zone

Although the presence of extensive gas hydrate on the Cascadia margin, offshore from the western U.S. and Canada, has been inferred from marine seismic records and pore water chemistry, solid gas hydrate has only been found at one location. At Ocean Drilling Program (ODP) Site 892, offshore from central Oregon, gas hydrate was recovered close to the sediment-water interface at 2–19 m below the seafloor (mbsf) at 670 m water depth. The gas hydrate occurs as elongated platy crystals or crystal aggregates, mostly disseminated irregularly, with higher concentrations occurring in discrete zones, thin layers, and/or veinlets parallel or oblique to the bedding. A 2- to 3-cm thick massive gas hydrate layer, parallel to bedding, was recovered at ∼ 17 mbsf. Gas from a sample of this layer was composed of both CH 4 and H 2 S. This sample is the first mixed-gas hydrate of CH 4 H 2 S documented in ODP; it also contains ethane and minor amounts of CO 2 . Measured temperatures of the recovered core ranged from 2 to −1.8°C and are 6 to 8 degrees lower than in-situ temperatures. These temperature anomalies were caused by the partial dissociation of the CH 4 H 2 S hydrate during recovery without a pressure core sampler.During this dissociation, toxic levels of H 2 S (δ 34 S, +27.4‰) were released. The δ 13 C values of the CH 4 in the gas hydrate, −64.5 to −67.5‰ (PDB) , together with δD values of −197 to −199‰ (SMOW) indicate a primarily microbial source for the CH 4 . The δ 18 O value of the hydrate H 2 O is +2.9‰ (SMOW) , comparable with the experimental fractionation factor for sea-ice. The unusual composition (CH 4 H 2 S) and depth distribution (2–19 mbsf) of this gas hydrate indicate mixing between a methane-rich fluid with a pore fluid enriched in sulfide; at this site the former is advecting along an inclined fault into the active sulfate reduction zone. The facts that the CH 4 H 2 S hydrate is primarily confined to the present day active sulfate reduction zone (2–19 mbsf), and that from here down to the BSR depth (19–68 mbsf) the gas hydrate inferred to exist is a ≥99% CH 4 hydrate, suggest that the mixing of CH 4 and H 2 S is a geologically young process. Because the existence of a mixed CH 4 H 2 S hydrate is indicative of moderate to intense advection of a methane-rich fluid into a near surface active sulfate reduction zone, tectonically active (faulted) margins with organic-rich sediments and moderate to high sedimentation rates are the most likely regions of occurrence. The extension of such a mixed hydrate below the sulfate reduction zone should reflect the time-span of methane advection into the sulfate reduction zone.

Earth and Planetary Science Letters↗
USGS1980

A high-temperature hydrothermal deposit on the seabed at a Gulf of California spreading center ( Guaymas Basin).

A submersible dive on a turbidite-covered spreading axis in Guaymas Basin photographed and sampled extensive terraces and ledges of talc. The rock contains siliceous microfossils, smectite, and euhedral pyrrhotite as well as rather pure iron-rich talc. S and O isotopes indicate precipitation around a hydrothermal vent, at about 2800C. - Authors

Earth and Planetary Science Letters↗