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Controls on the formation of authigenic minerals in association with decaying organic matter: an experimental approach

Sagemann, Jens, Bale, Simon J., Briggs, Derek E. G. and Parkes, Ronald John 1999. Controls on the formation of authigenic minerals in association with decaying organic matter: an experimental approach. Geochimica et Cosmochimica Acta 63 (7-8) , pp. 1083-1095. 10.1016/S0016-7037(99)00087-3

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Carcasses of the shrimp Crangon crangon were incubated in a marine medium under oxic conditions at 15°C which was inoculated with a consortium of sulfate-reducing, sulfide-oxidizing, and fermentative bacteria. These standard conditions were varied by adding sediment, omitting sulfate, adding glucose, omitting the inoculum, adding phosphate, and enhancing the buffer capacity. The chemical gradients generated by decay were monitored over a period of 29 days with O2, pH- and sulfide-microelectrodes. In most of the experiments oxygen was depleted, pH decreased and sulfide accumulated around the carcass within a week, creating steep chemical gradients, and decay was predominantly anaerobic. By 29 days maximum change in O2 concentration was from around 200 to 0 μM, in pH from 7.5 to 6.2, and in sulphide concentration from 0 to 5.6 mM. Although weight loss and general decay were least when only indigenous bacteria were present, only CaCO3 crystal bundles formed and there was no soft tissue preservation. In contrast, where decay and weight loss were more extensive anaerobic sulphate reduction was intense, pH decreased markedly, and some muscle tissue was replicated in CaPO4. The pH close to the decaying carcass seemed to determine whether CaCO3 or CaPO4 formed. Paradoxically, the exceptional preservation of soft-tissues in fossils requires elevated rather than restricted microbial activity as this leads to anaerobically driven authigenic mineral formation.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Publisher: Elsevier
ISSN: 0016-7037
Last Modified: 04 Jun 2017 02:07

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