History of Miocene temperate-type carbonate shelf in a compressive setting (northern Apennines), constrained by a chemostratigraphycal, microfacies and compositional study

A detailed chemostratigraphic study associated with microfacies and compositional analysis has been performed on a early middle Miocene shallow-water shelf deposited on a wedge-top basin in the northern Apennines. More than 140 samples were collected in the representative outcrop of Torriana (Val Marecchia valley, Romagna Apennines) in order to identify factors controlling the inception and crisis of the shelf. The succession is constituted by 100 m thick mixed siliciclastic-carbonate rocks, unconformably overlying the allochthonous Ligurian units. The evolution of the carbonate shelf passed true four main phases, as shown by the detailed microfacies and compositional study, that evidence the progressive decrease of the carbonate productivity, gradually replaced by detrital sedimentation. The basal portion consists of rhodalgal rudstones and grainstones dominated by echinoids, bryozoans, coralline algae and benthic foraminifera. The progressive increase of terrigenous components and planktonic and benthic taxa marks the gradual transition to a mixed carbonate-siliciclastic shallow water-facies. The top of the succession is characterized by fine-grained sediments rich in glaucony. The main factors controlling the evolution of the shelf are increased subsidence of the basin, related to the thrust migration, and terrigenous contributions from the erosion of the rising Apennines areas. The stable isotope study show that the carbonate production has been influenced not only by regional factors, but also by a global fertility event, as the Monterey Event, recorded in the Mediterranean during the late Burdigalian - Serravallian.