Geología de la cueva

Peer reviewe

Genesis and evolution of wetlands on perched surfaces as result of the degradation of a previous network due to drainage changes: the Albuera complex, Badajoz

Geomorphological and hydrochemical characteristics of the ponds complex of La Albuera is analysed in relation to their perched position on the «Raña» surfaces. The wetlands are classified as a fluvial controlled continental type, favoured also by local subsidence processes. Their origin needs to be related to dewatering capacity loss allowing ponds preservation on the impervious surfaces, also favoured by subsidence. The degradation of the previous drainage pattern is forced by the modern streams shift and incision, and the former network has not yet been properly captured and integrated by the present river system.Proyectos BTE 2003-04572 y CGL2004-033049 de la MCYT y proyecto HIDROHUMED, financiado por el Instituto Geológico y Minero de España

La Cueva de Castañar y su centro de interpretación

Comunicación presentada en Cuevatur 2016: VI Congreso Español sobre Cuevas Turísticas, Nerja (Málaga), 2016.[ES] La Cueva de Castañar constituye una cavidad única tanto por la variedad de minerales y formas de sus espeleotemas, como por el tono rojizo de sus paredes. Estas dos características responden a las características de los materiales sobre los que se desarrolla la cueva. Son materiales correspondientes al Ediácarico (635-541 M.a.), que incluyen una amplia variedad de rocas (dolomías, magnesitas, pizarras y areniscas). Estos materiales, muy ricos en magnesio y sílice, son los que se disuelven y alteran para dar lugar a la formación de la cavidad y de sus espeleotemas. La alteración de las pizarras y areniscas, la disolución de las dolomías y magnesitas y la infiltración de arcillas desde el suelo dan lugar a la formación de un fino tapiz de color rojo intenso que se deposita sobre las paredes de la cueva, sobre el que muchas veces nuclean los espeleotemas. La disolución de las dolomías y magnesitas aporta mucho magnesio a las aguas que circulan por la cueva, lo cual favorece la formación no sólo de calcita (que es lo habitual), sino también de aragonito. Pero además la composición de las aguas no se ha mantenido constante, lo que ha favorecido que se produjeran muchas transformaciones entre los minerales ya formados. En definitiva, el amplio espectro mineralógico y las variadas transformaciones mineralógicas que se observan en la cueva, hacen de esta un laboratorio natural y por tanto una cavidad única, que se debe conocer, para así poderla conservar en las mejores condiciones posibles. Estas condiciones son las que hacen que el número de visitantes sea muy limitado, por ello el Centro de Interpretación inaugurado en 2010, cumple sobradamente la labor de dar a conocer los valores únicos de la Cueva de Castañar.[EN] Castañar Cave is a unique cavity due to the variety and morphology of the speleothems it contains, as well as to the red colour of their walls. These characteristics are due to the hostrocks in which it developed, Ediacaric (635-541 M.a) dolostones, magnesites and siliciclastic rocks. These materials very rich in Mg and silica, weather and dissolve to give place to the formation of the cavity and their speleothems. The weathering of the siliciclastic rocks, the dissolution of dolostones and magnesites and the infiltration of the clays from the overlying soil, allows the formation of a thin red (clays and Fe-oxides) layer that coats the cavity, and constitute the nucleation site for many speleothems. The dissolution of dolostones and magnesites supplies Mg to the cave waters enabling the formation not only of calcite, but also aragonite and dolomite (which are rarer in caves). In addition water cave composition has changed over time, allowing many transformations between the previously formed minerals. When relatively more dilute waters prevail aragonite transforms into calcite or even both can dissolve, forming the large pores visible in some speleothems. On the contrary Mg-rich minerals (huntite, dolomite and Mg-rich clays) form in more concentrated waters. In short, the wide mineralogical spectra and their transformations make this cave a unique cavity and a natural lab, whose detailed study will help to preserve it under the best possible conditions. This is why the number of visitors is very limited; however the renewed Centro de Interpretación shows in great detail the characteristics of the Castañar Cave.Este trabajo se incluye en los proyectos: “Estudio ambiental y geológico del Monumento Natural Cueva de Castañar”, financiado por fondos FEADER (contrato Gobierno de Extremadura y CSIC) y CGL2014-54818P del MINECO.Peer reviewe

La Comarca de Las Villuercas

Peer reviewe

Geosites proposal and landscape conservation in Extremadura

Se analiza el relieve de Extremadura como método para la comprensión y conservación del paisaje geológico, no solo por sus componentes de singularidad y rareza sino también por su visibilidad y capacidad escénica. Se proponen ejemplos a tener en cuenta para su preservación, bien por representar rasgos genuinos de los grandes conjuntos distintivos del paisaje o por sus aspectos geomorfológicos singularesThe relief of Extremadura is examined as a method for landscape understanding and geological conservation, not only due to its components of rarity and uniqueness, but also for its visibility and scenic capacity. Examples to consider for preservation are proposed, either by their unique geomorphologic features or by showing the genuine character of large distinctive landscape unit

Dissemination of the Geological Heritage of Extremadura through computer tools

Este proyecto se integra en la línea de trabajo desarrollada para el estudio del Patrimonio Geológico de Extremadura. Con él se pretende dar continuidad a la labor realizada de investigación y catalogación de los lugares de interés geológico más representativos de la región ampliando la información a partir de herramientas informática^ sistemas de infomtación geográfica y empleo de una aplicación de visualización y localización de datos en la red, que permita el acceso a dicha información de manera fácil e interactiva. El fin es hacer llegar la información al usuario de forma más clara y visual facilitando el trabajo de consulta, contribuyendo así a una mayor difusiónThis project is integrated in the line of work developed for the study of the Geological Heritage of Extremadura. It aims to continue the research and cataloguing of the most representative geological sites of the region by expanding information through computer tools, geographic information systems and the use of an application of visualization and location of data in the network, that allows the access to this information in an easy and interactive way. The purpose is to make the information available to the user in a more clear and visual way facilitating the consultation work thus contributing to a greater promotio

Dolomite and huntite formation in moon-milk deposits from Castañar de Ibor Cave (Cáceres)

The Castañar the Ibor Cave formed by dissolution of the Precambrian dolostone beds of the Ibor Group. The cave contains a variety of calcitic and aragonitic speleothems, and also moon-milk deposits composed of huntite, dolomite and minor hydromagnesite. Both huntite and dolomite tend to form spheroidal structures. Huntite formation occurred mostly on microbial films that in part corrode the speleothems. Spherulites of dolomite could form later on by transformation of the previously formed huntite, that acted as a precursor for dolomite formation. Both the huntite precursor and the microbial activity allow the presence of dolomite under environmental condition

Structural and host rock controls on the distribution, morphology and mineralogy of speleothems in the Castañar Cave (Spain)

The Castañar Cave (central western Spain) formed in mixed carbonate–siliciclastic rocks of Neoproterozoic age. The host rock is finely bedded and shows a complex network of folds and fractures, with a prevalent N150E strike. This structure controlled the development and the maze pattern of the cave, as well as its main water routes. The cave formed more than 350 ka ago as the result of both the dissolution of interbedded carbonates and weathering of siliciclastic beds, which also promoted collapse of the overlying host rock. At present it is a totally vadose hypergenic cave, but its initial development could have been phreatic. The cave's speleothems vary widely in their morphology and mineralogy. In general, massive speleothems (stalactites, stalagmites, flowstones, etc.) are associated with the main fractures of the cave and bedding planes. These discontinuities offer a fairly continuous water supply. Other branching, fibrous, mostly aragonite speleothems, commonly occur in the steeper cave walls and were produced by capillary seepage or drip water. Detailed petrographical and isotope analyses indicate that both aragonite and calcite precipitated as primary minerals in the cave waters. Primary calcite precipitated in waters of low magnesium content, whereas aragonite precipitated from magnesium-rich waters. Differences in isotope values for calcite (−5.2 ‰ for δ18O and −9.6 ‰ for δ13C) and aragonite (δ18O of −4.5 ‰ and δ13C of −3.5 ‰) can be explained by the fact that the more unstable mineral (aragonite) tends to incorporate the heavier C isotope to stabilize its structure or that aragonite precipitates in heavier waters. Changes in the water supply and the chemistry and instability of aragonite caused: (1) inversion of aragonite to calcite, which led to the transformation of aragonite needles into coarse calcite mosaics, (2) micritization, which appears as films or crusts of powdery, opaque calcite, and (3) dissolution. Dolomite, huntite, magnesite and sepiolite were identified within moonmilk deposits and crusts. Moonmilk occurs as a soft, white powder deposit on different types of speleothems, but mostly on aragonite formations. Huntite and magnesite formed as primary minerals, whereas dolomite arose via the replacement of both huntite and aragonite. Owing to its variety of speleothems and location in an area of scarce karstic features, the Castañar Cave was declared a Natural Monument in 1997 and is presently the target of a protection and research programme. Although the main products formed in the cave and their processes are relatively well known, further radiometric data are needed to better constrain the timing of these processes. For example, it is difficult to understand why some aragonite speleothems around 350 ka old have not yet given way to calcite, which indicates that the environmental setting of the cave is still not fully understood.Peer reviewe

Manifiesto a favor de la enseñanza de la Geología

Manifest en defensa d'incloure la Geologia com a assignatura pròpia de la modalitat en el Batxillerat de Cièncie