Person:
Martín García, Rebeca

First Name

Rebeca

Last Name

Martín García

URI

https://hdl.handle.net/20.500.14352/75280

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Geológicas

Department

Mineralogía y Petrología

Area

Petrología y Geoquímica

Identifiers

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Now showing 1 - 10 of 29

El centro de interpretación de la Cueva de Castañar: un ejemplo de difusión de la investigación en Geología Sedimentaria
(2011) Martín Pérez, A.; Alonso Zarza, Ana María; Martín García, Rebeca; Gil Peña, I.; Meléndez, A.; Herrero Fernández, María Josefa; Rodríguez Berriguete, Álvaro; Pérez-Monserrat, Elena M.; Charco Romero, María
Relationships between colour and diagenesis in the aragonite-calcite speleothems in Basajaún Etxea cave, Spain Author links open overlay panel
(Sedimentary Geology, 2014) Martín García, Rebeca; Alonso Zarza, Ana María; Martín Pérez, Andrea; Schröder-Ritzrau, Andrea; Lud, Thomas
Basajaún Etxea Cave, North Spain, contains a wide morphological and colour variety of speleothems. Most of them are composed of aragonite, but calcite speleothems are also found. Their most common colour is white, but there are also pink, green and turquoise speleothems, in different areas of the cave. Mg-rich dissolution waters from the cave's crystalline dolostone and magnesite host rock favour aragonite precipitation and drive important diagenetic changes. In this paper we will discuss how diagenesis modifies speleothem texture, mineralogy and geochemistry, causing significant changes in the colour. We also discuss how speleothems that have undergone diagenesis may also be useful indictors of paleoclimatic conditions. Our work shows that diagenesis changes the colour of the speleothems because of the mobility of the chromophore elements during this process. Along with this elemental alteration comes the loss of the primary isotopic signals of speleothems. Detailed petrological studies of speleothems should precede their analysis for palaeoclimatic reconstruction so that influence of areas affected by diagenesis can be eliminated. In addition, diagenetic signals also contain valuable information on the changes of the waters within the cave, and the overall evolution of speleothems and the cave itself.
Tobas carbonáticas como resultado del riego con aguas subterráneas ricas en CO2 de origen volcánico
(Enseñanza de las ciencias de la tierra, 2019) Rodríguez Berriguete, Álvaro; Alonso Zarza, Ana María; Martín García, Rebeca; Cabrera, Mª Carmen
Weathering of host rock and corrosion over speleothems in Castañar cave, Spain: an example of a complex meteoric environment
(Carbonates and Evaporites, 2011) Martín García, Rebeca; Martín Pérez, Andrea; Alonso Zarza, Ana María
In Castañar cave, weathering processes have been identified on the host rock and speleothems. The result of these processes over speleothems, usually called corrosion, causes the loss of brightness and the formation of a powdery matt outer band. This band is composed by crystals <4 µm that cover the surface of the speleothems and changes the original texture. Corrosion is caused by partial dissolution of the aragonite and calcite that form the speleothems and results in the formation of these small crystals which are not washed away and remain in situ. The presence of similar bands inside and on the surface of the speleothems indicates that corrosion occurs not only at present time, but it has occurred several times interrupting the development of the speleothems. Castañar cave host rock consists of beds of Fe-rich dolomite and magnesite interbedded with greywackes and shales. Weathering of these rocks produces a clay-rich residue of intense red colour formed by quartz, clay minerals and iron oxides and hydroxides. This residue was formed by in situ alteration of the host rock either by dissolution of the dolomite Fe-rich (insoluble residue) or by hydrolysis of some components of greywackes and shales. In touristic caves, the alteration of both speleothems and host rock has usually been related to the acidification of the atmospheric moisture caused by CO2 from the breath of visitors. However, the presence of corrosion lines inside and on the surface of the speleothems and the fact that some of the non-visited galleries of the cave also present alteration features, indicates that this process did also occurred in past times and hence is not related to the presence of visitors. These weathering processes accounted for the outstanding chromatic contrast of the interior of the cave and show that the growth and formation of speleothems cannot be studied without taking weathering into account.
Structural and host rock controls on the distribution, morphology and mineralogy of speleothems in the Castañar Cave (Spain)
(Geological Magazine, 2010) Alonso Zarza, Ana María; Martín-Pérez, Andrea; Martín García, Rebeca; Gil-Peña, Inma; Meléndez, Alfonso; Martínez-Flores, Esperanza; Hellstrom, John; Muñoz-Barco, Pedro
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.
Caracterización petrológica de los niveles magnesíticos y las dolomías encajantes de Edad Proterozoica Superior- Cámbrico Inferior, Grupo Ibor, Castañar de Ibor, Cáceres
(Geogaceta, 2010) Herrero Fernández, María Josefa; Martín Pérez, Andrea; Gil Peña, Inmaculada; Alonso Zarza, Ana María; Meléndez Hevia, Alfonso; Martín García, Rebeca
Detailed petrographic observations of Upper Proterozoic –Lower Cambrian deposits of the Castañar de Ibor allows the characterization of the diagenetic history of these rocks. Graywackes, shales and limestones were deposited during the Upper Proterozoic-Lower Cambrian within a siliciclastic-carbonatic marine platform. Dolomite replaced mostly limestones, but also cemented the siliciclastic deposits. Later on magnesium-rich fluids circulating along stylolites, bedding planes and fractures partially replaced the dolostones and some siliciclastic beds. Finally, a new dolomitisation phase produced replacement of the magnesite by dolomite and dolomite cementation.
Clay minerals associations in palaeoweathering profiles from Central Spain: genesis and implications
(Clay minerals, 2012) Doval, Mercedes; Martín García, Rebeca; La Iglesia Fernández, Ángel; Alonso Zarza, Ana María
This study examines part of the thick palaeoweathering mantle that formed on the northern area of the Spanish Central System. The study of a compound profile indicates that despite weathering processes, the primary structure of the metamorphic rocks is preserved, and is only partially lost in some intervals of the upper part of the compound profile. Macro/micromorphology, mineralogy and geochemical changes within the profiles revealed two weathering paths. In the first path, Fe-chlorite weathered to chlorite-smectite mixed-layer/smectite/kaolinite+ iron oxides. In the second path, biotite and/or muscovite weathered to kaolinite + iron oxides. The profiles show a progressive decrease, from base to top, in mica and mixed-layers and an increase in smectite and kaolinite. Thus, the profiles only comprise the lower or intermediate zones of the weathering mantle. The weathering occurred under humid climates; the lower zones of the profiles were poorly drained, whereas the topmost zones were better drained and more oxidizing. The results obtained indicate that detailed mineralogical studies are very useful to reconstruct the characteristics of the weathering mantles, and as palaeogeographic and palaeoclimatic indicators.
Diagenesis of a drapery speleothem from Castañar Cave: from dissolution to dolomitization
(International Journal of Speleology, 2012) Martín Pérez, Andrea; Martín García, Rebeca; Alonso Zarza, Ana María
A drapery speleothem (DRA-1) from Castañar Cave in Spain was subjected to a detailed petrographical study in order to identify its primary and diagenetic features. The drapery’s present day characteristics are the result of the combined effects of the primary and diagenetic processes that DRA-1 underwent. Its primary minerals are calcite, aragonite and huntite. Calcite is the main constituent of the speleothem, whereas aragonite forms as frostwork over the calcite. Huntite is the main mineral of moonmilk which covers the tips of aragonite. These primary minerals have undergone a set of diagenetic processes, which include: 1) partial dissolution or corrosion that produces the formation of powdery matt-white coatings on the surface of the speleothem. These are seen under the microscope as dark and highly porous microcrystalline aggregates; 2) total dissolution produces pores of few cm2 in size; 3) calcitization and dolomitization of aragonite result in the thickening and lost of shine of the aragonite fibres. Microscopically, calcitization is seen as rhombohedral crystals which cover and replace aragonite forming mosaics that preserve relics of aragonite precursor. Dolomitization results in the formation of microcrystalline rounded aggregates over aragonite fibres. These aggregates are formed by dolomite crystals of around 1 μm size. The sequence of diagenetic processes follows two main pathways. Pathway 1 is driven by the increase of saturation degree and Mg/Ca ratio of the karstic waters and is visible in the NW side of the drapery. This sequence of processes includes: 1) aragonite and huntite primary precipitation and 2) dolomitization. Pathway 2 is driven by a decrease in the degree of saturation of calcite and aragonite and Mg/Ca ratio of the cave waters, and it is observed in the SE side of the drapery. The diagenetic processes of the second pathway include: 1) calcitization of aragonite; 2) incomplete dissolution (micritization) of both aragonite and calcite; 3) total dissolution. This study highlights the importance of diagenetic processes on speleothems and their complexity. The correct interpretation of these processes is crucial for the understanding of possible changes in the chemistry of waters, temperature, or pCO2 and so is critical to the correct interpretation of the paleoenvironmental significance of speleothems.
Gypsum speleothems in lava tubes from Lanzarote (Canary Islands). Ion sources and pathways
(Sedimentary Geology, 2019) Huerta, Pedro; Martín Pérez, Andrea; Martín García, Rebeca; Rodríguez Berriguete, Álvaro; La Iglesia, Á.; Alonso Zarza, Ana María
Lava tubes from Lanzarote Island in the Canary Archipelago commonly show white speleothems that stand out from the black basaltic rock. Mineralogical analyses of the speleothems from El Covón and Chifletera lava tubes show that gypsum is the dominant mineral with minor amounts of halite. Speleothems composed of microcrystalline gypsum (up to 150 μm long) are: coatings, globules, or extensive white powder accumulations covering the tube floor. Those composed of macrocrystalline gypsum with millimetric-size tabular and lenticular crystals are: crusts and stalactites. Uranium series dating of speleothems show ages ranging from 6217 ± 1644 yr to 40,039 ± 4748 yr. δ34S and the δ18O of gypsum speleothems (δ34S is 20.97‰ V-CDT and δ18O is 9.78‰ V-SMOW) is similar to that of sulphate dissolved in seawater. 87Sr/86Sr from speleothems (0.708665–0.708976) suggests that the main source of Ca is seawater, but additional Ca contributions from aeolian dust have reduced the Sr isotope values. These data support the idea that gypsum precipitates in the lava tube by evaporation of marine spray or solutions derived from marine spray. Two probable vias for ions input into the lava tube are considered: 1) sea spray circulating through the lava tube; 2) low-frequency rain infiltration leaching the marine spray salts precipitated at the surface. The constant supply of ions from sea spray, air currents in the cave, and the fast, but partial, evaporation due to the high relative humidity in the lava tube favours accumulation of major amounts of gypsum and subordinately halite. Scarcity of precipitation in the western Canary Islands prevents dissolution of gypsum speleothems.
Geoquímica isotópica (δ18O yδ13C) de los espeleotemas de aragonito, calcita y dolomita de la Cueva de Castañar de Ibor (Cáceres)
(Geotemas, 2008) Martín Pérez, Andrea; Martín García, Rebeca; Alonso Zarza, Ana María
En la cueva de Castañar de Ibor (Cáceres), aparecen una gran variedad de espeleotemas de aragonito, calcita, dolomita, huntita y magnesita. Muchos de estos minerales son de origen primario, pero también se han observado transformaciones diagenéticas recientes como disolución, micritización, inversión aragonito–calcita y dolomitización. En este contexto se ha realizado un estudio preliminar de los isótopos estables de algunos espeleotemas centrándonos en los que son de calcita, aragonito y dolomita, para ver si su composición isotópica puede aportar datos sobre sus condiciones de formación y transformación. Se observa un enriquecimiento en isótopos pesados en las muestras de aragonito respecto a la calcita, lo cual es indicativo de la formación del aragonito a partir de soluciones más enriquecidas en isótopos pesados que la calcita. La dolomita presenta también valores más altos en δ18O, sin embargo, se produce un enriquecimiento en isótopos ligeros del δ13C lo cual podría ser explicado por una posible participación de actividad orgánica en su formación. [ABSTRACT] In Castañar de Ibor cave (Cáceres), aragonite, calcite, dolomite, huntite and magnesite speleothems are found. These minerals can be primary in origin, but also suffer recent diagenetic processes such as dissolution, micritization, aragonite-calcite inversion or dolomitization. In this context, a preliminary study of stable isotope has been done focusing on calcite, aragonite and dolomite, in order to check if their isotopic geochemistry can help to understand their formation and transformation conditions. The aragonite is a little more enriched in the heavy isotopes than the calcite. This indicates that aragonite precipitated from waters enriched in δ18O and δ13C. Dolomite shows higher values in δ18O as well, but there is a lighter value for 13C, what may indicate organic activity.