• journal_title：Geology
• Contributor：Patrick Meister ; Marcus Gutjahr ; Martin Frank ; Stefano M. Bernasconi ; Crisógono Vasconcelos ; Judith A. McKenzie
• Publisher：Geological Society of America
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.1130/G31810.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：39
• issue：6
• firstpage：563
• section：Articles

Early diagenetic dolomite formation in methanogenic marine sediments is enigmatic because acidification by CO₂, a by-product of methanogenesis, should lead to carbonate dissolution and not precipitation. However, petrographic relationships indicate that dolomite breccia layers with δ¹³C values of ∼+15‰, recovered from the lower slope of the Peru continental margin (Ocean Drilling Program Site 1230), formed deep in the methanogenic zone during tectonic activity of a décollement. Based on radiogenic Sr isotope ratios (⁸⁷Sr/⁸⁶Sr > 0.711) and positive δ¹⁸O values (+6‰), we present evidence that the dolomite breccias mainly formed from fluids originating from deep sedimentary units within the accretionary prism, where they interacted with continental crust and/or siliciclastic rocks of continental affinity. Due to silicate alteration and dehydration, such fluids are likely alkaline and thus have the potential to neutralize the acidification imposed by the high dissolved CO₂ concentrations. This scenario provides a potential mechanism by which dolomite formation can be induced deep in a highly active methanogenic zone.