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

The fossil stromatolites of the Gamuza Beds, south of Caborca, Sonora, were discovered in 1941 and afterwards assigned to "Collenia" or ''Cryptozoon" in a tentative inanner. The finding of Conophyton and Jacutophyton at two localities allows to corroborate the previous assignation of the Gamuza Beds to the Late Precambrian, at least up to the uppermost level with Jacutophyton. The Units 10 to 12 of the Gamuza Beds (sensu Anderson et al., 1978) do not carry stromatolites and lack other guide fossils. Their attribution to the Precambrian is therefore tentative. Excellent outcrops of stromatolite bioherms in the area allow the reconstruction and paleoecological interpretation fundamental in local and regional correlation (basin analysis). The bioherms developed in a marine environment and, at least temporally, at the subtidal zone and below the wave base.

This is the first detailed report of these authors on the Rancho El Ocote local fauna, from which the Neohipparion material is discussed. From this locality, Neohipparion otomii Mooser, 1959 and Neohipparion monias Mooser, 1963, were previously reported. An objective analysis however, shows that both species are junior sinonyms of Neohipparion floresi Stirton, 1955 from the Yepómera local fauna, middle Pliocene of Chihuahua State. The Neohipparion material from this  collection is also referable to N. floresi, thus extending the geographic range of this species from the State of Chihuahua to the State of Guanajuato, in Central Mexico. Futhermore a discusión to clarify the nomenclatorial status of the genus Neohipparion in Mexico is enclosed.  

The area studied is located in the arid zones of the States of Nuevo León and Coahuila, within the Don Martin irrigation district. It has an extension of 50,000 hectares of which, at present, only 16,000 are irrigated. The area is underlain predominantly by sedimentary rocks, mainly limestone and gypsum of the upper Tertiary. Climate is hot and arid, with mean precipitation of 490 mm and mean annual temperature of 22.4º C. One of the reasons for carrying out this work was to recognize factors that have contributed to the genesis of soil formation in the area under study. The distribution and evaluation of salinity and/or sodicity of different soil units are characterized. Natural vegetation has been greatly altered by man's influence and by overgrazing. Vegetation is characterized by mezquite (Prosopis glandulosa), (Boutelow trifida), and nopal (Opuntia leptocaulis, Cercidium texanum and Setairina). Crops are constituted by wheat, corn, sorghum, onion and cotton... In order to continue, download the full paper in PDF.

A volcano-plutonic sequence, associated with pelagic sedimentary rocks containing Albian ammonites, was discovered in the Bacubirito area, northern Sinaloa. The sequence, with its stratigraphic order apparently inverted, seems to have been thrusted from the northwest over phyllonitic green rocks of unknown age. From base to top, the sequence consists of four, mutually conformable units which are: Unit A, limestone and chert with its base strongly tectonized; Unit B, alternating shaly limestone, calcareous shale, chert with radiolarians and interbedded limestone, felsic tuff, siliceous shale, and some volcanogenic graywacke; Unit C, basaltic pillow lavas with a sedimentary interval in its upper part; and Unit D, gabbroic and doleritic rocks, partly metamorphosed under possible suboceanic conditions.

El archipiélago de las Islas Marías se encuentra localizado a 110 km del Puerto de San Blas, Nayarit y se ubica geográficamente a los 21 °15’- 21° 50’ N y 106° 14’ W en el Océano Pacífico; está formado por cuatro islas conocidas con el nombre de María Magdalena, María Cleofas, San Juanico y María Madre, esta última tiene una superficie de 144 km2. El archipiélago fue comprado por el Gobierno Federal y desde el año de 1903 es utilizado como Colonia Penal Federal, actualmente es un Centro de Readaptación Social. En la parte norte de la Isla María Madre se encuentra un afloramiento de 5,600 metros de longitud conocido con el nombre de Arroyo Hondo, se inicia al suroeste del Campamento Venustiano Carranza y termina en el extremo norte de la Isla, en un lugar conocido con el nombre de Playa Caleras.

Dans le secteur occidental de l'Axe Transmexicain existent différents volcans, de taille importante qui montrent une évolution interessante aussi bien dans la nature des dynamismes éruptifsque par la varieté des laves émises, celles-ci ont une composition qui varie depuis des andésites riches en silice jusqu'à des dacites, riodacites et parfois des rhyolites(Ceboruco-Tequila). Cette evolution continue est liée à l'existence de chambres magrnatiques sous ces édifices ce qui facilite les phenome'nes de differenciation magmatique. Alignes selon les fractures régionales, s'observent egalement differents volcans monogéniques qui ne sont pas en relation avec la chambre magmatique des édificesprincipaux, comme le démontrent les caractères mineralogiques.Ces laves sont typiquement calco-alcalines, cependant les roches basaltiques montrent des caractères transitionnels. La répartition particulière des volcans de la zone occidentale de l'Axe Transmexicain, est due au fait que dans ce secteur se produit la subduction de la Plaque de Rivera, tandis que plus à l'Est c'est la Plaque de Cocos qui s'enfonce sous la Plaque Nord-Americaine.

I welcome the opportunity provided by Demant and Vincent's discussion (1978) of Mahood (1977) to correct an error in my original interpretation of the geological evolution of the Sierra La Primavera. The paper was based on observations made during a single field season and on less than a dozen K-Ar dates; I attempted to indicate the preliminary nature of my conclusions in the title of the article. As pointed out by Demant and Vincent, the fundamental error in my interpretation was the assumption that the Tala Tuff was one of the younger eruptive units at Primavera when, in fact, it is one of the older. In this reply, I would like first to present my revised view of the geologic evolution of the Sierra La Primavera and, second, to reply specifically to som of Demant and Vincent's points... In order to continue, download the full paper in PDF.

The ostracod species Havanardia havanensis and H. sohni are described. They were collected in recent bioclastic sediments of Quintana Roo's continental shelf, between Isla Mujeres and Isla Cozumel. The simples show the following environmental characteristics: an average temperature of 28.5º C, an average salinity of 36‰ and an average depth of 28 m. This genus is considered to be characteristic of reef environments. H. havanensis is restricted to the Mar Caribe area.

Un subcomité de la Comisión Internacional de Nomenclatura (IMAC) ha trabajado sobre la clasificación y lexicología del grupo mineralógico de pirocloros, publicando sus decisiones en Amer.Miner. 62.5 (1977) 403. Se exponen aquí, como nota informativa, los resultados de sus investigaciones... In order to continue, download the full paper in PDF.

Mexican Triassic floras are of limited geographical distribution. Only a few localities contain abundant plants of this age, since well-preserved Triassic plants are found only in four localities in the States of Sonora, Tamaulipas, San Luis Potosí and Hidalgo, all from Upper Triassic sediments. Among the dominant plants of these floras, there are cycadophytes, ferns and pteridosperms, while equisetals and conifers are rather scarcely represented. This paper includes general aspects of the Triassic plants, as well as a review of the stratigraphy and of the macroscopic vegetation of the Mexican Upper Triassic continental rocks.