Geology Reference
In-Depth Information
Fig. 18.3
(
a
) Sketch of the estimated maximum extent of the allo-
chtonous south Pyrenean Foreland Basin illustrating the narrow,
elongated geomorphology of the semi-enclosed sea encompassing
the Jaca and T-G-A Basins (modifi ed after Plaziat
1981
) . (
b
) Sketch
of the inferred paleogeography and water depths of the T-G-A Basin
sea during the underfi lled foredeep stage of the Late Ilerdian
(approximately 53 Ma) based on the work of the authors referred to
in the text. The main siliciclastic depositional systems are indicated
The basin had an asymmetrical transverse section
with the strongest subsiding parts along the northern
basin margin and along the south-side of the develop-
ing Montsec Thrust. Highest Early Eocene subsid-
ence rates occurred during the Ypresian. Sedimentation
rates, however, were also highest along the northern
basin margin, such that a transverse section through
the basin may have been approximately symmetrical
or even asymmetrical with a depositional basin axis
further south. The basin had pronounced sea-fl oor
topography due to the effects of the southward mov-
ing thrust sheets. The E-W oriented Montsec Thrust
probably formed a shallow-water anticlinal topo-
graphic high on the sea fl oor across which exchange
(intermittent?) of marine waters could occur between
the areas of the present-day Ager Basin and Tremp-
Graus Basin. This situation was sustained by the rela-
tively rapid eustatic sea-level rise at the start of the
Early Ypresian (Pujalte et al.
2009
) .
As a result, the total basin length was approximately
200 km (Mutti et al.
1985a
) with an approximately
50 km long and shallower (approximately 40-60 m)
T-G-A Basin section east of the Montsec oblique blind
thrust (Fig.
18.3
). The paleo-width of the T-G-A Basin
