Revista Mexicana de Ciencias Geológicas

Covers, Revista Mexicana de Ciencias Geológicas, vol. 41, num. 1, April 2024

Revista Mexicana de Ciencias Geológicas — 2024-03-26

Covers, Revista Mexicana de Ciencias Geológicas, vol. 41, num. 1, April 2024

From Meteorite to Meteor-Wrong: Investigating a controversial specimen from Cuba

Yasmani Ceballos-Izquierdo — 2024-03-26

The meteorite “Cuba”, whose type of mass is catalogued as MNCN No. 17294 (Museum of Natural Sciences, Madrid, Spain), has long been considered an official meteorite, included in the Meteoritical Society’s online database. However, the provenance and nature of this metallic object remain uncertain due to inconsistencies in its weight, density, hardness, fall location, and chemical composition. This paper argues that this specimen is not a meteorite by examining its chemical and textural properties using modern analytical techniques and by considering alternative explanations for its origin. The application of scanning electron microscopy and energy-dispersive X-ray spectroscopy has helped to confirm the terrestrial nature of the specimen. These results were compared with a specimen supposed to be a meteorite fragment, and with the other two masses labelled as “Cuba” in other museum collections.

Density, length and connectivity of fractures in a fault zone: the case of the San Miguel de Allende fault

Alberto Vásquez-Serrano — 2024-03-26

We analyze the number, length, distribution, and fracture connectivity associated with the San Miguel de Allende fault (FSMA). For this analysis, we estimated parameters such as density, box dimension, fragmentation dimension, and connectivity. Our results show that within the damage zone of the FSMA, three fracture generation events occurred. The first (D1) is associated with the Late Cretaceous-Paleogene orogenic event and formed subvertical calcite veins with NE-SW and NW-SE orientations. The other two events (D2 and D3) are related to the Cenozoic activity of the FSMA in the Oligocene-Miocene, generating subvertical open fractures, and gypsum and amorphous quartz veins, with NE-SW, NW-SE, and N-S preferential orientations. Fractures in the damage zone are mainly extensional, hybrid, and shear. They have an average density of 3000 fractures/m², a box dimension between 1.31 and 1.84, and a fragmentation dimension between 1.86 and 3.81. Its connectivity exceeds the threshold of 2 connections per fracture (C=2) in the ternary diagram of nodes I, Y, and X, which suggests good connectivity between the fractures, while the parameter F_m, which characterizes the architecture of the fault zone and permeability, shows that the damage zone of the FSM acts as a conduit. Based on our results, we suggest that fracture reactivation is an effective mechanism for strain accommodation and increases the number, connectivity, and permeability of fractures in the damage zones.

Spatial and temporal distribution of palaeoclimatic records in the Maya Area

Haydar Martinez-Dyrzo — 2024-03-26

Palaeoclimatic research has been performed in the Maya Area (MA), using mainly lake sediment cores and speleothems. Most of the studies have been performed in the lowlands, leaving the highlands unexplored. Lake sediments records contain a diversity of proxies (e.g. Mineralogy, isotopes, pollen, charcoal, diatoms, chemicals, magnetic susceptibility, among others) and temporal resolution, making them frequently not easy to compare and leaving numerous gaps of information. Practically all stalagmites are focused on using δ¹⁸O as a proxy of effective rainfall during the Maya periods, having only some explored the role of palaeostorms and hurricanes as well as the paleoclimatology of the pre-Maya and modern periods. In this review paper, the location and temporal frame of palaeoenvironmental records of the MA and their proxies are presented, showing the zones and periods that possess environmental information and assessing their resolution. The comparison shows that more high-resolution records with a multi-proxy approach covering most of the Holocene are needed to understand the climate change in different zones of the MA. Finally, the geographic distribution of the diverse recorded hydroclimate responses based on the records is presented for three critical moments in the Maya History that have been associated with dry periods in the Great Maya Droughts hypothesis. This geographic perspective shows that dry events were not presented in all the MA during these moments although they were vastly recorded in both high- and lowlands. The geographic perspective also shows a negligible drought effect in the central lowlands for the Maya Hiatus period, where this cultural phenomenon was identified first. But signals of droughts are presented in other zones of the MA for this period. The distribution of the drought signal also shows that sites that thrived during the Maya Collapse period were in the regions that suffered the strongest droughts, whilst many sites that were abandoned were in regions rich in hydric resources. Explanations are reviewed for these contradictions. Finally, the works towards the development of mathematical models of the environmental variables are briefly reviewed, pointing out the lack of a proper computational model that has been fed by the palaeoclimatic data developed by the records in the MA.

EDITORIAL, Special Section "20 years of the Centro de Geociencias, Universidad Nacional Autónoma de México"

Susana Alaniz-Álvarez — 2024-03-28

The maturity of a scientific community is manifested in its publications. During 2024 we will transform from the Centro de geociencias (CGEO) to the Instituto de Geociencias of the Universidad Nacional Autónoma de México (UNAM). We wanted to celebrate this step, after 20 years of its creation on the UNAM campus Juriquilla, with the publication of a special section in the Mexican Revista Mexicana de Ciencias Geológicas (RMCG). The RMCG is one of the 39 Mexican scientific journals included in the Journal Citation Report of the Web of Sciences. For the celebration, ten review articles and six frontier science articles have been published over six issues (39-2 to 41-1). The review ones show a synthesis of the work carried out by senior researchers, giving an overview of how knowledge on various topics has advanced to date... (to continue, please download the PDF file).

Glaciological studies in Mexico, 60 years of academic work: A summary

Alejandro Carrillo-Chavez — 2024-03-26

Glaciers have played a very important role in controlling the climate during most of the geologic history of our planet Earth. Of course, the glaciers have always been at higher latitudes (north and south), and some on high-altitude mountains. Current glaciers in Mexico are those inherited from the Last Glacial Maximum, (26000 - 19000 years before the present), increasing in size during the period of the Little Ice Age (1300 to 1850 common era), and they are unique in several ways; they are located at 19° north latitude, and they received snow precipitation from both the Pacific Ocean and the Gulf of Mexico (Atlantic Ocean). Research on glacial chronology, physical glaciology, and glacial geochemistry at Universidad Nacional Autónoma de México has provided valuable information on climate and environmental changes at different time scales, from millennial to decadal, and even annual. The first part of this work deals with the reconstruction of the glacial history in Mexico and establishing a glacial chronology from the Last Glacial Maximum to the Little Ice Age. The second part of this work focuses on monitoring recent changes (the last 60 years, 1960s to 2023) of the glacier extent on Iztaccíhuatl, Popocatépetl, and Citlaltépetl (the three highest mountains in Mexico), as well as having an updated inventory of all the glaciers at those mountains. Changes in glacier extent and thickness of ice are directly related to the increase in air temperature, variation in precipitation patterns, and glacier dynamics on some of the last glaciers of the northern tropics. The third part or this work focuses on a compilation of geochemical data from 17 years (from 2006 to 2013) of sampling ice (shallow ice cores) and snow at Iztaccíhuatl and Citlaltépetl glaciers. This database has the potential for providing interesting and useful information on natural and anthropogenic-induced changes related to the occurrence of heavy metals in tropical glaciers in the northern hemisphere of North America. Black carbon concentrations analyzed in snow and glacier ice, and preliminary data on stable isotopes of Zn, also add information on natural vs. anthropogenic sources of heavy metals in central Mexico.

20 years after the peak of oil in Mexico: analysis of the hydrocarbon sector and implications for the future of energy

Luca Ferrari — 2024-03-26

Two decades ago, Mexico reached the peak of oil production and 15 years ago that of natural gas. Since then, oil production has halved and gas production decreased by one third, while proven crude oil reserves are 26 % of those existing in 2004. Despite the obvious geological decline, the idea persists that the oil and gas sector is a fundamental part of the country’s future. In this paper we present a review and critical analysis of the production and refining of hydrocarbons in recent decades, as well as some probabilistic scenarios of future production, to provide objective elements for discussion on the viability of a model based on fossil fuels.

Our analysis indicates that in the past two decades Mexico has entered an irreversible process of diminishing returns, which implies an increase in energy and economic costs both in exploration and production and in refining, as well as a growing dependence on natural gas imports. The depletion of the giant fields offshore Campeche is being offset by a growing number of fields of much smaller size and rate of production and greater depth. Coupled with the need for enhanced recovery methods in mature fields this has steadily lowered the energy return on investment (EROI), which is currently less than half that of 2004. Consequently, although since 2019 the level of production has stabilized, the net energy available to society and to economy is decreasing, while energy and economic costs are increasing.

In the refining sector, there is a growing deficit between national production and demand for gasoline and diesel, which is offset by imports. Despite a change in trend in the last three years, our analysis indicates that even refining all the oil produced in Mexico, the amount of gasoline produced would not be enough to satisfy the current level of consumption. On the other hand, the consumption of natural gas by PEMEX itself in the production and refining sectors has been growing until reaching 60 % of the national gas production. Paradoxically, the effort to reduce the import of refined products produces an increase in the import of natural gas, which already represents 70 % of the national demand.

The probabilistic analysis indicates no chance of discovering more giant fields and that what remains to be discovered are mostly small or very small fields. The decline scenarios that we present, based on the historical behavior of reserves and production, adjust much better to actual behavior than those published in previous years by the Ministry of Energy. These scenarios indicate that by 2030 there would be a production of around 1.25 million barrels of crude oil per day, without considering the exploitation of unconventional resources. The latter, however, could only provide a temporary palliative to the decline in hydrocarbon production with a high environmental, energy and economic cost. Considering the growing socio-environmental impact and the effects on the climate of the production and consumption of fossil energy, it is necessary to think about a de-escalation of the oil activity, formulating a plan for a gradual exit from the dependence on fossil fuels that necessarily implies a decrease in energy consumption.

U-Pb geochronology and Hf isotopes of the Grenvillian Río Hondo gneisses, Puebla: redefining the western edge of Oaxaquia

Luigi A. Solari — 2024-03-26

In situ Río Hondo (Puebla, southern Mexico) gneiss samples, as well as clastic samples recovered from the nearby-outcropping latest Paleozoic Matzitzi Formation, a fluvial unit mainly sourced by Grenvillian rocks, were historically interpreted as representative of the northernmost exposures of the Oaxacan Complex, the largest outcrop of ortho and metasedimentary units, made up of mostly 1.0–1.3 Ga protoliths, affected cfby local migmatization (ca. 1.1 Ga) and granulite facies metamorphism at ca. 0.98 Ga, constituting the most prominent outcrop of the Oaxaquia microcontinent.

U-Pb geochronology and Lu-Hf isotopic determinations in zircon by LA-(MC)-ICP-MS were performed on both in situ and clast samples. In situ basement samples record a ca. 1.2 crystallization event, together with a younger one at ca. 1.02 Ga. both lacking inherited >1.3 Ga components. The clasts have an unimodal zircon U-Pb age distribution, recording a crystallization event at ca. 1.2–1.27 Ga. Scarce inherited zircon cores between ca. 1.4–1.6 Ga were found, with only a few samples with a broader age distribution, suggesting a detrital protolith with zircon cores as old as ca. 1.8 and 2.4 Ga. No zircon overgrowths or geochemical-petrographic evidences are indicative of granulite metamorphism. Furthermore, all the studied metaigneous samples show discordant zircon ages produced by Pb loss events barely constrained between the latest Paleozoic to the Mesozoic.

Hf isotopes reveal that zircon crystals from clasts have a range of εHf _{(1.25 Ga)} ≈+1 to +5 and yield Hf model ages from 1.7 to 1.9 Ga. On the other hand, the The zircon Hf isotopes of one analyzed basement sample reveal a higher range of εHf _{(1.25 Ga)} ≈+7 to +9, and Hf model ages from 1.5 to 1.6 Ga.

Both ≈1.2 Ga and 1.02 Ga events are consistent with magmatic ages previously documented elsewhere in Oaxaquia, interpreted as indicating portions of the NW Amazonia-Oaxaquia arc system with cratonic influence or to slices of Baltica thrust over Oaxaquia during the Grenville orogeny. However, the absence of granulite facies indicators, such as zircon metamorphic ages and/or granulite paragenesis (typically, in other Oaxaquia samples, orthopyroxene and garnet) are interpreted as prime evidence that the studied samples didn’t undergo such high grade of metamorphism. Río Hondo gneisses, as this sequence is informally named, must belong to a source that had the influence of an older continental crust and can be tentatively associated either with rocks recently described in the Sierra de Juárez, or those belonging to the central basement of the Maya block, currently exposed farther to the SE in Chiapas.

Groundwater flow and transport in fractured geologic media: A review

Marcos Adrián Ortega Guerrero — 2024-03-26

The groundwater flow and the transport of solutes and contaminants in fractured media play a very important role in various hydrogeological and geological processes. Fractures are discontinuities that occur in practically all types of rocks, consolidated and semi-consolidated sediments, in which it has interacted with the hydrological cycle at different scales of space and time. This article reviews 20 years of research in the CGEO of different selected examples in Mexico, from local to regional scales, associated with 1) Gravitational Groundwater Flow Systems, 2) The hydrogeochemical interaction of groundwater with fractured rocks through which it circulates, 3) Instrumentation and coupled numerical analysis of flow parameters and time-varying geomechanics, during consolidation associated with pumping, 4) Analysis of fracture generation with the development and application of coupled flow and geomechanical equations, 5) Formation of new minerals, 6) Sustenance of ecosystems, 7) Artificial fracturing of soils for their conservation and infiltration of rainwater improvement; and on the issue of transport in 8) Natural solute migration mechanisms, 9) Contaminants induced by pumping, 10) Spills of hydrocarbon derivatives in low permeability and double porosity media due to fracturing and 11) Heat. The results show the importance of fractured media in groundwater recharge in mountainous areas and flow towards granular media in quantity and quality, where residence times of a few years to thousands are involved, which implies modifying water and ecosystem management criteria, in the country; the complexity of these processes requires different methodologies for their evaluation, among them the instrumentation and calibration of numerical models from 1D to 3D for analysis, predictions and the proposal of restoration, sustainability and management solutions; they also help to prevent, control and mitigate the negative impacts on health and the environment caused by the induction of geogenic elements and by various types of pollutants; fractured media also support numerous terrestrial and marine ecosystems, and in the case of damaged agricultural soils, artificial fracturing allows increasing rainwater infiltration and improving productivity in adaptation to climate change and reducing the extraction in aquifers where safe capacity has been exceeded; unfortunately, excessive extraction in closed basins is causing fracturing of the aquitards, both hydraulic and due to differential settlement, which favors the migration of pore water rich in elements harmful to human health and the environment, whose natural function was its protection. All this requires designing mechanisms for the transfer of scientific knowledge to society and decision makers to propose novel restoration and sustainability strategies, under the new paradigm of Gravitational Groundwater Flow Systems.

Computational Geodynamics Laboratory: 15 years of numerical modeling and high-performance computing at the Centro de Geociencias, Universidad Nacional Autónoma de México

Marina Manea — 2024-03-26

The rapid development of computer technology in the last decades provided scientists with new opportunities to expand their research fields and in the same time to compress the necessary time to obtain research based scientific conclusions. This fast tendency also significantly affected the scientific discovery trend, and in many research fields we observe a transition from standard laboratory experiments to numerical experiments. In the particular research field of Earth Sciences, computational modeling constitutes a powerful predictive tool that fills a geological and geophysical data gap. The geological record covers well the Earth’s surface but is quite limited in depth, whereas geophysical information can provide depth-based information but it is limited in time to present day. Therefore, there is a large data gap in time and space that cannot be covered unless some indirect and intuitive prediction method is used. In this picture, numerical simulations come as an essential research tool. In this work, we provide a review about the research progress obtained in the last 15 years using high-performance computing at the Computational Geodynamics Laboratory at the Centro de Geociencias, Universidad Nacional Autónoma de México.