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

Pisa, Italy

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.