New morphostratigraphic and chronological constraints for the Quaternary palaeosurfaces of the Molise Apennines (southern Italy).

The Molise Apennines feature numerous relicts of palaeosurfaces, mostly of erosional origin, which represent the remnants of gently-rolling ancient landscapes now hanging at different altitudes above the local base-levels of erosion. Their genesis can be related to prolonged periods of relative tectonic stability alternating with periods of uplift, or to the interplay between steady tectonic uplift and climatic fluctuations. Four orders of palaeosurfaces were recognized: I (> 1100 m a.s.l), II (900-1000 m a.s.l), III (750-850 m a.s.l.), IV (600-720 m a.s.l.). The most ancient orders (I and II) are cut into the bedrock and are located at the top of the Matese and Montagnola di Frosolone massifs. The youngest palaeosurfaces (III-IV), partially cut into Quaternary deposits, are found along the valley flanks of the main river systems and within the Boiano, Carpino, Isernia and Sessano intramontane basins. The present study deals with the dating of the Sessano Basin Palaeosurface which is related to the IV order and is cut into the basin infill. The 40Ar/39Ar age of a tephra layer (437 ± 1.9 ky), intercalated at the top of the succession, supported by archaeo-stratigraphic, palynological and palaeopedological data, allowed the SBP surface to be constrained to 350-300 ky. The SBP chrononological position represents an important morpho-stratigraphic marker: it is the first ante quem and post quem date that allows the chronological position of the other orders of palaeosurfaces to be better constrained.