Sedimentology, architecture, and sequence stratigraphy of coarse-grained, submarine canyon fills from the Pleistocene (Gelasian-Calabrian) of the Peri-Adriatic basin, central Italy

Abstract

The Plio-Pleistocene stratigraphic record of the Peri-Adriatic basin (eastern central Italy) is well exposed along the uplifted western margin of the basin and consists of a series of coarse-grained slope canyon fills encased in a thick succession of hemipelagic mudstones. This study deals with the detailed sedimentology, stratal architecture, and sequence-stratigraphic interpretation of two of these submarine canyon-fills (namely CMC1 and CMC2) exposed at Colle Montarone. These strata contain widespread evidence of gravity-driven sedimentation processes, with high- and low-density turbidity currents, slumps and cohesive debris flows being responsible for most of the sediment transport and deposition. Beds are organised into four recurrent lithofacies, each corresponding to a specific deep-water depositional element: (i) clast-supported conglomerates (channel complexes); (ii) thin-bedded sandstones and mudstones (levee-overbank); (iii) very thinly-bedded mudstones (tributary channels); (iv) pebbly mudstones and chaotically bedded mudstones (mass-transport complexes). One of the most conspicuous attributes of the canyon-fill sediments exposed at Colle Montarone is their pronounced cyclic packaging, resulting from several pulses of erosion and fill. The lithofacies listed above combine to form a number of discontinuity-bound stratal packages, or high-frequency depositional sequences, each characteristically having an overall fining-upward character. Within sequences, systematic vertical trends in their constituent lithofacies define two main stratigraphic motifs, namely Motif-1 and Motif-2, which are typical of CMC1 and CMC2, respectively. Each sequence is deemed to reflect cyclical changes in volume, composition, and rheology of sediment gravity flows entering the canyons and comprises a basal unconformity (sequence boundary), succeeded by a high net-gross channel-levee complex (lowstand systems tract), overlain by a succession of either a low net-gross heterolithic deposits (early transgressive systems tract, Motif-1 sequences) or mass-transport deposits (transgressive to falling stage systems tract, Motif-2 sequences). Given the severe Icehouse climatic regime during the Pleistocene, the cyclic arrangement is most reasonably attributed primarily to repeated glacio-eustatic fluctuations in global sea level, which regulated the flux of terrigenous clastic sediment to the slope and basin-floor settings. Results from this paper are directly applicable to the oil and gas industry when making predictions of reservoir and seal relationships within slope turbidite systems developed during periods of high-frequency, eustatic sea-level fluctuations.