PROVENANCE AND EVOLUTION OF MIOCENE TURBIDITE SEDIMENTATION IN THE CENTRAL APENNINES, ITALY

A study of the siliciclastic detritus within the calcareous Miocene turbidite sandstones of the central Apennines has elucidated the provenance of these sandstones. Three ratios: Q/(Q + F), K/F, and Mc/M, have been used and binary correlations of these parameters show that: (1) the sandstones of the Marnoso-Arenacea are characterized by a northern Alpine supply, mainly derived from metamorphic rocks and subordinately from granitic rocks, (2) a secondary supply of western provenance, interbedded within the Marnoso-Arenacea, shows a typical arkosic composition and suggests that granitic rocks of Alpine-type were associated with the Ligurides; (3) the Urbania and Serraspinosa sandstones consist of detritus derived from sources almost identical to those supplying the Marnoso-Arenacea: (4) all the sandstones of the remaining central Apennine basins are characterized by a siliciclastic supply similar to the arkosic one; the rare carbonate fragments can be referred to the Apennine units. The continuity of the Alpine arc in the Tyrrhenian area strongly suggests a connection between the western crystalline units and turbidite sedimentation in the basins examined. The crystalline units are associated with a segment of the Alpine chain tectonically linked to the Liguride nappes (Apennine source areas) during the eastwards migration of the Apennines deformation. The crystalline units were gradually eroded during the Burdigalian to Early Pliocene interval when the Laga basin was completely filled. Currently the term "Alpine" is used as synonymous with northern provenance. However, a detailed study carried out over ten years, revealed a western Alpine supply associated with an Apennine source area; we therefore suggest that it is necessary to distinguish a northern Alpine provenance from a western Alpine supply.