Morphotectonic approach to the drainage analysis in the North Marche region, central Italy

The Umbro-Marchean Apennines form an arcuate NW–SE fold-and-thrust belt of NE convexity. The orogen developed from the Early Miocene, and shortened the more than 5 km-thick Meso-Cenozoic stratigraphic succession by about 30%. The internal part of the mountain chain is, however, overprinted by SW-dipping extensional normal faults that bound the Plio-Pleistocene continental basins. Nevertheless, the distribution of river terraces all along the main river valleys, clearly indicates that Middle–Upper Pleistocene and Holocene vertical uplift dominated over local anticlinal uplift for the entire studied area. The drainage network of the Marche region, in the external part of the Umbro-Marchean Apennines, has an overall sub-parallel pattern, oriented mainly SW–NE, and transversely breaches the main calcareous anticlinal ridges before reaching the Adriatic coast. Emergence and drainage initiation may have begun as early as the Messinian. Cave systems formed during the erosion history and document former stream levels. The breaching of the high-amplitude anticlinal ridges was controlled mainly by joint systems, and locally, by NNE–SSW striking faults. In turn, both superimposition and stream-piracy phenomena could have played a significant control in the drainage network development and, in places, complex mechanisms involving antecedence cannot be ruled out for streams bypassing anticlinal ridges.