The Origin and Distribution of Gas Hydrates in Marine Sediments

Kennicutt, Mahlon C.; Brooks, James M.; Cox, H.B.

doi:10.1007/978-1-4615-2890-6_24

Cited by 9 publications

(9 citation statements)

References 24 publications

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“…A biological origin of the gas would involve local methanogenesis by microbial reduction of CO 2 or acetate derived from organic carbon in the sediments [Wellsbury and Parkes, 2000]. A supply of organic carbon (greater than $0.5 wt % of the sediment [e.g., Kennicutt et al, 1993]) would be needed, plus burial rapid enough to prevent oxidation of the organic matter in the sulphate reduction zone of the shallow subseafloor environment. Ocean Drilling Program work off New Jersey encountered abundant gas in the under-compacted/overpressurized Pleistocene section of the upper slope [Shipboard Scientific Party, 1998].…”

Section: Origin Of the Gasmentioning

confidence: 99%

Large‐scale elongated gas blowouts along the U.S. Atlantic margin

et al. 2004

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[1] In May 2000 we surveyed a series of en echelon, asymmetric depressions along the outer shelf off Virginia and North Carolina using high-resolution chirp and side-scan sonar. The features, which are elongated parallel to the shelf edge and have steep landward walls, are $4 km long, 1 km wide, and up to 50 m deep. On the basis of internal stratal geometry interpreted from chirp profiles, the depressions do not appear to result from simple, down-to-the-east, normal displacement along deep-seated faults or structure. Rather, the depressions seem to have been excavated primarily by gas expulsion, creating large-scale asymmetric gas escape structures that have been termed ''gas blowouts.'' Gas appears to have been trapped beneath a shelf edge delta that is a few tens of meters thick and exhibits internal soft sediment deformation suggestive of progressive downslope (seaward) creep. These new data suggest the blowouts occurred when thin-skinned deformation and creep of the surficial deltaic sediment layers combined with updip/ upslope gas migration, ultimately leading to gas pressure in excess of the overburden. The location of the expulsion craters along the shelf edge and their elongated, asymmetric shapes strongly suggests a causal relation between the downslope creep of the delta and the expulsion event. We suggest a positive feedback between upward migration of gas-rich fluids through the low-stand delta and the downslope creep processes. While the complex interplay between differential permeability, overpressure, and upslope fluid migration remains poorly understood, we suggest such interactions may play an important role in controlling slope stability.

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Section: Origin Of the Gasmentioning

confidence: 99%

Large‐scale elongated gas blowouts along the U.S. Atlantic margin

et al. 2004

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“…The molecular mass (Da) of the DNA was consistently above 9.3U10 6 . Total DNA from each sample was subsequently used separately to construct rRNA gene libraries.…”

Section: Construction and Screening Of 16s Rrna Gene Libraries From Cmentioning

confidence: 99%

“…In addition, it has been estimated that the methane contained in gas hydrates world-wide represents more than double the total amount of carbon in known fossil fuel reserves [5] and thus gas hydrates are of global signi¢-cance. As the bulk of the methane in gas hydrates is of biogenic origin [6], these deposits are also of microbiological interest. Despite the evidence demonstrating that bacterial populations and activities are stimulated in deep gas hydrate deposits, there is no detailed information about the types of bacteria present or their diversity.…”

Section: Introductionmentioning

confidence: 99%

Methanogen and bacterial diversity and distribution in deep gas hydrate sediments from the Cascadia Margin as revealed by 16S rRNA molecular analysis

Marchesi

2001

FEMS Microbiology Ecology

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The microbial community of a deep (to 234 m below the sea floor) sediment gas hydrate deposit (Cascadia Margin Ocean Drilling Program Site 889/890, Leg 146) was analysed for the first time by molecular genetic techniques. Both bacterial and methanogen diversity were determined by phylogenetic analysis of ribosomal DNA sequences. High molecular mass DNA, indicative of active bacteria, was present in all of the samples. Ribosomal RNA genes were amplified from extracted DNA extracted from sediment using bacteria, and methanogen specific PCR primers, the latter designed in this study. Phylogenetic analysis of approximately 400 bacterial clones demonstrated that 96% were members of the Proteobacteria. These clones were affiliated with the K, L and Q subdivisions, with Caulobacter (Zymomonas group), Ralstonia and Pseudomonas phylotypes predominating. The methanogen clones were of low diversity and clustered in three sub-groups. Two of these sub-groups (contained 96% of the 400 clones) were closely related to Methanosarcina mazeii, while the third sub-group clustered in the Methanobacteriales. This analysis of a deep sediment gas hydrate environment shows a bacteria and methanogen community of limited diversity and confirms that the gas hydrate zone is biogeochemically active. These results are consistent with the presence of bacterial populations capable of methanogenesis throughout the core, and suggest that the methane hydrate at this site is at least partially biogenic in origin. ß

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“…The global distribution of gas hydrates has been deduced primarily from bottom simulating reflectors (BSRs) and the occasional collection, hundreds of meters deep in the subsurface during deep-sea drilling (i.e., DSDP and ODP) cores. Brooks and coworkers [1][2][3][4][5][6] have documented the occurrence of gas hydrates in shallow subsurface marine sediments overlying several of the hydrocarbon generative basins throughout the world (e.g., Gulf of Mexico, Northern California, and offshore Nigeria). The gas hydrates have generally been collected from the upper five meters of piston cores taken at water depths greater than 400 m. These gas hydrates occur in close proximity to faults and other conduits for gas migration.…”

Section: Introductionmentioning

confidence: 99%

The Nature of Gas Hydrates on the Nigerian Continental Slope

Brooks¹,

Bryant

Bernard³

et al. 2000

Annals of the New York Academy of Sciences

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Gas hydrates were collected in six‐meter piston cores during surface geochemical exploration (SGE) surveys in the deep and ultra deepwaters of Nigeria during 1991, 1996, and 1998. To date, gas hydrates have been collected in about 21 cores out of the more than 800 core collections on the Nigerian margin. This represents a 2.5% recovery ratio of gas hydrated cores on this margin at sites that are potential conduits for the upward migration of hydrocarbons (i.e., the core locations are sited based on two‐ and three‐dimensional seismic overfaults, mounds, acoustic wipe‐outs, etc.). Unlike the Northern Gulf of Mexico where the authors have retrieved a significant percentage of thermogenic hydrates in piston cores, all the gas hydrate collections offshore Nigeria to date are primarily biogenic in nature (methane more than 99% of the hydrocarbon gases; δ13C generally light, −60 to −117%). A few of these gas hydrated sites do contain a mixed thermogenic gas component (ethane to butane gases up to a few hundred ppm of total hydrocarbon gas) but even at these sites the primary gas in the hydrates is methane.

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The Origin and Distribution of Gas Hydrates in Marine Sediments

Cited by 9 publications

References 24 publications

Large‐scale elongated gas blowouts along the U.S. Atlantic margin

Large‐scale elongated gas blowouts along the U.S. Atlantic margin

Methanogen and bacterial diversity and distribution in deep gas hydrate sediments from the Cascadia Margin as revealed by 16S rRNA molecular analysis

The Nature of Gas Hydrates on the Nigerian Continental Slope

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