Alcune osservazioni di geologia del quaternario nell'alta valle del Fiume Ufita (Appennino Irpino, Italia meridionale)

Abstract

: A preliminary reconstruction of the events which took place in the high valley of the Ufita River (northern Irpinia, southern Italy) during the Quaternary has been made on the basis of geomorphological and stratigraphical data. Ancient morphological elements such as paleosurfaces, remains of the paleohydrographic network and glacis are visible along the northeastern slope of the valley (Baronia area). On the southwestern slope, along the Frigento-Mt. Forcuso ridge, these elements are less evident because of widespread landsliding phenomena. On the right of the Ufita River, a glacis is limited by a fault slope near the valley bottom; the fault slope has a NW-SE direction and evolved into "triangular facets" in soft rocks. In the upper part and along the facets, between +120 m and +22 m above the valley bottom, there are alluvial cone and fluvial deposits (terraces of the 1st, 2nd and 3rd order). Along the valley bottom, wide inactive alluvial fans and terraced alluvial deposits are present between +20 m and +3 m above the present river bed (4th, 5th and 6th order terraces). In several tracts of its course, the river directly cuts through the clayey-arenaceous substratum of Pliocene age. A SW-NE stretching normal fault near Grottaminarda possibly contributed to the formation of a fluvial-lacustrine basin in Upper Pleistocene times. The basin is filled by more than 120 m thick clastic deposits. These deposits have been subdivided into four facies: i) colluvial deposits, ii) alluvial deposits, iii) lacustrine and palustrine sediments, iv) detrital and colluviai deposits with landslide debris. The substratum of the basin has a graben structure, the deepest part of which is more than 120 m deep in the axial area.