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

A study was carried out on the sedimentary stratigraphic units in the Balandra coastal lagoon floor and in the outcrops of its surroundings, which possess the widest registered record known for the late Quaternary of the La Paz bay, including the late Pleistocene. The oldest Pleistocene unit is represented by a marine terrace located three or four meters above mean sea level, from which a sample of coral was dated using the uranium-series method at 288,000 ± 50,000 years B. P. The age of this unit is considered to be incorrect because the elevation of its top is lesser than other terraces of the region of similar age... In order to continue, download the full article in PDF

Two sequences of pre-Tertiary volcano-sedimentary rocks with island arc affinities have been differentiated in the Zacazonapan area, State of Mexico. These rocks are part of the Tierra Caliente complex or the tectonostratigraphic Guerrero terrane. The lower sequence, grouped as pre-Cretaceous metamorphic rocks, is essentially made up of about 1,500 m of carbonaceous phyllite interbedded with greenschist (chlorite-actinolite-epidote schist) and metarhyolite lenticular bodies. This package is characterized by penetrative foliation associated with recumbent tight to isoclinal folding under greenschist facies conditions... In order to continue, download the full article in PDF

The city of Zacatecas has grown rapidly in the last 15 years. Some irregular human settlements cover at present old-mined areas or not developed or even explored mining areas. The main areas considered in this paper are the loam of Las Bolsas, southeast of the city of Zacatecas, and the El Orito zone, in the southwest. The loam of Las Bolsas now is covered by irregular urban neighbourhoods, overlying the Tertiary polymictic red conglomerate of Zacatecas. Within this zone, there are at least five polymetallic veins with silver, lead, zinc, copper and gold mineralization. There also exist about ten shafts and some old mine workings as well as small adits and dumps. The old shafts of San Ignacio, El Gato and La Esperanza are now located within the city, as well as the old mines of Quebradilla, Buena Vista, El Piquete and El Edén. The El Orito zone covers over 3 km2, and it is occupied by the suburbs known as La Pimienta, Lomas del Lago and Jesús González Ortega, among others. Outcropping in this zone, there was an important swarm of narrow siliceous veins, with a low-grade gold mineralization. This structural vein system runs almost north-south and was never economically evaluated... In order to continue, download full text in PDF.

A tectonic depression, La Sauceda graben, constitutes the southeastern boundary of the Sierra de Guanajuato and separates it from the Sierra de Codornices. Continental volcanic and sedimentary rocks of Cenozoic age cut by normal faults are found throughout the area of study. Five phases of faulting have been identified and these can be separated into two distinct age groups; the first ranges from Paleocene?-Eocene time until the later part of the early Oligocene and the second is Pliocene-Pieistocene in age. The rocks that outcrop in this area also belong to the time spans mentioned previously, leaving a gap of approximately 25 Ma from which there is no record. Faults show two prominent directions, NW-SE and NE-SW, and were probably formed as a result of the differences in the physical properties of the Mesozoic rocks in this region... In order to continue, download the full article in PDF

Benthic-foraminifer assemblages in two cores obtained from the sea floor of the eastern part of the mouth of the Gulf of California were statistically studied using "factor analysis". Q mode allowed distinction of three intervals in -the geologic column, which are associated with benthic-foraminifer biofacies, recognized in turn by R mode. The biostratigraphic setting was established correlating with 18O isotopy, carried out al levels with the highest relative abundance of the radiolarian Cycladophora davisiana, within the area of the gulf. A minimum age of 19,000 years was established for the studied cores... In order to continue, download the full article in PDF

In the surroundings of the city of Aguascalientes, Mooser and Dalquest, in 1975, described the Cedazo local fauna and assigned an Illinoian age to it. The preliminary results of recent studies carried on the Pleistocenic sediments suggest that several lithologic and biostratigraphic units are present. Each unit contains a poor but distinctive mammal fossil assemblage. The lowest unit contains cf. Aiuralagus, this fact constituting the first record in Mexico of this fossil; remains of Holmesina sp. were collected, which are similar in size and morphology to those reported from the Inglis local fauna of Florida... In order to continue, download the full article in PDF

Due to the abundance, variety and preservation of the paleobiota, the Tlayúa quarry is one of the most important fossiliferous localities of the Albian of North America. It is located near Tepexi de Rodríguez, approximately 60 km SE of the city of Puebla, in the northern part of the Mixteca Alta region. The name Tlayúa Formation is formally proposed for the limestone outcropping in the quarry and along the Barranca de Tlayúa. lt consists of an incomplete sequence of 300 m in thickness, that was divided in three members: Lower, Middle and Upper. The age of the formation in the type locality ranges from early to late Albian, time limits that can vary outside of the study area... In order to continue, download the full article in PDF

The only Cenozoic fossil echinoid recorded from the Pacific coast to mainland Mexico, between the Guatemalan border and Puerto Vallarta, at the entrance to the Gulf of California, is Encope micropora L. Agassiz (Palmer and Hertlein, 1936, p. 66) from the Pleistocene Colotepec Formation of the southern coast of Oaxaca (Caso, 1951, 1961; Buitrón, 1978). Recently, several Cenozoic marine basins have been discovered along the Pacific Coast (Durham et al., 1981). In two of these basins, one near La Mira, Michoacán, and the other near Santa Cruz, Oaxaca, fossil keyhold urchins (genus Encope) were found. Near La Mira, the echinoid occurs in the lower part of the marine beds cropping out around the Ferrotepec iron mines (Sicartsa Mining Company). These beds are of late early to early middle Miocene age and rest unconformably on the ore bearing strata of pre-Cenozoic age (Durham et al., 1981). Download full text.

A mineralogical study using X-ray diffraction on samples from Los Humeros geothermal wells showed that the clay minerals follow a zonal distribution… in order to continue, download the full paper in PDF.

Base on the analysis of major geomorphological features and considering the geological and structural characteristics of the Sierra de Guanajuato, it was established that this range is constituted by 12 principal independent blocks… in order to continue, download the full paper in PDF.