Studies of the metallogeny of northwestern Mexico (Baja California to Chihuahua to Durango) at the mining district, geologic province, and regional scale, show that deposit formation and preservation is an intricate interrelationship between magmatism, tectonism, and hydrothermal activity. These are not only complicated by superimposed factors including erosion, enrichment, and cover, but in northern Mexico, tectonic translation as well. Using palinspastic reconstructions the relative positions of geologic units are restored to their pre-extensional configuration. Metallic "belts" are heterogeneous with numerous metal associations and deposit types superimposed in the same area. The reconstructions show that magmatism and mineralization were coeval and coincident. Superimposed environments and processes cover, erode, enrich, and preserve mineralization thus substantially affecting perceived metal distribution. Cover sequences including mid-Tertiary ignimbrites and late Tertiary clastic sediments preserve and commonly conceal mineralization. Mid-Tertiary and older extensional events preserve near surface deposit types (e.g, supergene blankets, Jurassic rift-related deposits). At the Sierra Madre Occidental (SMO) province scale, ore deposit types exhibit enormous variation from adularia sericite-dominated to advanced argillic to closely pluton related. The advanced argillic alteration with gold+/-copper+/-silver deposit types appears related to magmatic centers occurring in both the older (pre-Oligocene) and younger (Oligocene) volcanic sections and is a major focus of this dissertation. Acidic alteration-related deposits make up some of the largest Au occurrences including the Mulatos >2 million ounce gold district. Extensive kaolinitic alteration halos (>8 km²) zoned around a core of vuggy silica and quartz+/-pyrophyllite host enargite-pyrite ores. Sulfide isotopes are near zero δ³⁴S(pyrite) = -5 to -3%; δ³⁴S(enargite) = -6 to -4%) with corresponding barite (δ³⁴S = +18-22%). Phase equilibria and isotopes indicate early pyrophyllite-pyrite ores formed at ∼ 300°C with later barite-pyrite-dickite ores deposited at T = ∼ 260°C. Oxygen and hydrogen isotopes show possible mixing between magmatic and meteoric waters with a late (shallow) meteoric (heavier D, lighter δ¹⁸O) overprint. District tilting (∼ 25°NE) exposes >1.5 km altered section containing two separate centers. Alunite occurs late, rarely and is above pyrophyllite, suggesting a vertical transition in acid sulfate systems.

The response of geomorphic systems to disturbance has been a major focus of geographic research. Nevertheless, because the sensitivity of geomorphic systems to external perturbation is complex, the response of those systems is still poorly understood for many agricultural systems in various geographic settings. This study investigates geomorphic sensitivity and soil erosion under traditional slash-and-burn cultivation. The response of soil erosion to this agricultural practice was investigated in selected plots at different stages of cultivation, representing a chronosequence of slash-and-burn cultivation for the study site. Selected physical and hydrological properties were measured in the field or determined in the laboratory from soil samples obtained from the selected plots. Soil erosion was monitored for the selected plots using bounded runoff plots. Finally, the response of soil erosion to slash-and- burn was assessed at the watershed scale by adapting the Revised Universal Soil Loss Equation to local field conditions. The study results showed that soil’s selected physical and hydrological properties differed according to the age of cultivation. In general, soil properties, such as organic matter, aggregate stability, and infiltration, showed signs of deterioration during the cultivation phase and improvement during the fallow stage of slash-and-burn cultivation. These differences in turn resulted in differences in the erodibility of the soil and the response of soil erosion at the plot scale. The soil erosion rate was observed to be higher during the cultivation stage of slash-and-burn cultivation and lower during the fallow stage. The lowest rate of erosion was recorded in natural forest plots. Overall, soil erosion rates were low considering the study site’s mountainous nature. The results of this study suggest that the response of soil erosion under the practice of slash-and burn cultivation could be minimal in a potentially sensitive humid tropical mountainous environment depending on the specific cover produced, the environmental factors, and the specific cultural management, such as cropping and tilling practices. Maintaining adequate ground cover through cropping and fallow management is the key to keeping soil erosion minimal under the practice of slash-and-burn cultivation in the study area. / text

Décollements are important tectonic elements in thin-skinned fold-thrust belts. However, few studies have addressed the internal structure of décollements because most are deeply buried and internal features typically cannot be resolved in seismic reflection images. Upper Jurassic evaporite exposures in the Potosí uplift of northeastern Mexico provide a unique tectonic window into the décollement of the Laramide-age Sierra Madre Oriental fold belt. In order to constrain the three-dimensional geometry of décollement structures, I mapped a ~20 km2 portion of the décollement at a scale of 1:10,000. I created a new stratigraphy for the décollement interval during mapping, and made detailed structural observations at targeted sites. The ~900 m thick décollement interval consists of gypsum with five carbonate members (up to 120 m thick) and numerous thin (<5 m) carbonate interbeds. These carbonate units delineate map-scale structural patterns and define two structural domains. The middle and upper parts of the décollement in the western domain contain map-scale folds with local map-scale boudinage and thrust faults. The eastern domain exposes the lower part of the décollement, and contains thrust repetitions of carbonate members and a regionally-persistent basal shear zone. These map relationships indicate a stratigraphic variation in structural style. Western domain folds and eastern domain thrust sheets both appear to be related kinematically to overburden folding. In contrast, the basal shear zone accommodated décollement-parallel shear strain in response to overburden translation. Folding and faulting of carbonate members and intervening gypsum units drove localization of simple shear into the basal shear zone, because only the lowermost gypsum interval maintained a favorable orientation sub-parallel to the regional transport direction throughout deformation. This investigation demonstrates that décollements have complex internal structural patterns that are below typical seismic resolution and lateral variations in structural style that cannot be reconstructed from single well cores or small outcrops. Décollement stratigraphy controls variations in strain magnitude within the décollement interval, so that previous models that invoke homogeneous strain within the décollement are incorrect. Complex, laterally-variable structural style and stratigraphic control of strain distribution could be general characteristics of décollements where the décollement interval contains significant contrasts in bed rheology. / text

No description available.

Birds are one of the best studied animal groups in the world but are also amongst the most endangered. The wealth of ecological information has shown habitat protection to be vital to bird biodiversity, but habitat loss and degradation continue to defeat conservationists. / Community-based biodiversity conservation efforts have been recently recognized as an important option for safeguarding ecosystems while reducing land use conflicts arising from the material, cultural and spiritual needs of local inhabitants. Community involvement is particularly critical for conservation in anthropogenic habitats. Few studies have linked the ecological impacts of community land use practices with the auto-ecological requirements of dependent bird species. In this study I examine the conservation possibilities for the endangered Sierra Madre sparrow (Xenospiza baileyi) by considering three basic elements: the ecological requirements of the bird, the effects of traditional land use practices in shaping the habitat, and the economic and social conditions that influence current and future land use decisions. I draw on ecological field studies, on traditional ecological knowledge systems, and studies of the political ecological context that influences local practices. / The studies were carried out from 2000-2003 and employed a combination of ethnographic, participative and spatial-ecological approaches to address human-land interactions and their impacts on the sparrow habitat. Social data were obtained through nine workshops which included site visits, transect walks, participatory mapping, oral histories and semi-structured interviews. Ecological data were obtained from landscape ecology analysis, vegetation post-disturbance assessments and detailed bird's nest-site selection analysis. / Results indicate that local people, principally herders, hold a rich knowledge of fire use to achieve diverse purposes, including pasture renewal, grassland maintenance and grass species selection, and prevention of dangerous fires. In order to accomplish their goals, herders have established rotational fire and grazing regimes that consider timing, frequency, location and extent of these disturbance-based practices. This rotational system was found to benefit the Sierra Madre sparrow by maintaining the grassland at the scales needed by the sparrow for nesting. Multiscale habitat recommendations for the species' conservation were derived from this socio-ecological interaction and dynamics. / Unfortunately, external conservation perspectives and interests and internal land tenure conflicts have altered this rotational regime and local perspectives on resource management that threaten the resilience of this social-ecological system. Consequently, traditional ecological knowledge on grassland management can be on risk of disappearing and, with it, important native grasses and grasslands are being made vulnerable. The survival of the Sierra Madre sparrow in particular and of associated biodiversity in general, is in peril if these conflicts are not solved in a relatively short time. A community-based fire co-management program is recommended to promote integrative bird conservation-local development scenarios.

Many low matrix-porosity hydrocarbon reservoirs are productive because permeability is controlled by natural fractures. The understanding of basic fracture properties is critical in reducing geological risk and therefore reducing well costs and increasing well recovery. Unfortunately, neither geophysics nor borehole methods are, so far, accurate in the acquisition of key fracture attributes, such as density, porosity, spacing and conductivity. This study proposes a new protocol to predict key fracture characteristics of subsurface carbonate rocks and describes how using a relatively low-cost but rock-based method it is possible to obtain accurate geological information from rock samples to predict fracture attributes in nearby but unsampled areas. This methodology is based on the integration of observations of diagenetic fabrics and fracture analyses of carbonate rocks, using outcrops from the Lower Cretaceous Cupido Formation in the Monterrey Salient of the Sierra Madre Oriental, northeastern Mexico. Field observations and petrographic studies of crosscutting relations and fracture-fill mineralogy and texture distinguish six principal coupled fracturing-cementation events. Two fracture events named F1 and F2 are characterized by synkinematic calcite cement that predates D2 regional dolomitization. A third fracture event (F3) is characterized by synkinematic dolomite fill, contemporaneous with D2 dolomitization of host strata. The fourth event (F4) is characterized by synkinematic D3 baroque dolomite; this event postdates D2. The fifth fracture event (F5) is characterized by C3 synkinematic calcite, and postdates D3 dolomite. Finally, flexural slip faulting (F6) is characterized by C3t calcite, and postdates D3 dolomite. Carbon and oxygen stable isotopes were used to validate the paragenetic sequences proposed for the Cupido Formation rocks. The dolomite isotopic signatures are consistent with increasing precipitation temperatures for the various fracture cements, as is expected if fractures grew during progressive burial conditions. Three main groups of calcite cement can be differentiated isotopically. Late calcite cement may have precipitated from cool waters under shallow burial conditions, possibly during exhumation of the SMO. The development of the Structural Diagenetic Petrographic Study protocol, and its integration with geological, geophysical and engineering data, can be applied to oil fields in fractured carbonates such as those located in Mexico, to validate its applicability. / text

The Tarahumara are one of the most isolated and intact indigenous groups in Mexico. Their agriculture has traditionally been practiced within the steep canyons and uplands of the Sierra Madre Occidental in southwestern Chihuahua. Adapting to these rugged conditions, the Tarahumara developed a variety of agricultural techniques that allowed them to be self-sufficient in food production and independent of external inputs. As varied and ingenious as their techniques are, they share one main objective -- to overcome the lack of organic matter in the stony mountain soils. Since the arrival of the Spaniards, the addition of organic matter has involved large amounts of animal manure to increase organic matter in the soil and maintain fertility. The focus of this study is to investigate new agricultural techniques that the Tarahumara are adopting due to the pressures of globalization and alleged climate change. These new technologies may still include many traditional agricultural methods, but they are increasingly using commercially available fertilizers and other modern agricultural additions, thereby losing self-sufficiency. This study includes in depth interviews with 28 Tarahumara farmers to better understand the modern agricultural techniques, their motivations, and overall sustainability. Soil samples determined the viability of Tarahumara agricultural techniques on soil fertility by examining the visual description, organic matter content, soil texture, and a chemical analysis. The analyses showed that traditional Tarahumara agricultural practices are efficient and sustainable, while modern additions are often ill-suited for their environment and are disruptive to Tarahumara culture. / text

Thesis--George-August-Universität. / Spanish summary. Includes bibliographical references (p. 137-142).

Magíster en Ciencias, Mención Geología / En este trabajo de tesis se presentan los resultados de estudio geológico de exploración minera de la zona El Refugio, estos en función de la posible mineralización epitermal de metales preciosos. En esta zona de estudio existen evidencias de alteración hidrotermal (argílica y fílica), donde se ha identificado mineralización aurífera de baja ley en vetas con valores de 0,3 a 0,6 g/t Au. El área de estudio El Refugio se localiza en el flanco oriental de las montañas de la Sierra Madre Occidental, muy cerca del borde con la Mesa Central y dentro de la prolífica faja de mineralización de plata de México. Localmente se ubica en la porción centro-norte del estado de Durango dentro de terrenos de la jurisdicción de los municipios de Rodeo e Indé, y a 150 km al norte en línea recta de la ciudad de Durango. Con el mapeo geológico estructural realizado, a escalas 1:20.000 y 1:2.000, se definieron las estructuras y vetas relacionadas al sistema de fallas San Luis - Tepehuanes con dirección NW-SE y a la distensión que generaron las fosas y pilares donde se localiza el semi-graben de Rodeo. Con las edades U-Pb en circones obtenidas durante el presente trabajo, de 47,8 ± 0,2 y 49,5 ± 0,2 Ma, se interpretan dos edades de cristalización de los cuerpos hipabisales, ubicando a estos en el Eoceno temprano a medio, relacionado regionalmente a las estructuras del sistema de falla San Luis - Tepehuanes y al semi-graben de Rodeo como contemporáneos a estos eventos. Por medio de las dataciones U-Pb realizadas en este trabajo y los emplazamientos de estos cuerpos relacionados a las estructuras mencionadas, se postula que la mineralización del área El Refugio podría estar asociada al emplazamiento de los cuerpos datados Eoceno temprano a medio. La mineralización encontrada en el área El Refugio permite postular un potencial exploratorio por Au-Ag, asociado a ambientes epitermales de metales preciosos. La aseveración anterior es confirmada por estudios de inclusiones fluidas que permiten clasificar los sistemas de vetas en el área de estudio en depósitos epitermales de baja a intermedia sulfuración. Por medio de los estudios geoquímicos mediante ICP-óptico para 31 elementos más oro (Au), por ensaye al fuego, se determinó que el único elemento blanco de exploración es el Au, relacionado a los elementos As y Sb como trazadores. A través de un análisis de factores de estos datos geoquímicos se determinaron los principales factores con más alta implicancia y los cuales agrupan ciertos elementos según su ocurrencia natural. Se determinaron cinco factores. Los factores 1 a 3 reflejan aspectos litológicos y los factores 4 y 5 son representativos de una mineralización de tipo Au-Sb-As. Si bien no existe buena correlación estadística entre Au y Sb-As, estos elementos presentan una relación especial y de ambiente similar, principalmente en vetas y cuerpos hipabisales. El análisis de dispersión del elemento Au, con interés económico, se relaciona directamente al emplazamiento de las vetas del área de estudio con valores que representan anomalías del orden de 0,09 a 0,236 ppm. Además, antecedentes geoquímicos de otros estudios recientes indican que en algunas vetas del área a 0,50 m de profundidad existen leyes del orden de 0,1 a 10,0 g/t de Au y entre 18 y 77 g/t de Ag. Esto permitirá proponer esta zona de estudio, como un potencial prospecto de exploración y programar trabajos de obra directa en los lugares donde las anomalías de contraste positivo presentadas son evidentes. Se recomiendan estudios geológicos de detalle con realización de muestreo en trincheras o zanjas en las vetas.

No description available.