Interpreting siliciclastic-carbonate detrital modes in Foreland Basin Systems: an example from Upper Miocene arenites of the Central Apennines, Italy

In the central Apennines, interacting siliciclastic and carbonate marine clasticwedges filled the foreland basin system during the late Miocene. Conjunction of collisionalthrust tectonics and prethrusting normal faults generated a complex foredeepwith intrabasinal structural highs that represented additional source areas tothe basin.Detrital modes of the late Miocene central Apennines orogenic system range incomposition from intrabasinal carbonate to quartzofeldspatholithic and calclithitearenites. The external zone of the foredeep is characterized by hemipelagic deposits,called the Orbulina Marl. Their arenite beds are composed by intrabasinal carbonate,with dominant bioclasts and minor intraclasts, and glauconite derived from anactive shallow-marine carbonate source. These hemipelagic deposits are partly coevalwith and partly overlain by siliciclastic turbidites of the Frosinone and the Argilloso-Arenacea Formations, and they represent deposition within local foredeep depocenters.Siliciclastic turbidite sandstones are quartzofeldspatholithic, which documentsprovenances from metamorphic, plutonic, ophiolitic, and sedimentary rocks. Carbonateintrabasinal structural highs were the main source for carbonate breccias,intrabasinal arenites, and calclithites of the Brecce della Renga Formation, the depositsof which are locally interbedded with the coeval siliciclastic turbidite sandstones.Evolution of late Miocene sandstone detrital modes reflected the changing natureof the central Apennines thrust belt through time and the complex architecture of theforeland basin system; it records the history of accretion, deformation of the foredeep,and progressive areal reduction of carbonate-producing areas along with thesedimentary and structural evolution of local intrabasinal highs.