Late-Quaternary alluvial fans in the Northern Marche Apennines: implications of climate changes

Abstract

O. Nesci O. et al., Late Quaternary alluvial fans in the northern Marche Apennines: implications of climate changes. (IT
ISSN 0394-3356, 2010)
Alluvial fans, fan-like deposits, and piedmont aprons are widespread at mountain-front and foothill sectors of the Umbria-Marche
Apennines. They are currently regarded as significant geomophological features strictly dependent on either tectonic or climatic controls. Close relationship with tectonics, that are usually stressed by the location of such landforms along fault scarps or other active
morphostructures, can be assessed only in the most internal areas of the Umbria-Marche Apennines, dissected by extensional tectonics. Conversely, in the piedmont and foothill sectors of the chain, the climatic control on fan deposition and entrenchment become dominant, whereas tectonic constrains can be only indirectly detected. Namely, within the Umbria-Marche Apennines, the late
Quaternary cyclical and systematic episodes of fan deposition and entrenchment at the mouth of tributaries, usually following the
main fluvial filling along the trunk valleys, are well known. Nonetheless, the main causes that have cyclically controlled the fluvial and
alluvial-fan deposition and their subsequent dissection have not been thoroughly investigated yet. In this work we report a general
overview on the geomorphological setting of the late Quaternary alluvial fans associated with the major fill-terraces that compose the
typical staircase of river terraces in the Northern Marche territory. In particular, for the aggradational suites of the late Quaternary fillterraces, we discuss the meaningful stratigraphic relations between the fluvial sediments of the trunk streams and the alluvial-fan
deposits originating from the tributaries.
We also suggest a possible correlation between the cyclical recurrence of the principal episodes of fluvial aggradation/alluvial-fans
formation and dissection and the principal late Quaternary climate fluctuations.