Methane seepages recorded in benthic foraminifera from Miocene seep carbonates, Northern Apennines (Italy)

Benthic foraminifera from seep carbonates and from enclosing non-seep marls present within Miocene formations in the Northern Apennines (Italy) were investigated as proxies of methane seepage in the marine environment Negative delta(13)C values of benthic foraminifera from these seeps indicate unambiguously the local influence of CO(2) produced by microbial anaerobic methane oxidation on the benthic ecosystem. Calcareous species living within methane seeps display delta(13)C values ranging from -9.04 to -25.74 parts per thousand PDB, whereas in the coeval surrounding marls the same species display delta(13)C values from -1.54 to 0.62 parts per thousand PDB. Different species (Cibicidoides kullenbergi C. pachyderma, Siphonina rethiculata, Planulina wuellestorfi, Bolivina miocenica, Brizalina dilatata, Vulvulina pennatula, and Cibicides praecinctus) in different seep carbonates indicate that benthic foraminifera, independently of the taxa and of microhabitat preferences, have more negative delta(13)C values than those found in the enclosing marls. Therefore each species represents a potential proxy for past seafloor methane emissions. In addition to the calcareous species, the agglutinated species Vulvulina pennatula displays -27.5 parts per thousand PDB in seep carbonates against -2.69 parts per thousand PDB in the enclosing marls. This suggests that the species utilized strongly (13)C depleted carbonate particles from authigenic carbonate precipitation during the mineralization of their tests.