Carbonate deposits related to active seeps are documented along most continental margins and are characterized by peculiar seep-related facies and by chemical(isotope signature),paleontological and mineralogical marke...Carbonate deposits related to active seeps are documented along most continental margins and are characterized by peculiar seep-related facies and by chemical(isotope signature),paleontological and mineralogical markers.Their fossil analogues are recognized all over the world by the same features and occurred since the beginning of Phanerozoic.In this paper,we present a new seep outcrop(Castagneto village,Reggio Emilia,northern Italy)belonging to the late Eocene Loiano Formation which,to our knowledge,is in Italy the most ancient seep deposit with not-reworked chemosymbiotic fauna.The outcrop can be roughly divided into two portions,a northern part showing abundant presence of macrofossils in silty carbonate matrix and subhorizontal subdivisions,and a southern part,where macrofossils are almost absent,characterized by sub-vertical internal subdivisions and a clear vertical structure consisting of the rhythmic alternation of light and dark mineralization.Detailed analysis of samples from the southern portion showed the occurrence of authigenic calcite and pyrite,the latter with a peculiar framboidal texture.This feature,together with the occurrence of chemosymbiotic species and~(13)C isotope depletion,suggests possible hydrocarbon-rich fluid-related genesis and provides useful criteria for identifying hydrocarbon-rich fluid-related deposits in geologic units.展开更多
文摘Carbonate deposits related to active seeps are documented along most continental margins and are characterized by peculiar seep-related facies and by chemical(isotope signature),paleontological and mineralogical markers.Their fossil analogues are recognized all over the world by the same features and occurred since the beginning of Phanerozoic.In this paper,we present a new seep outcrop(Castagneto village,Reggio Emilia,northern Italy)belonging to the late Eocene Loiano Formation which,to our knowledge,is in Italy the most ancient seep deposit with not-reworked chemosymbiotic fauna.The outcrop can be roughly divided into two portions,a northern part showing abundant presence of macrofossils in silty carbonate matrix and subhorizontal subdivisions,and a southern part,where macrofossils are almost absent,characterized by sub-vertical internal subdivisions and a clear vertical structure consisting of the rhythmic alternation of light and dark mineralization.Detailed analysis of samples from the southern portion showed the occurrence of authigenic calcite and pyrite,the latter with a peculiar framboidal texture.This feature,together with the occurrence of chemosymbiotic species and~(13)C isotope depletion,suggests possible hydrocarbon-rich fluid-related genesis and provides useful criteria for identifying hydrocarbon-rich fluid-related deposits in geologic units.
