Y. Tambareau et al., TECTONOSEDIMENTARY EVOLUTION OF THE NORTH ERN CENTRAL AND EASTERN PYRENEES DURING THE PALEOCENE AND THE EARLY EOCENE, Bulletin de la Societe geologique de France, 166(4), 1995, pp. 375-387
During the Palaeocene and the lowermost Eocene, the sedimentary succes
sion of the north-Pyrenzan basin. east of the Lannemezan Plateau, is m
ainly formed of marine shallow water and continental formations. The b
asin was bounded on the north by the Montagne Noire and on the south b
y the rising Pyrenean Range, which had been growing since the Cretaceo
us. From the analysis of the deposits we can demonstrate the occurrenc
e of well-individualized sedimentary units which record numerous fluct
uations of the marine gulf which was open toward the Atlantic ocean an
d among which five major advances of the sea eastward. These units can
be amalgamated into three main tectono-sedimentary units lying unconf
ormably over each other in the margin of the basin. These units are: t
he upper Cretaceous-Vitrolian unit, the Thanetian unit, and the Ilerdi
an-Lutetian unit. The main marine advances can probably be connected t
o eustatic fluctuations, such as the lower Ilerdian transgression. Som
e other factors controlled the sedimentary organization of Thanetian a
nd Ilerdian deposits which were due to tectonic effects at the basin s
cale or even at the local scale. The stratigraphic and structural data
lead us to conclude that the area of deposition of the Palaeocene and
Ilerdian formations of the Pyrenees was an E-W asymmetrical syncline
with an axis plunging westward. The northern boundary of this area was
stable whereas the southern boundary where syntectonic formations are
depositing, was active. The deformation was a shortening, the deforma
tion propagating piggy-back and the structures are fault propagation f
olds related to blind thrusts. The effect of the tectonic was the form
ation of progressive unconformities and the migration northward of the
depocentre of sedimentation