Physical-mechanical behavior of fresh and completely altered rocks as an important factor of slope instability in the El Rosario Monarch Butterfly Sanctuary, Michoacán, Mexico

Slope instability in the Butterfly Biosphere Reserve (RBMM) Michoacán, Mexico, is a widespread phenomenon that results from the complex interaction among different factors such as climate, slope, and the spatial distribution of different rock units. The climate is temperate subhumid, with rains in summer and an annual average rainfall of 700 to 1250 mm. The main physiographic units of the area are volcanic mountains, with slopes greater than 30 degrees. The main scope of this study is to characterize the physical-mechanical properties of fresh and completely altered lower Miocene andesitic lavas of the Sierra de Angangueo (Cerro El Campanario, province of El Rosario, Michoacán) by implementing laboratory tests (bulk density, permeability, porosity, uniaxial compressive strength). The fresh rock sample presents total porosity, permeability, and UCS values of 0.262 mD, 17.1 %, and 63.5 MPa, respectively. Instead, the altered rock display values of 393.71 mD, 60.9 %, and 0.26 MPa. Our results suggest that the slope and the degradation of the rock properties induced by alteration are the conditioning factors of instability in the region. Atypical rainfalls may act as triggering mechanism for slope failure.

Mobile mud layer underneath the desiccated maar lake of Rincón de Parangueo and insights into its microbial fingerprints

We surveyed a subsurface layer of saturated mobile mud and its microbial fingerprints below the desiccated bottom of a maar lake at Rincón de Parangueo (RP), Mexico. A multi-scale approach was followed using geological fieldwork, coring of the sediments, ground penetrating radar survey, physico-chemical characterization including X-ray diffraction and scanning electron microscope, and high-throughput DNA sequencing methods. The mobile mud is an organic-rich silty clay, with high values of alkalinity, volumetric water content and conductivity. Mud mobility has been attributed to overpressure caused by disequilibrium compaction of sediments related to active subsidence and pore overpressure produced by an input of groundwater and gas content in the sediments and resulted in a diverse set of structures related to mud tectonics such as injection domes and fluid seeps through fractures. Extraction and sequencing of sedimentary environmental DNA in the mud layer were performed for Bacteria and Archaea. Despite the small number of samples obtained, the microbial fingerprint from the sedimentary environmental DNA at subsurface shares similarities with the microbial communities identified on the crater surface. Additionally, we identify the DNA of specific methanogenic microorganisms in the mud, such as Bathyarchaeia, Methanomassiliicoccales, and Methanobacteriales, and we speculate on their probable role in gas production and pore overpressure in the mud layer. The underground mud at Rincón de Parangueo represents a geologically dynamic environment with conditions that are favorable for the thriving of microbial communities.

Deformación frágil en rocas del Mioceno de la región Morelia-Cuitzeo, Michoacán: implicaciones en el sistema geotérmico local

La deformación frágil se relaciona con la presencia de fallas y fracturas que afectan a la corteza superior de la Tierra. La distribución que tiene la deformación frágil y el arreglo que presentan las fallas y fracturas son variables poco conocidas, a pesar de que tienen una gran influencia en la generación de permeabilidad y son importantes para entender fenómenos como la deformación localizada. En este trabajo se explora la distribución de la deformación frágil y el arreglo de las fracturas que afectan a rocas andesíticas del Mioceno en el área de Morelia-Cuitzeo mediante un análisis cuantitativo de la deformación a escala mesoscópica. Las rocas miocénicas del área de estudio están afectadas por dos familias de fracturas (F1 y F2) relacionadas con dos eventos de deformación frágil (D1 y D2) ocurridos entre el Mioceno y el Holoceno. Las fracturas F1 tienen un rumbo preferencial NNW-SSE y acomodan una extensión ENE-WSW de ~2.5 %. Por otro lado, las fracturas F2 cortan a las fracturas F1, tienen un rumbo ENE-WSW y se relacionan con una extensión ~N-S de 6.8 %. Ambas familias de fracturas tienen un arreglo de fracturas agrupadas y una intensidad de fracturas promedio similar de aproximadamente 17 fracturas/metro. Este comportamiento en la intensidad de fracturas, ante una cantidad de deformación por extensión distinta, se atribuye al tipo de roca. La cantidad de extensión asociada a las dos familias de fracturas se distribuye de manera heterogénea en las rocas, lo que contribuye de manera significativa con la porosidad secundaria (porosidad de fracturas). Adicionalmente, la cantidad y el arreglo de las fracturas sugieren que las rocas miocénicas pueden ser la capa permeable del sistema geotérmico de la zona del lago de Cuitzeo.

Geology and geochemistry of jasperoids from the ‘Montaña de Manganeso’ district, San Luis Potosí, north-central Mexico

Large outcrops of jasperoids occur in the ‘Montaña de Manganeso’ mining district in north-central Mexico. They range from massive manganiferous jasperoids to highly brecciated, hematitic jasperoid. The jasperoids of ‘Montaña de Manganeso’ occur mainly as replacements of limestone, sandstone and shale, commonly nearby high-angle fault systems. The mineralogy of the jasperoids consist of quartz and its polymorphs (chalcedony, tridymite and cristobalite), Fe-Mn oxyhydroxides, calcite and minor barite. Many outcrops show evidence of several periods of brecciation and silicification. The geochemical signature of the jasperoids suggests that silicification was product of hydrothermal activity. The jasperoids display enrichment in elements of hydrothermal provenance such as Ba, Sr, As, Cr, Mo, Sb, Ni, Zn and Cu, whereas are strongly depleted in the elements indicative of clastic sources such as Ti, K, Th and Zr. Element ratios such as (Fe+Mn)/Ti, Al/(Al+Fe+Mn), Fe/Mn and U /Th, along with the Al-Fe-Mn and Fe-Mn-(Ni+Co+Cu)×10 ternary diagrams confirm a hydrothermal origin. Low ∑REE, an enrichment of LREE over HREE, negative Ce anomalies and positive Y anomalies (YPASS/HoPAAS) also support the hydrothermal processes. The geological evidence, in the form of a feeder zone and extensive hydrothermal alteration, show that the silica forming the rocks originated from ascending hot fluids.

Sewage sludge from Taxco de Alarcón wastewater treatment plant as substrate to cultivate Panicum maximum

The management and disposal of the sewage sludge (SS) generated by a wastewater treatment plant (WWTP) as part of the municipal wastewater (MWW) treatment process is one of the main socio-environmental issues faced by this type of system. Taxco de Alarcón, Guerrero, in southern Mexico has had a WWTP operating since 2016, and the SS disposal is a task that must be addressed by the WWTP. Thus, the aim of this work was to evaluate the growth capacity of Panicum maximum, also known as mombaza grass (MG), by using SS generated within the "Taxco de Alarcón wastewater treatment plant" as substrate. To do so, 4 g of MG seeds were scattered over 5 kg (dry basis) of SS. As a control, a commercial compost soil was used, hereafter called pattern soil (PS). The experiment was carried out in triplicates for three months and drinking water (water used for human consumption) was used for crop irrigation. Each month a MG harvest was carried out. The response variables analyzed for MG were germination time (one month after plant emergence), height (HMG), growth rate GrMG, and yield (YMG), whereas in the SS and PS the content of organic matter was analyzed. Furthermore, the chemical composition was analyzed using scanning electron microscopy and X-ray energy dispersion spectroscopy (SEM-EDS) on the MG, SS, and PS. The results showed that MG germinated faster on PS (5 days) than germination on SS (7 days). However, the MG grown on SS reached a considerably higher height (45 cm) compared to the height reached on PS (17 cm). Furthermore, the maximum GrMG over SS was also higher than the maximum GrMG observed on the PS, 3.64 and 1.40 cm∙day-1, respectively. In terms of YMG, it was observed that on SS it reached an average monthly YMG of 416 g∙m-2, whereas in PS it reached a YMG of 72 g∙m-2. The chemical analysis detected P, K, Ca, Mg, and S, considered macronutrients in both substrates. Besides, some micronutrients identified in SS were Cu, Fe, Mn, and Zn, whereas in PS it was also possible to detect micronutrients except Mn and Zn. All the macronutrients detected in the substrates were observed in the harvested MG. However, in the MG harvested in PS, Mn and Zn were not detected. Hence, a feasible disposal strategy for the SS generated by the Taxco de Alarcón WWTP is as a substrate for grass forage MG by its high organic matter content, the significant presence of macro and micronutrients, and the performance shown by MG cultivated in SS. Furthermore, the SS characteristics provide added value and can be considered as organic amendments of agricultural soils.

Silicic magmas in the Michoacán-Guanajuato Volcanic Field: an overview about plumbing systems, crustal storage and genesis processes

The origin of silicic rocks in the Michoacán-Guanajuato volcanic field (MGVF) has been understudied since the volcanic field attracted the attention of researchers. Using geochemical, petrological and structural data from the literature, here we propose a model for the origin of silicic magmas. We found that all volcanic rocks known to date in the MGVF can be divided in 40 % andesite, 33 % basaltic andesite, 15 % basalt, 2 % trachybasalt to trachyandesite, and 10 % dacite-rhyolite. The structural systems that deformed the crust in the MGVF are NNW-SSE-oriented normal faults of the Taxco-San Miguel de Allende fault system, developed during the Oligocene, and the Morelia-Acambay fault system consisting of ENE-SSW to E-W sinistral strike-slip faults developed during the Oligocene-Miocene. In addition to bibliographic data, we present a gravimetric-magnetometric model to investigate the characteristics of the local basement where magmas acquire their final silicic composition, and a seismic tomography model to investigate the deep plumbing system that contribute to form the silicic rocks emplaced on the surface. The only report of assimilation experiments we found in the MGVF literature suggest that plagioclase and pyroxene are more easily digested than quartz by hotter magmas. The digestion of these mineral phases has a direct consequence on the generation of dacites and rhyolites. We propose that regardless of the genesis of andesitic melts, such intermediate magmas arrive to the upper-crust and are forced to evolve within local compression zones where they melt the local granitic basement and form crystal mushes. The compositional variability of silicic rocks in the MGVF is a consequence of the variable mixing between the intermediate magmas and the granitic partial melts.

Spherical data validation of rock discontinuities orientation from Drone-derived 3D Point Clouds

This work presents a methodology for the statistical validation of discontinuity surfaces obtained from point clouds using digital photogrammetry from drones. Our methodology allows you to review the quality of the data obtained with photogrammetry and decide whether these measurements are representative of the discontinuity surfaces that they analyze. It consists of three steps, the first one being a shape analysis that allows defining which statistical model should be used: Fisher for circularly symmetric clusters or Bingham fits better for axially symmetric clusters. This step also makes the most significant difference to other works since our methodology starts from the premise that not all discontinuity surfaces are flat. Therefore, Fisher parameters do not allow validating data that do not correspond to a plane. In the second step of the methodology, we calculate the consistency parameters that depend on the statistical model defined in step 1. The parameters are similar for both models; both estimate κ which indicates how much the sample is concentrated around the mean orientation and validates the existence of this and which is the value of the generating angle of a cone with a 95 % confidence limit that it contains within the mean orientation. Finally, step 3 is used when there are control measurements to compare the point cloud data and define if both samples characterize the same discontinuity surface in the rock mass. The results obtained on a rock outcrop allowed us to observe that the measurements obtained from the drone faithfully represent the discontinuity surface analyzed when these were compared with the measurements made manually with the compass. Furthermore, the dispersion parameters (

Evidencias geológicas, geomorfológicas y geofísicas de deformación asociada a la falla Cerritos y su implicación en el peligro sísmico de Morelia, Michoacán, México

La falla Cerritos pertenece a la porción oeste del Sistema de Fallas Morelia-Acambay, ubicada al suroeste de la ciudad de Morelia, en el estado de Michoacán, México; es una zona con alta densidad de fallas activas con geometrías segmentadas y arreglos en échelon, donde se han desarrollado semi-grabens y grabens de dimensiones variables que inclusive influyen en el alineamiento y distribución del vulcanismo monogenético holocénico. En la superficie, estas fallas afectan unidades litológicas de edades miocénicas hasta suelos modernos. Debido a la peligrosidad sísmica que se ha reportado para algunas de las fallas de Morelia, se realizó un análisis interdisciplinario de la falla Cerritos, que había permanecido poco estudiada hasta la fecha. La falla Cerritos es una falla normal con una ligera componente lateral izquierda, una longitud de 12 km y un relieve topográfico bien definido de 130±5 m (100 m de desplazamiento visible + 30 m de desplazamiento subsuperficial obtenido por el estudio de resistividad invertida). Esta falla muestra un rumbo ENE-OSO (255°) y un echado de 76° hacia el NNO. En un afloramiento de la falla Cerritos, a unos cuantos metros del trazo de falla principal, se identificó una cuña coluvial con abundante materia orgánica, fechada con el método de radiocarbono en 3.37–3.21 cal ka AP. El análisis geológico y geomorfológico de la falla reveló que es una estructura tectónicamente activa, relativamente joven y con índices geomórficos que indican mayor actividad en su sector oriental. El escarpe y la acumulación de sedimentos lacustres en el bloque caído sugieren movimiento activo vertical (levantamiento y subsidencia, respectivamente) a lo largo de esta falla. Los resultados obtenidos mediante los análisis de sísmica de refracción, tomografía de resistividad eléctrica y magnetometría terrestre revelaron la geometría de la falla en profundidad, en donde sobresale la presencia de un plano principal lístrico y una zona de deformación en el bloque caído que se extiende en superficie hasta 75 m desde el pie del escarpe principal. Esta zona de deformación se caracteriza por la formación de anticlinales tipo roll-over y dos grabens de colapso crestal delimitados por estructuras secundarias, los cuales funcionan como depocentros de materiales clásticos y bloques caídos. Finalmente, el análisis de actividad y potencialidad indicó que esta estructura tiene tasas de desplazamiento de 0.03±0.01 mm/año, con desplazamientos verticales promedio de 0.5 m por evento, y un tiempo de recurrencia promedio de 16700 años. La Falla Cerritos tiene la capacidad de producir eventos de ruptura con magnitudes de Mw 6.2 a 6.6 por sí sola, o bien, puede interaccionar en un evento extremo con las fallas adyacentes Morelia y Cointzio, produciendo eventos de ruptura multi-falla con magnitudes de hasta Mw 6.9.

Revisión de datos paleomagnéticos de flujos de lava asociados al Campo Volcánico Michoacán Guanajuato: implicaciones sobre el comportamiento del campo magnético terrestre durante el Plio-Cuaternario

La disponibilidad de edades radiométricas para el Campo Volcánico Michoacán-Guanajuato permite obtener un registro detallado de las variaciones del campo magnético de la Tierra durante los últimos 5 Ma. En el presente trabajo, analizamos 112 direcciones paleomagnéticas confiables respaldadas por igual número de edades radiométricas absolutas. Luego de descartar las polaridades geomagnéticas transicionales siguiendo el criterio de paleolatitudes menores a 45°, se calcularon las direcciones paleomagnéticas medias globales. En términos generales, se observa que la dirección media concuerda, dentro del intervalo de incertidumbres, con las direcciones paleomagnéticas esperadas obtenidas según los polos de referencia Plioceno-Cuaternario. La tasa de variación secular, estimada a través de la dispersión de los polos geomagnéticos virtuales calculados, y la anomalía de inclinación coinciden con los modelos de distribución latitudinal reportados para la latitud de 20° N. Un hallazgo interesante, resultado de esta compilación de direcciones paleomagnéticas, es la posible evidencia de eventos geomagnéticos relativamente cortos o excursiones dentro de los Crones de Matuyama y Brunhes, los cuales pueden ayudar a refinar la escala de tiempo de inestabilidad geomagnética. Además, se presenta una compilación inédita y una descripción minuciosa de más de 1000 aparatos volcánicos realizada por el Dr. Víctor Hugo Garduño Monroy que, sin duda alguna, servirá como una guía para los estudios paleomagnéticos durante las siguientes décadas.

Errata a Fauna de tiburones y rayas de la Formación Tirabuzón (Plioceno) en el Cañón El Álamo, sierras de La Reforma – El Aguajito, Baja California Sur, México [Rev. Mex. Cienc. Geol., 37-1 (2020), 40-63]

En el artículo indicado arriba se omitieron de modo no intencionado las Tablas 1 y 2. Estas tablas se reproducen continuación y han sido anexadas al artículo original. Los editores lamentan la omisión.