Sedimentary structures and facies of fine grained deep water carbonate turbidites in a Paleocene-Middle Eocene flysch complex, Monte Sporno, northern Apennines, Italy

Abstract: The Monte Sporno flysch unit consists of regularly alternating calcareous turbidites and subordinate hemipelagic clays, deposited in a basin plain environment near, but above, the calcite compensation depth (CCD). Evidence for turbidity current emplacement includes sole markings, Bouma intervals and resedimented shallow-water microfossil species in a deep-water trace fossil assemblage (Nereites ichnofacies). Three main compositionary facies with different provenance has been distinguished mainly on basis of terrigenous influx, sedimentary structures, trace fossils, calcium carbonate content and present microfossils. These are siliciclastic turbidite facies, where primary and secondary sedimentary structures (Bourna intervals) are well developed, and carbonate turbidite facies, where biogenic structures are common and well developed (mainly ichnogenera Chondrites, Zoophycos and Helminthoida). The carbonates were derived from north , while erosional structures indicate a west-southwestern source area for the clastics. The third facies is represented by hemipelagic clays. These are distinguished from turbidite derived clays in colour, thickness, micro fabric, calcium carbonate content and finally , because they represent a recurrent facies that complete Bouma intervals. It is also shown that upward decrease of calcium carbonate content through turbidites is directly related to the different depositional processes i.e. turbiditic deposition and hemipelagic settling.