Evoluzione morfostrutturale del margine orientale dell'Appennino meridionale tra il Molise e la Basilicata durante il Plio-Pleistocene e rapporti con la sismicità

Morphostructural evolution of the eastern margin of the Southern Apennines between Molise and Basilicata during the Plio-Quaternary. Relationship with seismicity

Abstract

This study investigates the eastern sector of the Southern Apennines between Molise and Basilicata based on residual paleosurface findings lying at different elevations (from approximately 600 m to 1000 m). This sector is characterized by high seismicity connected with Plio-Quaternary compressive tectonics due to crustal deformations. Plio-Pleistocenic terrigenous marine deposits, resting unconformably over the Mesozoic and Pliocenic deformed terrains of the chain, are present along this sector (Acerenza, Calvello, S. Arcangelo). Pleistocenic continental fluvio-lacustrine basins (Boiano-Sepino, Benevento, Caudina Valley, Serino, Montella, Lioni, Baragiano, upper Melandro-Agri rivers valley, Mercure) and volcanic deposits are also present. The paleosurface cuts unconformably all the terrains dated from the Mesozoic to the Early Pleistocene and fossilizes the Miocenic and Pliocenic tectonic phases. Moreover, the top surface is fossilized by the Vulture volcanic rocks, dated from 0.8 to 0.5 m.y. The paleosurface is characterized by a not deeply excavated hydrographic drainage not connected with fault slopes, which are strongly controlled by high morphodynamics due to fluvial and mass erosion. Morphological, stratigraphical, and structural studies permit the explanation of the origin and significance of the summit paleosurface and seismicity, by reconstructing the stages of morphotectonic evolution during the Plio-Quaternary phases in the geodynamic framework of the eastern sector. It has been noticed that the elevation of the studied area was proximal to the Pleistocene shoreline; therefore, the regional paleosurface was prevalently formed by marine abrasion and partially by subaerial erosion, coinciding with probable periodic emersions during the Early-Middle Pleistocene. An upward rise followed by the dislocation of the summit paleosurface occurred during the Early-Middle Pleistocene phases, subsequently fossilized by the Vulture volcanic rocks. The fast rise and the tectonic dislocations causing the breakup of the paleosurface have modified the fluvial drainage and determined active slope morphodynamics in argillaceous terrains. The dislocation of the abrasion marine paleosurface caused the development of slopes and hydrographic drainages, at present more unbalanced. The seismicity of the studied area is connected with the seismogenetic structures bordering the western and eastern margins of this sector, deformed by recent crustal compressive tectonics.