Facies and sequence architecture of a tropical foramol-rhodalgal carbonate ramp: Miocene of the central Apennines (Italy)

Integrated data from sedimentological and microfacies analyses have been used to reconstruct the stratigraphic and architectural evolution of a carbonate ramp exposed in the central Apennines. The platform was a wide homoclinal ramp characterized by rhodalgal, bryomol and foramol skeletal-grain associations that developed under tropical-subtropical conditions. Based on facies distribution and palaeoecology, the rampcanbe subdividedinto: (1) aninner zonewhosemain components include balanids, molluscs and branching red algae; (2) a middle zone characterized by rhodoliths and larger foraminifera; and (3) an outer ramp consisting of: (a) a proximal zone dominated by bryozoan colonies, bivalves and echinoids: (b) an intermediate zone where the main components are benthic and planktonic foraminifera, worm tubes, fragmented echinoids and bivalves; and (c) a distal zone where marls and calcarenites contain silica-sponge spicules, planktonic foraminifera and mollusc-bryozoan-echinoid debris. Strontium-isotope dating has been essential in generating a detailed chronostratigraphy. The reconstructed architecture reflects two second-order depositional sequences. The lower sequence (uppermost Aquitanian to Serravallian) is composed of a lowstand systems tract, a well-developed transgressive systems tract and a thin highstand systems tract. The architectural pattern of the lower sequence first shows aggradation, followed by retrogradation and finally a pronounced contemporaneous progradation. Changes in trophic resources and tectonic phases have been interpreted as the main factors controlling the sequence architecture. The upper sequence, starting in the Serravallian, was strongly controlled by tectonic subsidence and its diachronous termination was a consequence of the downflexure of the foreland related to the eastward migration of the Apennine foredeep system