FLUVIAL TERRACES AS GROWTH STRATA MARKERS OF ACTIVE TECTONIC DEFORMATION IN THE EMILIA-ROMAGNA AND MARCHE APENNINES, ITALY

Topography of the Italian peninsula has been built in part by sustained growth of the Apennine orogenic wedge, but the continued growth of that wedge, particularly at the prowedge deformation front is highly debated. Collaborative research associated with the RETREAT project along the Bidente River in the north-central Apennines near Forli and the Musone River in the central Apennines west of Ancona suggests that late Quaternary fluvial terraces are tectonically deformed, and thus that folds are still growing. A sequence of six Holocene to late Pleistocene paired bedrock strath terraces is recognizable along the Bidente River. Bidente terrace ages come from new radiocarbon dates as well as landscape and soil-geomorphic correlation to the well-mapped and dated fluvial terrace sequence of the Reno River. Our results show that rates of vertical fluvial incision are about 1mm/yr. Reconstructed Bidente terrace longitudinal profiles exhibit upstream convergence and downstream divergence centered on an axis ~40 km inland from the Po plain, suggestive of a growing fold(s). A similar conclusion comes from four prominent late Quaternary fill terraces that are preserved in the Musone River, draining the eastern side of the central Apennines. Bedrock channel reaches are associated with both resistant Cretaceous limestones as well as non-resistant Pliocene mudstones. Bedrock incision rates increase in an eastward direction from ~0 mm/yr at the Apennine mountain front to about 1 mm/yr east of Cingoli Ridge, the foreland-most carbonate-cored anticline of the central Apennines. The longitudinal profile of the late glacial (~30-15 ka) terrace diverges from the modern channel in a downstream direction across and in front of Cingoli Ridge, again suggestive of a growing fold. An ongoing GPS experiment will assist in constraining shortening across the Apennine front at the latitude of Ancona. Receiver stations are positioned such that the shortening exhibited in the Musone fluvial terrace stratigraphy may be discernable from longer wavelength shortening across the width of the central Apennines.