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Keith A. Kvenvolden

Publications and source records attributed to Keith A. Kvenvolden.

At least 73 records · Page 4Linked to original sources
USGS1983

Pressure core barrel; application to the study of gas hydrates, Deep Sea Drilling Project Site 533, Leg 76

A pressure core barrel (PCB), developed by the Deep Sea Drilling Project, was used successfully to recover, at in situ pressure, sediments of the Blake Outer Ridge, offshore the southeastern United States. The PCB is a unique, wire-line tool, 10.4 m long, capable of recovering 5.8 m of core (5.8 cm in diameter), maintained at or below in situ pressures of 34.4 million Pascals (MPa), and 1.8 m of unpressurized core (5.8 cm in diameter). All excess internal pressure above the operating pressure of 34.4 MPa is automatically vented off as the barrel is retrieved. The PCB was deployed five times at DSDP Site 533 where geophysical evidence suggests the presence of gas hydrates in the upper 600 m of sediment. Three cores were obtained holding average in situ pressures of 30 MPa. Two other cores did not maintain in situ pressures. Three of the five cores were intermittently degassed at varying intervals of time, and portions of the vented gas were collected for analysis. Pressure decline followed paths indicative of gas hydrates and/or dissolved gas. The released gas was dominantly methane (usually greater than 90%), along with higher molecular-weight hydrocarbon gases and carbon dioxide. During degassing the ratio of methane to ethane did not vary significantly. On the other hand, concentrations of higher molecular-weight hydrocarbon gases increased, as did carbon dioxide concentrations. The results from the PCB experiments provide tentative but equivocal evidence for the presence of .gas hydrates at Site 533. The amount of gas hydrate indicated is small. Nevertheless, this work represents the first successful study of marine gas hydrates utilizing the PCB.

Initial Reports of the D.S.D.P.↗
USGS1983

Molecular and isotopic compositions of hydrocarbons at Site 533, Deep Sea Drilling Project Leg 76

In an investigation of gas hydrates in deep ocean sediments, gas samples from Deep Sea Drilling Project Site 533 on the Blake Outer Ridge in the northwest Atlantic were obtained for molecular and isotopic analyses. Gas samples were collected from the first successful deployment of a pressure core barrel (PCB) in a hydrate region. The pressure decline curves from two of the four PCB retrievals at in situ pressures suggested the presence of small amounts of gas hydrates. Compositional and isotopic measurements of gases from several points along the pressure decline curve indicated that (1) biogenic methane (δ13C = -68‰; CJ/CJ = 5000) was the dominant gas (>90%); (2) little fractionation in the C,/ C2 ratio or the C carbon isotopic composition occurred as gas hydrates decomposed during pressure decline experi ments; (3) the percent of C3 , i-C4 , and CO2 degassed increased as the pressure declined, indicating that these molecules may help stabilize the hydrate structure; (4) excess nitrogen was present during initial degassing; and (5) Cj/Q ratios and isotopic ratios of C gases were similar to those obtained from conventional core sampling. The PCB gas also con tained trace amounts of saturated, acyclic, cyclic, and aromatic C5 -C14 hydrocarbons, as well as alkenes and tetrahydrothiophenes. Gas from a decomposed specimen of gas hydrate had similar molecular and isotopic ratios to the PCB gas (δ13C of -68% for methane and a q/ Q ratio of -6000). Regular trends in the δ 13C of methane ( 95 60%) and C{ /C2 ratios (-25000 — 2000) were observed with depth. Capillary gas chromatography (GC) and total scanning fluorescence measurements of extracted organic material were characteristic of hydrocarbons dominated by a marine source, though significant amounts of perylene were also present.

Initial Reports of the D.S.D.P.↗
USGS1983

Concentrations and carbon isotopic compositions of CH4 and CO2 in gas from sediments of the Blake Outer Ridge, Deep Sea Drilling Project Leg 76

The principal gaseous carbon-containing components identified in the first 400 m of sediment at Deep Sea Drilling Project Site 533, Leg 76, are methane (CH4 ) and carbon dioxide (CO2 ). Below a sub-bottom depth of about 25 m, sedi ment cores commonly contained pockets caused by the expansion of gas upon core recovery. The carbon isotopic com position (δ13C %0 relative to PDB standard) of CH4 and CO2 in these gas pockets has been measured, resulting in the following observations: (1) δ 1 3CC H 4 values increase with depth from approximately -94% in the uppermost sediment to about -66% in the deepest sediment, reflecting a systematic but nonlinear depletion of 12C with depth. (2) δ 1 3Cc θ 2 values also increase with depth of sediment from about - 25% to about - 4%, snowing a depletion of 12C that closely parallels the trend of the isotopic composition of CH4 . The magnitude and parallel distribution of δ 13C values for both CH4 and CO2 are consistent with the concept that the formation of the CH4 resulted from the microbiological reduction of CO2 from organic substances. These results imply that CH4 and CO2 incorporated in gas hydrates at this site are biogenic.

Initial Reports of the D.S.D.P.↗
USGS1981

Age estimations based on amino acid racemization: Reply to comments of J.F. Wehmiller

Determining geologic ages of fossils by amino acid racemization techniques is often difficult because of the uncertainties in assumptions about diagenetic temperatures. Two kinetic model methods have been employed. Method 1, used by us, assumes that racemization of amino acids in the bivalve mollusk Saxidomus giganteus from Willapa Bay, Washington, follows linear kinetics. Ages are calculated by means of first-order kinetic equations. Method 2, used by Wehmiller, involves an empirical non-linear kinetic model Method 1 is simpler in concept and more easily applied. Wehmiller claims that ambiguities in paleotemperature arise when method 1 is used and that these ambiguities can be reconciled by the use of method 2. We show that application of method 1 can also provide reasonable temperature histories and leads to age estimates that are consistent with the geologic history of the sedimentary deposits at Willapa Bay.

Geochimica et Cosmochimica Acta↗
USGS1981

Geochemistry of amino acids in sediments from Clear Lake, California

By studying the geochemistry of amino acids, we attempt to clarify uncertainties in the radiocarbon chronology and in correlations of ash beds and pollen spectra in lacustrine sediment from Clear Lake, California. Two amino acids, aspartic acid and alanine, are considered in detail. Relative concentrations of aspartic acid decrease with depth, a result likely due to diagenesis and to preferential adsorption and hydrolysis in clay. Relative concentrations of alanine show the reverse effect with depth, probably due, in part, to the generation of alanine from other amino acids during diagenesis. The aspartic acid racemization rate calibrated by radiocarbon yields anomalously low age and temperature estimations for Clear Lake when kinetic assumptions from a study in Lake Ontario are used. However, the “apparent” alanine racemization rate correlates well with the alanine racemization rate determined for sediments from Lake Biwa, Japan. Our age assessment based on alanine supports a time-depth curve obtained from oak pollen and oxygen isotopes for Clear Lake representing a time span of about 130,000 yr.

California↗
USGS1981

Thermogenic hydrocarbons in unconsolidated sediment of Eel river basin, offshore northern California

Thermally produced hydrocarbons were recovered from unconsolidated sediment ponded within a bathymetric depression on the surface of a shale diapir in the offshore Eel River Basin of northern California. Evidence that the hydrocarbons are thermogenic consists of the following: (1) very high concentrations of hydrocarbon gases, particularly ethane through butanes (C 2 -C 4 ); (2) methane having a carbon isotopic composition (relative to the PDB standard) of −43 and −44 per mil; (3) presence of gasoline-range (C 5+ ) hydrocarbons; and (4) presence of a complex mixture of heavy hydrocarbons (C 15+ ) with n-alkanes having a petroleumlike distribution. This mixture of gaseous and liquid hydrocarbons likely originated deep within the basin and migrated to the surface through fractures and faults developed during the emplacement of the diapir. The presence of thermogenic hydrocarbons in unconsolidated surface sediment indicates that conditions for petroleum generation have existed within this offshore basin.

California↗
USGS1981

Organic geochemistry in the Deep Sea Drilling Project

Since the beginning of the Deep Sea Drilling Project DSDP in 1968 and extending through 1975 organic geochemical studies have been undertaken on about 2300 samples recovered on Legs I through 44 from sediments beneath the ocean floors These studies have provided fundamental information regarding the distribution of carbon in oceanic sediments and have yielded a better understanding of the processes that alter and transform organic matter in the marine environment. Beginning with Leg 38 organic geochemists have been included as members of the scientific staffs of those legs of particular organic geochemical interest They have advised operations personnel on matters concerning potential hazards such as drilling into significant accumulations of oil and gas and have collected samples for the scientific community The shipboard organic geochemical laboratory is equipped with sophisticated instrumentation to provide those meassurements helpful in advising the drilling operation. Since Leg 15 samples for organic geochemical studies have been maintained at 180Cat the DSDP sample repository at the Scripps Institution of Oceanography La Jolla California Samples aredistributed to the scientific community but at least one quarter of all cores is retained for possible future studies. Organic geochemical studie sgenerally relate to one of these topic areas (I) petroleum potential source rock evaluation (2) thermal history and gradients (3) diagenesis (4) gas hydrates (5) novel geochemical fossils (6) sources of organic materials (7) paleo depositional environments and (8) geochronology Much of the organic geochemical work on hydrocarbons and kerogen has been directed to the potential of sediments as sources of petroleum The organic matter found thus far during drilling is dominantly of terrestrial origin and thermally immature but much of the organic matter could be a potential source of petroleum mainly gas if buried more deeply. Three new technologies will help advance organic geochemical knowledge of ocean sediments I pressure core barrel for evaluation of gas hydrates 2 hydraulic piston core to study in detail sources and early diagenesis of organic matter and 3 riser for the study of late diagenesis and catagenesis

Society of Economic Geologists Special Publication↗
USGS1980

Origin of gasoline-range hydrocarbons and their migration by solution in carbon dioxide in Norton basin, Alaska.

Carbon dioxide from a submarine seep in Norton Sound, Alaska, carries a minor component of gas- and gasoline-range hydrocarbons. The molecular and isotopic compositions of the hydrocarbon gases and the presence of gasoline-range hydrocarbons indicate that these molecules are derived from thermal alteration of marine and/or nonmarine organic matter buried within Norton basin. In the gasoline-range hydrocarbons, individual cyclic and branched-chain molecules are much more abundant than straight-chain hydrocarbons. This distribution suggests that the hydrocarbon mixture is an immature, petroleumlike condensate of lower temperature origin than normal crude oil. The submarine seep provides a natural example in support of a carbon dioxide solution transport mechanism thought to be operative in the migration of hydrocarbons in certain reservoirs.

Alaska↗
USGS1979

Biogenic and thermogenic gas in gas-charged sediment of Norton Sound, Alaska

Chemical and isotopic compositions of sediment gas from Norton Sound have been determined for near-surface, gas-charged sediments at two sites identified in acoustic profiles and bottom observations. At one site air-driven vibracorer penetrated sediment saturated with methane. The isotopic value suggests that the methane originated from active biological processes operating on peat in the top 4 m of sediment. At the other site, characterized by a large subsurface acoustic anomaly , smaller near-surface acoustic anomalies and active seepage of gas, the vibracorer obtained sediment saturated with gas composed of 98% CO2. Associated with the CO2 are minor concentrations of petroleum-like light hydrocarbons. The carbon isotopic compositions of CO2 and methane along with the chemical distribution of gaseous hydrocarbons indicate that at this site these gases are derived from thermal processes operating at depth in Norton Basin. Apparently CO2 from the decarbonation of marine limestone acts as a carrier for hydrocarbon gases that have been generated from organic matter buried in the basin. The gases reach the surface by faults and escape at the seafloor as a submarine seep. The presence of near-surface gas-charged sediment in Norton Sound reduces the stability of the seafloor. Areas where sediments are charged with gas may pose potential hazards for engineering developments.

Alaska↗
USGS1979

Modern biogenic gas-generated craters (sea-floor “pockmarks”) on the Bering Shelf, Alaska

As many as 1,340 small craters per square kilometre cover the sea floor of Norton Sound in the northeastern Bering Sea. The craters are circular pits, 1 to 10 m in diameter and less than 1 m deep, observed on sonographs over 20,000 km 2 of northern Norton Sound sea floor. Craters typically are associated with acoustic anomalies, near-surface peaty mud, and gas-charged sediment. The peaty mud is a thick (>1.5 m), nonmarine pre-Holocene deposit that is now covered by a 1- to 3-m-thick layer of Holocene marine mud in the area of the craters. The peaty mud (2% to 8% organic carbon) contains abundant biogenic methane [C 1 /(C 2 + C 3 ) = 256 to 7,669] with carbon isotope (δ 13 C) values of −69‰ to −75‰- Decomposition of organic debris in the peaty mud apparently charges the mud with gas. The peaty and gassy zones attenuate sound waves and cause acoustic anomalies on high-resolution seismic profiles in the area with craters. The craters are forming now, as shown by the disruption of modern ice gouges by the craters. In the absence of storms, the gas apparently is trapped in the peaty mud in a saturated state by the cover of Holocene mud. Periodically, possibly during storms, the gas escapes through the thin Holocene cover and forms craters.

Alaska↗
USGS1979

Location and hydrocarbon content of a gravity core from the offshore Eel River basin, northern California

The core was collected from ponded sediment near the crest of a diapir-like feature on the Eel Plateau. The measured hydrocarbons are likely to have been derived from deep in the Neogene sedimentary section of the Eel River Basin. Their presence at the surface may indicate migration along fractures in or bordering the diapiric feature and seepage into unconsolidated sediments that are ponded locally within structural and bathymetric depressions. The extent of low molecular weight hydrocarbons at or near the-surface elsewhere in the basin is unknown, but the information based on hydrocarbon composition obtained at this site indicates the possibility that thermogenically-derived hydrocarbons have formed and accumulated in the sedimentary rocks of the offshore Eel River Basin.

California↗