Nutrients, sea level and tectonics: constrains for the facies architecture of a Miocene carbonate ramp in central Italy

In the western part of the central Apennines, Lower-Middle Miocene carbonates were deposited on a tropical-subtropical carbonate ramp. They record two long-term cycles, the first of which is illustrated in this paper. Between 21 and 17.5 Ma, Miocene carbonates, paraconformably overlying the Cretaceous limestones, record a transgressive event during a time of global (2nd order) sea-level lowstand. It is postulated that this deviation is related to an increase in tectonic subsidence. Between 17.5 Ma and 16-15 Ma, with a progressive relative sea-level rise, the inner-middle ramp facies belt stepped back, whereas the bryozoan-dominated outer ramp facies belt stepped back but simultaneously prograded. This bloom of suspension-feeding organisms is interpreted to reflect an increased nutrient availability, hence a change from oligotrophic to eutrophic conditions. Strontium-isotope dates constrain correlation of the second phase with a eutrophic event possibly linked to the influence of the neighbouring Apenninic accretionary wedge and foredeep system.