Geoparque Mundial UNESCO

Nº23 – Ibor-Guadalupe Anticline

Geoparque Villuercas > Nº23 – Ibor-Guadalupe Anticline


It is located in the central area of the Geopark and occupies two wide valleys in which the River Ibor flows towards the Tajo and the River Guadalupe towards the Guadiana. The northern area of the anticline can be reached by the road that links Guadalupe and Navalmoral de la Mata (the EX-118), which affords extensive views over the valley of the River Ibor at numerous points. One of the best is the vantage point of La Báscula at km 23 of this road some 500 m south of Navalvillar de Ibor. This road also gives access to the cave of Castañar de Ibor, the jewel of the karst relief that characterises the area.

The Pozo de la Nieve (Snow Well) on the ascent to the Risco de la Villuerca and the Guadalupe viaduct over the watercourse itself are perfect vantage points for contemplating the valley of the River Guadalupe.


The arrangement of the materials that make up the Ibor anticline, its composition, and the fossils it contains reveal the origins of its rocks and the fact that they were part of an extensive marine or coastal platform.

The limestone of the core represents ancient reefs consisting of Cloudina, stromatolites, and calcareous algae, which are fossil structures characteristic of shallow water. In the shales of the core other filamentous forms of the primitive fauna and fauna of the Ediacaran can be found: vendotaenids and Sabellitides.

The Armorican quartzites of the Ordovician conjure up the image of a long beach of siliceous sands (today recrystallised) in which it is easy to find the fossilised traces (Cruziana, DaedalusSkolithos…) of the organisms that lived there.

The richness of its calcareous materials (limestones, dolomites, and siderites) has been known since antiquity. Indeed they have been used both for the lime industry as can be seen from the numerous lime kilns in the area (La Calera geosite) and for the iron and steel industry deriving from the so-called “iron seams of the Grupo Ibor”.



Geologically this is a very extensive folding structure that extends in a NW-SE direction and is part of the great synclinorium of Las Villuercas. A synclinorium is a series of anticlines and synclines with a final shape more reminiscent of a great syncline. It was formed during the Hercynian Orogenic Movement that occurred during the Carboniferous period over 300 million years ago.

From the vantage point of La Báscula it is easy to understand that the rocks (Armorican quartzites) that form the crests of the sierras on both sides of the anticline are part of the same geological formation that was in its day arranged in the form of a great cupola (antiform). Today only its remains are visible as the whole of the core of the megastructure of the cupola has disappeared to become a valley (inverted relief) in which the River Ibor flows, with only part of the flanks or edges of the anticlinal cupola surviving (e.g. the Camorro de Castañar and Camorro de Navalvillar). The quartzites that can be observed on the crests are Ordovician in age (less than 460 m.y.) while on the hillsides and towards the valley bottom older rocks of the so-called “Grupo Ibor” can be found: shalessandstoneslimestones, etc. from the Ediacaran period (-550 to -560 m.y.).