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546,196 artículos
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Año:
2019
ISSN:
2007-2902, 1026-8774
Rodríguez-Castañeda, José Luis
Universidad Nacional Autónoma de México
Resumen
The study área is in west-central Sonora. It is characterize by rocks of various age wich range from Paleozoic through Mesozoic and Tertiary. The Paleozoic consists of limestones rich in chert, quarzite, limestone with abundant crinoids and shells. Some of these rocks are locally metamorphosed or recrystalized. The presence of six specimens of coral gives a Mississippian age to this sequence. Around the city of Hermosillo, metamorphosed limestone with abundant wollastonite crops out these rocks have been assigned to the Permian. A detritic carbonate sequence sonsisting of argillaceous limestone, siltstone, calcarenite, occasionally cossbedded, limestone, brecciated quartzite and lenses of microconglomerate containing reworked fragments of fusulinids, crinoids, chert and fragments of quartzite, was identified and its age is Middle to Upper Triassic... In order to continue, download the full paper in PDF.
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Año:
2019
ISSN:
2007-2902, 1026-8774
Ferriz, Horacio
Universidad Nacional Autónoma de México
Resumen
The lithostratigraphic units of the San Marcos caldera are described in this article. The caldera is a silicic volcanic system of Eocene (?) age, located in the eastern foothills of the Sierra Madre Occidental, about 30 km NW of the city of Chihuahua. Volcanic activity began with plinian eruptions that led to the collapse of the San Marcos caldera, which had an estimated diameter of 20 km and a mínimum vertical displacement of 250 m. The plinian eruptions continued after collapse, filling the depression with the rhyodacitic Victorino Ignimbrite. Resurgent (?) doming of the floor of the caldera probably took place shortly after the emplacement of the Victorino Ignimbrite. Between the resurgent dome and the walls of the caldera a moat zone was formed, in which conglomerates, sandstones, and thin ignimbrites of the clastic member of the Cumbres Formation accumulated... In order to continue, download the full paper in PDF.
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Año:
2019
ISSN:
2007-2902, 1026-8774
Celis-Gutiérrez, Socorro
Universidad Nacional Autónoma de México
Resumen
La antigua laguna de Salina Grande se encuentra en el Estado de Sonora (31°32' N y 114°07' W) y tiene una extensión aproximada de 3.4 km de longitud por 1.5 km de anchura.
Queda comprendida dentro de la provincia fisiográfica de Sierras Sepultadas en la subprovincia del Desierto de Sonora (Raisz, 1964), constituida principalmente por depósitos fluviales, deltaicos, eólicos y marinos pliocuaternarios, con espesor de varios cientos de metros.
El principal criterio para considerar estos depósitos como pleistocénicos es la altitud de los mismos con respecto al nivel medio del mar actual (Malpica et al., 1978; Ortlieb y Malpica, 1978; Ortlieb, 1980).
En esta región se observan sedimentos fluviales alternando con marinos que podrían estar relacionados con movimientos neotectónicos regionales o con factores geodinámicos externos (variaciones de nivel del mar por glacioeustatismo, períodos húmedos y secos, etc.).
In order to continue, download the full paper in PDF.
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Año:
2019
ISSN:
2007-2902, 1026-8774
Ortega-Gutiérrez, Fernando
Universidad Nacional Autónoma de México
Resumen
Axial strain measurements on 73 granitic pebbles within a metaconglomerate in the Paleozoic Tecomate Formation, allowed the statistical definition (harmonic mean) of a strain ellipsoid implying a linear shortening of 65% along the shortest axis (Z) and extension of 150% along X (longest axis), whereas the intermediate axis (Y) was extended only 17%. The Flinn value K= 0.66 lies in the field of flattened ellipsoids, but close to the constricted types.
Eventhough pressure-solution is present at several pebble contacts, constant volume deformation was assumed. Because of this and of the higher ductility of the matrix (foliation is deflected around the pebbles), the calculated values must be considered mínimal in relation to the total deformation affecting the metaconglomerate and the unit that contains it.
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Año:
2019
ISSN:
2007-2902, 1026-8774
Coral Hinostroza, Gladys N.; Segura-Vernis, Luis R.
Universidad Nacional Autónoma de México
Resumen
The qualitative and quantitative determinations were made of the foraminifera present in 65 samples of lagoon sediment. From these results, it was possible to discuss the significance of such indexes as total population, living population, number of genera and species, aglutinated foraminifera and the relation between the living and total population.
Results indicate that the largest population of living organisms was found in the shallow lagoon margins which have marshland characteristics. The fauna is composed of nine genera and 10 species with a non-uniform abundance. Representative species are: Ammotium salsum (Cushman and Brönnimann), Miliammina fusca (Brady) and Eponidella cf. E. gardenislandensis Akers... In order to continue, download the full paper in PDF.
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Año:
2019
ISSN:
2007-2902, 1026-8774
Roldán-Quintana, Jaime
Universidad Nacional Autónoma de México
Resumen
The San Felipe District is located in the east-central portion of the State of Sonora, 136 km northeast of the city of Hermosillo. The oldest rocks are Early Cretaceous contact metamorphics; these rocks originally represented a sequence of andesitic flows and tuffs, and isolated outcrops of limestones, conglomerates and siltstones. Conformably overlying these rocks is a volcanic sequence, including rhyolites, ignimbrites and tuffaceous sandstones of a probable Paleocene age. Unconformably overlying the previous units is the Báucarit Formation, early Miocene in age, consisting of sandstones, conglomerates and clay horizons, including some basaltic-andesite flows interbedded mainly at the lower section. Younger clastic deposits unconformably overlie older rocks; a Pliocene age has been assigned to these clastics... In order to continue, download the full paper in PDF.
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Año:
2019
ISSN:
2007-2902, 1026-8774
Ferrusquía-Villafranca, Ismael; Carranza-Castañeda, Óscar
Universidad Nacional Autónoma de México
Resumen
Seven Neohipparion species from three local faunas in as many Mexican States have been described ; these are: Neohipparion montezuma (Leidy) 1882, Neohipparion peninsulatum (Cope), 1885 and Neohipparion rectidens (Cope), 1886 from the Tehuichila local fauna, middle Pliocene of Hidalgo State; Neohipparion floresi Stirton, 1955 and Neohipparion arellanoi Stirton, 1955 from the Yepómera local fauna, middle Pliocene of Chihuahua State; Neohipparion otomii Mooser, 1959 and Neohipparion monias Mooser, 1963 from the Rancho El Ocote local fauna, middle Pliocene of Guanajuato State.
The study of the extensive collection from the last locality called for a taxonomic revision of these species... In order to continue, download the full paper in PDF.
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Año:
2019
ISSN:
2007-2902, 1026-8774
Hernández-Silva, Gilberto
Universidad Nacional Autónoma de México
Resumen
Located in a semi-arid zone, the area under study covers 6,385 hectares in which alluvions from the Quaternary predominate and, in a lower proportion, sandstone and lutites. It belongs to the closed hydrological basin of El Salado. lts climate is dry and temperate; the prevailing vegetation is formed by associations of cactaceous, inerm, evergreen bushes, as well as reduced areas of grassland.
Twenty one profiles were made according to land characteristics, sampling was carried out by layers and horizons. A total of 130 samples was gathered and analyzed, both physically and chemically; field observations of the profiles were also made... In order to continue, download the full paper in PDF.
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Año:
2019
ISSN:
2007-2902, 1026-8774
Buitrón, Blanca Estela; Silva-Sánchez, Bertha
Universidad Nacional Autónoma de México
Resumen
Two species of exocyclic echinoids (Oligopygus rotundus Cooke, and Eupatagus (Eupatagus) mooreanus Pilsbry) are described from outcrops of the Tantoyuca Formation (upper Eucene) from sites located in the northeastern part of the State of Veracruz. These species previusly were ciled from the Moodys Branch Formation (upper Eocene) of Florida, U. S. A.
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Año:
2019
ISSN:
2007-2902, 1026-8774
de Pablo-Galán, Liberto
Universidad Nacional Autónoma de México
Resumen
The interelement correction factors alfa or mass absorption correction factors are computed for 35 elements of geochemical interest affected by 65 interfering elements of equal geochemical interest and abundance. The concept of effective wavelength of the analyzed element and a spectrometer geometrical factor of 1.5 are used. The systematic variation of the alfa factors with the atomic number defines applications and pertinent corrections in analytical geochemistry.
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