The lithostratigraphic description of the covers of three Lower Penninic
nappes (Monte Leone, Lebendun and Antigorio) allows the comparison of
their sedimentary content and their thickness. It has been established
that the Lebendun nappe is formed by an ante-Triassic paragneissic core
(Valgrande gneiss), and a Mesozoic sedimentary cover in reversed
position. The cover series shows a continuous detritic sedimentation,
off which the material comes from a continental erosion related to the
early Lias rifting phase of the Alpine Tethys. The erosion has reached
the basement, resedimented as pebbles and sandstones. This can be
observed in both Lebendun and Antigorio covers.
The definition of a unit named <<serie intermediaire>> between the
Lebendun and the Antigorio covers has important palinspastic
implications for both nappes. The unit is composed of a banded marble, a
garnet bearing gneiss and a calcschist with great blocks.
The comparison between the thickness of Antigorio and Lebendun covers
suggests a shoulder position for Antigorio. and a proximal rift basin
position tor Lebendun. The general thickness decrease of the series
towards the SW points to a NE origin for the Lebendun clastics, taking
into account the increase of tectonic deformation in the region trending
from east to west. The detritic sedimentation ends with the basin
drowning during the Malm, represented by a pure marble sealing the
erosive disconformity of the Antigorio cover, and the clastic deposits
of Lebendun. Three hypotheses are proposed for the calcschists age and
attribution of the <<serie intermediaire>>: A: they belong entirely or
partially to the Lebendun cover and correspond to a conglomeratic
deposit of Cretaceous-Tertiary Niesen flysch type, of proximal facies.
The tectonic limit could be situated in the middle of the calcschists at
the level of the huge blocks encountered. B: they belong to Antigorio
and correspond to an upper Lias-Dogger synrift deposit, then the marble
is liassic. C: they belong to Antigorio and have been deposited
following the Lebendun basin inversion (Cretaceous-Tertiary). that
generates Tertiary wildflysch deposits, coming from the South for the
ultrahelvetic and from the North for the Niesen.