Geoparque Mundial UNESCO

Nº06 -Puerto Llano Fault

Geoparque Villuercas > Nº06 -Puerto Llano Fault

LOCATION AND ACCESS

The pass of Puerto Llano of Cañamero is located between the towns of Cañamero and Guadalupe. The local road EX-102 as far as the junction with the EX-116 gives easy access.

The fault is situated below a thick mantle of colluvium of the Sierra de Belén where the visitor can observe Armorican quartzites that have been strongly crushed along a wide and deep mylonitic strip. As the area to be visited is very near the road and right on a bend, it is dangerous to stop there and on the adjacent verge. It is best to observe the fault from the opposite verge away from the road.

ATTRACTIONS OF THE VISIT

Recognising the fault with all its elements, together with the mylonitic area in the Armorican quartzites and its covering layer of colluvium.

The works of an abandoned railway line can be seen in the vicinity. The trace, width, and depth of this fault cannot have been taken into account during the project of the railway line that was to run from Villanueva de la Serena to Talavera de la Reina. A long tunnel of 1363 m was to cross the fractured Armorican quartzites of the Sierra de Belén from east to west at Puerto Llano on the eastern flank of the wide Ruecas syncline. The greatest drawback of this route was the rugged relief and the hardness of the quartzite rocks of the sierra, together with the crushed and mylonitic area of this great fault. This prompted the decision to abandon definitively all work on the line, as the Puerto Llano tunnel had been affected by several dangerous landslides because it was hard to brace it given the methods of the time. These setbacks justified the total abandonment of the railway project by a Ministerial order of 22nd September 1962.

GEOLOGICAL INTERPRETATION

Read Geological Interpretation

This great tectonic fault orientated perpendicular to the folding was formed by the Alpine orogeny of the mid Cenozoic (Tertiary era) and determined the subsidence of the extensive depression situated south of Las Villuercas that is now occupied by the Vegas Altas del Guadiana. A huge tectonic lake (“Lago Sereniano”) formed in this depression; it filled with clayey sediments during the Miocene and finally in the Pliocene was completed by the alluvial material of the rañas.

As can be seen in the diagram, we have here a kind of reverse fault known as an overthrust. Overthrusts generally have a smaller dip (inclination angle) than typical reverse faults, owing to which the drift of the hangingwall on the footwall may be the reason for the folding that produces mountain ranges. This fault runs all along the south flank of Las Villuercas and is partially concealed by the deposits of the rañas, but its tectonic expression can be found in the Sierra de las Paredes and the Sierra de los Poyales (the raised block of Garciaz).