Proceedings of the 3rd IASME / WSEAS International Conference on GEOLOGY and SEISMOLOGY (GES'09)

El Castillo Mountain prehistoric caves (Cantabria, North of Spain). Structural geology, karstic development and prehistoric art manifestations. World Heritage, UNESCO 2008

A. FOYO; M.A. SANCHEZ, C. TOMILLO & E. IRIARTE Applied Geology Research Group. Ground and Material Sciences Department Civil Engineering School University of Cantabria Avda. de los Castros s/n, Santander, Cantabria SPAIN

Abstract: - One of the main factors in the development and evolution of a karstic system are the structural characteristic of the rock masses. The karstic system of the El Castillo Mountain has been developed along of planes of different kinds of discontinuities, like thrust faults originated during the Hercinian orogeny and a dense net of fractures generated during the Alpine orogeny. Here we show the description of the structural geology and the possible relationship between the geological discontinuities of the rock mass and the prehistoric painting sites.

Key-Words: Structural geology, prehistoric caves, prehistoric painting sites

1 Introduction of Bronze [1], which represents a continuous The karstic system of the El Castillo Mountain is registration of about of 200.000 years of the human developed next to Puente Viesgo village Community of Cantabria, North of Spain (Fig.1a). It is constituted by multiple small holes and seven main cavities: El Castillo (The Castle), El Oso (The Bear), El Lago (The Lake), Las Chimeneas (The Chimneys), La Flecha (The Arrow), La Pasiega and Las Monedas (The Coins). All of them they are located inside the El Castillo Mountain, a conical and calcareous promontory 355 m heights over sea level (Fig. 1b). From many years ago, the narrow relationship between the geological structure of the rock masses and the karstic development has been described by many authors [5, 6, 7, 8, 9], and the caves are even a) more sensitive in their evolution with the geological structure than the superficial waters and their valleys [10]. On the other hand, in the El Castillo Mountain caves, alike the narrow relations with the tectonic history of the rock mass, there is a curious coincidence between the structural discontinuities and the geological support of the prehistoric pictures, as well as with the vein of ochre, which is the prime matter to elaborate the colouring materials for painting. In the El Castillo Mountain, El Castillo main cave it has been one of the most research cavities, because the stratigraphy of their prehistoric deposit includes lithic industry [2], and animal and human rest, Neanderthal and of Homo sapiens fossils [1], from b) the upper Acheulean prehistoric period until the Age

ISSN: 1790-2769 148 ISBN: 978-960-474-058-1 Proceedings of the 3rd IASME / WSEAS International Conference on GEOLOGY and SEISMOLOGY (GES'09)

Figure 1. . a) Situation Map. b) General view of El as the Little Nape of the El Castillo cave [12], and as Castillo Mountain other multiple micro napes, conserve the orientation history. Also, together with The Chimneys, The of the general structure (Fig. 3). Pasiega and The Coins caves, they contain some magnificent samples of prehistoric art manifestations of the Solutrean and Magdalenian prehistoric periods [3].

2 Geological characteristics of the El Castillo Mountain

2.1 Stratigraphy and Petrology El Castillo Mountain is made of a sequence of Carboniferous limestones, Namurian to Westfalian geological age [11], and it is part of the Cabuérniga Tectonic Shield, that corresponds with the stratigraphical and structural continuation of the Cantabrian Units formed during the Hercynic orogenenic events. In general, they are massive and fractures limestones that can be defined as biomicrites, mudstone-packstone, that contain idiomorphic quartz occasionally [11]. The weathering surfaces are of gray to white colour and in a fresh sample it presents a marked dark gray colour.

2.2 Structural characteristics Figure 2. Tectonic schedule around the El Castillo From the structural point of view the El Castillo Mountain. Modified from [11]. Mountain is part of a large geological structure denominated as the Cabuerniga Tectonic Shield, and Finally, together with these main two types of the formation of Carboniferous limestones, inside of structures, there is a dense net of fractures defined as the caves are developed, it is integrated in the shield smaller order structures (Fig. 3). In general, these with an orientation W-E (Fig. 2). During the late fractures correspond with two families of N-S and phases of the Hercynian orogenic event [11], and as NW-SE orientation, and always with a vertical- a result of the efforts of the North to South subvertical development. It is considered that they compressive deformation, it has taken place the have been originated during the late Alpine events, displacement toward the south of the carboniferous or even more recent age, corresponding at the formations by means of long thrust fault structure, distension phases of the orogenic cycles. All the like geological napes, over the materials of age fractures crossing and displace the napes and micro Mesozoic age, which there are represented in all napes hercynian structures and consequently, they their chronological extension: Triassic sands and must be the last manifestation of tectonic deformation shales, Jurassic limestones and Cretaceous marls. around the El Castillo Mountain. As consequence of the hercynian orogenic events, the development of different thrust fault structures 2.3. Relationship between the Hercynic and with a general orientation NE-SW, produce the Alpine structures and the development of the displacement of the limestones toward the South, and karstic system. they cause the overlapping of carboniferous materials The development of the karstic system of the El over it self (Fig. 3). The presence of long napes is Castillo Mountains they have a narrow relation with common in the Asturian and Cantabrian regions and the orientation of the mayor and dominant smaller they are the structural patterns during the late order discontinuities that affect at the limestone hercynian orogenic events[11]. Around the El formation. As consequence of the massive character Castillo Mountain, three of these structures have been of the limestones, in absence of stratification planes, identified, being specially important the denominated

ISSN: 1790-2769 149 ISBN: 978-960-474-058-1 Proceedings of the 3rd IASME / WSEAS International Conference on GEOLOGY and SEISMOLOGY (GES'09)

the karstic conduit has been developed throughout of of the Las Monedas cave and North East sector of the different kinds of fracture planes. the La Flecha cave.

Figura 3. Geological map around the El Castillo Mountain and situation of the cavities.

The main tectonic structure corresponds with the front of the Cabuerniga Shield. However, the 3 Relationship between the geologic evolutions of the karstic conduits have had taken and structural characteristics of the place preferably in favour of the secondary structures like the thrust faults de different kinds, napes and cavities and the prehistoric art micro napes with a structural direction NE-SW , manifestations. originated during the Hercynian events. An example The relationship between development and evolution specially important is the Nape of the El Castillo cave karstic system and the geological and structural (Fig. 3), which define the entrance of the cave and it characteristic of the limestone formations are more or configures the great rocky refuge that it was the less well known. However, in the El Castillo living zine of the oldest palaeolithic inhabitants. Mountain caves, it must be added a peculiar relation Alike, this structural element it has controlled the between the karstic development controlled by the development of the first great room and the initial geologic structure and the prehistoric art galleries [12]. manifestations. That relation consists on two Together with the Hercynic napes and little napes, elements: a) the karstic system include two important the discontinuities of small order r like Alpine deposits of ochre mineral, that they are neccessary to fractures they constitute the second structural element the production of coloring materia, and b) a curious that it has controlled the development of the cavities relationship exists between the panels or walls were and karstic conduits, specially when the karstic the prehistoric mans painting and the structural gallery presents a marked longitudinal development control in the development of the galleries. (Fig. 3), i.e. in the West sector of the El Castillo cave, The deposits of an ochre mineral are located in and the West sector of the El Oso cave, main gallery the Cueva del Oso and in the Cueva de Las Chimeneas. The minerals appear along discontinuity

ISSN: 1790-2769 150 ISBN: 978-960-474-058-1 Proceedings of the 3rd IASME / WSEAS International Conference on GEOLOGY and SEISMOLOGY (GES'09)

NE-SW, which is to say, the Hercinian nape surfaces Culture Department of the Regional Government of (Fig. 3). Cantabria. Furthermore, the cavities with prehistoric art References: representations are El Castillo, Las Chimeneas, La [1] Garralda, M.D. ¿Y si las gentes del nivel 18B de Pasiega and Las Monedas. We are confirmed that, in la Cueva de El Castillo fueran neandertales?, En these cavities, painting walls, panels of paintings, it el Centenario de la Cueva de El Castillo, Edited has a curious coincide with surfaces that correspond by the Centro Asociado a la UNED en Cantabria, directly with the discontinuity planes, Hercynic nape 2006, pp. 434-452. surfaces such as in the El Castillo or in La Pasiega [2] Lloret Martíne de la Riva, M and Maíllo caves (Fig. 3), as well as typical fracture Fernández, J.M. Aproximación tecnológica a los discontinuities like in Las Monedas cave. The reason niveles 18b, 18c y 16 de la cueva de El Castillo could be that these discontinuity planes have been (Puente Viesgo, Cantabria). En el Centenario de generated many surfaces with a little, rough and la Cueva de El Castillo, Edited by the Centro lightly porous surfaces. The later development and Asociado a la UNED en Cantabria, 2006, pp. 493- karstic evolution, it has caused an intense laundry of 512. the residual clays, became as appropriate surfaces to [3] Soto-Barreiro, M.J., Cronología radiométrica, be the final support of the art manifestations (Fig. 4). Ecología y Clima del Paleolítico Cantábrico, Monografías 19, Museo Nacional y Centro de Investigación de Altamira, 2003. [4] Giménez de la Rosa, M. La Colección antigua de arte mueble e industria ósea. En el Centenario de la Cueva de El Castillo, Edited by Centro Asociado a la UNED en Cantabria, 2006, pp. 459- 470. [5] Veni, G., A geomorphological strategy for conducting environmental impact assessments in karst areas. Geomorphology, 31, 1999, p. 151- 180. [6] Maire, M.R. Connaissances actuelles sur le karst profond de Larra (Pyrénnées Atlántiques,

Figure 4. Prehistoric pictures made along a micro Navarra, Huesca). In: Reunión Monográfica sobre nape in the final gallery of El Castillo cave el karst Larra 82, 1983, p. 55-79. [7] Audra, P. Karsts alpins. Genèse de grands reseaux souterrains. Exemples: le Tennengebirge 4 Summary and conclusions (Autriche), lÍle de Crémieu, la Chartreuse et le Vercors (France). Karstologia Mémories 5, 1994.

[8] Alberto Foyo, Juan L. Suárez, Carmen Tomillo, The karstic systems of the El Castillo Mountain Miguel A. Sánchez, Análisis previo de la relación contain seven big cavities. Four of them have an entre la estructura geológica y el desarrollo del important prehistoric art manifestation and, in the modelado cárstico en el Macizo de Ardines, case of the El Castillo cave, the rest of occupation Ribadsella, Asturias. In: Primer Symposium and human fossils from the Neanderthal epoch. From Internacional de Arte Prehistórico de the geologic point of view these cavities allow to Ribadesella. Edición Rodrigo Balbín y Primitiva propose the existence of a narrow relation between Bueno. 2003, Asturias, España, pp. 153-160. the structural properties of the limestone rock masses [9] Foyo, A., Sánchez, M.A., Tomillo C. & Irirarte, and the location of the art pictures. The epikarst has E., Geological risk assessment of the area around been developed in favour of discontinuities type the Tito Bustillo Prehistoric Cave. Human napes, generated during the compressive stages of Heritage (UNESCO, 2008). Asturias, North of the Hercynic orogeny, and different kinds of st Spain. In: 1 WSEAS International Conference on fractures formed during the Alpine orogeny. Environmental and Geological Science and

Engineering. Malta. 2008. pp. 127-130. Acknowledgements [10] Palmer, A.N. Cave Geology. Published by Cave

Books, Cave Research Foundation. 2006. The Applied Geology Research Group of the [11] IGME, 1979. Mapa y memoria explicativa de la University of Cantabria, would like grateful to the Hoja 58 (Los Corrales de Buelna) del Mapa

ISSN: 1790-2769 151 ISBN: 978-960-474-058-1 Proceedings of the 3rd IASME / WSEAS International Conference on GEOLOGY and SEISMOLOGY (GES'09)

Geológico de España a escala 1:50.000 (2º Serie). IGME, Madrid. [12] Foyo, A., Tomillo, C. & Sánchez, M.A., El entorno geológico de las cuevas del Monte El Castillo en Puente Viesgo, Cantabria. En el Centenario de la Cueva de El Castillo, Edited by the Centro Asociado a la UNED en Cantabria, 2006, pp. 368-379. [13] Iriarte, E., Foyo, A., Sánchez, M.A., Tomillo, C and Setien, J., The origin and geochemical characterization of red ochres from the Tito Bustillo and Monte Castillo Caves (Northern Spain). Archaeometry (doi: 10.1111/j.1475- 4754.2008.00397.x)

ISSN: 1790-2769 152 ISBN: 978-960-474-058-1