Naehr, Thomas H. and Eichhubl, Peter and Orphan, Victoria J. and Hovland, Martin and Paull, Charles K. and Ussler, William, III and Lorenson, Thomas D. and Greene, H. Gary (2007) Authigenic carbonate formation at hydrocarbon seeps in continental margin sediments: A comparative study. Deep-Sea Research. Part II, Topical Studies in Oceanography, 54 (11-13). pp. 1268-1291. ISSN 0967-0645. http://resolver.caltech.edu/CaltechAUTHORS:20130429-140926092
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Authigenic carbonates from five continental margin locations, the Eel River Basin, Monterey Bay, Santa Barbara Basin, the Sea of Okhotsk, and the North Sea, exhibit a wide range of mineralogical and stable isotopic compositions. These precipitates include aragonite, low- and high-Mg calcite, and dolomite. The carbon isotopic composition of carbonates varies widely, ranging from −60‰ to +26‰, indicating complex carbon sources that include ^(13)C-depleted microbial and thermogenic methane and residual, 13C-enriched, bicarbonate. A similarly large variability of δ^(18)O values (−5.5‰ to +8.9‰) demonstrates the geochemical complexity of these sites, with some samples pointing toward an ^(18)O-enriched oxygen source possibly related to advection of ^(18)O-enriched formation water or to the decomposition of gas hydrate. Samples depleted in ^(18)O are consistent with formation deeper in the sediment or mixing of pore fluids with meteoric water during carbonate precipitation. A wide range of isotopic and mineralogical variation in authigenic carbonate composition within individual study areas but common trends across multiple geographic areas suggest that these parameters alone are not indicative for certain tectonic or geochemical settings. Rather, the observed variations probably reflect local controls on the flux of carbon and other reduced ions, such as faults, fluid conduits, the presence or absence of gas hydrate in the sediment, and the temporal evolution of the local carbon reservoir. Areas with seafloor carbonates that indicate formation at greater depth below the sediment–water interface must have undergone uplift and erosion in the past or are still being uplifted. Consequently, the occurrence of carbonate slabs on the seafloor in areas of active hydrocarbon seepage is commonly an indicator of exhumation following carbonate precipitation in the shallow subsurface. Therefore, careful petrographic and geochemical analyses are critical components necessary for the correct interpretation of processes related to hydrocarbon seepage in continental margin environments and elsewhere.
|Additional Information:||© 2007 Elsevier Ltd. Accepted 16 April 2007; Available online 20 July 2007. We thank the captain and crew of R/V Point Lobos and the pilots of ROV Ventana for their dedicated efforts to obtain many of the samples used in this study. We also thank G. Bohrmann, J. Greinert, D. Orange, D. Stakes, J. Martin, and many other colleagues for years of stimulating discussions. We are grateful for the comments provided by J. Peckmann and an anonymous reviewer, which greatly improved the paper. We also thank M. Dalthorp for her critical remarks and C. Glenn and G. Filippelli for the editorial handling of the paper. Financial support for this study was provided by the David and Lucile Packard Foundation, the Monterey Bay Aquarium Research Institute, through a TAMUCC Faculty Summer Research Grant, and NSF-EAR award 0421410.|
|Subject Keywords:||Seeps; Methane; Authigenic; Carbonate; Continental margins|
|Official Citation:||Thomas H. Naehr, Peter Eichhubl, Victoria J. Orphan, Martin Hovland, Charles K. Paull, William Ussler III, Thomas D. Lorenson, H. Gary Greene, Authigenic carbonate formation at hydrocarbon seeps in continental margin sediments: A comparative study, Deep Sea Research Part II: Topical Studies in Oceanography, Volume 54, Issues 11–13, June 2007, Pages 1268-1291, ISSN 0967-0645, 10.1016/j.dsr2.2007.04.010.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||30 Apr 2013 14:34|
|Last Modified:||30 Apr 2013 14:34|
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