Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

We present the volcanic stratigraphy from the southwestern portion of Lake Cuitzeo, Michoacán located inside the central sector of the Trans-Mexican Volcanic Belt province, where found a graben-type caldera structure. Six volcanic sequences were identified with ages ranging from early Miocene to late Pleistocene that include: 1) Copándaro-Tarímbaro Sequence (CoTS) originated during the early Miocene, contains intercalations of basaltic andesite lavas and ignimbrites with a high degree of hydrothermal alteration, 2) The Tarímbaro Sequence (TS), dated at 18.7 Ma, consists of basaltic andesitic lavas and trachyandesites, 3) The Chucándiro Ignimbrite Sequence (ChIS) with ages of 16.88 ± 0.34, 16.72 ± 0.24 and 16.88 ± 0.22, contains three ignimbritic lithofacies forming a plateau perpendicularly tilted to the NE-SW normal faults. Brecciated deposits (lag breccias) occur at the base of the ignimbrites which follow the trace of the Morelia-Acambay fault system (MAFS). These depositsoverlay the 4) the El Caracol sequence (SEC) dated from 13.73 ± 0.24 Ma to 3.02± 0.03 Ma, that consists of four volcanic units of basalts, andesites, and basaltic andesites. These rocks interbedded with a late Miocene lacustrine unit dated with an index fossil. The lacustrine deposits are overlaid by the 5) Quinceo-Tetillas Sequence (QT): dated at 1.48 ± 0.016 Ma, that consists of lahars (flows hyperconcentrated flows) and fall deposits covered by products of Quinceo (1.5 ± 0.14 Ma) and Tetillas (0.4 ± 0.08 Ma) volcanoes. Finally, the youngest sequence is represented by the 6) Chucándiro cinder cone (CCh): with an age of 0.161 ± 0.014 Ma of andesitic composition. The structural and geochemical analysis show that the Copándaro-Tarímbaro (SCoT), the Tarímbaro (ST), and the Chucándiro (SICh) ignimbritic sequences are closely associated with a transition event between the volcanism of the SMO and the TMVB. Based on the geometry of the Chucandiro Graben, the location of the lag breccia along. the trace of the master faults, the NE-SW direction of secondary faults and the distribution of the ignimbrites, it is proposed that this sequence was originated in the Early Miocene from a graben-type caldera named Chucándiro. Its origin is related to the extensional tectonic setting of the MAFS. In this contribution is reported the onset of the trastension in this central sector of the TMVB during the early Miocene with ages older than 17.1 Ma. Our results indicate that the onset of TMVB in the area occurred during late Miocene with the emplacement of monogenetic volcanism inside the graben followed by lacustrine sedimentation that continues nowadays.

The Morelia-Acambay Fault System (MAFS) is located in the central-western part of the Trans-Mexican Volcanic Belt (TMVB). The MAFS is a 30 km wide-transtensional shear zone made up of E-W and ENE-WSW oriented faults. Since middle Miocene (7–9 Ma), the seismotectonics of this fault system has controlled the evolution of E-W tectonic depressions (Zacapu, Cuitzeo, Morelia, and Acambay), and the lacustrine environments. This paper describes the spatial variation of the state of recent deformation through the structural analysis of fault populations measured in the field and the definition of the regional stress regime from the analysis of the focal mechanisms of shallow intraplate earthquakes. Kinematic data indicate that the MAFS formed under a maximum NE-SW oriented horizontal compression (Ey). Today, the NE-SW faults act as left-lateral oblique slip faults, the main W-E faults as left lateral normal faults; and the NE-SW faults are displayed in en échelon setting. A variation in the direction of Ey is deduced from our data: Ey in fact remains NE-SW oriented in the north-western part of the MAFS, whereas it rotates toward the NNE-SSW and E-W directions in the western (Pázcuaro-Zacapu-Morelia-Cuitzeo-Acámbaro) and eastern (Maravatio-Acambay) MAFS sectors, respectively. Data integration indicates that the main stress axes trajectories remained constant since the Pliocene. Some of the faults of MAFS are presently active, as demonstrated by the distribution of historical epicenters (1858, 1912, 1979 and 2007). These results are of primary relevance for future seismic risk studies in the region. The most reasonable explanation to account for the transtensional regime occurring in the central part of the TMVB is the oblique convergence between the lithospheric plates and, in particular, the partition of the subduction angle in the northern part of the Mesoamerican subduxiton zone.

Groundwater metal pollution is a major concern in mining areas. This study proposes a new addition to the DRASTIC method (DRASTIC+Lu) to assess groundwater vulnerability to metal pollution in mining areas by combining remote sensing (to locate metal pollution sources) and the DRASTIC index. The study was performed in a mining area in northwestern Mexico showing current and historical mining activities. The proposed methodology allowed locating known and unknown sources of metal pollution (mining tailings, active/inactive mines, and areas with exposed natural geochemical anomalies). Generally, the addition of the land use (Lu) parameter causes not only a decrease in vulnerability but also highlights very high vulnerable areas and identifies new ones in the vicinity of metal pollution sources. This result is relevant to focus stewardship efforts in very high vulnerable areas. Results allowed to identify the need to implement protection and restauration measures in the Sonora river channel and its vicinity. The proposed method could be implemented in other mining areas around the world –at a low cost– to locate unknown metal pollution sources and clearly identify very high vulnerable areas that play a key role in the protection of groundwater resources.

The discovery of the first Mexican fossil specimen belonging to the species Xiphactinus audax is reported here. This specimen was recovered in the Coniacian-Campanian marine deposits of the Austin Group at the Piedritas site, within the homonymous ejido, Municipality of Ocampo, north of Coahuila. Although the specimen is strongly fragmentary, partially preserved by impressions or molds of the bones, and only shows parts of the head, the opercular series, and the pectoral fins, this has enough anatomical features that allow its specific taxonomic determination. Among these diagnostic features, this fossil has a well-developed ethmopalatine bone, a well-developed supraoccipital crest, a maxilla anteriorly higher than the rest of the bone, and a very robust palatine articular head. Particularly, this fossil exhibits two distinctive features of the genus Xiphactinus, a row of conical teeth, irregularly sized and distributed in the maxilla and dentary bones, as well as a pectoral radius 1 extremely developed and at least 2.5 times wider than the subsequent ray. At the same time, its teeth are smooth and have no sharp edges or carenae, which allows its specific identification. The present discovery complements the geographical distribution of Xiphactinus confirming its wide longitudinal distribution throughout America.

The lacustrine system developed in the basin of Mexico has been of great interest in studies of various geological and social disciplines. Its sediments preserve the history of the environmental changes that occurred during the late Quaternary. Between 2016 and 2018, a set of lacustrine sediment cores were collected in the Xochimilco sub-basin, located south of the basin of Mexico. From these sedimentary sequences, a master sequence was constructed that represents the upper 66.5 m of the lacustrine deposits. For the establishment of its stratigraphic column, 15 lithotypes were defined from their sedimentary components in which the clastic components made up of silicates dominate, mostly silt and clay in size. The most abundant biogenic fraction is diatoms that frequently form oozes, and ostracods are a common component in most of the sequence, which locally form hashes. Interbedded with the clastic and biogenic lithotypes are volcaniclastic deposits. Eight lithological units were defined based on their dominant lithotypes. The time scale of the sequence is still uncertain for the oldest sediments; however, it is estimated that it covers the last 300000 to 350000 years. From this temporality, environmental oscillations of millennial scales are inferred. Diatom-rich laminated sediments represent the deepest phases in the lake. The deposits with higher biogenic and authigenic calcareous components indicate the phases of higher ionic concentration during which the lake was shallower. The detailed analysis of the stratigraphy and the description of the sedimentary components in Xochimilco allows to establish an initial interpretation of the variations in the depositional environments, and provides the base from which the detailed studies of paleoclimatic indicators will be supported.

This work presents Frackita-v1 code, written in MATLAB®. Frackita-v1 is a tool that automatizes the calculation of parameters, such as Box dimension, Correlation dimension, Lyapunov exponent, Coefficient of variation, and fracture intensity. These parameters are fundamental to knowing the fracture size distribution, density, and spatial arrangement. This last variable is important because it’s related to fluid flow process and strain localization. Frackita-v1 covers the current necessity of a 1D analysis software for education, research, and industry. The code uses spacing data obtained from scanlines on thin sections, outcrops, and aerial photographs or satellite images. In addition, the Frackita-v1 code produces synthetic fracture patterns that help to understand the calculated parameters. The implemented methods are scale-independent and can be applied to spacing data from micro- to macro-scales.

Covers, Revista Mexicana de Ciencias Geológicas, vol. 39, num. 1, april 2022

This work intends to observe the changes in the sedimentation and fauna patterns of the Eagle Ford and Indidura Formations that outcrop in the state of Coahuila. These sedimentary successions were deposited during the Cenomanian-Turonian within the Sabinas basin and are composed of clayey, carbonated, bioclastic, and sandy facies. Nine microfacies (Mf) were described: Mf-1 is formed of mudstone, Mf-2 of shale and wackestone with opportunistic foraminifera, Mf-3 of wackestone from specialist foraminifera; Mf-4 of wackestone and packstone of radiolaria, Mf-5 of wackestone and packstone with filaments, Mf-6 of peloidal grainstone, Mf-7 of bioclastic grainstone, Mf-8 of calcarenites, and Mf-9 of interbedded volcanic tuffs in the sedimentary succession. The occurrence of the Oceanic Anoxic Event (OAE-2) is present within the sedimentary succession, indicated by the deposits of black shale rich in organic matter, the massive death of planktonic foraminifera, abundant filaments, crystals of pyrite, and high concentrations of redox elements such as V, Mo, and Mn. However, the deposit conditions present a variation in the concentration of oxygen, micronutrients, and organic matter throughout the paleogeography. Elements such as Ni and Zn in microfacies 1, 2, 3, and 4 show high productivity, which is associated with the presence of planktonic or radiolarian organisms. Other chemical elements such as Al, K, and Zr show an increase in detrital material within the basin, associated with clayed and sandy microfacies. The organic matter content is higher for microfacies 2 to 5, and it is considered of autochthonous origin. The variation in the oxic-anoxic conditions is notorious due to the planktonic-benthic foraminifera ratio and the geochemical relationship between the Mo, Va, Ni, and S elements. In the Indidura Formation, the ages of U–Pb in zircon grains from tuff layers restrict the deposit between 98.2 ± 0.9 Ma to 91.7 ± 0.8 Ma, during Cenomanian-Turonian, although the presence of Praeglobotruncana at the base restricts the deposit to the late Cenomanian-Turonian. While the age of the Eagle Ford Formation is indicated by the Cenomanian-Turonian genera of Rotalipora cushmani, Hedbergella, and Helveglobotruncana helvética.This work intends to observe the changes in the sedimentation and fauna patterns of the Eagle Ford and Indidura Formations that outcrop in the state of Coahuila. These sedimentary successions were deposited during the Cenomanian-Turonian within the Sabinas basin and are composed of clayey, carbonated, bioclastic, and sandy facies. Nine microfacies (Mf) were described: Mf-1 is formed of mudstone, Mf-2 of shale and wackestone with opportunistic foraminifera, Mf-3 of wackestone from specialist foraminifera; Mf-4 of wackestone and packstone of radiolaria, Mf-5 of wackestone and packstone with filaments, Mf-6 of peloidal grainstone, Mf-7 of bioclastic grainstone, Mf-8 of calcarenites, and Mf-9 of interbedded volcanic tuffs in the sedimentary succession. The occurrence of the Oceanic Anoxic Event (OAE-2) is present within the sedimentary succession, indicated by the deposits of black shale rich in organic matter, the massive death of planktonic foraminifera, abundant filaments, crystals of pyrite, and high concentrations of redox elements such as V, Mo, and Mn. However, the deposit conditions present a variation in the concentration of oxygen, micronutrients, and organic matter throughout the paleogeography. Elements such as Ni and Zn in microfacies 1, 2, 3, and 4 show high productivity, which is associated with the presence of planktonic or radiolarian organisms. Other chemical elements such as Al, K, and Zr show an increase in detrital material within the basin, associated with clayed and sandy microfacies. The organic matter content is higher for microfacies 2 to 5, and it is considered of autochthonous origin. The variation in the oxic-anoxic conditions is notorious due to the planktonic-benthic foraminifera ratio and the geochemical relationship between the Mo, Va, Ni, and S elements. In the Indidura Formation, the ages of U–Pb in zircon grains from tuff layers restrict the deposit between 98.2 ± 0.9 Ma to 91.7 ± 0.8 Ma, during Cenomanian-Turonian, although the presence of Praeglobotruncana at the base restricts the deposit to the late Cenomanian-Turonian. While the age of the Eagle Ford Formation is indicated by the Cenomanian-Turonian genera of Rotalipora cushmani, Hedbergella, and Helveglobotruncana helvética.

In the above article, the data of the reference: Schmitt, A.K., Martín, A., Stockli, D., Farley, K.A., Lovera, O.M., 2013, (U-Th)/He zircon and archaeological ages for a late prehistoric eruption in the Salton Trough (California, USA): Geology, 2013, 41 (1), 7-10. Are not correct, they must be: Schmitt, A.K., Martín, A., Weber, B., Stockli, D.F., Zou, H., Shen, C.C., 2013, Ocean magmatism in sedimentary basins of the northern Gulf of California rift: Geological Society of America Bulletin, 125(11-12), 1833-1850.   In-text citations to these authors remain unchanged. This erratum has been attached to the online version of the paper on april 8th, 2022. The editors apologize for this mistake.   Original paper: DOI: http://dx.doi.org/10.22201/cgeo.20072902e.2022.1.1659

Solitary corals currently assigned to the genus Plesiosmilia are common elements in Late Jurassic to Early Cretaceous coral faunas. The genus itself is poorly defined and its systematic position is questionable. Moreover, examination of type material has shown that the genus lumps corals of different morphologies. Here, one common coral type is separated in a new solitary coral genus as well as two new phaceloid coral genera with a comparable morphology. The three new and another three existing genera are collected in a new family. The newly described material comes from the Upper Valanginian-Lower Hauterivian of San Juan Raya (Puebla) and the Lower Albian of Rayón (Sonora, both Mexico).