Authigenic carbonate precipitates from the NE Black Sea: a mineralogical,geochemical, and lipid biomarker study |
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| Authors: | A Bahr T Pape G Bohrmann A Mazzini M Haeckel A Reitz M Ivanov |
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| Institution: | 1.MARUM-Zentrum für Marine Umweltwissenschaften der Universit?t Bremen,Bremen,Germany;2.Physics of Geological Processes (PGP),University of Oslo,Blindern,Norway;3.IFM-GEOMAR,Kiel,Germany;4.UNESCO MSU Center for Marine Geology and Geophysics, Faculty of Geology,Moscow State University,Moscow,Russia |
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| Abstract: | Carbonate precipitates recovered from 2,000 m water depth at the Dolgovskoy Mound (Shatsky Ridge, north eastern Black Sea)
were studied using mineralogical, geochemical and lipid biomarker analyses. The carbonates differ in shape from simple pavements
to cavernous structures with thick microbial mats attached to their lower side and within cavities. Low δ13C values measured on carbonates (−41 to −32‰ V-PDB) and extracted lipid biomarkers indicate that anaerobic oxidation of methane
(AOM) played a crucial role in precipitating these carbonates. The internal structure of the carbonates is dominated by finely
laminated coccolith ooze and homogeneous clay layers, both cemented by micritic high-magnesium calcite (HMC), and pure, botryoidal,
yellowish low-magnesium calcite (LMC) grown in direct contact to microbial mats. δ18O measurements suggest that the authigenic HMC precipitated in equilibrium with the Black Sea bottom water while the yellowish
LMC rims have been growing in slightly 18O-depleted interstitial water. Although precipitated under significantly different environmental conditions, especially with
respect to methane availability, all analysed carbonate samples show lipid patterns that are typical for ANME-1 dominated
AOM consortia, in the case of the HMC samples with significant contributions of allochthonous components of marine and terrestrial
origin, reflecting the hemipelagic nature of the primary sediment. |
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| Keywords: | Black Sea AOM Authigenic carbonates Methane seepage Dolgovskoy Mound |
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