Methane-derived authigenic carbonates from modern and paleoseeps on the Cascadia margin: Mechanisms of formation and diagenetic signals

Show simple item record Joseph, Craig en Campbell, Kathleen en Torres, Marta E en Martin, Ruth A en Pohlman, John W en Riedel, Michael en Rose, Kelly en 2014-10-29T20:43:49Z en 2013-11 en
dc.identifier.citation Palaeogeography, Palaeoclimatology, Palaeoecology, 2013, 390 pp. 52 - 67 en
dc.identifier.issn 0031-0182 en
dc.identifier.uri en
dc.description.abstract Authigenic carbonate precipitation occurs within marine sediments where sulfate-dependent anaerobic methane oxidation occurs. Geochemical and isotopic analyses of authigenic carbonates are commonly used as indicators of carbon sources and environmental conditions present during carbonate formation, but burial diagenesis and recrystallization can overprint these signals. Plane polarized light (PPL) and cathodoluminescent (CL) petrography allows for detailed characterization of carbonate phases and their subsequent alteration. Petrographic, isotopic, and geochemical characteristics of modern offshore authigenic carbonates from central and northern Cascadia are compared with Oligocene–Pliocene fossil seep carbonates uplifted on the Olympic Peninsula. Coupled analyses show the value and complexity of separating primary vs. secondary signals with relevance to understanding fluid-burial history in methane seep provinces on tectonically active convergent margins. The modern, offshore, near-seafloor diagenetic environment (S. Hydrate Ridge and Barkley Canyon) is dominated by acicular and microcrystalline aragonite and high-Mg calcite (HMC, > 12 mol % Mg). PPL and CL data illustrate that aragonite and HMC phases recrystallize to intermediate-Mg calcite (IMC, 5–12 mol% Mg) during burial and diagenesis and eventually to low-Mg calcite (LMC, < 5 mol% Mg). This diagenetic progression is accompanied by a decrease in Mg/Ca and Sr/Ca ratios. Typically an increase in Ba/Ca is consistent with a high-barium content of the methane-bearing pore fluids that drive recrystallization. CL images also discern primary carbonates with high Mn/Ca ratios, including biogenic peloids, from secondary phases related to deep fluid migration through high permeability conduits. In the secondary phases, the Mn/Ca reflects Mn-enrichment that characterizes deep sourced fluids venting at Barkley Canyon. Mn-enrichment is accompanied by depletion in 18O attributable to elevated fluid temperatures during recrystallization. en
dc.language aa en
dc.publisher Elsevier Science en
dc.relation.ispartofseries Palaeogeography, Palaeoclimatology, Palaeoecology en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. Details obtained from en
dc.rights.uri en
dc.title Methane-derived authigenic carbonates from modern and paleoseeps on the Cascadia margin: Mechanisms of formation and diagenetic signals en
dc.type Journal Article en
dc.identifier.doi 10.1016/j.palaeo.2013.01.012 en
pubs.begin-page 52 en
pubs.volume 390 en
dc.rights.holder Copyright: Elsevier Science en
pubs.end-page 67 en
dc.rights.accessrights en
pubs.subtype Article en
pubs.elements-id 373904 en Science en School of Environment en
pubs.record-created-at-source-date 2014-10-30 en

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