Guidebook

Volume n° 2 - from B16 to B33
B16
B16 -
Leaders: R. Bourrouilh, L. Moen-Maurel, J. Muñoz, A. Teixell
DAY 4
from St Jean Pied de Port to Jaca
The road to Larrau and to the Port de Larrau will drive
us through the Mendibelza conglomerates.
Morning:
Stop 4.1a:
Pic d’Orhy South-verging Thrust and
Fold structures
Introduction : resting on the Mendibelza
conglomerates, a huge series of Upper Cretaceous
shallow water carbonates form the main frame of
the Pyrenean High Chain. We already observed
these limestones the fi rst day, in the Ossau Valley,
forming the high peaks of the Eaux Chaudes Massif.
These “calcaires des cañons ” or “canyon limestones”
develop from Cenomanian to Lower Campanian.
Then, a carbonate fl ysch facies up to the Lower
Lutetian progressively appears.
Access: from Larrau, road D 26 climbs up to the Port
Figure 3.9 - Tilted blocks and European-Iberian margin.
de Larrau, 1,575 m high. We will Stop at 1,400 m
elevation, near the thrust surface (fi g.4.1a1).
Structural landscape and interpretation: looking
westwards we can observe the S-shaped southverging
folds of the Orhy peak, 2,017m high, forming
a souththrusted anticline, involving the Upper
Cretaceous fl ysch, followed by an south-verging
overturned syncline, formed by the Paleocene-Lower
Eocene fl ysch (fi g.4.1a2).
Here we can see one of the highest fold-and-thrust
tectonic units.
For further information: see the geological map at
1/50 000, n° XIV-47, Larrau.
Stop 4.1b:
Port de Larrau: Structural Panorama
Access: drive on D 26 up to the Port de Larrau, 1,573
m high.
We are now in the heart of the Pyrenean High Chain,
just below Orhy Peak and with the ample panorama of
the Iberian plate in front of us.
Structural landscape and Interpretation: the High