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

Full item page

Search Results

Now showing 1 - 10 of 28

Significado paleoambiental de los ooides y oncoides de las calizas del Barranco de Azuaje (Gran Canaria)
(Geogaceta, 2024) Rodríguez Berriguete, Álvaro; Alonso Zarza, Ana María; Martín García, Rebeca; Martín Pérez, Andrea
Diversos tipos de ooides y oncoides se encuentran en travertinos y tobas a lo largo de 3 km del Barranco de Azuaje (Gran Canaria). Los ooides muestran formas esféricas a elipsoidales, de 0,1 mm->2 mm de tamaño, y envueltas concéntricas regulares. Los oncoides son de 0,4 mm a varios milímetros en general, con laminación. La mineralogía es aragonítica y aragonítica-calcítica en travertinos, y calcitítica en tobas. Los núcleos son intraclastos, moldes de partes de plantas o son indistinguibles de las envueltas. Las láminas de granos con envueltas aparecen comúnmente pasando a estromatolitos, pero también a otras facies (rafts, tallos colgantes, briófitas, etc.). En general, y considerando las características de núcleos y envueltas, asociaciones de facies y su distribución, los depósitos de ooides y oncoides representarían etapas diferentes de: (a) disponibilidad de partículas sueltas que sirven como núcleos, (b) formación de envueltas, (c) inmovilización de los granos y (d) fosilización del depósito por la formación de costras sobre el mismo. Todas estas etapas estarían relacionadas con condiciones físicas, químicas y biológicas específicas y sus variaciones, relacionadas con la dinámica sedimentaria del barranco.
Diagenesis of continental carbonate country rocks underlying surficial travertine spring deposits
(Quaternary International, 2017) Rodríguez Berriguete, Álvaro; Alonso Zarza, Ana María; Martín García, Rebeca
Diagenesis of Miocene-Pliocene continental rocks in extensional Teruel Basin related to deposition of a travertine at surface has been studied. Most of the diagenetic processes described here are in relation tothe travertine deposition, so they are not widespread along the basin. Due to their high induration degreethese rocks may be misinterpreted with travertine/tufa facies, so there is a need of clear criteria for their recognition as they can supply important hydrological and paleoenvironmental information. The diagenetic processes, that deeply modified the substrate, include dissolution, recrystallization and cementation and lead to a high induration of the Miocene-Pliocene rocks. These processes were driven by groundwater flow leading to travertine deposition at surface and appeared to be closely related to the fluvial incision of Alfambra River and to extensional fracturation during Middle Pleistocene times probably under humid conditions. The cementation sequences and the organization of fractures and vadose micrite point to alternating vadose-phreatic conditions and syndiagenetic movements of the faults. Isotopic signal show lighter d18O than that of the unaltered Miocene-Pliocene rocks and similar d13C, suggesting lighter oxygen signal in waters during interglacial Pleistocene periods, and a common origin for carbon from marine Mesozoic rocks from the substrate of the basin. All of that suggest the strong control of tectonics, and climate at different timescales in diagenesis of the rocks serving as substrate for surficial travertine deposition.
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.
Features and Origin of Red Clays in Castafiar Cave: A Touch of Colour
(Advances in Research in Karst Media, 2010) Martín Pérez, Andrea; Martín García, Rebeca; Alonso Zarza, Ana María; Herrero Fernández, María Josefa; Andreo, Bartolomé; Carrasco, Francisco; Durán, Juan José; LaMoreaux, James W.
In Castaiiar Cave (Caceres, Spain), coatings of red clays cover the walls of the chambers, coexisting with diverse speleothems of aragonite, calcite, huntite and dolomite. The mineralogy of the clays is mainly illite, chlorite, kaolinite, smectite, quartz and Fe oxides and hydroxides such as goethite. They can be transported into the cave by infiltration waters or form by in situ alteration of the host rock: layers of dolomite rich in Fe and magnesite interbedded with greywackes and shales. Present-day hydrological conditions in the cave and conditions during the formation of speleothems have determined that the clays have not been transported by any flooding or seepage, but mostly staying in situ, and not included into carbonate crystal forms . Thus, most of the well-preserved speleothems are white and not stained, conforming an interesting chromatic contrast with the red clays that represent an additional attraction in this show cave.
Loss of primary texture and geochemical signatures in speleothems due to diagenesis: Evidences from Castañar Cave, Spain
(Sedimentary geology, 2009) Martín García, Rebeca; Alonso Zarza, Ana María; Martín Pérez, Andrea
Geochemical signals from speleothems are commonly used in the investigation of palaeoenvironments. In most cases, however, little attention is paid to whether or not these signals are primary or altered by diagenesis. The speleothems of the Castañar Cave (Cáceres, Spain), which are initially formed of calcite or aragonite, have undergone a variety of meteoric diagenetic processes such as micritization and neomorphism (inversion), that collectively modify their primary features (textures, mineralogy, geochemical signals). The mean δ13C and δ18O values of the aragonites in the cave are −8.66 and −4.64 respectively, whereas the primary calcites have mean δ13C and δ18O values of −9.99 and −5.77, respectively. Following the diagenetic process of micritization, the aragonite isotopic signals averaged −7.63 δ13C and −4.74 δ18O and the calcite micrite signals −9.53 δ13C and −5.21 δ18O. Where inversion took place, some secondary calcites after the aragonite show preserved aragonite, whereas others do not. The secondary calcites without aragonite relics show isotopic values slightly higher than those of the primary calcite due to the inheritance of the aragonite signal. Where aragonite relics are preserved, the isotopic signatures are very similar to those of the aragonite micrite. In addition, the stable isotopic values and Sr and Mg contents of the speleothems became also modified by micritization and/or inversion. These diagenetic processes were driven by the changes in composition of the cave waters over time and space, but also, in the case of aragonite, by its initial unstable mineralogy. The present results highlight how important diagenesis is in caves and how the initial features of cave minerals may be lost. These changes alter the geochemical signals shown by speleothems, which may have an impact on the interpretation of the results obtained in palaeoenvironmental studies.
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.
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.
Stability assessment of shallow limestone caves through an empirical approach: application of the stability graph methodto the Castañar Cave study site (Spain)
(Bulletin of Engineering Geology and the Environment, 2016) Jordá Bordehore, Luis Jordá; Martín García, Rebeca; Alonso Zarza, Ana María; Jordá Bordehore, Rafael; Romero Crespo, Paola Leonor
The Castañar Cave (central W Spain) was formed within mixed carbonate-siliciclastic rocks of the Neoproterozoic age. The host rock is finely bedded and presents 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 was formed more than 350,000 years ago as a result of the dissolution of interbedded carbonates along with weathering of siliciclastic beds, which also promoted the collapse of the overlying host rock. Currently, it is a vadose cave, but its initial development could have been phreatic. The cave is well known for the outstanding quality of its aragonite speleothems. At present, the cave only receives restricted scientific and educational visits, and therefore it is advisable to perform a preliminary stability assessment through the application of internationally accepted engineering criteria for the evaluation of underground space stability. The aim of this study is to apply engineering rock mass classifications and an empirical approach for tunneling design to the preliminary assessment of karstic caves. The stability of some of the rooms was assessed by the stability graph method, widely used to analyze polyhedral mining rooms, but there are no existing references for its application to karstic caves. The stability of karstic caves can be assessed similarly to man-made excavations, but due to its geological heritage, recognition must always be non destructive. Geotechnical observation points are useful tools fulfill this requisite, and have been applied to the Castañar Cave. The Q index and the stability graph method have both proven to be useful, but due to the polyhedral shape of the cave, the Stability Graph technique has presented more realistic results.
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
Unravelling calcrete environmental controls in volcanic islands, Gran Canaria Island, Spain
(Palaeogeography, Palaeoclimatology, Palaeoecology, 2020) Alonso Zarza, Ana María; Rodríguez Berriguete, Álvaro; Martín Pérez, Andrea; Martín García, Rebeca; Menéndez, Inmaculada; Mangas, José
Volcanic islands are unique contexts to analyze the controls on calcrete development in settings with varied relief, climate and vegetation, and lacking carbonate host rocks. This paper discusses the formation of Quaternary calcrete profiles in Gran Canaria volcanic Island, under direct influence of the SAL (Saharian Air Layer). Calcrete profiles are multi-storey and composed of prismatic, massive, laminar, pisolithic, ooid-bearing, sandy mudstones with rhizoliths and brecciated horizons. Host rocks include basalts, siliceous mudstones, volcanic sands and gravels and bioclastic-rich sands. Carbonate is mostly calcite but some dolomite occurs in massive horizons. The main microfabrics include laminated micrite, fine crystalline dolomite, desiccated micrite, micrite-clay groundmass, oriented Mg-rich clays, peloids, spherulites and coated grains. δ13C varies from −3.26 to −9.18‰ VPDB and δ18O from +0.86 to −3.24‰ VPDB. The 87Sr/86Sr ratios are between 0.707504 and 0.708860, indicating that calcium was mostly supplied from the CaCO3-rich aeolian dust coming from the Sahara Desert. Calcrete profiles are mostly pedogenic with roots and microorganisms enabling carbonate precipitation within the soils. The correlation trend of δ13C and δ18O points to a climate control on precipitation, with the heavier isotope values in the horizons containing dolomite. Sedimentation rates interplayed with calcrete formation processes and erosion to outline the profiles/horizons. Amalgamated laminar horizons formed when the rate of calcrete formation was higher than sedimentation and erosion, whereas areas or periods with relatively higher sedimentation allowed the separation of calcrete horizons. The direction of the winds supplying aeolian dust, and the varied relief, vegetation and climate favored better development of calcretes in the relatively arid and lowland areas of the eastern side of the island. Our study shows that calcretes contain the record of the paleoenvironmental controls that operated in volcanic islands with no previous carbonate substrates.