A multi-scale analysis of sedimentary carbonate facies and post-sedimentary diagenetic features of theCalcare di Base Formation, the precursor to evaporites in Upper Messinian successions of NorthernCalabria and Central Sicily, has revealed their microbial bio-mediated origin. Massive to laminated microbialboundstones represent the most common sedimentary facies forming flat to low relief cm to mscale stromatolitic and thrombolitic bodies. The fabric of the micrite varies from peloidal to aphanitic,and almost always preserves filamentous bacteria which characterized the original microbial mat. Themat was dominated by sulphur-oxidizing bacteria belonging to the Thiotrichaceae, but there is evidencefor a more complex community with sulphate- and/or nitrate-reducing bacteria, all being responsible forthe mediation of the carbonate precipitation. Microbial boundstones are rich in pseudomorphs of Casulphateand halite, which formed during the deposition of the microbial carbonate. Layers of primarygypsum are interbedded locally with carbonates suggesting the presence of restricted marine conditions.The stable O and C isotopic composition of the carbonates, that vary from dolomite to aragonite andcalcite, suggests a complex interplay between arid to humid climatic changes, expressed cyclic interbeddingof the carbonate with marl-marlstone. Later diagenetic events mainly consist of phreaticmeteoric recrystallization and cementation. Although considered as diachronous, the microbial carbonatescan be mapped out over a distance of more than 500 km across southern Italy; this indicatesnear-constant environmental conditions upon the central Mediterranean shelf at the beginning of thesalinity crisis. Deposition of the extensive subaqueous microbial deposit that largely comprises theCalcare di Base is envisaged to have taken place across a shallow to moderate depth platform with localslopes into deeper water areas, where some resedimentation occurred.
|Numero di pagine||16|
|Rivista||Marine and Petroleum Geology|
|Stato di pubblicazione||Published - 2017|
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