Datazione radiometrica di un deposito colluviale in un conoide situato nel settore meridionale della Piana del Cavaliere, Appennino laziale-abruzzese

14C dating of a colluvial deposit in an alluvial fan in the southern part of the Piana del Cavaliere, Latium-Abruzzi Apennines

Abstract

The ¹⁴C dating of a colluvial deposit, coupled with, stratigraphy and sedimentology, permits to infer phases of relative rhexistasy and biostasy, which marked the late Holocene evolution of the upper Fosso Luisa alluvial fan (Camerata Nuova – Rome). Along a man-made cut within the fan, about 700 m long, the following stratigraphic succession can be observed: a lower level with matrix-supported calcareous gravel, with etherometric roundedm clasts and grading; an intermediate level with fine-grained colluvial deposits; an upper level with clast-supported calcareous gravel, with etherometric rounded clasts and reverse grading. The ¹⁴C dating of the organic matter in the colluvial deposits gave an age of 3.270 ± 50 years B.P. The deposition of coarser and finer sediments must be the product of quite distinct environmental conditions. Our new datings enable us to time constrain the major changes in the environment which influenced the geomorphological evolution of the upper alluvial fan. The succession of depositional events can be summarized as follows (older to younger): – A phase of relative rhexistasy, older than 3.270 ± 50 years B.P., accounting for deposition of the lower gravel bed. – A phase of relative biostasy, younger than 3.270 ± 50 years B.P., with deposition of colluvial deposits. – Another phase of relative rhexistasy, much younger than 3.270 ± 50 years B.P., with deposition of the upper gravel. – A modern phase of prevailing biostasy.