La piana del T. Conca e le pianure minori nord-marchigiane: forme, depositi ed evoluzione

The Conca Rivers plain and the minor plains of the Northern Marche: forms, deposits and evolution

Abstract

The alluvial plains of the Northern Marche rivers (Conca, Foglia, Metauro, Esino) are characterized by wide valley floors with paired and convergent terraces, due both to climatic changes and continuous recent uplift. At the end of the valley plains, five to ten km far from the coast line, the alluvial deposits become gradually thicker and are contained in a broad flat-floored through, entrenched 50 m below the sea level. The succession and the late evolution (Upper Pleistocene and Holocene) of these forms may be reconstructed as follows: a) Würm2-Würm3 interstadial, posterior to 31 000 B.P.: sea level lower than the present: back-wasting, lateral planation and entrechement of the rivers down to 30-50 m below the present sea level; b) Würm3 and following cataglacial phase: progressive, fast and total filling of the valleys and formation of wide alluvian fans; age of wood remains in the middle-upper part, 10 000 B.P.; c) late cataglacial phase (Early Holocene): new stream entrenchement and formation of new terrace scarps; d) Holocene climatic optimum (maximum of the Versilian transgression, high stand, about 6 000 B.P.): formation of a cliff and wave-cut platform, partial filling of the former river entrenchement; e) Late Holocene (recent phase): coast line retreat due to widening of the litoral and delta deposits; minor coast line and river profile variations, because of anthropic activity. Traces of neotectonic activity are also present, i.e. tilting of the older alluvial plain and terraces convergence.