Depositi alluvionali terrazzati nel medio bacino del fiume Cesano (Appennino nord-marchigiano): analisi conoscitiva e cronologia radiometrica

Terrace fluvial deposits from the middle basin of Cesano river (Northern Marche Apennines): reconnaissance study and radiometric constraints on their age

Abstract

A geomorphologic and stratigraphic study dealing with the «3rd-order» terrace alluvium outcropping between the villages of S. Lorenzo in Campo and S. Michele al Fiume (middle basin of Cesano river) has been carried out. In addition five macrofragments of fossil wood, collected in three gravel-pits within the intermediate Würmian fluvial sequences laid down by braided-streams, were dated with the radiocarbon method. The obtained ¹⁴C ages, ranging from 37,300±2200 to 31,700 ± 1050 yr B.P., allowed a significant refining of the chronologic framework for the development of the «3rdorder » valley terraces throughout northern Marche. Despite some of the dated samples were reworked, it results that aggradation phase took place through middle Würm. Based on a tentative correlation among the deposition phases in the Cesano river valley and in the nearly Metauro and Conca river basins for a hich other ¹⁴C dates are available, it is argued that sedimentation of the fluvial braided-stream alluvium commenced prior to 41,000 – 44,000 yr B.P. Further, it is noticed that although the studied alluvium is rather homogeneous as far as lithology, sedimentology and granulometry are concerned, its accumulation was recurrently affected by subordinate cut-and-fill processes which likely account for the origin of buried terraces.