The composition and provenance of the Tortonian and Messinian turbidites in the context of the structural evolution of the Central Apennines along the “Ancona-Anzio” line

Abstract

The “Ancona-Anzio” line is a complex tectonic system separating the Umbro-Marchide domain from the Latium-Abruzzi platform in the Central Apennines. It played a decisive role in turbiditic sedimentation in the four Latium-Abruzzi basins (Salto, Tagliacozzo, Liri and Sacco) in the Tortonian and in the Laga basin during the Messinian. Petrographic studies show that the composition of the turbiditic sandstones is the same in all the basins. In particular: (1) K-feldspar is always present in greater quantities than plagioclase; (2) the rock fragments consist mainly of carbonates and granitic-type rocks. The provenance of the turbidites is to be found in the western areas, from a fragment of the Alpine Chain that was associated with the Ligurids nappes during the eastward migration of the Apennines deformation. This fragment was probably eroded gradually between the Langhian and the Lower Pliocene with the filling-in of the Laga Basin. The presence of clasts derived from the erosion of crystalline rocks and from the Ligurids nappes has been documented as early as the Langhian in the basin of the Marnoso-Arenacea. During the Tortonian, the Latium-Abruzzi platform was lower than the Umbro-Marchide region and the gravity flows with western provenance were able to feed the four basins formed within the platform. Between the end of the Tortonian and the beginning of the Messinian, the relative uplift of the Latium-Abruzzi platform, due to displacements along the “Ancona-Anzio” line, caused the cessation of turbiditic sedimentation in the basins formed within the platform. The progressive eastward shift of the Apennine Chain favoured the migration of turbiditic sedimentation towards the outer foreland Laga basin.