Characterization of the micrites in the Late Miocene vermetid carbonate bioconstructions, Salento Peninsula, Italy: Record of a microbial/metazoan association

The high fluorescence of the type (II) and (III) micrite can be related to organic matter derived respectively from decaying metazoan and microbial organisms. Twofold organic matter origin was supported by FT-IR and GC-MS analyses, carried out on the extracted organic matter. Micrite (I) shows very low intensity of organic matter functional groups, confirming its abiotic origin. The spectra of the automicrite (III) are characterized by the presence of stretching C=C vibrations attributable to alkene and/or unsaturated carboxylic acids, that may be synthesized by microbes. GC-MS investigations indicate the presence of extended hopane series, straight chain saturated (C14, Cl6), monounsaturated (C16, C18), and diunsaturated Cl8-acids, diagnostic of microbial activity. Microbial communities appear to have played a prominent role in the deposition and stabilization of Salento micrite-vermetid carbonate bioconstructions. The type (III) micrite, classifiable as microbialite or automicrite, can be regarded a sort of “primary framework” of these small “bioconstructions”.