Nonvolatile Organic Matter at Sites 565-570, Deep Sea Drilling Project Leg 84

Kennicutt, M.C.; Brooks,; McDonald, J M; Pflaum, T J

doi:10.2973/dsdp.proc.84.128.1985

Cited by 5 publications

(4 citation statements)

References 17 publications

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“…As mentioned above, the average TOC in the Nankai Trough gas hydrate-bearing sediments is 0.5 %, whereas other gas hydrate-bearing sediments show much higher TOC contents, such as in the Blake Ridge (1.4 % average between 200 and 450 mbsf; Shipboard Scientific Party, 1996), offshore Guatemala (1.7 % average between 0 and 400 mbsf; Kennicutt et al, 1985) and offshore Peru (3.0 % average between 6 and 750 mbsf; Shipboard Scientific Party, 1988). Waseda (1998) suggests that at least 0.5 % TOC is generally required for in situ formation of gas hydrate of microbial origin in marine sediments.…”

Section: Gas Hydrate Accumulationmentioning

confidence: 86%

The Geochemical Context of Gas Hydrate in the Eastern Nankai Trough

Waseda¹,

Uchida²

2004

Resource Geology

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. Geochemical studies for gas hydrate, gas and organic matter collected from gas hydrate research wells drilled at the landward side of the eastern Nankai Trough, offshore Tokai, Japan, are reported. Organic matter in the 2355 m marine sediments drilled to Eocene is mainly composed of Type III kerogen with both marine and terrigenous organic input. The gas hydrate‐bearing shallow sediments are immature for hydrocarbon generation, whereas the sediments below 2100 mbsf are thermally mature. The origins of gases change from microbial to thermogenic at around 1500 mbsf. Carbon isotope compositions of CH4 and CO2, and hydrocarbon compositions consistently suggest that the CH4 in the gas hydrate‐bearing sediments is generated by microbial reduction of CO2. The δ13C depth‐profiles of CH4 and CO2 suggest that the microbial methanogenesis is less active in the Nankai Trough sediments compared with other gas hydrate‐bearing sediments where solid gas hydrate samples of microbial origin were recovered. Since in situ generative‐potential of microbial methane in the Nankai Trough sediments is interpreted to be low due to the low total organic carbon content (0.5 % on the average) in the gas hydrate‐bearing shallow sediments, upward migration of microbial methane and selective accumulation into permeable sands should be necessary for the high concentration of gas hydrate in discrete sand layers.

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Section: Gas Hydrate Accumulationmentioning

confidence: 86%

The Geochemical Context of Gas Hydrate in the Eastern Nankai Trough

Waseda¹,

Uchida²

2004

Resource Geology

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“…All analytical methods used in this study are described in detail elsewhere (Kennicutt et al, 1985;Kennicutt and Jeffrey, 1981a,b). Organic carbon and nitrogen concentrations were determined by combustion with a Per kin Elmer Model 240C Elemental Analyzer.…”

Section: Methodsmentioning

confidence: 99%

Nonvolatile Organic Matter in Sediments from Sites 614 to 623, Deep Sea Drilling Project Leg 96

Kennicutt¹,

DeFreitas²,

Joyce³

et al. 1986

Initial Reports of the Deep Sea Drilling Project

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The bulk organic matter in sediments from the upper Pleistocene Mississippi Fan and two intraslope basins is primarily terrestrial in origin. Carbon to nitrogen elemental ratios, δ 13 C of the organic matter, the presence of plant biowaxes, and lithologic associations form the basis of this interpretation. The molecular-level compositions of the extractable organic matter suggest significant levels of non-indigenous thermogenic hydrocarbons at all sites. The alkane hydrocarbons are composed of both biogenic (mainly plant biowaxes) and thermogenic hydrocarbons. The thermogenic hydrocarbons are primarily present as an unresolved complex mixture. Increasing amounts of hydrocarbons with depth at the Mississippi Fan sites suggest that the thermogenic hydrocarbons have migrated upward from deeper sediments. Vertical gradients in the intraslope basins were less dramatic, although an upward migration source is inferred. Upward movement of thermogenic hydrocarbons, from deeper sediments where sufficient temperatures are present to produce these hydrocarbons, appears to be a regional phenomenon given the widespread occurrence at these sites.

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“…Shallow gas found within Pleistocene layers of the Green Canyon region is mainly formed by biogenic in situ production [ Lorenson et al ., ; Sassen et al ., ] due to high Cenozoic rates of sedimentation and large TOC input [ Hutchinson et al ., ]. We have introduced in situ biogenic gas formation in all sedimentary layers above the salt (Pliocene and Pleistocene) with a constant initial TOC value of 1 wt % and constant initial HI of 100 mg HC/g TOC, which is in accordance to DSDP data from Site 96 [ Kennicutt et al ., ] and a typical average value acceptable for this kind of marine setting [ Frye , ]. Additionally, biogenic methane formation was modeled (1) throughout Lower Cretaceous to Upper Miocene sediments assuming initial TOC values from 0.8 wt % (e.g., Upper Cretaceous marls) to 1.6 wt % (e.g., Wilcox formation, Paleocene, and Eocene) and initial HI values from 100 mg HC/g TOC to 220 mg HC/g TOC, accordingly, and (2) in the three source rocks present in the region according to the reported initial TOC and HI values (see Table ).…”

Section: Modeling Approachmentioning

confidence: 99%

3‐D basin‐scale reconstruction of natural gas hydrate system of the Green Canyon, Gulf of Mexico

Burwicz

Reichel

Wallmann

et al. 2017

Geochem Geophys Geosyst

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Our study presents a basin‐scale 3‐D modeling solution, quantifying and exploring gas hydrate accumulations in the marine environment around the Green Canyon (GC955) area, Gulf of Mexico. It is the first modeling study that considers the full complexity of gas hydrate formation in a natural geological system. Overall, it comprises a comprehensive basin reconstruction, accounting for depositional and transient thermal history of the basin, source rock maturation, petroleum components generation, expulsion and migration, salt tectonics, and associated multistage fault development. The resulting 3‐D gas hydrate distribution in the Green Canyon area is consistent with independent borehole observations. An important mechanism identified in this study and leading to high gas hydrate saturation (>80 vol %) at the base of the gas hydrate stability zone (GHSZ) is the recycling of gas hydrate and free gas enhanced by high Neogene sedimentation rates in the region. Our model predicts the rapid development of secondary intrasalt minibasins situated on top of the allochthonous salt deposits which leads to significant sediment subsidence and an ensuing dislocation of the lower GHSZ boundary. Consequently, large amounts of gas hydrates located in the deepest parts of the basin dissociate and the released free methane gas migrates upward to recharge the GHSZ. In total, we have predicted the gas hydrate budget for the Green Canyon area that amounts to ∼3256 Mt of gas hydrate, which is equivalent to ∼340 Mt of carbon (∼7 × 1011 m3 of CH4 at STP conditions), and consists mostly of biogenic hydrates.

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Nonvolatile Organic Matter at Sites 565-570, Deep Sea Drilling Project Leg 84

Cited by 5 publications

References 17 publications

The Geochemical Context of Gas Hydrate in the Eastern Nankai Trough

The Geochemical Context of Gas Hydrate in the Eastern Nankai Trough

Nonvolatile Organic Matter in Sediments from Sites 614 to 623, Deep Sea Drilling Project Leg 96

3‐D basin‐scale reconstruction of natural gas hydrate system of the Green Canyon, Gulf of Mexico

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