Takacs, K. G.; Borowski, W. S. (2003): Authigenic sulfide mineralization induced by anaerobic methane oxidation in methane-rich, gas-hydrate-associated sediments; stratigraphic patterns of sulfide-sulfur concentration and sulfide-sulfur isotopic composition. Geological Society of America (GSA), Boulder, CO, United States, In: Anonymous, Geological Society of America, South-Central Section, 37th annual meeting; Geological Society of America, Southeastern Section, 52nd annual meeting, 35 (1), 4, georefid:2005-075325

Active sulfide mineralization occurs at the sulfate-methane interface (SMI) in modern, deep-water, continental-margin sediments that overlie accumulations of methane gas hydrate at the Blake Ridge (southeastern North America). Sulfide minerals (elemental sulfur, S degrees ; iron monosulfides, approximately FeS; and pyrite, FeS (sub 2) ) at the present-day sulfate-methane interface are enriched in (super 34) S relative to sulfide minerals in the sulfate reduction zone. These enrichments of (super 34) S occur because of focused anaerobic methane oxidation (AMO) at the SMI carried out by a consortium of methanotrophs and sulfate-reducing microbes, and because of non-steady-state diagenesis. (super 34) S enrichments are a potential diagenetic indicator identifying occurrences of high methane delivery to the sulfate-methane interface and the action of the AMO consortium. A key question is: Are these enrichments of (super 34) S preserved in the sedimentary record? We extracted sulfide sulfur from authigenic sulfide minerals contained in sediments collected at Site 995, Ocean Drilling Program (ODP) Leg 164. Chromium reduction was used to extract sulfide sulfur and we measured sulfide sulfur concentration using iodometric titration. In separate extractions, we precipitated sulfide sulfur as Ag (sub 2) S for sulfur isotopic analysis. Sulfide mineral concentration at the present-day sulfate-methane interface occurring at approximately 20 m is as high as 0.57 wt % sulfur. Preliminary data from the depth interval of 20 to 703.80 m (sediments >0.085 to 6.0 Ma in age) show sulfide concentration ranging from 0.04 to 1.03 wt % sulfur. Twenty-six percent of samples (8 of 30) show sulfide sulfur concentrations higher than that of the present-day SMI. This implies that the diagenetic front at the SMI was stratigraphically stable for longer periods of time, and/or that methane flux to the SMI was higher than observed today. Isotopic data show that (super 34) S enrichments within sulfide minerals persist in the geologic record, and we infer that these enrichments identify SMIs that occurred in the geologic past.
West: -75.3118 East: -75.3118 North: 31.4812 South: 31.4812
Expedition: 164
Site: 164-995
Data access:
Provider: SEDIS Publication Catalogue
Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=2005-075325 (c.f. for more detailed metadata)
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