Occurrence of photosynthetic microbial mats in a Lower Cretaceous black shale (central Italy): a shallow-water deposit |
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Authors: | Muriel Pacton G Gorin N Fiet |
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Institution: | (1) Department of Geology-Paleontology, University of Geneva, 1205 Geneva, Switzerland;(2) UMR-CNRS 8148, Bat. 504, Paris-Sud University, 91405 Orsay Cedex, France |
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Abstract: | 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. |
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Keywords: | Palaeoenvironment Bacteria Amorphous organic matter Extracellular polymeric substances Sorptive preservation pathway Oceanic anoxic event |
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