Miocene chemoherms of the northern Apennines, Italy

In the Miocene of the northern Apennines, methane-derived limestones from v arious geologic settings represent important examples of fossil chemoherms and provide a basis for more accurate interpretations of seepage systems. T he systematic study of fossil chemoherms has allowed the definition of new field and compositional criteria for the recognition of these deposits, whi ch were previously based almost exclusively on negative carbon isotope comp osition and peculiar chemosynthetic communities; this has constrained the r elations between seepage and sedimentary and tectonic instability processes . We suggest that the peculiar brecciated structures associated with fossil chemoherms are related to diapirism or overpressured pelitic sediments due to fluid venting. Fluidization of sediments increases the instability of m udstones in which chemoherms are contained, thus favoring gravity slumping processes and the reworking of many chemoherms.