Evolution and History of Filling of Early Pleistocene, Coarse-Grained Slope Canyons (Peri-Adriatic Basin, Central Italy)

The early Pleistocene stratigraphic succession of the Peri-Adriatic Basin, eastern central Italy, records the filling of an elongate, north-south oriented piggy-back basin located east of the growing Apennine fold-thrust belt. During the Gelasian (2.58-1.80 Ma), gravel- and sand-sized sediments derived from the central Apennines were abundantly supplied into the basin through a series of transverse to longitudinal slope erosional fairways. These sediment conduits are preserved in the rock record as a series of exceptionally exposed canyon-fill successions that provide a rare opportunity to evaluate, from an outcrop perspective, how this type of deepwater depositional system evolves and fills under the indirect effects of glacio-eustatic sea-level changes. The present study uses stratigraphic sections, photopanels, paleocurrent data, and careful lithological mapping to constrain the internal organization of four of these canyon fills, which we refer to as the Ascensione, Castignano, Offida, and Notaresco canyons. A detailed facies analysis suggests that a variety of subaqueous gravity flows were involved in sediment transport and deposition, including slumps, cohesive debris flows, and high- and low-density turbidity currents. Four main lithofacies that reflect major depositional elements have been identified within the canyon-fill successions and are: (i) clastsupported conglomerates (gravel-rich channel complexes); (ii) medium- to thick-bedded sandstones (channel terminus lobes); (iii) medium- to very thin-bedded sandstones (levee-overbank); (iv) pebbly mudstones and chaotic beds (mudstone-rich mass-transport deposits). The canyon fill strata are organized in lithofacies sequences that tend to follow a predictable pattern and to define vertically stacked fining-upward packages, resulting in highly cyclic successions. Each of these fining-upward packages comprises the sedimentary record of discrete phases of canyon activity, showing transition from a higher energy depositional style to a lower energy mode of sedimentation interrupted by a period of erosion and bypass of sediment to areas further downslope. These recurring fluctuations in canyon activity and sedimentary regime are thought to be related to the switching on and off of coarse clastic sediments to the deepwater basin that, in turn, likely resulted from the contemporary glacio-eustatic changes in sea level.