Relationship between extensional tectonic style and the paleoclimatic elements at Laguna El Fresnal, Chihuahua Desert, Mexico

A multi-disciplinary (geomorphology, ecology, sedimentology, geology, gravimetry, ground penetrating radar, and direct current resistivity) study established a relation among the subsurface structure of Laguna El Fresnal, the geomorphic units, and the vegetation. According to gravity data, Laguna El Fresnal is an asymmetric fault bounded basin typical of the Basin and Range province and the Rio Grande rift. The geomorphic units along the eastern and western sides of El Fresnal basin show marked differences. The western slope is characterized by a variety of sedimentary deposits and geomorphic features, such as alluvial fans, debris flows, braided stream deposits, sheet flood deposits, erosional surfaces, paleosols and fluvial paleosystems of dendritic and parallel types. In contrast, the eastern slope has only aeolian deposits covering structures of alluvial origin. The vegetation also shows this asymmetry. Along the western slope vegetation is composed, from the highest to the lowest elevations, of Juniperus ssp., yucca, Echinocereus ssp., and Prosopis ssp.; whereas, on the eastern slope, the vegetation is mostly composed of small Prosopis ssp. associated with Larrea tridentata communities. The Juniperus ssp. vegetation represents remnants of an environment (Upper Pleistocene age?) more humid than at present. The stratigraphy of the morphological units was tentatively established. Three depositional lobes (QI, QII, and QIII), and three generations of alluvial fans (QIV, QV, and QVI) were defined. Silty-clayey sediments of aeolian origin (loess) from the basin constitute unit QVII. The structure of the first 3–4 m of units QVII and QI were established using a ground penetrating radar. Vertical electric soundings indicate at least 40 m of clay sediments beneath the plain. The contrasting differentiation between geomorphic units and vegetation at both slopes of the basin indicates that the western border of the basin is or was uplifting

Shallow crustal structure of the junction of the grabens of Chapala, Tepic-Zacoalco and Colima, Mexico

Gravity data is used to infer the shallow crustal structure of the Tepic graben adjacent to the City of Guadalajara. This depression does not constitute a symmetric graben with steep master faults but rather a complex transition zone. Blocks detached from the granitic sierras are downfaulted and tilted to the northeast along the frong of these sierras. Farther to the north, the granitic basement deepens gradually. However, it steepens at the limit between the Sierra Madre Occidental and the Jalisco Block. Northwest of our study area, the limit is located north of the Plan de Barrancas fault. At the east the limit is located closer to the southward prolongation of the Plan de Barrancas fault. The change in position occurs near La Primavera caldera. The La Primavera caldera, Tequila volcano, and vents of cinder and lava cones are emplaced along NW-SE weakness zones in the batholith. The crust of the Sierra Madre Occidental adjacent to the limit features NE-SW lineaments perpendicular to those of the neighbouring Jalisco Block (JB)

Vulnerability to contamination of the Zaachila aquifer, Oaxaca, Mexico

The aquifer of Zaachila was evaluated following conventional methods (DRASTIC, AVI, and GOD). Depth to the water table was established from a set of wells. Accordingly, the groundwater flows from N to S. Hydraulic conductivity ranges between 1.81647E-05 and 1.70411E-04 m/s, while transmissivity varies between 22.01 and 220.85 m2/day. The net mean annual recharge was estimated at 98 mm/year. The aquifer is constituted mainly by sand, gravel and clay. The soil cover is up to 1.5 m thick and is constituted by lime, clay and sandy material. According to GOD, some zones of this aquifer have a medium to high vulnerability. DRASTIC assigns a high vulnerability to large part of the area. The highest values are observed in the southern and middle sections, from Oaxaca city to the south including San Bartolo Coyotepec, as well as Zaachila town and airport. The AVI method assigns to the valley a high to very high vulnerability. A sensitivity analysis suggests that depth to water table is the key factor determining vulnerability, followed by impact to the vadose zone and soil type

Subsurface structure of the Tecocomulco sub-basin (northeastern Mexico basin), and its relationship to regional tectonics

Gravity, magnetics, DC resistivity, VLF profiles, geologic mapping, and analysis of regional lineaments in the Tecocomulco sub-basin of the northeastern Mexico Basin were carried out. To the south, the structure is of the half-graben type. To the north, the basin gets wider. Three NW-SE faults bound the half-graben to the E while only one delimits it to the W. Faults delimiting the half-graben, as well as several cinder cones and the neighboring ranges delimiting the basin, have a NE-SW orientation. The half-graben structure is due to tilting towards the NW of regional shallow crustal blocks. A chain of cinder cones interrupts the southward surficial drainage towards the neighboring Apan Basin, but we infer a communication at depth between these two sub-basins through a narrow graben. The faults in the Tecocomulco basin might still be active, as inferred by low-level seismic activity. DC resistivity helped to characterize the stratigraphic sequence of the volcano-sedimentary infill. The Acoculco caldera is not a piston-like caldera but a collapsed graben caldera. The Chichicuautla caldera has been downfaulted to the south by a NW-SE fault. The gravity signature of the southern half of this caldera is masked by the presence of a structural high, or by mafic bodies

Subsurface structure of the Tecocomulco sub-basin (northeastern Mexico basin), and its relationship to regional tectonics

Gravity, magnetics, DC resistivity, VLF profiles, geologic mapping, and analysis of regional lineaments in the Tecocomulco sub-basin of the northeastern Mexico Basin were carried out. To the south, the structure is of the half-graben type. To the north, the basin gets wider. Three NW-SE faults bound the half-graben to the E while only one delimits it to the W. Faults delimiting the half-graben, as well as several cinder cones and the neighboring ranges delimiting the basin, have a NE-SW orientation. The half-graben structure is due to tilting towards the NW of regional shallow crustal blocks. A chain of cinder cones interrupts the southward surficial drainage towards the neighboring Apan Basin, but we infer a communication at depth between these two sub-basins through a narrow graben. The faults in the Tecocomulco basin might still be active, as inferred by low-level seismic activity. DC resistivity helped to characterize the stratigraphic sequence of the volcano-sedimentary infill. The Acoculco caldera is not a piston-like caldera but a collapsed graben caldera. The Chichicuautla caldera has been downfaulted to the south by a NW-SE fault. The gravity signature of the southern half of this caldera is masked by the presence of a structural high, or by mafic bodies

Intraguild predation on the whitefly parasitoid eretmocerus eremicus by the generalist predator geocoris punctipes: A behavioral approach

A gravity study was conducted across the northern Oaxaca terrane and its bounding faults: the Caltepec and Oaxaca Faults to the west and east, respectively. These faults juxtapose the Oaxaca terrane against the Mixteca and Juarez terranes, respectively. The Oaxaca Fault also forms the eastern boundary of the Cenozoic Tehuacán depression. On the west, at depth, the Tehuacán valley is limited by the normal buried Tehuacán Fault. This gravity study reveals that the Oaxaca Fault system gives rise to a series of east tilted basamental blocks (Oaxaca Complex). The tectonic depression is filled with Phanerozoic rocks and has a deeper depocenter to the west. The gravity data also indicate that on the west, the Oaxaca Complex, the Caltepec and Santa Lucia faults continue northwestwards beneath Phanerozoic rocks. A major E-W to NE-SW discontinuity is inferred to exist between profiles 1 and 2. " 2014 Elsevier Ltd.",,,,,,"10.1016/j.jsames.2014.09.020",,,"http://hdl.handle.net/20.500.12104/42339","http://www.scopus.com/inward/record.url?eid=2-s2.0-84921911977&partnerID=40&md5=19f002b473bbe8dae489966860b562a3",,,,,,,,"Journal of South American Earth Sciences",,"39

Interpretation of gravity profiles across the northern Oaxaca terrane, its boundaries and the Tehuacán Valley, southern Mexico

A gravity study was conducted across the northern Oaxaca terrane and its bounding faults: the Caltepec and Oaxaca Faults to the west and east, respectively. These faults juxtapose the Oaxaca terrane against the Mixteca and Juarez terranes, respectively. The Oaxaca Fault also forms the eastern boundary of the Cenozoic Tehuacán depression. On the west, at depth, the Tehuacán valley is limited by the normal buried Tehuacán Fault. This gravity study reveals that the Oaxaca Fault system gives rise to a series of east tilted basamental blocks (Oaxaca Complex). The tectonic depression is filled with Phanerozoic rocks and has a deeper depocenter to the west. The gravity data also indicate that on the west, the Oaxaca Complex, the Caltepec and Santa Lucia faults continue northwestwards beneath Phanerozoic rocks. A major E-W to NE-SW discontinuity is inferred to exist between profiles 1 and 2. © 2014 Elsevier Ltd