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The diversity of diatoms in the hot springs of the Comanjilla geothermal zone in northern Guanajuato, Mexico was studied. Hot springs are extreme ecosystems that, despite having high temperatures, constitute an environment for many thermophilic microorganisms (bacteria, cyanobacteria, and diatoms). The thermal water studied is classified as hyperthermal water (45°C to 100°C), of deep origin, and with low mineralization, are of type sulfuric sodium chloride, since the dissolved content of hydrogen sulfide (H2S) is found in concentrations higher than 1mg/L, and its smell is similar to the one of rotten eggs, presents a pH of 7.6 to 9.1 that represents neutrophilic to alkaliphilic environments, with a variable electrical conductivity (EC) (658-698 µs / cm) and total dissolved solids (TDS) (314-24 ppm). In the same way, these hot springs present microbial mats that consist of several stratified layers of green and orange color of 100 cm2, each one, which are dominated by specific types of microorganisms such as bacteria, cyanobacteria, but mainly diatoms, the latter were studied applying the scanning electron microscope and the optical microscope. The morphological characteristics observed in the optical microscope and in the scanning electron microscopy indicate the presence of diatoms of the Bacillariophyceae class, represented by Sellaphora disjuncta (55%), Achnanthes brevipes var. intermedia (45%). This diatom present in thermophilic microbial mats in the sulphurous geothermal zone of Comanjilla represents: a) the first report of said microorganisms in the study area and Mexico; b) an ecosystem of great interest from the biotechnological and industrial point of view; c) an important taxon in terms of diversity and technology; d) an applications in biofuels, environmental monitoring, wastewater treatment, manufacture of fertilizers, production of secondary metabolites, medical compounds, energy sources and food industry and within nanotechnology. It is important to mention that the physical and chemical characteristics of thermal water such as temperature, pH, dissolved solids, electrical conductivity, hardness, alkalinity and silica concentrations, were the major environmental factors influencing the distribution of diatoms in sulphurous hot springs.

We present a geological map that shows the distribution of Cenozoic igneous rocks in the central portion of the Tampico-Misantla Basin in eastern Mexico at 1:500,000 scale. This map covers an area of ~25000 km2, including part of the States of Veracruz, Hidalgo, and Puebla. It was made as background information for the geophysical exploration of the CONACYT Fronteras de la Ciencia project 1787 “Un acercamiento a los Yacimientos no Convencionales a partir de Métodos Electromagnéticos de exploración”. This map resulted from the compilation of cartographic and geochronological (28 K-Ar isotopic ages) information from available literature, complemented and improved with photogeology and regional reconnaissance tours along several roads that cross the region. Main Cenozoic units were recognized during fieldwork. Particular emphasis was placed on identifying igneous rocks, especially intrusive bodies, as this was one of the main goals of the CONACYT Project, by using geophysical methods, and characterizing the geometry of the basin. The map is now available to the community interested in the Cenozoic evolution of east-central Mexico. Besides that, it will be the basis of the research that the group is carrying out in the Eastern Mexican Alkaline Province and the eastern Sierra Madre Oriental Cenozoic magmatism.

Four different consolidants for adobe buildings conservation were synthetized and evaluated. Adobe bricks materials tested from several Mining Haciendas of the seventeenth and eighteenth centuries located in Guanajuato, Mexico; these materials were characterized using XRD analysis, granulometry, porosity, moisture content, and mechanical resistance. The four consolidants synthetized are formulations based on TEOS (F1); TEOS with silica nanoparticles (F2); TEOS with PDMS-OH (F3) and hybrid consolidant formed by TEOS, PDMS, and nanoparticle silica (F4). The consolidants were tested and evaluated by porosity changes, absorption, and durability. The results show that colloidal silica improves the fulfill porosity by TEOS gels and the PDMS improves the flexibility on TEOS gel avoiding the crack. Thus, the addition of both components to TEOS gel results as an excellent consolidant treatment to adobe materials.

The characterization of the pre-Hispanic and colonial adobes used in the construction of buildings in Mexico was carried out to know the differences between their processes and manufactures. The eight samples obtained correspond to adobe blocks 0.45 m long x 0.35 m wide and 0.12 m thick, which were part of the interiors of houses, the structure of fences, and hacienda galleys. These samples were investigated using X-ray Diffraction, X-ray Fluorescence, and Scanning Electron Microscopy techniques to determine the morphometry of the material and its chemical and mineralogical composition. Likewise, some analyzes were performed to determine their mechanical properties (simple compressive strength), physical properties (granulometry, solid density, cohesion, plasticity index, porosity, and moisture content), and biological (organic matter content). The results obtained in terms of the granulometric distribution indicate that pre-Hispanic adobe has a higher content of sand than silt-clay and gravel, while the colonial adobes present a low or null content of gravel with a higher content of silt-clays. Regarding the organic matter content, the colonial adobe presents the highest percentages compared to those of the pre-Hispanic adobes. Taking into account the above the pre-Hispanic adobes have better resistance and durability than colonial adobes due to their granulometric distribution, low organic matter content, good cohesion, high plasticity index, and the use of materials found in their natural environment, while the colonial used recycled materials, coming from the economic activity to which the hacienda was dedicated, for example, agriculture, mining, livestock, this has given rise to different manufacturing techniques and construction styles that reflect the state of conservation of buildings throughout the pre-Hispanic and colonial times. The granulometric distribution that pre-Hispanic adobe provides favorable physical and mechanical qualities for any construction technique, so it is recommended to use this formula to manufacture resistant and durable adobe.

This study describes monument-mapping method for detected damages, and verify in qualitative and quantitative way the decay of stone on historical building. Proposes a methodology that woul...

In the present study, the hydrochemical dynamic and the water quality of La Purísima reservoir, Central Mexico, have been determined. The reservoir presents total dissolved solids (TDSs) between 146 and 328 mg L

DBTL as neutral polycondensation catalyst was employed to obtain organic modified silanes (ORMOSILs), which were studied as anticorrosive films for aluminum at saline corrosion. The ORMOSILs were synthesized using TEOS as silica precursor, different alkylalkoxysilanes (trimethoxy(methyl)silane, triethoxy(octyl)silane, 3-aminopropyl(triethoxy)silane and DBTL-catalyst were employed under the free solvent sol–gel process. Results of chemical characterization of ORMOSILs coatings show that under SEM technique coatings have homogenous films, and there are a crosslinking between silica and organic modified under the Infrared spectroscopy and 29Si CPMAS-NMR techniques. On the other hand, Brinell hardness and Pull-Off adhesion tests show that all ORMOSILs increase the aluminum surface hardness between 1 and 10%, and the ORMOSILs critical forces for adhesion are in the range of 106–132 N; therefore, the ORMOSILs coatings have an excellent adhesion to aluminum surface, furthermore, the saline corrosion test shows that organic modified silica avoid the pitting aluminum corrosion; corrosion rate decreases about 60–85%; the anticorrosive behavior according to modified-silica was determined as: SiO2–NH2 > SiO2–Me ∼ SiO2–Octyl.

We assess the element pollution level of water reservoir sediments using environmental magnetism techniques as a novel approach. Although “La Purísima” Water Reservoir is an important source for multiple activities (e.g. recreational, fishing and agricultural) in Guanajuato state, it has been receiving for the last centuries a high load of pollutants by mining extraction, urbanization and land-use change from the Guanajuato Hydrological Basin. The analyses of environmental magnetism, geochemistry, X-ray energy dispersive spectroscopy, scanning electron microscopy and multivariate methods were applied to study sediments from the reservoir and basin. Accordingly, they indicate the presence of iron oxides (magnetite and hematite) and iron sulfides (pyrite and greigite), which evidences relevant differences in particle size and concentration within the water reservoir (median mass-specific magnetic susceptibility χ = 23.2 × 10−8 m3/kg), as well as with respect to the river basin sediments (median χ = 88.8 × 10−8 m3/kg). The highest enrichment factor EF values (median values of EF = 2–10 for As, Co, Ba, Cu, Cd, Ni and EF > 20 for S) are mainly associated with historical mining activities that have led to an enrichment of potentially toxic elements on these water reservoir sediments. We propose the use of concentration and grain size dependent magnetic parameters, i.e. χ, remanent magnetizations and anhysteretic ratios ARM/SIRM and χARM/χ, as proxies for Ba, Co, Cr, Ni, P and Pb pollution in these river and water reservoir sediments. Such parameters allow to evaluate this sedimentary environment, and similar ones, through useful and convenient proxies. Fil: Chaparro, Marcos Adrián Eduardo. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentina Fil: Ramírez Ramírez, Margarita. Universidad de Guanajuato. División Ciencias de la Vida; México Fil: Chaparro, Mauro Alejandro Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Matemática; Argentina Fil: Miranda Avilés, Raúl. Universidad de Guanajuato; México Fil: Puy Alquiza, María Jesús. Universidad de Guanajuato; México Fil: Böhnel, Harald N.. Universidad Nacional Autónoma de México. Centro de Geociencias; México Fil: Zanor, Gabriela Ana. Universidad de Guanajuato. División Ciencias de la Vida; México

espanolLa arquitectura estratigrafica fluvial del Conglomerado Guanajuato en la Sierra de Guanajuato, registra parte del relleno de las cuencas extensionales continentales, formadas durante el Cenozoico, despues de la Orogenia Laramide en la Mesa Central de Mexico. Los estratos de grano grueso del Conglomerado Guanajuato representan el deposito de un canal mayor de 1 a 2 km de ancho por mas de 100 km de largo. Estos depositos comprenden un intervalo conglomeratico de 2000 m de espesor intercalado con depositos de areniscas y lutitas. El analisis de facies indica que el conglomerado Guanajuato se deposito en abanicos aluviales y ambientes fluviales. Las facies del Conglomerado Guanajuato incluyen un conglomerado de matriz arenosa que muestra evidencia de deposicion dominada por la traccion, depositos de flujo de escombros y depositos de flujo hiperconcentrado, interpretados como flujos de gravedad turbulenta, dichos depositos se encuentran intercalados por areniscas con estratificacion horizontal, estratificacion cruzada, ondulitas, marcas de lluvia, flautas, marcas de ranuras, lutitas masivas, lutitas con laminacion paralela y grietas de desecacion. Con base en la asociacion de facies, se determinaron cinco elementos arquitecturales y 14 facies en nueve localidades estudiadas, esto, como resultado de la sedimentacion del Eocene post-Laramide en el sur de la Mesa Central. El Conglomerado Guanajuato se divide en dos miembros: miembro inferior y miembro superior. El miembro inferior sobreyace al conjunto Mesozoico (complejo intrusivo y secuencia eruptiva del arco de Guanajuato) presentando un espesor de entre 700 y 1300 m. El miembro inferior se compone de dos partes: 1) La parte basal incluye capas de conglomerado intercaladas con areniscas y flujos de lava. 2) La parte superior constituida por depositos de flujo de escombros y flujo hiperconcentrado, areniscas y lutitas. El miembro superior se caracteriza por un conglomerado de matriz de clastos soportados intercalados con depositos de areniscas y lutitas. La estratificacion cruzada, imbricacion, clastos aislados, areniscas de grano grueso, indican depositos de un sistema fluvial. La arenisca de grano fino, las marcas de lluvia, la laminacion paralela, las grietas de desecacion, pueden interpretarse como sedimentos de barras laterales depositados por canales de desplazamiento durante las condiciones de flujo bajo. Los patrones de distribucion de los sedimentos y la arquitectura estratigrafica sugieren que el sistema deposicional del Conglomerado Guanajuato corresponde a un ambiente fluvial trenzado para el miembro inferior, mientras que el miembro superior corresponde a un ambiente de abanico aluvial. EnglishThe fluvial stratigraphic architecture of the Cenozoic Guanajuato Conglomerate in the Sierra de Guanajuato records part of the infill of continental extensional basins formed after the Laramide Orogeny in the Mesa Central, Mexico. Coarse-grained strata of the Guanajuato Conglomerate represent the deposit of a major channel belt (1 to 2 km wide by >100 km long). This channel belt deposits comprises a 2000 m-thick conglomeratic interval interbedded with deposits of matrix-supported gravel, sandstones and mudstones. Facies analysis indicates that Guanajuato Conglomerate were deposited in alluvial fans and fluvial environments. Facies of the Guanajuato Conglomerate include sandy matrix conglomerate (that shows evidence of traction-dominated deposition), debris-flow (Gms) and hyperconcentrated-flow deposits (Sgpc) (interpreted as turbulent gravity flows), and sandstones with plane to horizontal stratification and planar and through cross-stratification, ripples, rain mark, flutes, groove marks, and massive mudstones, mudstones with fine lamination and with desiccation cracks. Based on established facies associations, five architectural elements and 14 facies were determined from nine locations as a result of Eocene post-Laramide sedimentation in the southern Mesa Central. The Guanajuato Conglomerate was divided in two members: Lower and Upper members. The Lower Member unconformably overlies a Mesozoic assemblage (intrusive complex and eruptive sequence assemblage and Guanajuato arc assemblage) and has a thickness between 700 and 1300 m. The Lower Member is composed of two parts: 1) The basal portion includes conglomerate layers interbedded with sandstones and lava flows. The upper part of the Lower Member conglomerate is caused by debris-flow and hyperconcentrated-flow, major tabular and lenticular sandstone, and siltstone. The Upper Member is characterized by clast-supported conglomerate interbedded with sandstone-mudstone beds. The crudely stratified, imbrications, pebble clusters, coarse to pebbly sandstone, indicate channel lag deposits within a heavy loaded fluvial system. The finegrained sandstone, rain mark, parallel lamination, desiccation cracks, may be interpreted as side bar sediments deposited by shift channels during lower flow conditions. Sediment distribution patterns and stratigraphic architecture, suggest that the depositional system is a braided fluvial for the Lower Member, while the Upper Member corresponds to alluvial fan environment.

"The colonization of Guanajuato and its environs began in the decade of 1540-1550, when some Spaniards entered the territory of Guanajuato for the purpose of the distribution of ranches, in search of valuable minerals, and to evangelize. In the following years, the silver-gold deposits were discovered. From the earliest records, it can be deduced that the mineral deposits were discovered in about 1552, and more intensely in the year 1557. Mining production generated large amounts of mine tailings. The first mining haciendas were established along the Guanajuato River, promoting the human settlements and development of the city of Guanajuato. The haciendas in Guanajuato were a very well-developed economic system. As they grew up, they became federal states, which were self sufficient with their main objective to benefit from the ore obtained from the mines. The design and architectural style of these haciendas were determined by their activity, so, the material they used for their construction was adobes composed of mud and mine tailings, taken from the surroundings of the Guanajuato River. In this work, we study the physical, mechanical and chemical properties of six samples of adobe bricks, collected from several buildings of the seventeenth and eighteenth centuries in Guanajuato city (Mining Hacienda San Juan Nepomuceno, Mining Hacienda San Jeronimo, Mining Hacienda Duran, Mining Hacienda San Clemente, Mining Hacienda Purisima and Mining Hacienda Rayas) in Mexico. The adobe specimens were investigated by the techniques of Inductively Coupled Plasma MassSpectrometry, X-Ray Diffraction and Scanning Electron Microscopy, in order to know their chemical and mineralogical composition; likewise, some analyzes were performed to determine their mechanical properties (simple compressive strength), physical properties (granulometry, real density, total porosity and moisture content), and biological properties (organic material content). These studies aim to establish a basis of knowledge, essential for the safety assessment of adobe constructions, and to contribute to the conservation of the adobe architecture. The analytical results support that the six adobe samples exhibited different behavior, depending on the property tested. Adobe samples have a higher percentage of fines (70%). According to the Unified Soil Classification System, the adobes studied correspond to silt of low compressibility. Inductively Coupled Plasma Mass Spectrometry analysis showed that adobe bricks share the same chemical composition, varying the concentration of heavy metals (Cu, Be, Zn, Sn, Pb, Ni, Co, V, Sb, Hg and Cr). The Cu, Zn, Pb and Sn presented in the adobes indicate that they were the product of a metallurgical process. The presence of Hg indicates that the method of benefit was by amalgamation used in the sixteenth, seventeenth and eighteenth centuries in the New Spain to obtain silver. With respect to the results obtained in X-Ray Diffraction, we confirmed the presen"

Green volcanic tuff has been used in the construction of very important historic buildings in the city of Guanajuato, Mexico, a UNESCO World Cultural Heritage city since 1988. The chemical and mineralogical composition as well as the physical properties observed in the stone (Loseros tuff) presently used to restore such buildings suggests the need for preventive treatment to delay the decay process. A hybrid formulation based on tetraethyl orthosilicate (TEOS), colloidal silica, and hydroxyl-terminated polydimethylsiloxane (PDMS-OH) has been used to treat the volcanic tuff. Several studies were performed in order to evaluate the properties of the stone after treatment; such as determination of the percentage of formulation deposited, as well as variations in porosity, hardness, and salt crystallization resistance.

Salina de Ambargasta es un sistema playa ubicado en la región subtropical de Sudamérica (29 °S), influenciado por el Sistema Monzónico Sudamericano. Se analizó el registro isotópico de δ13C y δ18O en carbonatos a lo largo de dos núcleos sedimentarios fechados previamente por 14C AMS, a fin de identificar los cambios hidrológicos desde los ca. 45000 años cal. AP hasta la actualidad. Adicionalmente, se calcularon los coeficientes de correlación de Pearson entre los isótopos estables y entre cada isótopo con los valores de Pérdida por Ignición (PPI550 y PPI1000) en los sedimentos. Posterior a un intervalo seco documentado a los ca. 45000 años cal. AP, los valores de δ13Ccarbonatos más negativos (promedio = -5.10 ‰) evidenciaron un periodo más húmedo entre los ca. 39600 y 23600 años cal. AP (MIS 3), que contribuyó al desarrollo de lagunas perennes carbonatadas y efímeras sulfatadas. Por su parte, los valores de δ18Ocarb fueron más positivos (promedio = -2.76 y máximo = 4.86 ‰) sugiriendo periodos sujetos a altas tasas de evaporación. Desde los ca. 23600 años cal. AP al Presente (MIS 2 y MIS 1), los sedimentos presentaron composiciones promedio de δ13Ccarb relativamente más positivas (-4.50 ‰) y valores promedio de δ18Ocarb comparativamente más negativos (-4.35 ‰), reflejando un aporte menor de agua al sistema y una evaporación más baja, respectivamente. A partir de este registro se consideró el inicio del Último Máximo Glacial (UGM) en Ambargasta, definido en el sur de Sudamérica entre los ca. 25000 y 18000 años AP. En la secuencia de la laguna perenne carbonatada (ca. 39600 – 26700 años cal. AP) la existencia de un sistema lacustre hidrológicamente cerrado fue evidenciado por la correlación entre δ13Ccarb y δ18Ocarb (r = 0.62). Las correlaciones entre PPI550 y PPI1000 positivas (laguna carbonatada; r = 0.88; ca. 39600 – 26700 años cal. AP) y negativas (lagunas sulfatadas; r promedio = -0.81; ca. 39600 – 23600 años cal. AP) indicaron altas productividades asociadas a la precipitación de evaporitas durante etapas de concentración evaporítica (excursiones positivas en las relaciones isotópicas). Esta investigación permitió inferir que entre los ca. 39600 y 23600 años cal. AP existió una etapa más húmeda y cálida con respecto al periodo ca. 23600 años cal. AP-Presente en la región de Ambargasta (Argentina central). Este trabajo documentó cambios importantes en la relación Precipitación/Evaporación a lo largo del Pleistoceno tardío y Holoceno, y aportó información clave sobre ventanas de tiempo poco exploradas en el sureste de Sudamérica, que en conjunto permitirán definir patrones regionales de la variabilidad paleoclimática durante el Cuaternario. Salina de Ambargasta is a playa system located at the subtropical region in South America (29°S), and influenced by the South American Monsoon System. The present work analyzed the isotopic records of δ13C and δ18O in carbonates throughout two sedimentary cores, previously dated by 14C AMS, in order to identify hydrological changes from ca. 45000 years cal. BP to the present. Additionally, the Pearson correlation coefficients were inspected among the stable isotopes, and also between each isotope and the Loss on Ignition (LOI550 and LOI1000) values in the sediments. Following a dry phase at ca. 45000 years cal. BP, the most negative isotopic values of δ13Ccarb (average: -5.10‰) reflected a more humid period between ca. 39600 and 23600 years cal. BP (MIS 3) that favored water inflow into perennial carbonate and ephemeral sulfate lakes. Values of δ18Ocarb were more positive (average: 2.76 and maximum: 4.86‰) suggesting periods influenced by high evaporation rates. From ca. 23600 years cal. BP to the present (MIS 2 and MIS 1), average compositions of δ13Ccarb were relatively more positive (-4.50‰), and δ18Ocarb average values were comparatively more negative (-4.35‰), indicating less water input to the system and lower evaporation, respectively. From these records, the beginning of the Last Glacial Maximum (LGM) in Ambargasta is dated between ca. 25000 and 18000 years cal. BP in southern South America. In the sequence of the carbonate perennial lake, the existence of a hydrologically closed lacustrine system (ca. 39600 – 26700 years cal. BP) was revealed by a correlation between δ13Ccarb and δ18Ocarb (r = 0.62). Positive correlations between PPI550 and PPI1000 (carbonate lake; r = 0.88; ca. 39600 – 26,700 years cal. BP) and negative (sulfate lakes; average r = -0.81; ca. 39600 – 23600 years cal. BP) indicated high productivities associated with precipitation of evaporites during evaporative concentration stages (isotope positive excursions). This research allows inferring that between ca. 39600 – 23600 years cal. BP, a more humid and warmer stage occurred with respect to the period between ca. 23600 years cal. BP and the present in the Ambargasta region (central Argentina). This work documents important changes in the Precipitation/Evaporation ratio throughout the Late Pleistocene and Holocene, and provides vital information about time windows practically unexplored in southern South America. Taken together, these allow defining regional patterns of paleoclimatic variability during the Quaternary. Fil: Zanor, Gabriela Ana. Universidad de Guanajuato; México. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Piovano, Eduardo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Ariztegui, Daniel. Universidad de Ginebra; Suiza Fil: Vennemann, Torsten. Universite de Lausanne; Suiza Fil: Martínez Jaime, Oscar A.. Universidad de Guanajuato; México Fil: Puy Alquiza, María Jesús. Universidad de Guanajuato; México

In many mining districts, metal pollutants from mine tailings have historically been dumped into local streams. The purpose of this study was to determine the concentrations of Pb, Cu, Zn, Mo, Sb, Cs, Cr, Sc, Co, Ni, and Li in eight overbank-sediment profiles from the Guanajuato River, in the Guanajuato mining district and to establish geochemical background values using direct and indirect methods. The background levels calculated using the direct method in pristine overbank deposits were similar to or slightly higher than the upper crustal values for Sc, Cr, Co, Ni, Zn, and Mo (17.3, 108.7, 18.7, 44.4, 97.2, and 1.1 mg/kg, respectively). In contrast, levels of Cu, Cs, and Pb were up to two times higher than crustal values (93.1, 11.2, and 37.5 mg/kg, respectively), and the median concentration of Sb was 8.2 mg/kg, up to 20 times the crustal level. These natural anomalies can be explained by the presence of mineral deposits in the Guanajuato mining district. Ni and Cr were provided by the ultramafic rock...

We present new stratigraphic evidence for a migration of the Upper Volcanic Supergroup that formed the Sierra Madre Occidental (SMO) volcanic arc in northwestern Mexico during the Oligocene-Miocene. Particularly we discuss the transition from the frontal arc to the Comondú volcanic arc in Punta Coyote, Baja California Peninsula. This information complements the knowledge of the stratigraphic evolution of the Oligocene-Miocene volcanic arc in Baja California and its correlation with the Upper Volcanic Supergroup of the Sierra Madre Occidental in northwestern Mexico. We present new stratigraphic and sedimentologic data of the volcanosedimentary succession of the lower unit of the Comondú group near of La Paz, Baja California Sur, Mexico, in Punta Coyote. Facies analysis and new 40Ar /39Ar dating allowed to interpret the sedimentary environment and evolution of volcanic pulses in the lower unit of the Comondú group in Punta Coyote. The study area was part of the forearc basin westward to the SMO volcanic arc during the Oligocene to early Miocene. The sedimentary environment of the lower unit of the Comondú group was initially a braided river system that prograded to an alluvial fan environment and three tuffs units: Los Azabaches tuff (30.6±0.4 Ma), La Capilla and El Oro tuffs (22.0±0.4 Ma). The succession studied provides new stratigraphic information related to the evolution of the Oligocene-Miocene volcanic arc in the Baja California Peninsula and its correlation with the Upper Volcanic Supergroup of the SMO in northwestern Mexico.Se presentan nuevos datos sobre la estratigrafía y sedimentología de la sucesión volcanosedimentaria de la Unidad Inferior del Grupo Comondú (UIGC) al noreste de la ciudad de La Paz, en Punta Coyote, Baja California Sur, México. El análisis de facies, así como las nuevas dataciones 40Ar /39Ar permitieron interpretar la evolución del ambiente sedimentario y los pulsos volcánicos de la UIGC en Punta Coyote. De acuerdo al análisis realizado, el área estudiada formó parte de la cuenca de arco delantero al oeste del arco volcánico de la Sierra Madre Occidental durante el Oligoceno inferior al Mioceno inferior. El ambiente sedimentario de la unidad inferior del Grupo Comondú evolucionó inicialmente como un ambiente fluvial trenzado progradando a un ambiente de abanico aluvial donde llegaron a depositarse tres unidades tobáceas: toba los Azabaches (30.6 ± 0.4 Ma), toba La Capilla y toba El Oro (22.0 ± 0.4 Ma). La sucesión estudiada aporta nueva información en relación a la evolución estratigráfica del arco volcánico Oligoceno-Mioceno en la Península de Baja California y su correlación con los depósitos del Supergrupo Volcánico Superior de la Sierra Madre Occidental al noroeste de México.

En este trabajo se analizan los procesos de deterioro que ejercen las comunidades de liquenes en las areniscas siliceas de dos monumentos del siglo XIX y XX de la ciudad de Guanajuato: escalinatas de la Universidad de Guanajuato y la Escuela de Musica de la Universidad de Guanajuato. Ademas de contribuir al conocimiento del deterioro, se aportan datos sobre las especies liquenicas encontradas, las causas de su crecimiento y su papel en el desgaste del material petreo, con la finalidad de implementar medidas de proteccion y prevencion. Se observo la interfase liquen-roca usando tecnicas complementarias como microscopia optica, microscopia electronica de barrido (MEB), microscopia electronica de transmision (MET), metodo analitico de plasma acoplado por induccion (ICP-MS, por sus siglas en ingles) y espectroscopia por energia dispersiva de rayos X (EDS, por sus siglas en ingles). Se identificaron cinco especies de liquenes: Xanthoparmelia mexicana , Xanthoparmelia tasmanica ; Caloplaca aff. brouardii , Caloplaca aff. ludificans y Aspicilia sp. Dichos liquenes penetran de 0.5 µm a 50 µm en el substrato a traves de sus rizinas, ocasionando la disgregacion de minerales en la superficie rocosa (cuarzo, plagioclasa y feldespato). La disgregacion de minerales junto con una disminucion en la concentracion de SiO 2 , Al 2 O 3 , Zn y K 2 O y un aumento en CaO, Fe 2 O 3 y MgO demuestra un proceso de deterioro de los liquenes en los monumentos historicos de la ciudad de Guanajuato.

Este artículo presenta los resultados del estudio sobre la sedimentación, los ambientes sedimentarios, la evolución tectono-sedimentaria y paleogeográfica de los depósitos clásticos pos-Laramide y pre-vulcanismo de la Sierra Madre Occidental en la Sierra de Guanajuato. Los depósitos clásticos rojos analizados corresponden al Conglomerado Guanajuato y al Conglomerado Duarte del Eoceno que fueron depositados en la parte media y distal de abanicos aluviales. Los depósitos estudiados están constituidos de clastos de calizas, granito, andesita, rocas sedimentarias, diorita y piroxenita, que indican la erosión de bloques levantados del complejo basal de la Sierra de Guanajuato (Terreno Guerrero). El análisis composicional y petrográfico de clastos de calizas permitió reconocer calizas de cuenca y calizas de plataforma somera provenientes del complejo basal de la Sierra de Guanajuato (Cuenca Arperos). Las calizas de plataforma somera presentan fragmentos esqueletales de bivalvos, braquiópodos, gasterópodos, equinodermos y foraminíferos bentónicos del Berriasiano-Valanginiano. Los clastos de caliza de plataforma se interpreta que podrían proceder de facies someras limítrofes de la cuenca Arperos, cuyos afloramientos originales actualmente no afloran en la Sierra de Guanajuato.

En el presente trabajo analizamos la estratigrafía fl uvial de sedimentos de planicie de inundación del río Guanajuato, basándonos en la sedimentología, edades 14C y la geoquímica de elementos traza de sucesiones antropogénicas y naturales. Los sedimentos de planicie de inundación naturales o prístinos se depositaron en un ambiente de planicie de inundación entre 7460 ± 40 a. C. (parte inferior) y 500 ± 50 a. C. (parte media). Sobreyaciendo a los depósitos de planicie de inundación naturales se depositaron los sedimentos de planicie de inundación antropogénicos, relacionados con la actividad minera del distrito minero de Guanajuato durante épocas históricas, al menos desde el año1660 ± 40 d. C. La interpretación estratigráfi ca es sustentada con los resultados del análisis de elementos traza, los cuales revelan que los sedimentos antropogénicos contienen valores elevados de Pb, Zn y Cu, así como valores relativamente bajos de Cr y Ni, mientras que los sedimentos naturales tienen un comportamiento inverso, con valores bajos de Pb, Zn, Cu y valores altos de Cr y Ni. La combinación de la estratigrafía y la geoquímica demuestra ser útil en la identifi cación y la discriminación de sedimentos naturales y antropogénicos relacionados con la actividad minera histórica, en el distrito minero de Guanajuato.

Este artículo presenta los resultados del análisis de las facies que constituyen la Caliza Marina Basal depositada en el Mioceno superior en la porción SE de la cuenca de Santa Rosalía, Baja California Sur. La Caliza Marina Basal constituye el miembro inferior de la Formación Boleo que se depositó durante la etapa del proto-Golfo de California. El análisis petrológico y sedimentológico de una de las secciones mejor expuestas en la cuenca, y que denominamos sección El Morro, muestra que la Caliza Marina Basal se presenta en forma de encostramientos de 1 a 6 m de espesor sobre las rocas volcánicas de la Formación Comondú, y está constituida por facies de travertinos masivos, travertinos laminares, travertinos esponjosos, tufas y estromatolitos dómicos. Las facies de travertinos representan un ambiente fluvial, mientras que las tufas se depositaron en un ambiente lagunar costero. Tanto las facies fluviales como lagunares fueron cubiertas por facies de estromatolitos de ambiente marino intermareal. El cambio de ambiente fluvial pasando lateralmente a lagunar y cubierto por facies de ambiente marino intermareal, indica una transgresión que representa la instalación de la primera incursión marina en la cuenca de Santa Rosalía asociada con la apertura del Golfo de California.