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

The constant increase of human and industrial activities in Mexico City's metropolitan zone has been the cause of deterioration in sewage water quality. This water is used to irrigate the land now known as Irrigation District 03, State of Hidalgo, a water usage that dates from the beginning of this century. This water is characterized by its alkalinity, a fact that reduces the solubility of heavy metals. On the other hand, the soil mineralogy shows no evidence that parental material is the cause of possible abnormal accumulation of heavy metals. The Tepatepec series presents greater risks of a total heavy-metal retention due to the slow, but constant, increase in the contents of organic materials, and to its greater vulnerability as pH decreases. Mid textures and moderate permeability, which characterize the Actopan series, facilitate the loss and lixiviation of metals. The Progreso series presents less risks of heavy-metal solubilization due mainly to alkaline pH values and to high reserves of carbonates, sulphides and phosphates in soils supplied by calcareous parental material, thus originating insoluble compounds. All the extractable heavy metals studied show clearly an increase since 1974. From the soil characteristics in the three series, organic material had the greatest influence in the distribution of the heavy metals studied, being its greatest accumulation in the Ap horizons... In order to continue, download full text in PDF.

The limited extension of geological map coverage, the metamorphism of varying degrees that affected the rocks and their almost complete lack of fossils, make the basement beneath the marine fossiliferous Upper Jurassic and/or Lower Cretaceous sedimentary and volcanic cover rocks to be an unsolved geological problem in south-central Mexico, a región comprising about 20,000 km2 (Figure 1). Radiometric ages (Pb-α, K-Ar, Rb-Sr, U-Pb) obtained from these rocks are apparently contradictory or not conclusive (de Cserna et al., 1962; de Cserna, Fries, Rincón-Orta, Westley, Solorio-Munguía and Schmitter-Villada, 1974; de Cserna, Fries, Rincón-Orta, Solorio-Munguía and Schmitter-Villada, 1974; Guerrero-García et al., 1978; Urrutia-Fucugauchi and Linares, 1981; López-Infanzón and Grajales-Nishimura, 1984; Morán-Zenteno et al., 1990; Morán-Zenteno, 1992)... In order to continue, download full text in PDF.

A soil data-base facilitated by the Secretaría de Agricultura y Recursos Hidráulicos-204 sites-is used to evaluate selected physical and chemical properties of soils irrigated with sewage water. Semivariograms were elaborated to evaluate spatial dependence of boron, carbonates, electric conductivity, chloride, pH and organic matter for the upper 30 cm. Three of the six parameters-boron, electric conductivity and organic matter-seem to be relatively spatially dependent, but no clear dependence was found in the case of pH, carbonates and chloride... In order to continue, download full text in PDF.

Topaz- and/or tin-bearing rhyolite is common in Mexico. It lies within an extensive belt that extends from the western United States to central Mexico. These rocks are of special interest because they are interpreted as products of partial melting of Precambrian continental crust, extruded during periods of extensional tectonism. Furthermore, there are some economic ore deposits associated with topaz rhyolite. Topaz rhyolite occurs in the middle Oligocene (32-26 Ma) San Luis Potosí volcanic field (SLPVF). Topaz is found near the vents or in the lava flows of the San Miguelito Rhyolite (K-Ar: 29.2 ± 0.8 Ma). This rhyolite is characterized by the phenocryst assemblage quartz + sanidine + Na plagioclase + biotite + opaque minerals. These rocks crystallized from fluorine-rich magmas. Topaz and tin were formed as vapor-phase minerals... In order to continue, download full text in PDF.

The Sierra of Santa Catarina, located to the east of Mexico city, consists of an ENE trending group of Quaternary volcanic cones and associated lava flows. It covers an area of approximately 75 km2 and is surrounded by the lacustrine plain of the Basin of Mexico. This area is represented in detail on a large scale geomorphological map, which shows a total of 37 relief elements that are divided into the following categories: endogenous (volcanic: explosive, effusive and explosive-effusive), endogenous-eroded (volcanic erosive), and exogenous (erosive, cumulative and anthropic). The geomorphological cartography represents the relief in the year 1990; it has been modified since then by the extraction of material, which is leading to the destruction of all the volcanic cones. Volcanism migrated from west to east and is represented by six morphogenetic scoria cones, an andesitic dome anda maar... In order to continue, download full text in PDF.

The study area is located in north-central Sonora, 150 km northeast of Hermosillo. Lower-Middle Proterozoic to Holocene rocks occur in the area. The Precambrian rocks are among the southernmost ones of this age to crop out in Sonora. They include gneiss and schist (origin age of 1,800 Ma and metamorphism age of 1,650 Ma), granodiorite (1 ,700 Ma) and granite (1,100 Ma). The Paleozoic section is composed of a Cambrian (?) orthoquartzite. The Mesozoic consists of volcanic, volcano-sedimentary, and sedimentary rocks of Jurassic and Cretaceous age. The Tertiary comprises intrusive, volcanic, and sedimentary rocks. Volcanic and volcano-sedimentary rocks of Lower-Middle Jurassic (?) and Oxfordian ages, respectively, may form the southeastern part of a magmatic arc. Synorogenic deposits of the El Tuli formation record the beginning of the Upper Cretaceous earliest tectonism (Cenomanian-Maastrichtian), which was accompanied by a penecontemporaneous magmatism of a kind that is widespread in Sonora... In order to continue, download full text in PDF.

The Sierra of Oposura (or La Madera) is located at about 200 km to the NE of the city of Hermosillo. The study area lies within the subprovince of Parallel Valleys and Ranges of the physiographic province of the Sierra Madre Occidental. The Sierra of Oposura and the adjacent Valley of Moctezuma are limited by NW-SE trending normal faults and locally are the most important morphologic features. The pre-batholithic rocks consist of a sequence of limestone and shale of Early Cretaceous age. These rocks are overlain in angular unconformity by an Upper Cretaceous sequence of mainly andesític flows and tuffs, which also includes ignimbrite and conglomerate in the upper part. These two sequences are intruded by the Oposura Batholith. lntrusive contacts may be observed to the south and east of the study area. To the west, the batholithic rocks are in fault contact with Tertiary clastic rocks... In order to continue, download full text in PDF.

La Mola de Xert is a small well exposed carbonate platform that developed during the early Aptian in the eastern Iberian basin, Spain. Its geometry and development in a rift context are briefly reviewed and the palaeoecological distribution of the megafauna (mainly rudists) is described… in order to continue, download the full paper in PDF.

The lower Cretaceous rudist fauna of southern France consists of 61 species corresponding to 23 genera belonging to Diceratidae, Requieniidae, Monopleuridae, Caprinidae, Polyconotidae and Radiolitidae… in order to continue, download the full paper in PDF.

L'arc crétacique inférieur de Guanajuato (Mexique central) est constitué d'un complexe plutonique, un complexe filonien et des laves associées. Les laves, de composition basaltique, se présentent en coussins avec des intercalations rares de tufs de la même composition. Ces laves sont des tholéiites d'arc caractérisées par des teneurs faibles en TiO2, K2O, Zr et Y, mais relativement élevées en Nb (>5 ppm), ainsi que par des spectres de terres rares plats et/ou appauvris en terres rares légères. Le complexe filonien, que s'enracine dans des roches plutoniques acides, des diorites et des gabbros du sommet du complexe plutonique, est formé de dolérite et de basalte. Ces roches basiques présentent, avec les laves en coussins, les caractères géochimiques signalés précédemment et 7.1 < εNd (T=122.5 Ma) < 9.1, et sont donc cogénétiques avec ces dernières... In order to continue, download the full article in PDF