Alcune osservazioni sulla tettonica quaternaria nell'alta valle del F. Volturno (Molise)

The Volturno River valley is one of the valleys of the central Apennines Chain and is located between the Venafro and Matese mountains. Morphological features and stratigraphical data indicate the presence of two areas, which have had different tectonic and sedimentary history during Quaternary times. The northernmost area (Isernia area) is characterized by outcrops of ca. 150 m thick deposits of fluvial and lacustrine origin, which contain many layers of pyroclastic materials. The age of the deposits is Middle Peistocene. Four levels of terraces are present along this part of the valley. In the southernmost area (Venafro Plain) the oldest terraces are lacking and the morphology of the alluvial plain is flat. Stratigraphic data from boreholes drilled in the area (about 95), showed a lacustrine sequence having a thickness of more than 250 m, which has never been mentioned in previous studies. Along the western and southern margins of the plain, the lower part of the sequence is composed of slope breccias which become heteropic with silt and clay toward the centre of the plain. The central part of the sequence is characterized by tufaceous layers, whereas gravel prevails in the upper part. Boreholes found the base of lacustrine deposits at 40 m below present sea level, which indicates the Quaternary subsidence of the area. The aforementioned two areas (Isernia and Venafro areas) have had different tectonic history: the Isernia area was uplifted and dissected, whereas the Venafro area subsided with aggradation of lacustrine deposits. This different tectonic behaviour between the two areas was due to the effect of a NW-SE trending fault, stretching between the towns of Pozzilli and Capriati al Volturno.