GEOMETRY OF A MIOCENE SUBMARINE-CANYON AND ASSOCIATED SEDIMENTARY FACIES IN SOUTHEASTERN CALABRIA, SOUTHERN ITALY

Outcrops of the Stilo-Capo d'Orlando Formation (latest Oligocene-early Miocene) along the southeastern coast of Calabria (southern Italy) ex pose 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 fill s consist of large, lenticular conglomerate bodies that are 200-580 m thick and 3-6 km wide. The best example of these paleocanyons is locat ed near the town of Stilo, where the geometric relationships between p aleocanyon 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 o rganized, clast-supported, cobble-to-boulder conglomerate, deposited m ainly by high-density turbidity flows. The conglomerate is thickest ne ar Stilo and becomes progressively thinner southward, where a wedge of mudrock intervenes between the basement and the conglomerate. The mud rock wedge is composed of poorly bedded, intensely bioturbated mudston e with slump structures and represents slope deposits. Bedding within the mudrock wedge is better defined in its stratigraphically higher pa rt near the conglomerate body, where thin-bedded, normally graded sand stone layers with climbing ripples, horizontal lamination, and general thickening toward the canyon axis are present These layers are the de posits of dilute turbidity currents that occasionally spilled over the canyon margins when the depression was nearly filled. The conglomerat ic canyon fill and the adjacent muddy slope deposits are both overlain by a laterally continuous sequence, 160 m thick, composed of two unit s of fine-grained, thin-bedded turbidites alternating with two units o f thicker sandstone and minor pebble-conglomerate beds. The paleocanyo ns probably originated as subaerial valleys in response to a major fal l in relative sea level at 30 Ma and were later submerged by a combina tion of relative sea-level rise and concomitant tectonic activity. The sharp transition between coarse-grained, can yon-confined conglomerat e and the overlying fine-grained, unconfined thin-bedded turbidites ex ists throughout southern Calabria and may represent the effect of a si gnificant rise in relative sea level. Two other cycles of relative sea -level changes, probably resulting from local tectonic control, are in dicated by the upper part of the Stilo-Capo d'Orlando Formation.