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

Abstract

ABSTRACT 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.