Depositional System and Architecture of Oligo-Micoene Turbidite Successions in Cilento (Southern Apennines)

Detailed analysis of the extensively outcropping Miocene siliciclastic successions in Cilento (Southern Apennines) allowed the reconstruction of four depositional systems. The first, a sandy silt-rich turbidite system, is widespread in the whole area. It consists of thin-bedded turbidites in sheet sand lobes. Debris flow deposits truncate this system and mark the onset of the second one, an “atypical” sand-rich system that developed differently in different areas of Cilento. To the west, the turbidites evolve to conglomerates and massive sandstones that represent a progradation of sandy lobes to channels, whereas to the east they reveal the superposition of thick amalgamated packages of coarse-grained sandstones and conglomerates typical of confined erosion channels. In both areas the upper portion of the second system is characterized by finer and thinner beds, with intercalations of rare coarse, chaotic beds. At every location these successions gradually give way to the third system, a “sheeted system” consisting of alternating muddy and sandstone beds with a significant calcareous component and up to some decimetres in thickness. These deposits extend laterally for tens of kilometres, locally with abrupt decrease in thickness to the east; at times, the intercalated chaotic megabeds can be identified in the eastern area only. Only in the eastern area a fourth system, a sandy-gravelly system, develops with an angular erosion surface. It generally consists of amalgamated massive sandstones and conglomeratic bodies, which may be ascribed to wide low-sinuosity channels and their terraces along a steep, structurally confined slope. Based on the architecture of the approximately 2000 m-thick succession, it is possible to determine a different topography of the basin. This difference, which is also evident in petrographic data, is attributed also to the structural highs (developed through deformation of the substratum) that segmented the basin. The highs controlled the development of the second system. From the top of the second system and throughout the third system, possibly in relation to a changing floor and increase in relative water depth, the highs were less important in the confinement and ponding of flows. Conditions changed after the deposition of the uppermost chaotic megabed on which the fourth system lies. The boundaries of each of the recognized systems coincide with the boundaries of the lithostratigraphic unit defined by Nardi et al. (2003) and Cammarosano et al. (2004).