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

The occlusal pattern of the cheek teeth has traditionally been one of the most widely used features to determinate equid species. Nevertheless, its large ontogenetic variation and subjective assessment of characters has diminished its reliability. For this reason, many workers have reduced emphasis on the cheek teeth in identifying equid species and have turned their attention to other skeletal elements. We re-emphasize the analysis of the oclusal pattern to determine the number of equid species present in the Cedazo local fauna, Aguascalientes, Mexico. In contrast to previous studies, we only analyzed cheek teeth with an equivalent stage of wear and developed a computer program that integrates a digital image processor to analyze the occlusal pattern and also to take measurements of different features of the occlusal surface. Selecting teeth with an equivalent stage of wear reduced the usable sample size significantly. For this reason, the analysis concentrated on the third upper premolars (P3), because they represent the largest sample size. Specimens of Equus caballus, E. asinus and hybrids were also included to serve as controls. Principal Components and Canonical Discriminant Functions analyses were performed. The extant species were positively discriminated. Moreover, these analyses suggest the presence of two distinct P3 morphotypes for the fossil sample studied, which indicate the possible occurrence of at least two separate equid species for the Cedazo local fauna. However, it is prudent to collect more material and evaluate these results with a larger sample size and using the remaining tooth positions. The computer program developed in this study serves as a useful tool for analyzing the occlusal pattern of equid cheek teeth.

We describe ammonites from a newly discovered, fossil-bearing, marine Liassic locality (Lower Jurassic, Huayacocotla Fm.) in the vicinity of the Zongozotla Municipality (southern Sierra Madre Oriental) in the northern part of Puebla State (Mexico). The fossiliferous strata are about 1 m in thickness and yield ammonites and bivalves. The ammonites are Late Sinemurian in age and they represent a biohorizon which is correlated with the Paltechioceras gr. burckhardti horizon reported from the Tenango de Doria area. Ectocentrites hillebrandti n. sp. is described.

The sandstone of the Galeana Sandstone Member of Taraises Formation have been interpreted as an extended delta deposit, which had its origin from the Coahuila Block, and few authors have proposed that the source area could be associated with the Tamaulipas Archipielago. The present study documents the sedimentological characteristics of the Galeana Sandstone Member, and on the basis of facies analysis and paleocurrent data, the sedimentary environments, and its depositional evolution were determined. The sandstone of the Galeana Sandstone Member show seven facies associations, which are interpreted as tidal flat, prodelta, tidal-dominated delta front, deltaic barred mouths, sublittoral and subaqueous dune deposits. The tidal flat deposits are characterized by thinning-upward sequences, and they contain herringbone cross-bedding, lenticular and flaser bedding, as well as trace fossils of the genus Skolithos, Thalassinoides, Diplocraterion, and Rhizocorallium. The deltaic system, deltaic barred mouth, and sublittoral deposits are characterized by interbedded sandstone and shale that show thickening-upward and thinning-upward sequences, as well as scarce sedimentary structures such as parallel lamination, normal graded beds, lenticular stratification, herringbone cross-bedding, and Macaronichnus trace fossils. The subaqueous dune deposits show chaotic sequences with cross-bedding generated by dunes migration, reactivation surfaces, and ichnofossils of the genus Thalassinoides.The field data, such as paleocurrent and stratigraphic relationships suggest that: (i) sandstone of the Galeana Sandstone Member had a source area located to the east of Potrero Prieto locality, which could be the Tamaulipas Archipielago, and (ii) the depocenter is located in the Galeana area, as indicated by the observed changes in bed thicknesses and the presence of an angular disconformity.

Contamination of groundwater from point and non-point sources is one of the major problems of water resources in Jordan. Altogether one hundred and six groundwater samples were collected from twenty six karst springs emerging from Umm Rijam aquifer and three wells tapping Amman-Wadi As Sir aquifer, and investigated for NO3  concentrations. Results showed that NO3  concentration in spring water ranged from 8 to 192 mg/L with an average of 33 mg/L. Seventy seven percent of the samples collected from the springs had nitrate concentrations exceeding the threshold value of 20 mg/L of anthropogenic source, and eight percent of the samples collected had nitrate concentrations higher than 50 mg/L, the maximum acceptable nitrate concentration for drinking water. About eighty percent of the sampled springs had nitrate concentrations higher than 20 mg/L. The K-means cluster analysis performed on the collected samples revealed the presence of three major clusters. The data were processed for the possible presence of discordant outliers using the unpublished computer program UDASYS by Verma and Díaz-González. There is a wide spatial variation in the nitrate concentration in spring water. Monitoring the water quality of these springs showed that the lowest concentrations of nitrate were found in the wet season (January, February, and December), while the highest concentrations were found in the dry season (August, September). Nitrate concentration in Amman-Wadi As Sir aquifer ranges from <1 mg/L to 19.2 mg/L, with an average of 9.8 mg/L. Untreated domestic wastewater is most probably the major source of the nitrate in the spring water, as the study area is not served with sewer system, and domestic wastewater is collected in cesspools dug in the kartsed Umm Rijam Formation. Moreover, in the area under consideration there are no major industries or intensive agricultural activities. The results of this study are useful to highlight one of the most important environmental problems, namely the degradation of the water quality, and may serve to alert and encourage local and national authorities to take substantial steps and actions to protect and manage water quality.

 The optical characteristics, X-ray diffraction, unit cell, chemistry and crystallization conditions of an alkaline zeolite assemblage were studied. The zeolites have been found infilling amygdales and in the matrix of Tertiary olivine basalts from Junin de los Andes, Patagonia. The secondary minerals (albite, pumpellyite, interestratified chlorite/smectite (C/S), smectite, iddingsite, magnetite and hematite) are replacing phenocrysts of plagioclase, olivine and the matrix of the rocks. Zeolites are sodic, calco-sodic and potassic in composition. Na–chabazite, analcime, Ca-K phillipsite and paulingite are the first zeolites that crystallized. They were followed by acicular-fibrous zeolites as natrolite/Na-gonnardite, thomsonite, mesolite and scolecite. The formation of the first zeolites is consistent with low temperature (<100 ºC), low pressure (<0.1 GPa) and alkaline (pH 9–10) hydrothermal/geothermal meteoric fluids, which were favored by tensional fractures. The activity of Si decreased during the alteration process and the temperature increased toward 200 ºC allowing the analcime formation followed by the equilibrium assemblage natrolite/Na-gonnardite-thomsonite-scolecite and mesolite. 

The Tamazulapam region is located in the southern extension of the Caltepec fault, which places the Acatlán and Oaxaca complexes in contact. In the Tamazulapam region, both complexes crop out but the contact is covered by Mesozoic and Cenozoic rocks. This paper presents the detailed stratigraphy of the area and a structural analysis in order to establish if the Caltepec fault has exerted a structural control on the Cenozoic deformation. The structural analysis is difficult because the faults show a multiple fault pattern with complex kinematics. In order to resolve the kinematics of this region, we propose the use of Cinematic Compatibility Diagrams (CCD), which illustrate the whole possible movement of faults under a unique stress tensor. The CCD show that in the western side of the fault, where the Acatlan Complex constitutes the basement, the Cenozoic deformation occurred in two tectonic events, the first one under a tectonic transcurrent regime with a maximum shortening towards NE-SW during the late Eocene-Early Oligocene, followed by the second event, extensional, with maximum extension in the same direction, which occurred during late Oligocene (between 26 and 29 Ma). The direction and regime type of these events correspond with previous deformational events recorded in other areas in southern Mexico. In contrast, in the eastern side, where the Oaxaca Complex constitutes the basement, the deformation is heterogeneous, probably generated by the synchronous movement of the Oaxaca and the Tamazulapam faults above a detachment formed partially by anhydrites. The differences in the deformation styles on both sides of the southern extension of the Caltepec fault shows that, in this case, the basement fault influenced the deformation style of the Cenozoic units. 

The grain-size trend analysis (grain size, sorting and asymmetry) was determined from 43 stations to identify the path of sediment transport in the Chetumal Bay, Quintana Roo. The analysis of principal components and grain size trend analysis were applied to sediment textural parameters. It was established that better sorted sedimentary material is associated with stations with fine grain-size and vice versa. Vectors transport suggests a net transport of sediment in the direction S-SE and S-SW (for the sampling period), which is consistent with the direction of the surface and deep currents in the Chetumal Bay. The preferential deposition of fine and well-sorted material in the central part of the bay has excellent correlation with the contents of anthropogenic pollutants found in other studies.

The holotype of the first sauropterygian described from Mexico, Plesiosaurus mexicanus Wieland, 1910, was recently rediscovered and is here described and discussed for the first time in almost a century. The holotype specimen belongs to an indeterminate metriorhynchine crocodyliform. Doubts remain as to the stratigraphic origin of the specimen, whether Upper Jurassic or Lower Cretaceous. It adds a specimen to the recently recognised wealth of the Mexican Gulf in thalattosuchians. 

Three new improved equations of the Na/K geothermometer were developed through computational (artificial neural networks) and statistical tools (based on ordinary linear regression) from the analysis of a more representative world geochemical database (n=212) than hitherto used. The new Na/K geothermometers are given by the following equations:................see full paper  

The Zacatecas-San José de Gracia area, located at southern Zacatecas and northern Aguascalientes in the borderline between the Sierra Madre Occidental and the Mesa Central, is particularly important because it is located at the intersection of two regional fault systems: the San Luis-Tepehuanes fault system and the Aguascalientes graben. We mapped the area and measured the faults that affect the Cenozoic units in order to know the interaction between these two fault systems during the Cenozoic. Eight new Cenozoic litostratigraphic units were identified, four of which were dated, defining two felsic volcanic pulses: the first one occurred during middle Eocene, with the La Bufa ryolite at the base (48.91 ± 0.09 Ma) and La Virgen Formation at the top (36.8 Ma; Ponce y Clark, 1988: Economic Geology, 83, 1668-1682), the second pulse during the Oligocene, comprising rocks with isotopic ages of 28.0 ± 0.8 Ma (Garabato ignimbrite) and 27.0 ± 0.7 Ma (Sierra Fría rhyolite), with a magmatic gap between ~36 and 29 Ma. Two deformation events were recognized: The first one (D1) occurred in the Paleocene-early Eocene producing WNW and NNE normal faults. The second event (D2), of late Oligocene-early Miocene age, comprised two deformational phases (D2a and D2b) that reactivated preexisting structures and formed new ones. The first phase (D2a) activated NNE normal faults and the second phase (D2b) formed WNW normal faults. An horizontal stretching direction of ~N60ºE could have generated simultaneous (D1) and alternating (D2) activity in both fault systems, which can be explained if we consider that the observed fault directions are inherited from older basement structures.An apparent left-lateral displacement of the Aguascalientes graben is observed at its intersection with the San Luis-Tepehuanes fault system, but new data herein presented indicate that this apparent structural con figuration is inherited from older structures.