Along the coast of southern Italy, near Tempa Rossa, is an outcrop with a turbidite succession greater than 150 m (460 ft) thick. It is part of the Pollica Sandstones Formation, which is the oldest formation of the Cilento Group (Langhian to Lower Tortonian). The Cilento Group (Pollica and the overlying S. Mauro Formation) was deposited in a wedge-shaped basin above deposits that were formed during the early phases of the formation of the Southern Apennines. The Pollica Formation is comprised of several channelized deposits of coarse and very coarse-grained siliciclastic units. These are capped by and laterally grade into fine-grained facies and chaotic deposits. The S. Mauro Formation, thicker than the Pollica, is composed of fine-grained carbonates (re-sedimented pelagic and hemi-pelagic biogenic oozes) that occur in discrete beds (up to 60 m [190 ft] thick), alternating with fine- to medium-grained, laterally continuous, siliciclastic units. Turbidites and gravity-flow deposits comprise the lower part of this sand-rich system, which consists of several channels with small levees that are organized into 4 channel-filling stages (C1-C4). The thickness of each channel is >10-30 m (>30-100 ft) and the width may reach 300 m (984 ft). The base of the channels is erosive and sharp. The fill of the channels is dominantly a coarsegrained facies that consists of poorly sorted, crudely graded, pebbly sandstones (F2) and gravelly, high density turbidity currents (F 4-5). Lateral to the channels are thin (T architectures), fine-grained turbidites (F9 and subordinately F7 and F8) that are interpreted to be levee and overbank deposits. A decrease in the sand:mud ratio occurs away from the channels. There are chaotic zones within these units that are composed of slumps and cohesive debris flows (F1). They may reach thicknesses of 5-6 m (16-20 ft). The chaotic beds may also occur capping the channel, but in these cases, these are part of the abandonment phase of deposition. The thicker, mud-rich intervals (F9a and hemipelagic mud) near the top of the sequence may be accounted for by the switching of the channels. As the thicker muddy intervals occur only at the top of the succession, deposits from a switched channel, lateral to the one described, may overlap this previous channel. Between channel C3 and C4 is a sheet (S1) complex. It is characterized by an overall thickening-upward succession including thin beds (F9b) at the base, grading to thicker-bedded and parallel-sided beds (mostly F5 and F 7-8). The upper part of the sheet (lobe deposit) is highly amalgamated. Overlying S1 is another channel (C4). At the base of the channel are thin-bedded turbidites as well as slumps, debris flows, and gravelly high density flows. The channel fill is dominated by poorly sorted and crudely graded pebbly sandstones that are mostly parallel-bedded. The interpretation of this outcrop is that of aggradation of midfan channels.
A prograding Miocene turbidite system, Tempa Rossa cliffs, Italy
Cavuoto G;
2007
Abstract
Along the coast of southern Italy, near Tempa Rossa, is an outcrop with a turbidite succession greater than 150 m (460 ft) thick. It is part of the Pollica Sandstones Formation, which is the oldest formation of the Cilento Group (Langhian to Lower Tortonian). The Cilento Group (Pollica and the overlying S. Mauro Formation) was deposited in a wedge-shaped basin above deposits that were formed during the early phases of the formation of the Southern Apennines. The Pollica Formation is comprised of several channelized deposits of coarse and very coarse-grained siliciclastic units. These are capped by and laterally grade into fine-grained facies and chaotic deposits. The S. Mauro Formation, thicker than the Pollica, is composed of fine-grained carbonates (re-sedimented pelagic and hemi-pelagic biogenic oozes) that occur in discrete beds (up to 60 m [190 ft] thick), alternating with fine- to medium-grained, laterally continuous, siliciclastic units. Turbidites and gravity-flow deposits comprise the lower part of this sand-rich system, which consists of several channels with small levees that are organized into 4 channel-filling stages (C1-C4). The thickness of each channel is >10-30 m (>30-100 ft) and the width may reach 300 m (984 ft). The base of the channels is erosive and sharp. The fill of the channels is dominantly a coarsegrained facies that consists of poorly sorted, crudely graded, pebbly sandstones (F2) and gravelly, high density turbidity currents (F 4-5). Lateral to the channels are thin (T architectures), fine-grained turbidites (F9 and subordinately F7 and F8) that are interpreted to be levee and overbank deposits. A decrease in the sand:mud ratio occurs away from the channels. There are chaotic zones within these units that are composed of slumps and cohesive debris flows (F1). They may reach thicknesses of 5-6 m (16-20 ft). The chaotic beds may also occur capping the channel, but in these cases, these are part of the abandonment phase of deposition. The thicker, mud-rich intervals (F9a and hemipelagic mud) near the top of the sequence may be accounted for by the switching of the channels. As the thicker muddy intervals occur only at the top of the succession, deposits from a switched channel, lateral to the one described, may overlap this previous channel. Between channel C3 and C4 is a sheet (S1) complex. It is characterized by an overall thickening-upward succession including thin beds (F9b) at the base, grading to thicker-bedded and parallel-sided beds (mostly F5 and F 7-8). The upper part of the sheet (lobe deposit) is highly amalgamated. Overlying S1 is another channel (C4). At the base of the channel are thin-bedded turbidites as well as slumps, debris flows, and gravelly high density flows. The channel fill is dominated by poorly sorted and crudely graded pebbly sandstones that are mostly parallel-bedded. The interpretation of this outcrop is that of aggradation of midfan channels.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
