The Lower Miocene spongolitic sequence of the Central Apennines: a record of the Burdigalian siliceous event in the central Mediterranean

Abstract

A stratigraphic and sedimentological analysis of the Miocene spongolitic unit from Central Apennines is presented. The spongolitic succession of the Latium-Abruzzi Platform (informally named Guadagnolo Formation) represents the sedimentation along the platform margin domain. In all sectors of the platform, at least two informal members are distinguishable. The lower member, Chattian to Early Burdigalian in age is characterized by deposits dominated by larger benthic foraminifera. This member is divided in two intervals by a first spongolitic horizon of few meters thick. The more siliceous intermediate member (“spongolitic”), spanning the Burdigalian to Langhian, mostly consists of spongolitic marls and marly limestones. The upper member is only present in the north-western and northern margin and it is characterized by cross-bedded calcarenites. The Burdigalian time interval in Central Apennines is characterized by: a) spread of terrigenous spongolitic facies on the platform-to-basin zone and cherty-rich facies in the pelagic realm, b) spread of bryozoan-dominated facies on the platform domain, and c) positive C-isotope excursion related to high primary production The Oligo-Miocene volcanic activity in the western Mediterranean and its related increase in atmospheric CO 2 might have induced decreases in pH and carbonate ion concentrations in surface waters, favoring siliceous production in acidic seawaters. An increase in terrigenous material from the neighboring Apennine foredeep system, promoted a CaCO 3 reduction induced by terrigenous dilution. The combined effect of volcanism, changes in oceanic circulation and the Apennine foredeeprelated siliciclastic input, favoured the spreading for marly-spongolitic facies in the Central Apennines, as well as throughout the Mediterranean area.