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

Abstract

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 δ 13C 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 δ 13C values ranging from − 9.04 to − 25.74‰ PDB, whereas in the coeval surrounding marls the same species display δ 13C values from − 1.54 to 0.62‰ 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 δ 13C 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‰ PDB in seep carbonates against − 2.69‰ PDB in the enclosing marls. This suggests that the species utilized strongly 13C depleted carbonate particles from authigenic carbonate precipitation during the mineralization of their tests.