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ABSTRACT

Stacked cross-sets, up to 2.5 m thick, produced by sand wave migration and meniscate trace fossils produced by Echinocardium cordatum, both considered in the literature as typical of shallow-water marine depositional settings, commonly occur in the bathyal Plio-Pleistocene deposits of Monte Torre (Calabria, southern Italy).

The Plio-Pleistocene sediments form two coarsening-upward depositional sequences, separated by an unconformity and by a palaeobathymetric gap of at least 300 m. The lower sequence passes upwards from hemipelagic marls and thin-bedded turbidites to thick-bedded sandy turbidites, then to sand wave deposits alternated with sandy turbidites, and finally to base-of-slope megabreccias. Facies characteristics and relationships, and the occurrence of deep-sea faunal associations, indicate deposition in the bathyal zone. The facies of the upper sequence reflect a fan-delta environment, no deeper than a few tens of metres.

The depositional setting of the lower sequence, where the sand wave deposits and meniscate trace fossils occur, appears to have been a tectonically controlled seaway, connecting the Tyrrhenian and Ionian Seas. This seaway became progressively narrower with time, evolving into a strait. The overall coarsening-upward trend reflects the upward transition from a low to a high-energy environment, possibly caused by the tectonic narrowing of the seaway. Deposition and erosion from high-concentration turbidity currents and from tidal bottom currents were important processes. Periods of tectonic activity, producing first the uplift of the seaway margins and culminating with the uplift of the strait sequence itself, are marked by-scattered rockfall deposits.

The strait setting, causing the development of powerful, oxygenated bottom currents, produced optimal conditions in the bathyal zone for the colonization of sandy bottoms by a single infaunal r-selected species, Echinocardium sp.