New stratigraphic constrains of the para-autocthonous Caporalino- Sant'Angelo Unit belonging to the "Alpine Corsica" (Corte-Ponte Leccia area, Corsica)

Abstract

This paper is aimed to give new insights useful to enlighten the relationships between the Alpine Units (Alpine Corsica Auctt.) outcropping in the NE sector of Corsica and hence helpful to reconstruct the geodynamic history of this sector of the alpine belt. In Corsica, the Alpine Units consists of a stack of (frequently laminated) oceanic and continental units which overlying the Variscan hasement (Hercynian Corsica Auctt.) of the Corso-European foreland. In some areas, the pile of the Alpine Units is still a puzzle and both lithostratigraphy and age of some units are still debatable. In the Omessa area, between Corte and Ponte Leccia, the tectonic pile includes the Tenda Unit (cfr. Tenda Massif Auctt.), the Caporalino-Sant'Angelo Unit, the Santa Lucia Nappe and the Schistes lustrks s.1. Among these units, the type of deposit and the age of the succession assigned to the Caporalino-Sant'Angelo Unit is still matter of debate. Earliest geologist consider the Caporalino-Sant'Angelo unit as a continuous sedimentary succession which spans in age from Lower Jurassic to Eocene. Later, some of these authors confirmed the continuity of the sedimentation of the Lower Jurassic to Eocene deposits assigned to the Caporalino-Sant'Angelo Unit and interpret the Caporalino limestone as a shallow-water platform deposit or a pelagic succession characterized by carbonate platform input. In contrast with this interpretation, the Caporalino-Sant'Angelo Unit was considered as coarse grained deposits with huge olistoliths sedimented in a distinct Eocene basin. Aim of this paper is to improve the lithoshatigraphy and the biostratigraphy of the Caporalino-S.Angelo Unit in order to the make clear the type of deposit and the age of this (Alpine) unit and to suggest the palaeogeographic location of its sedimentary basin. Based on a new geological mapping of the Corte-Pontee Leccia area and the lithostratigraphy of the three key composite. sections, the Caporalino-Sant'Angelo Unit consists of three coarse-grained clastic intervals and eight levels. The lower interval is composed of hreccias conglomerates and sandstones. The middle interval mainly consists of hreccias conglomerates and olithosliths (e.g. Caporalino Limestone); in the upper part of this interval are mark and breccias with clasts of Caporalino Limestone. Fine-grained sandstones with pelitic intercalation and rare conglomeratic beds characterize the upper interval. According to the recovered microfossil (calcareous nannofossils and foraminifera) assemblages the entire Caporalino-Sant'Angelo Unit is Early to Middle Eocene in age. Consequently, the previous model of a continuous Jurassic- Eocene stratigraphic succession is no longer valid and thj following scenario could he outlined: 1) during the Early-Middle Eocene the Caporalino-S.Angeh unit settled in an siliciclastic basin which received coarse graineb deposits such as breccias and conglomerates, olistoshomes and olistoliths (mainly composed by Upper Jurassic platform limestones) and sandstones and intercalation of silty mark and conglomerates, 2) the coarse-grained clastic sediments and the Upper Jurassic calcareous olistoliths , could have an inner place of origin (they probably represent the remnants of a carbonate platform emplaced over the Corso hasement); 3) consequently the Caporalino Sant'Angelo Unit was a foredeep basin, situated between the outer margin represented by the European foreland, and the inner margin, constituted yet by the corso hasement and its calcareous cover, 4) later the Santa Lucia Nappe and the Schistes lushb were thrusted on the Caporalino-S.Angelo basin.