Composite sequence stratigraphic patterns in alluvial to shallow-marine successions: Examples from the Piacenzian of the Valdelsa Basin (Central Italy)

The sequence-stratigraphic analysis of continental and shallow marine successions is a helpful tool for investigating the cyclicity of the sedimentary record. A similar approach is adopted in the present study to illustrate the composite cyclothemic facies architecture that characterizes the Piacenzian strata of the southern Valdelsa Basin (Central Italy). Specifically, we integrated facies analysis, paleopedology, paleobiology of marine mollusk assemblages and biostratigraphy to assess the response of geomorphic, sedimentary and biotic systems to Piacenzian multifrequency relative sea-level fluctuations. This integrated approach resulted in the definition of a composite sequence-stratigraphic framework that includes a hierarchy of units ranging from the elementary to the composite depositional sequences, referred to the 5th to 3rd order cycles of sea-level fluctuations, respectively. A correlation with the Piacenzian oxygen isotopic signature of glacial and interglacial stages and related sea-level fluctuations associates the cyclic development of fluvial, coastal and shallow marine depositional systems to the mid-Piacenzian Warm Period and to the subsequent transition to the Gelasian. Thus, the glacio-eustatic control prevailed on the development of the described multi-scale cyclical pattern of sedimentation, compared to the role played by the deformation of the Northern Apennines orogen.