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Crustal structure from 2-D gravity and magnetic data modeling, magnetic power spectrum inversion, and seismotectonics in the Laguna Salada basin, northern Baja California, Mexico
Juan García-Abdeslem,Juan Manuel Espinosa-Carde?a,Luis Munguía-Orozco,Víctor Manuel Wong-Ortega
Geofísica internacional , 2001,
Abstract: We have constructed a 2-D model of the crustal structure that accounts for gravity and aeromagnetic data across the Laguna Salada basin, using independent inferences from seismic refraction studies and the Airy-Heiskanen model of isostatic compensation, mass density and magnetic susceptibility measurements, a mass density-log from a well, and inversion of the power spectrum from magnetic anomalies. The model suggests that the Sierra Juárez root extends down to about 42 km depth. The crust-mantle interface is at about 25 km depth in the Laguna Salada basin, the Sierra Cucapá, and the western side of the Mexicali valley. The base of magnetized crust is at about 16 km depth under the Sierra Cucapá. The geometry of the basin suggests a half-graben structure dipping eastward. The maximum sedimentary fill is about 3 km thick. The seismogenic zone is about 20 km thick, in good agreement with the depth to the base of the crustal magnetic layer. In the Laguna Salada basin, clusters of events indicate zones of weakness. Hypocenter depths were confined at a depth of up to 19.6 km, being deeper at the margins of Laguna Salada basin. The seismicity pattern correlates well with the regional fault system. Focal mechanisms suggest transtensional deformation in agreement with the regional tectonic framework.
Structural pattern of subsidence in an urban area of the southeastern Mexico Basin inferred from electrical resistivity tomography
Arango-Galván, Claudia;Torre-González, Brenda De la;Chávez-Segura, René E.;Tejero-Andrade, Andrés;Cifuentes-Nava, Gerardo;Hernández-Quintero, Esteban;
Geofísica internacional , 2011,
Abstract: most of the urban area in the basin of mexico is underlain by sediments of the former lakes of chalco, xochimilco, mexico, texcoco, xaltocan and zumpango, which offer poor foundation conditions for buildings. water supply requirements have led to overexploitation of the aquifers, and the increased exacerbating the rate of subsidence causes housing units and roads to deteriorate. in order to understand the location of the cracking and fracturing pattern, a geophysical study using electrical resistivity tomography was performed in a populated zone of the southeastern mexico basin. five two-dimensional resistivity profiles were acquired. discontinuities in the resistive horizon (probably in extrusive igneous material) were identified. the discontinuities could be related to cracks and fractures observed on the surface which had previously damaged housing construction. a three-dimensional resistivity profile was also obtained. the 3d image confirms results obtained from 2d models, and shows a resistive layer with lateral discontinuities. the inferred fracture pattern has a preferential nw-se direction, related to the a subsidence process produced by overexploitation of the aquifer in the area.
Glacial Cycles and Milankovitch Forcing  [PDF]
Shiv Priyam Raghuraman
Physics , 2015,
Abstract: Using a recent conceptual model of the glacial-interglacial cycles we present more evidence of Milankovitch cycles being the trigger for retreat and forming of ice sheets in the cycles. This model is based on a finite approximation of an infinite dimensional model which has three components: Budyko's energy balance model describing the annual mean temperatures at latitudes, Widiasih's ODE which describes the behavior of the edge of the ice sheet, and Walsh et al. who introduced a snow line to account for glacial accumulation and ablation zones. Certain variables in the model are made to depend on the Milankovitch cycles, in particular, the obliquity of the Earth's axis and the eccentricity of the Earth's orbit. We see as a result that deglaciation and glaciation do occur mostly due to obliquity and to some extent eccentricity.
冰期与Milankovitch理论  [PDF]
李培基
冰川冻土 , 1991,
Abstract: 本文综述了20年来冰期及其形成理论研究的突破性进展。随着新技术的应用,从深海沉积、大陆冰盖及湖相沉积中获得大量新的地质气候证据。地质气候时间序列的频谱分析,地球轨道变化和日照变化的精密计算以及气候模拟,终于导致了第四纪冰期研究上的重大突破和Milankovitch理论的复兴。在解释第四纪冰期的各种理论与假设中,唯有天文学理论得到了大量科学证据的有力支持。无论在时域和谱域方面,轨道变化在气候系统中都留下了清晰的足迹。
ALIMENTACION DE ODONTESTHES BONARIENSIS (CUVIER Y VALENCIENNES 1835) (ATHERINIFORMES, ATHERINIDAE) EN LA LAGUNA SALADA DE MAR CHIQUITA (CORDOBA, ARGENTINA) FEEDING OF ODONTESTHES BONARIENSIS (CUVIER Y VALENCIENNES 1835 1835) (ATHERINIFORMES, ATHERINIDAE) IN THE SALINE LAKE OF MAR CHIQUITA (CORDOBA, ARGENTINA  [cached]
Luis Sagretti,María de los Angeles Bistoni
Gayana (Concepción) , 2001,
Abstract: Se analizó el contenido estomacal de 258 individuos de pejerrey Odontesthes bonariensis, con el objeto de estudiar los hábitos alimentarios de esta especie en un ambiente de características particulares debido a su extensión y elevada salinidad. El material fue recolectado en la costa sur de la laguna Mar Chiquita, en muestreos con frecuencia estacional durante 1994-1995. Se determinó el espectro trófico, estableciéndose para cada ítem la frecuencia de ocurrencia, abundancia y volumen. Se calculó el Indice de Importancia Relativa (IRI). El pejerrey preda principalmente sobre organismos animales. Se encontraron variaciones en el componente principal de la dieta de acuerdo a la longitud alcanzada por el pejerrey, observándose una marcada ictiofagia en aquellos que superan los 200 mm de longitud estándar. La única presa íctica consumida fue Jenynsia multidentata, habiéndose registrado sólo dos casos de canibalismo. Las capturas de esta especie en la costa disminuyeron en oto o e invierno. Este factor podría ser la causa del cambio alimentario estacional. El alimento de mayor importancia registrado para verano y primavera fueron los peces, mientras que en oto o predominaron con un elevado valor de IRI los caracoles y en invierno los insectos. Dentro de estos últimos, los órdenes más importantes fueron Diptera y Hemiptera. Si nos basamos en la alimentación de O. bonariensis al estado adulto, se concluye que el pejerrey se comporta en la laguna Mar Chiquita como una especie ictiófaga The aim of this work was to study the feeding habits of silverside Odontesthes bonariensis in a habitat characterized by its extension and high salinity. Stomach contents of 258 individuals were analyzed. Seasonal frequency sampling was conducted in the southern coast of Mar Chiquita Lake during 1994-1995. The trophic spectrum was determined, establishing the frequency of occurrence, abundance and volume for each item. The Index of Relative Importance (IRI) was estimated. O. bonariensis behaves as a zoophagous species. The main component of the diet varied according to fish size, showing a marked ichthyophagy in those specimens with more than 200 mm in standard length. O. bonariensis fed almost exclusively on Jenynsia multidentata. Cannibalism occurred only twice. The capture of the latter species decreased in autumn and summer. This could explain the seasonal variation registered in the diet of the silverside (O. bonariensis). The main food item in spring and summer were fish, whereas snails Littoridina parchappe and insects were the most important preys in autumn and winter res
Uniformity of the upper Famennian Milankovitch cycle in China
Weicheng Hao,Shunliang Bai,Dayong Jiang
Chinese Science Bulletin , 2000, DOI: 10.1007/BF02886370
Abstract: Research on chemo-biostratigraphy reveals that the periodic fluctuation of Ce/La ratios in carbonate sequence may reflect Milankovitch 100 ka eccentricity cyclicity. The Ce/La curve of the upper Famennian of Huangmao (Guangxi) may be well correlated to that of Muhua (Guizhou) and of Mid-Tarim (Xinjiang). They correspond not only in curve-feature, but also in number of cycles. Huangmao and Mid-Tarim are now located 3 000 km apart, during the Devonian possibly they were located farther apart. This study proves that the simultaneous sedimentary record of Milankovitch eccentricity cycles with a recurrent interval of 100 ka may be traced at different long-range sites. These cycles simultaneously developed in different depositional settings among different facies suites as a result of regional to global climate forcing, thus supporting the Milankovitch Theory.
Simulating sub-Milankovitch climate variations associated with vegetation dynamics
E. Tuenter, S. L. Weber, F. J. Hilgen,L. J. Lourens
Climate of the Past (CP) & Discussions (CPD) , 2007,
Abstract: Climate variability at sub-Milankovitch periods (between 2 and 15 kyr) is studied in a set of transient simulations with a coupled atmosphere/ocean/vegetation model of intermediate complexity (CLIMBER-2). Focus is on the region influenced by the African and Asian summer monsoon. Pronounced variations at periods of about 10 kyr (Asia and Africa) and about 5 kyr (Asia) are found in the monsoonal runoff in response to the precessional forcing. In the model this is due to the following mechanism. For low summer insolation (precession maximum) precipitation is low and desert expands at the expense of grass, while for high insolation (precession minimum) precipitation is high and the tree fraction increases also reducing the grass fraction. This induces sub-Milankovitch variations in the grass fraction and associated variations in the water holding capacity of the soil. The runoff does not exhibit sub-Milankovitch variability when vegetation is kept fixed. High-latitude vegetation also exhibits sub-Milankovitch variability under both obliquity and precessional forcing. We thus hypothesize that sub-Milankovitch variability can occur due to the dynamic response of the vegetation. However, this mechanism should be further tested with more sophisticated climate/vegetation models.
Simulating sub-Milankovitch climate variations associated with vegetation dynamics  [PDF]
E. Tuenter,S. L. Weber,F. J. Hilgen,L. J. Lourens
Climate of the Past (CP) & Discussions (CPD) , 2007,
Abstract: Climate variability at sub-Milankovitch periods (between 2 and 15 kyr) is studied in a set of transient simulations with a coupled atmosphere/ocean/vegetation model of intermediate complexity (CLIMBER-2). Focus is on the region influenced by the African and Asian summer monsoon. Pronounced variations at periods of about 10 kyr (Asia and Africa) and about 5 kyr (Asia) are found in the monsoonal runoff in response to the precessional forcing. In the model this is due to the following mechanism. For low summer insolation (precession maximum) precipitation is low and desert expands at the expense of grass, while for high insolation (precession minimum) precipitation is high and the tree fraction increases also reducing the grass fraction. This induces sub-Milankovitch variations in the grass fraction and associated variations in the water holding capacity of the soil. The runoff does not exhibit sub-Milankovitch variability when vegetation is kept fixed. High-latitude vegetation also exhibits sub-Milankovitch variability under both obliquity and precessional forcing. We thus hypothesize that sub-Milankovitch variability can occur due to the dynamic response of the vegetation. However, this mechanism should be further tested with more sophisticated climate/vegetation models.
Subsidence and capillary effects in chalks  [PDF]
Pierre Delage,Christian Schroeder,Yu Jun Cui
Physics , 2008,
Abstract: Based on the concepts of the mechanics of unsaturated soils where capillary phenomena arise between the wetting fluid (water) and the non-wetting one (air), the subsidence of chalks containing oil (non-wetting fluid) during water injection (wetting fluid) is analysed. It is shown that the collapse phenomenon of unsaturated soils under wetting provides a physical explanation and a satisfactory prediction of the order of magnitude of the subsidence of the chalk. The use of a well established constitutive model for unsaturated soils allows a description of the hydro-mechanical history of the chalk, from its deposition to the oil exploitation.
Generalized Milankovitch Cycles and Longterm Climatic Habitability  [PDF]
David S. Spiegel,Sean N. Raymond,Courtney D. Dressing,Caleb A. Scharf,Jonathan L. Mitchell
Physics , 2010, DOI: 10.1088/0004-637X/721/2/1308
Abstract: Although the Earth's orbit is never far from circular, terrestrial planets around other stars might experience substantial changes in eccentricity that could lead to climate changes, including possible "phase transitions" such as the snowball transition (or its opposite). There is evidence that Earth has gone through at least one globally frozen, "snowball" state in the last billion years, which it is thought to have exited after several million years because global ice-cover shut off the carbonate-silicate cycle, thereby allowing greenhouse gases to build up to sufficient concentration to melt the ice. Due to the positive feedback caused by the high albedo of snow and ice, susceptibility to falling into snowball states might be a generic feature of water-rich planets with the capacity to host life. This paper has two main thrusts. First, we revisit one-dimensional energy balance climate models as tools for probing possible climates of exoplanets, investigate the dimensional scaling of such models, and introduce a simple algorithm to treat the melting of the ice layer on a globally-frozen planet. We show that if a terrestrial planet undergoes Milankovitch-like oscillations of eccentricity that are of great enough magnitude, it could melt out of a snowball state. Second, we examine the kinds of variations of eccentricity that a terrestrial planet might experience due to the gravitational influence of a giant companion. We show that a giant planet on a sufficiently eccentric orbit can excite extreme eccentricity oscillations in the orbit of a habitable terrestrial planet. More generally, these two results demonstrate that the longterm habitability (and astronomical observables) of a terrestrial planet can depend on the detailed architecture of the planetary system in which it resides.
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