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Article Dans Une Revue Biogeosciences Année : 2014

Authigenic phase formation and microbial activity control Zr, Hf, and rare earth element distributions in deep-sea brine sediments

Résumé

Sediments collected from hypersaline and anoxic deep-sea basins in the eastern Mediterranean (Thetis, Kryos, Medee, and Tyro) were characterised in terms of their miner- alogical composition, the distributions of rare earth elements (REE), Zr, and Hf and their content of microbial DNA. We identified two major mineralogical fractions: one fraction of detritic origin was composed of quartz, gypsum, and low- Mg calcite bioclasts (with 0 < Mg < 0 . 07 %) and another fraction of authigenic origin constituted of halite, dolomite, high-Mg calcite (with a Mg content of up to 22 %) and rare bischofite and showed a textural evidence of microbial as- semblages. We found that in the Medee and Tyro sediments, the shale- normalised REE pattern of these sediments is strongly en- riched in middle REE (MREE), whereas in the Thetis and Tyro basins, a positive Gd anomaly in the residue was ob- tained after the removal of the water-soluble fraction. In all investigated basins, Y / Ho ratio clustered around chondritic values, whereas Zr / Hf ratio ranged from slightly subchon- dritic to superchondritic values. Subchondritic Y / Ho and Zr / Hf values were mainly found in the high-Mg carbonate having a microbial origin. The observed preferential removal of Zr with respect to Hf without significant partitioning of Y with respect to Ho indicates that the Zr / Hf ratio and Y– Ho fractionations are influenced by the microbial activity in the sediments. We propose that the concurrent Y-Ho and Zr– Hf fractionations are a suitable tracer of microbial activity in marine sediments

Dates et versions

hal-01402769 , version 1 (25-11-2016)

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Citer

Paolo Censi, F. Saiano, Pierpaolo Zuddas, A. Nicosia, S. Mazzola, et al.. Authigenic phase formation and microbial activity control Zr, Hf, and rare earth element distributions in deep-sea brine sediments. Biogeosciences, 2014, 11, pp.1125-1136. ⟨10.5194/bg-11-1125-2014⟩. ⟨hal-01402769⟩
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