Microbial fabrics from Neogene cold seep carbonates, Northern Apennine, Italy

A number of hydrocarbon seep-carbonate masses are hosted within Miocene and Pliocene siliciclastic units along the Apennine Range and Sicily, and are mainly composed of micritic and microsparitic textures. Geomicrobiological analysis of some of these deposits shows that preserved microbial processes are few and the contribution of microbe-derived textures to their construction is volumetrically very limited. In the carbonate groundmass of two northern Apennine Miocene and Pliocene seep-carbonate deposits uncommon and well-preserved features suggest direct and indirect evidence of microbial activity. Some of these features are interpreted as the mineralization products of microbial textures, and include complex alveolar textures and fossilized biofilms that line and fill microconduits, pores and other voids, similar to living bacterial aggregations recovered in modern seep-carbonates. Other mineral structures, such as spheroids and rhombs, with concentric fabrics composed of calcite-dolomite alternations, abound as cement components and suggest a nucleation via bacterial sulfate reduction processes. A similar origin is also assumed for the acicular aragonite bundles that in the Miocene seep-carbonate mass enclose dense clusters of millimeter-size, filamentous morphologies of biological origin.