For our visitors interested in all geological aspects of the GeoPark, a detailed document is available from geoparquevilluercas.es
From the geological point of view, the region is part of the Central Iberian Zone of the Macizo Ibérico or Hespérico of the North West of the Iberian Peninsula, consisting mainly of Precambrian and Paleozoic materials, coated locally by Tertiary materials from continental facies.
The region of Las Villuercas is a mountain range formed by a series of quartzite hills and slate valleys aligned in parallel in the NW-SE direction (Armorican or Hercynian direction), limited to the east and west by the peneplains of La Jara and Trujillo-Cacereña respectively. This type of morphology is called apalachian or apalachense relief, by analogy with the landforms that occurred in the Appalachian Mountains of North America.
The peak height of this orographic macizo is "La Villuerca”, at an altitude of 1601 meters, located near the historic town of Guadalupe. The Sierra de Altamira (reaching 1,246 m.), the Sierra de La Palomera (which has the second highest peak in the Risco Cerval 1443m the Sierra de Viejas (1,374 m.), the Sierra de La Villuerca (1,601 m.) and the La Ortijuela (1,331 m.), as well as the mountains of Alcornocal, Castillejos, La Madrila and the Pimpollar that make up the western foothills of the Villuercas. These reliefs have been modeled on a structure folded by the Hercynian Orogeny in late Paleozoic, leveled during the Mesozoic giving rise to an erosion surface (peneplain) that experienced a rejuvenation in the Alpine Orogeny with a generalized rise, breaking up into numerous transverse faults in the Hercynian direction, which facilitated creation of the river network and the formation of the typical hatches.
The powerful sedimentary series, consisting of an alternance of hard rocks -Armorican quartzite-, with other despicable slates- provides the river network with optimal conditions for the development of the "Apalachian relief" by differential erosion.
These Hercynian folds constitute the main valleys of Las Villuercas, parallel to one another and approximately equal in height, degradated in lower altitude rungs because of the fracture originated during the Alpine Orogeny.
In various sectors of the northern and southern edges of the mountains, it is possible to observe tectonic lake depressions in which clays and akoses of continental origin pelleted during the Upper Tertiary Miocene, and on top of them, during the Plioquaternary, the sedimentary plains of Las Rañas, consisting of a clay matrix of fanglomerate boulders with abundant quartzite and slate of alluvial and torrential origin, it is also possible to distinguish a glacis level, high relative to the current water network by the engagement of the valleys in the Tertiary sediments and schist substrate. Notable examples of these sedimentary formations are the "Rana de las Mesas de Cañamero" and "Raña de Alía", the "Raña de las Mesillas" to the norh of the Castañar de Ibor and the "Rañas de Deleitosa" to the northwest of this town.
Finally, due to the effect of mechanical weathering on the quartzite peaks during the last geological period, the Quaternary, there are deposits of quartzite blocks, some large, which are disposed longitudinally in the foothills of the Sierras from the base of the ridge, accumulating in the depressions of the slope in a delicate balance with the slope. They are the typical "quarry" or "casqueras" as representative in The Villuercas.
The hydrographic network of Las Villuercas drains two main rivers: the Tajo to the North and the Guadiana to the South. Due to a tectonic threshold transverse to the Hercynian structures, las Villuercas provides drainage opposed to these two large rivers, being much greater the area and number of channels that target the Tajo.
The geological wealth of the Geopark territory, represented by more than forty geosites, is parallel to the paleontological richness of the territory where at certain levels of synclines we find abundant fossil samples of trilobites, brachiopods and graptolites of the Lower Palaeozoic.
In the central zone of the Massif of las Villuercas, corresponding to the anticline of Ibor-Guadalupe, there are the materials that make up the Extremadura dome which in its first stage consists of carbonate materials, marl, shale and graywacke that crop up along the east hillside of the valley and that are the most representative of the transition from the Precambrian and Cambrian periods, with greater development in the central area up to Castañar de Ibor. In this area is the Castañar de Ibor Cave Nature Monument, by the Regional Government of Extremadura, which attempts to safeguard its extraordinary wealth of great underground cavern development karst formations and elements of great beauty and fragility, among which the Aragonite crystallization is of exceptional scientific and educational interest and which has the iconic visual image of the Villuercas Geopark.
According to recent studies carried out by the University of Extremadura in Precambrian limestone near Navalvillar, we can also find an important paleontological site where the oldest metazoan fossils of the Iberian Peninsula are located. These stocks are Cloudina carinata, Precambrian fossils representing the first mineralized Ediacaran metazoans.
This new species, whose genus has been known from the early 70s, was described in Namibia together with other microfossils. Its location is very specific: Namibia, China and Europe and within Europe are a few locations in Extremadura in Spain.
The first description in Spain was written in the 80s by Pr. Teodoro Palacios Medrano, director of the research group of Paleontology and Stratigraphy of the Neoproterozoic and Paleozoic of the University of Extremadura and one of the members of the scientific committee of the Geopark. The fossils found have been uniquely preserved allowing them to be examined in three dimensions, showing its original form and many details of their exoskeleton. Cloudina includes a group of species of calcareous algae, which are included within the Ediacara fauna (Vendian, approx. 630-540 million years) thoroughly studied by Adolf Seilacher among other authors. Its external appearance is tubular, one of the first known group with calcified exoskeletons. The importance of Cloudina is in the progress on the study of the evolution of early metazoans, namely the onset of biomineralized skeletons. Two possible factors that determine the appearance of the first skeletons are being considered: changes in the environment, possibly a change in the chemical composition of the ocean and atmosphere, and / or biological changes, namely the appearance of predators, so that the skeleton served as a defense.
These structural and lithologic elements (alternation of synclinal and anticline folds, alternating quartzite and slate), and modeling forms (valleys parallel to each other, Rañas, glacis, quarries) clearly convey the characteristic landscape of Villuercas. The structural framework conditions both, the hydrographic network and the orientation of the slopes or the elevations of the mountains. The latter together with its layout in orographic screen to the penetrations of moist winds from the W-SW and its latitudinal positios, organize the distribution of the plant formations and the unique characteristics of the countryside.