Detecting syn-orogenic extension and sediment provenance of the Cilento wedge top basin (southern Apennines, Italy). Mineralogy and geochemistry of fine-grained sediments and petrography of dispersed organic matter

Wedge-top basins can provide highly sensitive information on the uplift and erosion history of an evolving collisional belt, but their burial and thermal history has generally been neglected because their siliciclastic infill records the very low temperature history, which is difficult to detect. This paper provides an integrated approach for defining the first order tectonic events shaping the southern Apennines in Neogene times through the study of a wedge-top basin. A new dataset of temperature-dependent clay minerals and vitrinite reflectance, alongside whole-rock geochemistry of the fine grained sediments, is provided for the uppermost Burdigalian-lower Tortonian succession of the Cilento Group, deposited in one of the largest wedge-top basins of the southern Apennines (Italy) and its substratum. The distribution of paleothermal indicators allowed us to model a detailed burial and thermal history of the basin, whereas whole-rock geochemistry allowed us to trace the provenance and alteration of sediments through time. Geochemical data on the fine grained fraction of sediments suggest a source area mainly characterized by felsic rocks with a modest mafic contribution, reflecting a prevalent upper crust composition. Chemical paleoweathering processes played a minor role, consistent with medium CIA and CIA′ values and sediments, subdued poor sorting and rapid deposition. The dataset from clay minerals and vitrinite reflectance analyses indicates a basin evolution marked by two phases of intense subsidence, interpreted as the result of syn-orogenic extension at shallow crustal levels intermitted with periods of low sedimentation rates, linked to gravitational instability of a vertically growing orogen.