Laier, Troels (1996): Mixing of methane and sulphate due to fluids flow in the Barbados accretionary prism

Leg/Site/Hole:
ODP 110
ODP 156
Identifier:
1997-017466
georefid

Creator:
Laier, Troels
Geological Survey of Denmark and Greenland, Copenhagen, Denmark
author

Identification:
Mixing of methane and sulphate due to fluids flow in the Barbados accretionary prism
1996
In: Anonymous, American Association of Petroleum Geologists 1996 annual convention
American Association of Petroleum Geologists and Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
5
79-80
Methane concentrations above background level in sulphate-containing (15 mmol/l) pore waters have been observed in the decollement zone of the Barbados accretionary prism. The peak in methane concentration in the decollement was found at a number of sites by headspace analysis of cores retrieved during ODP legs 110 & 156 at the toe of the accretionary prism. delta (super 13) C (sub 1) values between -22 per mil and -36 per mil indicate that methane oxidation occurs possibly due to sulphate reduction. Thus, the presence of both methane and sulphate at the same depths suggests mixing of fluids due to fluid flow. Fluid flow is also indicated by the distinct minima in chloride concentrations at the same depths. In the case of on-going methane oxidation, mixing of sulphate and methane fluids: is anticipated to have occurred fairly recently. Sulphate concentration decreases only little with depth in the Pleistocene to lower Miocene sediments where TOC is very low, <0.2%. Sulphate decreases more rapidly with depth in the Oligocene to Eocene sediments where numerous relatively thin turbidites occur. The turbidites have significantly higher TOC, 0.5-1.5%, than the interbedded hemipelagic sediments, TOC<0.2%. High methane concentrations were not found in any of the boreholes, but the trends in sulphate and methane in boreholes indicate that high methane concentrations exist in older sediments not reached by drilling. The decollement zone is composed of lower Miocene to upper Oligocene sediments near the toe of the prism, but deepens into stratigraphically lower sediments prism ward. Thus, methane originating from these older sediments may have been brought to shallower depths by active fluid flow in the decollement.
English
Coverage:Geographic coordinates:
North:75.0000
West:-80.0000East: 20.0000
South:0.0000

Geochemistry of rocks, soils, and sediments; accretionary wedges; aliphatic hydrocarbons; alkanes; Antilles; Atlantic Ocean; Barbados; C-13/C-12; carbon; Caribbean region; Cenozoic; chloride ion; chlorine; cores; decollement; Eocene; halogens; hemipelagic environment; hydrocarbons; isotope ratios; isotopes; Leg 110; Leg 156; Lesser Antilles; marine environment; methane; Miocene; mixing; Neogene; North Atlantic; Ocean Drilling Program; Oligocene; organic carbon; organic compounds; organic materials; oxidation; Paleogene; reduction; stable isotopes; sulfates; Tertiary; turbidite; West Indies;

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