ELEMENTS TO CORRELATE MARINE AND CONTINENTAL SEDIMENTARY SUCCESSIONS IN THE CONTEXT OF THE NEOTECTONIC EVOLUTION OF THE CENTRAL APENNINES

Abstract

The central Apennines show geologic and geomorphic features that report the strong influence of extensional tectonics and regional
uplift on their recent evolution. The goal of this paper is to find out the time constraints of the chain uplift, focusing on the elements of
correlation between marine and continental successions on both the Adriatic and Tyrrhenian sides. All along the range, the most
ancient landforms are gently rolling or flat summit surfaces. On the Tyrrhenian side, the interaction between the chain uplift and the
extensional tectonics related to the opening of the Tyrrhenian basin, generated several neoautoctonous basins that are older in
Tuscany (since the Tortonian) and younger in the Latium-Abruzzo area (since the Pliocene). On the Adriatic side, the combined action
of uplift and climatic changes, produced several depositional sequences, separated by angular unconformities. In the western basins,
progressively coarsening upward sediments, corresponding to the Globorotalia crassaformis biozone, are found. At Valle Ricca, in the
upper section of these deposits, a 2.1 Myr old volcanic layer, corresponding to the base of the Globorotalia inflata biozone, is present.
The Valle Ricca succession is truncated by an erosion surface over which marine and brackish sandy clay (Argille Sabbiose del ChianiTevere) lay down. Similarly, in the periadriatic basin, a volcanic layer, dated 2.1 Myr, has been found at Bellante, in the upper part of a pelitic sequence. An angular unconformity separates this sequence from overlaying conglomerate and sand, recording a progressively eastward shifting of the coastline as a consequence of the uplift. Contemporaneously, extensional tectonics progressively affected the Apennine chain giving rise to a number of intermontane depressions, within which coarse breccia and lacustrine-alluvial deposits were deposited. In the Rieti and L’Aquila basins, the finding of Equus stenonis and Mammuthus meridionalis refer the basal part of these deposits to an age not older than the lower Pleistocene. Around 0.8 Myr B.P., in correspondence with a base level drop induced by a sudden increase of uplift rate, the coastline rapidily shifted seawards and littoral sandy-pebbly sediments were deposited along both sides of the Apennines. Contemporaneously, increased stream erosion rates gave rise to the present valley network, within which the interaction of river incision and climate changes generated several orders of alluvial terraces. In this contest, a hunched backward river erosion breached most of intramontane depressions, draining off the lakes and causing the erosion of the basin sedimentary sequence.
In conclusion, according to all these considerations, we hypothesize that the topographic growth of the range was slow until the end of
the lower Pleistocene, when a strong increase of the uplift rate affected the chain and the surrounding coastal belts.