Evoluzione quaternaria del sistema di depressioni del Tirino (Appennino Abruzzese)

Abstract

The Tirino area, one of the easternmost depression systems of the central Apennines, runs along the southern prolongation of the Gran Sasso structural unit. The study of the Quaternary evolution of this area is particularly interesting for the definition of the interactions between the compressive phases, responsible for the thrusting of the chain over the terrigenous units, and the tectonic collapse of the depressed area. Detailed morpho-Iithostratigraphic studies allow to outline the Quaternary and neotectonic evolution of the area. The Lower Pleistocene-Holocene continental deposits have been ordered into five complexes: i) the old carbonate breccia and ii) the "Convento dei Cappuccini" complex (Lower Pleistocene), iii) the "Bussi" complex (Middle-Upper Pleistocene), iv) the "C. Spera" complex (Upper Pleistocene) and v) the "Capo d'Acqua" formation (Holocene). The oldest continental sediments are mostly clastic deposits from slope sedimentation. Their distribution suggests that the depositions area was much larger than the present depressed area. Sedimentation of talus deposits, together with a plentiful sedimentation in a lacustrine environment, continued during the Lower Pleistocene in a smaller area located within a basin, the size of which was similar to the most depressed areas of the present Tirino basin system. The Middle-Upper Pleistocene sedimentary complex is deeply entrenched into the oldest deposits. This sedimentary complex, characterised by abundant volcanic minerals, shows a prevalent lacustrine facies developed in two terraces weakly entrenched into one another. The Upper Pleistocene deposits are gravel sediments, which form major alluvial fans. A small fluvio-lacustrine basin rich in gastropods, mammals and archeological remains, developed during Holocene times in the "Capo d'Acqua" area. The Tirino depression system has an almost triangular shape bounded by a NW-SE and NNW-SSE trending fault system and by transverse systems. The age of the tectonic activity is defined on the basis of fault displacements evident in the Lower Pleistocene deposits. Middle-Upper Pleistocene deposits also show some evidence of tectonic activity. Given the scarcity of kinematic elements on the fault planes of neotectonic interest, the studies performed so far only allow the reconstruction of the vertical component of the observed tectonic movements.