Abstract

Outcrops of the Stilo-Capo d'Orlando Formation (latest Oligocene-early Miocene) along the southeastern coast of Calabria (southern Italy) expose a cross section, orthogonal to paleoflow, of the proximal part of a turbidite depositional system. Major erosion surfaces cutting into basement rocks define several submarine paleocanyons. Paleocanyon fills consist of large, lenticular conglomerate bodies that are 200-580 m thick and 3-6 km wide.

The best example of these paleocanyons is located near the town of Stilo, where the geometric relationships between paleocanyon fill and adjacent slope deposits are well exposed. At this locality, a 460-m-thick section of conglomerate cuts into the basement and is composed internally of smaller scale channel fills of poorly organized, clast-supported, cobble-to-boulder conglomerate, deposited mainly by high-density turbidity flows. The conglomerate is thickest near Stilo and becomes progressively thinner southward, where a wedge of mudrock intervenes between the basement and the conglomerate. The mudrock wedge is composed of poorly bedded, intensely bioturbated mudstone with slump structures and represents slope deposits. Bedding within the mudrock wedge is better defined in its stratigraphically higher part near the conglomerate body, where thin-bedded, normally graded sandstone layers with climbing ripples, horizontal lamination, and general thickening toward the canyon axis are present. These layers are the deposits of dilute turbidity currents that occasionally spilled over the canyon margins when the depression was nearly filled.

The conglomeratic canyon fill and the adjacent muddy slope deposits are both overlain by a laterally continuous sequence, 160 m thick, composed of two units of fine-grained, thin-bedded turbidites alternating with two units of thicker sandstone and minor pebble-conglomerate beds.

The paleocanyons probably originated as subaerial valleys in response to a major fall in relative sea level at 30 Ma and were later submerged by a combination of relative sea-level rise and concomitant tectonic activity. The sharp transition between coarse-grained, canyon-confined conglomerate and the overlying fine-grained, unconfined thin-bedded turbidites exists throughout southern Calabria and may represent the effect of a significant rise in relative sea level. Two other cycles of relative sea-level changes, probably resulting from local tectonic control, are indicated by the upper part of the Stilo-Capo d'Orlando Formation.

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