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Search Results: 1 - 10 of 4962 matches for " Molina-Garza "
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Chronostratigraphy and paleomagnetism of the Balsas Group in the Tuzantlán-Copalillo basin, northern Guerrero state, Mexico
Molina-Garza, Roberto S.;Ortega-Rivera, Amabel;
Revista mexicana de ciencias geológicas , 2006,
Abstract: the cenozoic sedimentary fill of the tuzantlán-copalillo basin, in northeast guerrero state, mexico, is assigned to two distinct stratigraphic units. the first unit consists of a 200 m thick fining upward section that grades eastward from massive cobble and boulder conglomerate into interbedded coarse conglomeratic sandstone and mudstone. the sandstone and mudstone fades of this unit has been referred to as the zacango beds, but together with the conglomeratic section to the west it is here assigned to the balsas group based on demonstrable correlation and lateral fades changes that link these strata. the second unit disconformably overlies the balsas group, and comprises a tuffaceous fluvio-lacustrine unit that has been mapped as the oapan formation. these strata are lithologically dissimilar to the formally defined oapan formation elsewhere in the balsas river basin. we do not consider the fluvio-lacustrine tuffaceous unit part of the balsas depositional cycle; we note, however, that including these strata in the oapan formation thus requires a re-definition of this unit. volcanic rhyolitic rocks were emplaced near the end of the balsas depositional event, and locally they are interbedded in the sequence. mineral separates ofbiotite and sanidinefor one of these volcanic units produced concordant 4ar/39ar dates of ca. 33 ma. we hypothesize that emplacement of volcanic rocks changed the depositional style in the basin by reducing stream gradient and closing drainages. oapan strata were thus deposited under different conditions than the balsas group. magnetostratigraphic sampling of a 130 m thick composite section from two localities, suggests that that the balsas group sequence in the tuzantlán-copalillo basin was deposited in the interval between chrons cl in and c12r, between about 37 and 32ma. the mean paleomagnetic direction for the amacuzac river locality (d=340.8°, 1=34.3°; k=62.6, n=9, α95=6.6°) is slightly discordant, whilst at the acapulco highway locality
Prevalencia de Trypanosoma cruzi en triatominos silvestres de Nuevo León, México
Molina-Garza,Zinnia Judith; Rosales-Encina,José Luis; Galaviz-Silva,Lucio; Molina-Garza,Daniel;
Salud Pública de México , 2007, DOI: 10.1590/S0036-36342007000100006
Abstract: objective: to determine the prevalence of trypanosoma cruzi in triatomines from nuevo león using the standardization of an improved enzyme-linked immunosorbent assay test. materials and methods: from july to september 2005, 52 triatomines were captured in general terán, a municipality located in nuevo león. they were analyzed using optical microscopy (om) and a polymerase chain reaction (pcr), as standards of reference, to develop a technique for detecting the parasite using enzyme-linked immunosorbent assay (elisa). results: using om and pcr, 31 triatomines were found to be positive and 21 negative. using elisa, 27 samples were identified as positive and 25 negative (specificity 100%, sensitivity 87%, negative predictive value 84%, and positive predictive value 100%). the prevalence of infected triatomines was 59.61% with om and pcr, and 51.92% with elisa. our data confirm that the elisa assay in triatomines is a fast, reliable and useful tool. conclusions: since it was possible to simultaneously analyze a large number of samples with high sensibility and specificity values, the elisa test proves to be useful for new epidemiologic studies having a high number of vectors. it is also less expensive than pcr. it is therefore recommended for epidemiological and preventive surveillance programs as a first screening test before conducting a confirmatory test using pcr.
Paleomagnetic study of Jurassic and Cretaceous rocks north of San Marcos fault, central Coahuila, México
González-Naranjo, G. A.;Molina-Garza, R. S.;Chávez-Cabello, G;
Geofísica internacional , 2008,
Abstract: upper jurassic and lower cretaceous continental strata at potrero colorado, in the core of sierra la fragua anticline in central coahuila, carry dual-polarity characteristic magnetizations that we interpret as near primary chemical remanent magnetizations. upper jurassic fluvial and eolian sandstones of the colorado beds yield a tilt-corrected mean of d=10.2° i=28.2° (n=18 sites, k=22.1, α95=7.5°). a steeper inclination magnetization observed in five sites of the colorado beds is interpreted as a secondary, post-laramide folding, magnetization. lower cretaceous fluvial sandstones of the san marcos formation yield a combined mean of d=358.1°, i=46.4° (n=13 sites, k=22.7, α95=8.9°), but the stratigraphically lower sites on the eastern side of the anticline have south-southwest directed and moderately steep negative magnetizations (mean of d=191.7° i=-54.9°; k=38.7, α95=9.8°, n=7 sites) which are statistically distinct from northwest directed magnetizations (mean of d=333.6° i=58.0°; k=28.3, α95=12.8°, n=6 sites) observed in stratigraphically higher sites in the west-central part of the anticline. we interpret the difference in declinations in the san marcos formation as the result of rotation during deposition of this unit. the characteristic shallow-inclination magnetization in jurassic strata is also discordant with respect to the late jurassic reference direction. both, the lower san marcos formation and the colorado beds indicate clockwise rotations of 38.5°±8.3° and 30.0°±2.3°, respectively. the sampling sites are located within a clastic wedge that records activity of the san marcos fault during late jurassic and early cretaceous time. these data indicate that during deposition of the colorado beds and san marcos formation, the fault behaved as a normal fault with a small right-lateral component. the area of potrero colorado is interpreted as a zone of relay in the normal san marcos fault, which accommodated clockwise rotation recorded by upper jurassic and lowe
Paleomagnetic study of Jurassic and Cretaceous rocks north of San Marcos fault, central Coahuila, México.
G. A. González-Naranjo,R. S. Molina-Garza,G. Chávez-Cabello
Geofísica internacional , 2008,
Abstract: Upper Jurassic and Lower Cretaceous continental strata at Potrero Colorado, in the core of Sierra La Fragua anticline in central Coahuila, carry dual-polarity characteristic magnetizations that we interpret as near primary chemical remanent magnetizations. Upper Jurassic fluvial and eolian sandstones of the Colorado beds yield a tilt-corrected mean of D=10.2° I=28.2° (n=18 sites, k=22.1, α95=7.5°). A steeper inclination magnetization observed in five sites of the Colorado beds is interpreted as a secondary, post-Laramide folding, magnetization. Lower Cretaceous fluvial sandstones of the San Marcos Formation yield a combined mean of D=358.1°, I=46.4° (n=13 sites, k=22.7, α95=8.9°), but the stratigraphically lower sites on the eastern side of the anticline have south-southwest directed and moderately steep negative magnetizations (mean of D=191.7° I=-54.9°; k=38.7, α95=9.8°, n=7 sites) which are statistically distinct from northwest directed magnetizations (mean of D=333.6° I=58.0°; k=28.3, α95=12.8°, n=7 sites) observed in stratigraphically higher sites in the west-central part of the anticline. We interpret the difference in declinations in the San Marcos Formation as the result of rotation during deposition of this unit. The characteristic shallow-inclination magnetization in Jurassic strata is also discordant with respect to the Late Jurassic reference direction. Both, the lower San Marcos Formation and the Colorado beds indicate clockwise rotations of 38.5°±8.3° and 30.0°±2.3°, respectively. The sampling sites are located within a clastic wedge that records activity of the San Marcos fault during Late Jurassic and Early Cretaceous time. These data indicate that during deposition of the Colorado beds and San Marcos Formation, the fault behaved as a normal fault with a small right-lateral component. The area of Potrero Colorado is interpreted as a zone of relay in the normal San Marcos fault, which accommodated clockwise rotation recorded by Upper Jurassic and Lower Cretaceous strata.
Magnetoestratigrafía de la Formación San Marcos del Cretácico Inferior, Coahuila, México: Implicaciones tectónicas y paleogeográficas
Arvizu-Gutiérrez, Irving Rafael;González-Naranjo, Gildardo Alonso;Stanley Molina-Garza, Roberto;Chávez-Cabello, Gabriel;
Boletín de la Sociedad Geológica Mexicana , 2011,
Abstract: we report the results of a magnetostratigraphic study of the san marcos formation in central coahuila, at two localities along the san marcos fault. these localities are characterized by outcrops of a sequence of conglomerates, immature sandstone and red mudstone, cemented by hematite; the sequence was deposited in a continental environment, and has been assigned to the early cretaceous. all specimens, from a total of 35 paleomagnetic sites, were subjected to alternating field and thermal demagnetization, the latter being the most effective in isolating the (high temperature) characteristic magnetization. the characteristic component is unblocked between 625° and 660 °c. both normal and reverse polarity magnetizations are represented, and the overall mean is of dec = 352.7 °, inc = 55.5 °, n = 3 localities (18 sites), k = 27.07, α95 = 6.8 °. this result suggests a small clockwise rotation with respect to the expected reference direction for the cretaceous, estimated from the apparent polar wandering curve for cratonic north america. however, the data suggest that there was relative rotation between localities, and the observed rotations are more likely explained as local vertical-axis rotations. the magnetic polarity zonation in the san marcos formation suggests that this unit represents the early barremian through early aptian. the correlation to global magnetic polarity timescale suggests that this unit is correlative with cupido formation, and that the transgressive littoral facies of the las uvas formation, as well as flooding of coahuila paleo-island at potrero colorado, occurred in the early aptian. the best correlation with the global magnetic polarity time scale corresponds to the interval from m5n (normal) to m0r (inverse) approximately between 131-125 ma. the sedimentation rate indicated by this correlation, assuming a constant rate, is relatively low (~30-50 m/ma) for an active tectonic environment and is more consistent with a region where accommodation
Paleomagnetism, structure and 40Ar/39Ar geochronology of the Cerro Mercado pluton, Coahuila: Implications for the timing of the Laramide orogeny in northern Mexico
Molina-Garza, Roberto S.;Chávez-Cabello, Gabriel;Iriondo, Alexander;Porras-Vázquez, Mario Alberto;Terrazas-Calderón, Guillermo Daniel;
Revista mexicana de ciencias geológicas , 2008,
Abstract: the cerro mercado pluton, emplaced in the coahuila fold belt, contains magmatic, ductile, and brittle fabrics that suggest local and regional deformation during igneous emplacement, later affected by regional deformation in the area. the cerro mercado pluton intruded, deformed and uplifted upper cretaceous strata in the southern edge of the central depression of the sabinas basin. a hornblende mineral separate from the pluton yielded a 40ar/39ar plateau age of 44.29 ± 0.19ma (1σ), interpreted as an approximation to the crystallization age of the monzonite. a younger biotite total fusion age of 41.23 ± 0.21 ma (1σ) from a different rock sample is interpreted to represent slow cooling (80°c/ma) of the cerro mercado pluton. paleomagnetic analyses of the pluton yieldwell defined remanent magnetizations of nearly uniform reverse polarity, with a grand mean of d=178.2° and i=-61.7° (n=9 acceptable sites; k=57.5, α.95 = 6.8°). these data are discordant with respect to the eocene reference direction, indicating apparent clockwise rotation (8°) and inclination steepening (21°). the simplest interpretation of the discordance is that northwestward tilting of the pluton occurred during basin inversion within a weakly right lateral transpressive regime with nnw directed contraction. the strain field is consistent with contraction during the laramide orogeny. also, remanence acquisition is contemporaneous with both tectonic and magmatic fabrics in the pluton indicating that it is syntectonic. this suggests - in agreement with stratigraphic data - that the laramide orogeny in central coahuila ended some time after about 44 ma. we propose that reactivation of the san marcos fault and other basement faults in the sabinas basin represents the last manifestation of shortening produced by the laramide orogeny. this was a short episode of deformation that ended by the time of emplacement of younger plutons of the candela-monclova magmatic belt ca. 41 ma. this indicates that culmination
Virus de la necrosis hipodérmica y hematopoyética infecciosa (IHHNV) y virus del síndrome de Taura (TSV) en camarón silvestre (Farfantepenaeus aztecus Ives, 1891 y Litopenaeus setiferus Linnaeus, 1767) de La Laguna Madre, Golfo de México
Guzmán-Sáenz,Francisco M; Molina-Garza,Zinnia J; Pérez-Casta?eda,Roberto; Ibarra-Gámez,José C; Galavíz-Silva,Lucio;
Revista de biología marina y oceanografía , 2009, DOI: 10.4067/S0718-19572009000300012
Abstract: the occurrence of infectious hypodermal and hematopoietic necrosis virus (ihhnv) and taura syndrome virus (tsv) in wild shrimp litopenaeus setiferus (white shrimp) and farfantepenaeus aztecus (brown shrimp) captured from the estuary of la pesca in la laguna madre tamaulipas, mexico, are reported. this study was performed for histopathology and amplification of nucleic acids. the prevalence of tsv was 6.6% (12/180) and 4.4% for ihhnv (8/180). most cases were observed from november to march (15/180). the presence of these viruses in wild shrimp from the la laguna madre, alerts about the risk that are having the wild populations and the shrimp farms that are contiguous with the gulf of mexico, so it is suggested to establish a program of sanitary monitoring and to verify the impact of both viruses in the near shrimp farms of the la laguna madre.
The relationships between volcanism and extension in the Mesa Central: the case of Pinos, Zacatecas, Mexico
Aranda-Gómez, José Jorge;Molina-Garza, Roberto;McDowell, Fred W.;Vassallo-Morales, Luis Fernando;Ortega-Rivera, María Amabel;Solorio-Munguía, José Gregorio;Aguillón-Robles, Alfredo;
Revista mexicana de ciencias geológicas , 2007,
Abstract: pinos volcanic complex is an uplifted area that exposes mesozoic strata and mid-tertiary volcanic and sedimentary rocks. its stratigraphy, deformation style, and volcanism are characteristic of the mesa central region of central mexico and the southeastern segment of the sierra madre occidental (smo) volcanic province. the oldest rocks in pinos are marine carbonate sedimentary and siliciclastic rocks that underlie a red bed sequence (pinos red beds) interlayered with felsic volcanic rocks, in turn partially covered by a voluminous lava dome complex. the pinos red bed sequence is at least 900 m thick and it is formed by well-lithified conglomeratic sandstone and matrix-supported, generally fine-grained to medium-grained, polymictic conglomerate. clasts in the pinos red beds were derived from the mesozoic basement, subaerial felsic volcanic rocks of unknown provenance, and tourmaline-bearing muscovite granite. interlayered volcanic rocks include ash-fall tuffs, a densely welded ash-flow tuff, and water-laid or reworked pyroclastic material. the main components of the dome complex are a dark-red, porphyritic potassium-rich trachyte, and a buff-colored, porphyritic rhyolite, for which we report lava mingling (the first one in the smo volcanic province). field relations at the pinos volcanic complex demonstrate a close temporal relationship between felsic volcanism and extension. faulting in pinos is complex as it includes arrays of cenozoic normal faults with ns, nw, and ne trends, for which cross-cutting relations are ambiguous. a combination of mapping, k-ar geochronology, petrographic work and interpretation of the magnetic polarity of the volcanic units allow us to establish that repeated pulses of synextensional volcanism occurred during the period between ~32 and 27 ma. these data demonstrate that extension in the mesa central is older than 29-27 ma, the oldest previously recognized episode of extension. the earliest (> 32 ma) pulse of extension may be related to
Tectónica de la sierra Cuesta El Infierno y su posible relación con fallas reactivadas cerca del levantamiento de Plomosas, Chihuahua, México
Oviedo-Padrón, Edgar Gerardo;Aranda-Gómez, José Jorge;Chávez-Cabello, Gabriel;Molina-Garza, Roberto Stanley;Iriondo, Alexander;González-Becerra, Paula Cecilia;Cervantes-Corona, Jorge Alfredo;Solorio-Munguía, José Gregorio;
Revista mexicana de ciencias geológicas , 2010,
Abstract: geologic and structural mapping of volcanic rocks in sierra cuesta el infierno, located on the western flank of the plomosas uplift, allowed us to divide the paleogene volcanic section into two succesions. the volcanic rocks unconformably overlie sedimentary rocks of the chihuahua fold belt. the lower volcanic succession felsic ash flow tuffs and epiclastic continental deposits) is separatedfrom the upper volcanic succession (andesitic lavaflows with interlayered rhyolitic ash flow tuff) by a small angular unconformity. the volcanic successions are exposed in northern and southern structural domains of the sci, which are separated by an inferred basement fault (n70°w) with a complex history. the basement fault acted since middle to late paleogene as a transfer zone that accommodated the deformation of fault systems with different trends in the areas located north and south of its trace. the basement fault also controlled the distribution ofsome of the ash flow tuffs, the eruption of the lava flows, and the local basin and range strain pattern during the cenozoic. a sse-plunging syncline with a n20°w trend associated with a system of listric normal faults parallel to the fold axis and a small roll-over anticline occur in rocks of the lower volcanic succession in the northern structural domain. the syncline is interpreted as a fault bendfold. in the southern domain of the study area, we recognize an accommodation zone between two antithetic listric faults that consists of a n45°w-trending antiform.
Paleomagnetic reconstruction of Coahuila, Mexico: the Late Triassic Acatita intrusives
Roberto S. Molina Garza
Geofísica internacional , 2005,
Abstract: The Acatita plutons intrude the upper Paleozoic of Las Delicias, southern Coahuila. We collected 96 samples from 15 sites in two plutons from Valle El Sobaco and Sierra Los Remedios for paleomagnetic and 40Ar-39Ar analyses. Separates of hornblende (215.9 ±1.9 Ma, 2σ confidence level), biotite (217.3 ±1.2 Ma), and K-feldspar (205.6 ±1.4 Ma) yield nearly flat age spectra although none of the data satisfy strict plateau criteria, possibly reflecting slight alteration. The preferred ages are interpreted as fairly precise records of Late Triassic cooling of the plutonic suite, which has yielded concordant U-Pb Zircon ages ca. 220 Ma. Most samples yield north-directed and steep positive magnetizations similar to the late Cenozoic expected field direction. Some samples, mostly from mafic enclaves, show northwest magnetization of shallow inclination (southeast at one site) with alternating fields above ~30 mT and thermal demagnetization above ~400°C. The overall mean direction, corrected for 15° northeast dip of the overlying lower Cretaceous strata (dec=342.7°, inc=+4.2°; k=35.4, α95=9.4°, n=8 sites) indicates moderate counterclockwise (14°±8°) rotation with respect to the Late Triassic cratonic reference (reference pole: 57.5°N / 84°E), and moderate southward displacement (7°±5°). The Acatita pole falls within a cluster of Late Triassic poles from Africa, South America, and North America as restored in North American coordinates. A major difficulty is distinguishing local, small-scale rotations, such as a gentle tilt of the pluton after magnetization, from regional events involving large-scale displacements. Rotations such as observed at Acatita are suggested by synfolding magnetizations (Eocene in age) in the transverse sector of the Sierra Madre Oriental and by primary magnetizations in Eocene volcanic rocks near Chihuahua. Therefore rotations of Coahuila Island may be a Cenozoic attribute related to late Laramide deformation. Reconstructions of western equatorial Pangea should place the Coahuiltecano terrane at or near its present position with respect to North America.
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