Weathering Processes on Sandstone Painting and Carving Surfaces at Prehistoric Rock Sites in Southern Spain

The sandstones which constitute the host rock for the prehistoric artwork in the Rock Groups of Tajo de las Figuras and Peñas de Cabrera (southern Spain) show a serious degree of alteration, due both to natural processes and those related to anthropogenic and animal activity. A detailed study was carried out on the petrological and compositional characteristics of the sandstones (fresh and altered rock) in both rock groups, and on the geological and climatological characteristics of the area in which they are located. The sandstones have very similar petrological and compositional characteristics in both areas. This likeness causes the nature of the natural weathering processes to be similar in the rock areas studied. These processes can be divided in terms of the predominant mechanisms of alteration into three inter-related categories: mechanical weathering, chemical weathering, and bio-induced alteration processes. However, the different climatic conditions of the areas in which the two rock areas are located directly influences the intensity of these processes. The precipitation and the range of temperature variation with heavy winter frosts in the area of El Tajo de las Figuras are significantly higher than in the area of Peñas de Cabrera; this translates into a higher rate of weathering at El Tajo de las Figuras. Regarding the anthropogenic action, two types of influence on the deterioration can be distinguished: a direct one, which consists of scouring and wetting of the walls in order to increase the chromatic contrast; and an indirect one, which is the extraction of blocks of sandstone in the upper part of rock shelters, which in turn encourages the development of the chemical weathering processes.This study forms part of the research agreement “Study and diagnosis of the archaeological groups and deposits of the Autonomous Community of Andalusia in their geomorphological, biological and climatic contexts” financed by the Culture Council, Junta of Andalusia (Spain)

Habitat Constraints in Epikarstic Waters of an Iberian Peninsula Cave System

14 páginas, 6 figuras, 11 tables et al..The epikarstic waters of a restricted sector of the Ojo Guareña cave (north Iberian Peninsula) were investigated to characterize the physico-chemical variation in an annual cycle, to improve the scarce knowledge of the aquatic cave fauna on the Iberian Peninsula, to look for distribution patterns of species per habitat along the annual cycle, and to search for the environmental basis (either physico- or hydro-geochemical) that could explain species distribution in the epikarst. The habitats studied included all puddles and gours present in the sector selected making a total of 51 chemical and 42 biological samples for the entire cycle. The waters show no appreciable contaminationand exhibit small chemical variations throughout the year which are patently affected by external weather conditions. The 53 taxa found belong to ten higher taxonomic groups (Oligochaeta, Turbellaria, Mollusca, Copepoda, Ostracoda, Isopoda, Bathynellacea, Tardigrada, Acarina and Cnidaria), and consist mainly of crustacea with a total of 27 species. Fourteen species were stygobionts (belonging to ten genera), nine of which are new to science and ten of which are endemic. Cave pools that appeared to be more stable in terms of water volume and mineralization, had a lower pCO2 and were carbonate oversaturated, harboured the greatest number of taxa. It is these pools that can maintain strictly cave dwelling species. Pools with lower levels of mineralization and greater water volume fluctuations had a lower diversity of fauna and in general lacked stygobiotic species.Projects PASCALIS EVK2-CT-2001-00121; Convenio Junta de Castilla y León-CSIC (2002-2004) and BTE2002-04492-C02-02.Peer reviewe

High radon levels in subterranean environments: monitoring and technical criteria to ensure human safety (case of Castañar cave, Spain)

Castañar cave contains the highest radon gas (222Rn) concentration in Spain with an annual average of 31.9 kBq m−3. Seasonal variations with summer minimums and maximum values in fall were recorded. The reduction of air-filled porosity of soil and rock by condensation or rainfalls hides the radon exchange by gas diffusion, determining this seasonal stair-step pattern of the radon activity concentration in underground air. The effective total dose and the maximum hours permitted have been evaluated for the guides and public safety with a highly detailed radon measurement along 2011 and 2012. A network of 12 passive detectors (kodalphas) has been installed, as well as, two radon continuous monitoring in the most interesting geological sites of the subterranean environment.A follow up of the recommended time (max. 50 min) inside the underground environment has been analysed since the reopen to public visitors for not surpassing the legal maximum effective dose for tourists and guides. Results shown that public visitors would receive in fall a 12.1% of the total effective dose permitted per visit, whereas in summer it is reduced to 8.6%, while the cave guide received a total effective dose of 6.41 mSv in four months.The spatial radon maps allow defining the most suitable touristic paths according to the radon concentration distribution and therefore, appropriate fall and summer touristic paths are recommended.This research was funded by the Regional Government of Extremadura (Spain) through EAFRD Axis 2 “Improving the environment and the countryside” and the Spanish Ministry of Economy and Competitiveness through project CGL2013-43324R and the programme Torres Quevedo (PTQ 13-06296 and PTQ 12-05601).A.F-C is funded by an IEF Marie Curie Action (FP7/2007–2013) under REA grant agreement n° 624204Peer reviewe

Calcitization of Mg±Ca carbonate and Ca sulphate deposits in a continental Tertiary basin (Calatayud Basin, NE Spain)

Diagenetic carbonates formed through early calcitization of evaporite (gypsum, anhydrite) and/or magnesium carbonate (dolomite, magnesite) deposits have been identified throughout the Tertiary Calatayud Basin (NE Spain). The diagenetic carbonates consist in all cases of low magnesian calcite and are related to main sedimentary discontinuities, which record episodes of significant subaerial exposure in the basin. Early calcite replacements predominate in sediments of the Intermediate Unit in central areas of the basin. Two types of diagenetic carbonates have been distinguished: (1) laminated diagenetic carbonates in which the original structure of sequences formed of laminated magnesite, dolomite and primary gypsum is preserved, though transformed in calcite; (2) brecciated diagenetic carbonates, which resulted from extensive dissolution of lenticular gypsum macrocrystals accompanied by dedolomitization processes of dolomite host rock. The replacement by calcite resulted from rapid transformation of evaporite deposits either at the contact of these deposits with overlying freshwaters or by percolating freshwater at very shallow burial depth. Stable isotope (carbon and oxygen) analyses of the diagenetic carbonates support influence of meteoric-derived carbonate-rich groundwater for their formation. The meteoric isotope signature is supported by its comparison with the stable isotope values determined from diagenetic calcites formed after magnesite in evaporite sequences during the Late Pleistocene and Holocene. The diagenetic carbonate bodies formed as a result of a progressive change from highly to moderately concentrated saline lake waters. This gradual evolution was related to a climatic shift from dry and hot to cooler and more humid conditions throughout the Miocene, a trend that has been also recognized in other large Tertiary basins of the Iberian Peninsula in this period

Tectono-Sedimentary Evolution of the Madrid Basin (Spain) during the Late Miocene: Data from Paleokarst Profiles in Diagenetically-Complex Continental Carbonates

An intra-Vallesian (Upper Miocene) paleokarst developed at the top of the Intermediate Miocene Unit in the continental intracratonic Madrid Basin is recognized. This paleokarst is an early shallow, tabular-shaped karst that shows a marked control by the depositional facies pattern and lithologies. By integrating morphological, petrological, and geochemical data, three hydrogeological zones were established throughout the paleokarstic profiles: (i) a paleo-vadose zone, characterized by vertically elongated caves and vadose cementation; (ii) a 3–7 m thick paleo-epiphreatic zone (paleo-water table fringe), with development of stratiform breccia bodies, the superimposition of both vadose and phreatic features, and the lowest Fe and Mn contents in host-rock carbonates; and (iii) a paleo-phreatic zone characterized by an increase in δ13C values and the predominance of phreatic cementation. The paleogeographic reconstruction for the intra-Vallesian paleokarst using profiles revealed relative topographic highs to the north and topographic lows to the south, drawing the paleokarst landscape. Immediately overlaying the paleokarst surface are fluvio-lacustrine facies belonging to the Miocene Upper Unit (Late Vallesian to Late Turolian). Their lowermost deposits consist of fluvial terrigenous facies deposited by approximately N–S fluvial streams, and pass upward into fluvio-lacustrine fresh-water limestones. This paleokarstic surface represents a major change in the evolution of sedimentary patterns of basin, from endorheic to exorheic conditions, as the result of a change from compressive to extensional conditions in the tectonic regime.This study was supported with funding provided by Research Group VIGROB-095 of the University of Alicante and projects PB89-0032 and PB89-0047 of the Government of Spain

Microclimatic studies in Paranhos water galleries, Porto (Portugal)

Sanz Rubio, Enrique et al.-- 4 pages, 3 figures, 4 references.-- Proceedings of the International Congress on Science and Technology for the Conservation of Cultural Heritage, held 2-5 october, Santiago de Compostela, España.Paranhos constitutes one of the main water galleries excavated in the granite substratum of Porto City (Portugal) to gather the groundwater for public use during the past six centuries. The interest of this water gallery is double: a) Cultural Heritage and scientific value, b) Underground geoturism. A multidisciplinary research to study the microclimatology, geochemistry, mineralogy and geomicrobiology of the Paranhos catchwork galleries is currently in progress. The characterization of the main environmental parameters (air-rock temperature, relative humidity, CO2, 222Rn, etc.) in the internal atmosphere would allow the establishment of: a) Fluid-rock interactions and development of a physical-chemical model of air-water-rock, as a base to define their relations with unusual mineral formations and microbial communities b) Microclimatic parameters and determination of effective radioactive dose for visitors based on 222Rn studies, as potential use as underground geotourism site under safe conditions.This research was supported by the Spanish Project CGL2011-25690.Peer reviewe

Detection of human-induced environmental disturbances in a show cave

Purpose: We investigated the effects of human-induced disruption in a subterranean stable environment containing valuable Palaeolithic paintings and engravings (Ardales Cave, Southern Spain) using a double analytical approach. Methods: An environmental monitoring system was installed in the cave to record temperature, relative humidity, carbon dioxide (CO2) and radon (222Rn) concentrations in air. In the same stations, an aerobiological sampling was conducted to quantify the level of airborne microorganisms. Results: The combination of different methods allowed us to detect the extent of human-induced changes, confirming that these can be very hazardous in certain cave areas that should be apparently outside the scope of human disturbances, either by their remoteness to the visitor entrance or by being briefly visited. Conclusions: The detection of evident anomalies in the environmental parameters and airborne microorganism concentration in the cave area housing the high density of paintings and engravings helps to control human disturbances and supports the direct application of this double approach for cave management purposes.Peer Reviewe

Geochemical Fingerprinting of Rising Deep Endogenous Gases in an Active Hypogenic Karst System

The hydrothermal caves linked to active faulting can potentially harbour subterranean atmospheres with a distinctive gaseous composition with deep endogenous gases, such as carbon dioxide (CO2) and methane (CH4). In this study, we provide insight into the sourcing, mixing, and biogeochemical processes involved in the dynamic of deep endogenous gas formation in an exceptionally dynamic hypogenic karst system (Vapour Cave, southern Spain) associated with active faulting. The cave environment is characterized by a prevailing combination of rising warm air with large CO2 outgassing (>1%) and highly diluted CH4 with an endogenous origin. The δ13CCO2 data, which ranges from −4.5 to −7.5‰, point to a mantle-rooted CO2 that is likely generated by the thermal decarbonation of underlying marine carbonates, combined with degassing from CO2-rich groundwater. A pooled analysis of δ13CCO2 data from exterior, cave, and soil indicates that the upwelling of geogenic CO2 has a clear influence on soil air, which further suggests a potential for the release of CO2 along fractured carbonates. CH4 molar fractions and their δD and δ13C values (ranging from −77 to −48‰ and from −52 to −30‰, respectively) suggest that the methane reaching Vapour Cave is the remnant of a larger source of CH4, which was likely generated by microbial reduction of carbonates. This CH4 has been affected by a postgenetic microbial oxidation, such that the gas samples have changed in both molecular and isotopic composition after formation and during migration through the cave environment. Yet, in the deepest cave locations (i.e., 30m below the surface), measured concentration values of deep endogenous CH4 are higher than in atmospheric with lighter δ13C values with respect to those found in the local atmosphere, which indicates that Vapour Cave may occasionally act as a net source of CH4 to the open atmosphere

Análisis geoambiental en medios hipogeos

8 páginas, 1 figura. Ed. Miguel Ángel Rogerio Candelera y Cesáreo Sáiz Jiménez. Primera Reunión de la Red de Ciencia y Tecnología para la Conservación del Patrimonio (Madrid, 28-29 de junio de 2011).Los coordinadores de los dos grupos de trabajo localizados actualmente en dos instituciones independientes (CSIC, Universidad de Alicante) se iniciaron científica y profesionalmente en el equipo de investigación de Geología - Geoquímica - Microclima aplicados a la Conservación del Patrimonio que se formó bajo la dirección de Manuel Hoyos Gómez a principios de la década de los 90. En el campo de la Conservación del Patrimonio, las investigaciones de ese grupo se centraron especialmente en la protección del arte rupestre y actualmente se enfocan al estudio integrado de ambientes subterráneos (cuevas, catacumbas,túneles, etc.) y de los procesos de deterioro del patrimonio que albergan. Los proyectos en los que los dos grupos trabajan abitualmente en estrecha relación incluyen datos de los parámetros climáticos y microclimáticos que caracterizan los sitios de estudio, de las características mineralógicas, geoquímicas y petrofísicas de los soportes y de las aguas de infiltración, y de los aspectos geomicrobiológicos de la interacción entre microoorganismos y los diferentes sustratos existentes (rocas, materiales de construcción, espeleotemas, etc.).Peer reviewe