Multiscale analysis of a migrating submarine channel system in a tectonically-confined basin: the Miocene Gorgoglione Flysch Formation, southern Italy

The Miocene Gorgoglione Flysch Formation records the stratigraphic product of protracted sediment transfer and deposition through a long-lived submarine channel system developed in a narrow and elongate thrust-top basin of the Southern Apennines (Italy). Channel-fill deposits are exposed in an outcrop belt approximately 500 m thick and 15 km long, oriented oblique to the palaeoflow, which was roughly south-eastward. These exceptional exposures of channel-fill strata allow the stacking architectures and the evolution of the channel system to be analyzed at multiple scales, enabling the effects of syn-sedimentary thrust tectonics and basin confinement on the depositional system development to be deciphered. Two end-member types of elementary channel architecture have been identified: high-aspect-ratio, weakly-confined channels, and low-aspectratio, incisional channels. Their systematic stacking results in a complex pattern of seismic-scale depositional architectures that determines the stratigraphic framework of the deep-water system. From the base of the succession, two prominent channel complex sets have been recognized, namely CS1 and CS2, consisting of amalgamated incisional channel elements and weakly-confined channel elements. These channelized units are overlain by isolated incisional channels, erosional into mud-prone slope deposits. The juxtaposition of different channel architectures is interpreted to have been governed by regional thrust-tectonics, in combination with a high subsidence rate that promoted significant aggradation. In this scenario, the alternating ‘in sequence’ and ‘out of sequence’ tectonic pulses of the basin-bounding thrusts controlled the activation of coarse-clastic inputs in the basin and the resulting stacking architectures of channelized units. The tectonically-driven confinement of the depositional system limited the lateral offset in channel stacking, preventing large-scale avulsions. This study represents an excellent opportunity to analyze the stratigraphic evolution of a submarine channel system in tectonically-active settings from an outcrop perspective. It should find wide applicability in analogous depositional systems, whose stratigraphic architecture has been influenced by tectonically-controlled lateral confinement and associated lateral tilting.