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Occurrence of photosynthetic microbial mats in a Lower Cretaceous black shale (central Italy): a shallow-water deposit

Pacton, Muriel ; Gorin, G. ; Fiet, N.

In: Facies, 2009, vol. 55, no. 3, p. 401-419

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    Titre
    • Occurrence of photosynthetic microbial mats in a Lower Cretaceous black shale (central Italy): a shallow-water deposit
    Auteur
    • Pacton, Muriel. Department of Geology-Paleontology, University of Geneva, 1205, Geneva, Switzerland
    • Gorin, G.. Department of Geology-Paleontology, University of Geneva, 1205, Geneva, Switzerland
    • Fiet, N.. UMR-CNRS 8148, Bat. 504, Paris-Sud University, 91405, Orsay Cedex, France
    Type de document
    • Postprint
    Identifiant OAI-PMH
    • oai:doc.rero.ch:317850
    Summary
    Cretaceous oceanic anoxic events (OAEs) were periods of high organic carbon burial corresponding to intervals with excellent organic matter (OM) preservation. This work focuses on the Urbino level, i.e., OAE1b, which is thought to be of regional extent. A detailed microscopical study of OM shows a dominance of microbial activity, characterized by a typical arrangement of exopolymeric substances (EPS) related to microbial mats, bacterial bodies, and some photosynthetic microorganisms, as shown by thylakoids. The latter lived where they have been found, i.e., at the sea bottom, which indicates that OM results from the diagenesis of benthic photosynthetic microbial mats, an interpretation supported through the comparison with a recent analogue. The exceptional preservation of such organic structures in OM points to the joint role of the selective and sorptive preservation pathways. These data and interpretation strongly differ from previous observations in OAE1b equivalents. They suggest that the Urbino level might be an atypical OAE of regional/local extent which was formed within the photic zone