Evoluzione geomorfologica ed ambientale tra il Pleistocene superiore e l'Olocene dell'area tra Castelbaronia e Vallata nell'alta valle del Fiume Ufita (Irpinia - Italia meridionale)

Abstract

This paper reports the results of a research aimed at defining the morpho-tectonic evolution of the upper valley of the Ufita River, northern Irpinia, during the Quaternary. Geomorphological, stratigraphical and archaelogical data are used as the basis for a first reconstruction of the Late-glacial and Holocene morphological and environmental modifications, which took place in the River Ufita upper valley between the towns of Castelbaronia and Vallata. The valley is located in a subsiding intermontane basin of an uplifting portion of the Apennines chain. In the study area several inherited morphological elements, such as old landscape (palaeo-landforms) and remnants of the palaeo-hydrographic network, can be recognized. On the left slope of the valley, along the Frigento- Mt. Forcuso ridge, these elements are less evident because of remarkably widespread landsliding phenomena. Along the opposite slope of the valley, in the territory of Baronia, a suspended glacis is delimited towards the river by a fault slope, which evolved as "triangular facets" in soft rocks. As a matter of fact a NW-SE oriented normal fault develops parallelly to the river and is active since the Middle Pleistocene. At the top and along the facets, between +120 m and +22 m above the bottom of the valley, alluvial cone and fluvial deposits can be found (1st, 2nd and 3rd order terraces). Along the bottom of the valley wide inactive alluvial fans and terraced alluvial deposits can be found between +20 m and +3 m above the present river bed (4th, 5th and 6th order terraces). The geomorphological evolutionary scheme of the valley is conditioned by tectonics also in very recent times. Suspended forms and deposits of different ages - such as the top palaeo-landsurface of the Upper Pliocene, the Early Pleistocene glacis, and the fluvial terraces and triangular facets of Middle-Upper Pleistocene-Holocene age - have been recognised. In the Holocene, the development of Palaeolithic and Neolithic cultures in the studied area is documented by numerous findings, as given in the literature. The morphological distribution of archeological sites highlights some chronological aspects of the geomorphological and palaeo-environmental evolution of the area. First, it is very clear the different distribution of archeological findings along the two sides of the valley, with a predominance of the sites on the Ufita River orographic right - the Baronia slope. This happens because, on the orographic left, the slope has always been affected by numerous wide landslides, which have confined possible settlement areas and may also have destroyed archaeological finds. The analysis of archaelogical sites on the Baronia slope, moreover, puts in evidence two main aspects: i) the progressive expansion of areas affected by instability phenomena since the Early Holocene onto the glacis; ii) the in time trend to the moving of human settlements from the glacis to the bottom of the valley and along the bottom of the valley from the oldest terraces (3rd order) to the latest terraces (4th and 5th order). In particular, Neolithic settlements are not found at a position lower than the 3rd order terraces, which are at elevations between +22 and +40 m above the river bed. On the other hand, some kilometers downstream, the 3rd order terrace develops in fluvial-lacustrine deposits of Upper Pleistocene age. Terracing would have taken place during the Late-glacial period. In the Holocene and historical times, new aggradation and erosion phases along the bottom of the valley gave rise to the 4th, 5th and 6th order terraces.