María Jesús Puy-Alquiza

Facies analysis, stratigraphic architecture and depositional environments of the Guanajuato conglomerate in the Sierra de Guanajuato, Mexico

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.

Organic modified silica obtained from DBTL polycondensation catalyst for anticorrosive coating

AbstractDBTL 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. HighlightsDBTL is proposed as poly-condensation catalyst between TEOS and alkylalkoxysilanes for the formation of anticorrosive coating.ORMOSIL increases the hardness of aluminum surface.DBTL forms ceramic hard coating with excellent adhesion.ORMOSIL–DBTL diminishes the corrosion rate at 60–85%.