Sedimentary filling of a wedge-top basin and realationship with the foredeep (Middle Miocene Marnoso-arenacea Formation, northern Apennines.

The Middle Miocene Marnoso-arenacea Formation (?Langhian to Serravallian in age), at Deruta in the northern Apennines of Italy, rests unconformably on an orogenic wedge adjacent to the Adriatic foredeep. Based on a detailed facies analysis, the succession reveals two genetically related depositional systems, representing a more lower distal delta-fed sand-rich system and an upper more proximal fan-delta slope system. Petrographic data confirm the genetic relationship between the two depositional systems, with the fan-delta slope feeding the basinward sand-rich system. The Deruta depositional setting shows a multi-step sedimentary evolution controlled by tectonically induced relative sea-level changes. The first stage, corresponding to a sea-level rise, promoted deposition in a wedge-top basin of pebbly sand and sand lobes (delta-fed). The second stage, characterized by intense tectonic activity (uplift) and sea-level fall, promoted accumulation of a prograding fan-delta slope replacing the sand-rich lobes. This phase was dominated by mass failures and methanogenic cold seepages. During these stages, the wedge-top basin was isolated from the adjacent foredeep. Only during the third stage was a connection was established, with the development of a deep-sea fan in the foredeep, fed by a deltaic depositional system.