Ethane enrichment and propane depletion in subsurface gases indicate gas hydrate occurrence in marine sediments at southern Hydrate Ridge offshore Oregon

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doi: 10.1016/j.orggeochem.2004.04.003
Author(s): Milkov, Alexei V.; Claypool, George E.; Lee, Young-Joo; Torres, Marta E.; Borowski, Walter S.; Tomaru, Hitoshi; Sassen, Roger; Long, Philip E.
Ocean Drilling Program, Leg 24, Scientific Party, Richland, WA
Author Affiliation(s): Primary:
BP America, Exploration and Production Technology Group, Houston, TX, United States
Other:
Korea Institute of Geoscience and Mineral Resources, South Korea
Oregon State University, United States
Eastern Kentucky University, United States
University of Tokyo, Japan
Texas A&M University, United States
Volume Title: Organic Geochemistry
Source: Organic Geochemistry, 35(9), p.1067-1080. Publisher: Elsevier, International. ISSN: 0146-6380
Note: In English. Based on Publisher-supplied data
Summary: The recognition of finely disseminated gas hydrate in deep marine sediments heavily depends on various indirect techniques because this mineral quickly decomposes upon recovery from in situ pressure and temperature conditions. Here, we discuss molecular properties of closely spaced gas voids (formed as a result of core recovery) and gas hydrates from an area of relatively low gas flux at the flanks of the southern Hydrate Ridge offshore Oregon (ODP Sites 1244, 1245 and 1247). Within the gas hydrate occurrence zone (GHOZ), the concentration of ethane (C2) and propane (C3) in adjacent gas voids shows large variability. Sampled gas hydrates are enriched in C2 relative to void gases but do not contain C3. We suggest that the observed variations in the composition of void gases is a result of molecular fractionation during crystallization of structure I gas hydrate that contains C2 but excludes C3 from its crystal lattice. This hypothesis is used to identify discrete intervals of finely disseminated gas hydrate in cored sediments. Variations in gas composition help better constrain gas hydrate distribution near the top of the GHOZ along with variations in pore water chemistry and core temperature. Sediments near the base of the gas hydrate stability zone are relatively enriched in C2+ hydrocarbon gases. Complex and poorly understood geological and geochemical processes in these deeper sediments make the identification of gas hydrate based on molecular properties of void gases more ambiguous. The proposed technique appears to be a useful tool to better understand the distribution of gas hydrate in marine sediments and ultimately the role of gas hydrate in the global carbon cycle. Abstract Copyright (2004) Elsevier, B.V.
Year of Publication: 2004
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; Aliphatic hydrocarbons; Alkanes; Carbon; Carbon cycle; East Pacific; Ethane; Gas hydrates; Gases; Geochemical cycle; Geochemistry; Hydrate Ridge; Hydrocarbons; Leg 204; Marine sediments; Natural gas; North Pacific; Northeast Pacific; ODP Site 1244; ODP Site 1245; ODP Site 1247; Ocean Drilling Program; Offshore; Oregon; Organic compounds; Pacific Ocean; Petroleum; Propane; Sampling; Sediments; Spatial distribution; United States
Coordinates: N443500 N443500 W1250700 W1250700
N443500 N443500 W1250900 W1250900
N443500 N443500 W1250900 W1250900
Record ID: 2009043061
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands