Conference PaperPDF Available

INTERPRETACIÓN SISMICA Y GRAVIMETRICA DE UN PERFIL A TRAVES DE LOS ANDES VENEZOLANOS

Authors:

Abstract

A geological transect orthogonal to venezuelan andes using seismic,gravimetric,surface geology and petrophysics data. Tectonics activity during late Miocene generated greates subsidence on the northern flank. Venezuelan andes are verging towards northwest
... The subsurface structure of the northern and southern foreland basins has been revealed from analysis of geophysical data acquired by oil exploration surveys, which has led to several interpretations at the regional, crustal or lithospheric scale including flexural basins, blind thrusts, retro-thrusting and triangular zones (e.g., Castrillo-Delgado, 1997;Audemard, 1999;. Because of limited access due to large variations in the topography, the deep structure of the inner part of the Venezuelan Andes is still not imaged by seismic reflection surveys, even if it can be inferred from gravimetric data Sánchez et al.;1994;. All these various approaches rely on fragmented geological, morphological and/or geophysical data, which therefore do not provide a clear understanding of the deep geometry of the tectonic structures at the scale of the Venezuelan Andes. ...
... Some authors favor the hypothesis of a SE-directed continental subduction of the Maracaibo crust under the Guyana shield Sánchez et al., 1994) (Figure 3c). The model has been further refined by by taking into account the inversion of the Late Jurassic grabens. ...
... proposed for the structure of Venezuelan Andes and the Maracaibo block area (inspired from English and Johnston, 2004). Models are proposed by: (a) Gonzalez de Juana, (1952), , ; (b) ; (c) ; De Toni and , Sánchez et al. (1994), ; (d) , ; (e) , . ...
Article
The geology of the Mérida Andes is well described at the surface, but its deep structure remains hypothetic. Our work integrated various information coming from geological observations, satellite images and geophysical data to propose a crustal scale deformation model of the mountain belt. In order to better understand the role played by the Boconó fault in the orogeny, we carried out a geomorpho-structural study in the La González basin whose opening is directly related to the movement along the fault. Based on balanced geological cross-sections and the orogenic float concept, we established a deformation model that explains both the strain partitioning and the escape processes. Major faults traces were used to build a 3D geological model of the orogen. The model shows that the escape of the Trujillo block is controlled by both lateral compression and gravity forces. Finally, we validated the escape model using a 2D numerical simulation that allows a better constraint of the distribution of the deformation that is directly linked to friction along faults.
... El contraste entre las profundidades del basamento de las cuencas de Maracaibo y Barinas-Apure, observado en mapas de anomalía de Bouguer (Bonini et al., 1997;Chacín et al., 2005), aboga por la asimetría del cinturón (Bucher, 1952;De Cizancourt, 1993;Hospers & VanWijnen, 1959). Existen diferentes interpretaciones de la data gravimétrica: a) Subducción continental en dirección SE: favorece la hipótesis de una subducción continental SE de la corteza de Maracaibo por debajo del escudo de Guayana (De Toni & Kellogg, 1993;Kellogg & Bonini, 1982;Sánchez Nuñez et al., 1994). El principal argumento de este modelo es el hundimiento del basamento de la cuenca de Maracaibo, la cual muestra una profundidad mayor respecto a la cuenca Barinas-Apure (Monod et al., 2010). ...
Article
Full-text available
RESUMEN En el marco del proyecto de Geociencia Integral de Los Andes de Mérida (GIAME), se realizaron investigaciones geofísicas y geológicas integradas, dentro de las cuales se encuentra la elaboración de modelos corticales de ondas P mediante la adquisición, procesamiento y análisis de datos de sísmica profunda. Se estudiaron tres perfiles denominados Sur del Lago, Centro Andes y Piedemonte, los cuales se ubican paralelos al eje axial de la cadena montañosa. Se elaboraron modelos 2D de velocidades con los cuales se pudo estimar tanto el espesor como las velocidades promedio de las principales estructuras interpretadas (sedimentos, corteza superior y corteza inferior). Considerando las profundidades de Moho, se realizó un mapa de espesores corticales para determinar su variación lateral. La profundidad cortical máxima fue de 52 km. La distribución espacial de los espesores corticales indican un desplazamiento de la raíz de Los Andes de Mérida de aproximadamente 40 km, al noroeste del eje axial de la cadena montañosa, lo que podría implicar un contexto tectónico formacional asimétrico. ABSTRACT Within the framework of the Integrated Geoscience Project of the Merida Andes (GIAME), multidisciplinary geophysical and geological investigations are carried out, which include the development of P-wave crustal models through the acquisition, processing and analysis of deep seismic data. Three profiles called "Sur del Lago", "Centro Andes" and "Piedemonte" were studied, which are located parallel to the axis of the mountain chain. 2D velocity models were developed with which both thickness and average velocities of the main interpreted structures (sediments, upper crust and lower crust) could be estimated. Considering the depths of Moho, a map of crustal thicknesses was made to determine its lateral variation. The maximum crustal depth was 52 km. The spatial distribution of crustal thickness indicates a displacement of the mountain root of approximately 40 km, towards northwest of the axis of the mountain range, which could imply an asymmetric formation of the Mérida Andes.
... En relación a los modelos de la cordillera que se basan en datos geofísicos, existen diversas aproximaciones que se han hecho con datos sísmicos someros y gravimétricos (Audemard, 1991;De Toni y Kellogg, 1993;Sánchez et al., 1994;Colletta et al., 1997;Chacín et al., 2005; Arnaíz et al., 2011), pero en términos generales, la estructura profunda del interior de la cadena de Los Andes de Mérida, todavía no ha podido ser visualizada a través de levantamientos de sísmica activa, debido a múltiples causas, entre las cuales destaca las grandes variaciones topográficas que han hecho complicado plantear estudios de estas características. Por otra parte, en la cuenca de Falcón si se han podido llevar a cabo estudios geofísicos profundos que han permitido generar los primeros modelos a escala cortical (Rodríguez y Graterol, 1975;Rodríguez y Sousa, 2003;Sousa et al., 2005;Bezada et al., 2007Bezada et al., , 2010; estos serán empleados como referencia para los futuros modelos sísmicos que se deriven de esta investigación. ...
Conference Paper
Full-text available
Los Andes de Mérida son el cinturón orogénico más importante de Venezuela y representan la culminaciónnororiental de Los Andes de Suramérica. Durante más de 60 años se han propuestos diversos modelos que explican la estructuración somera y profunda de esta región; sin embargo, la gran mayoría se basan en estudios hechos en ventanas de observación muy localizadas y no deberían representar el contexto generalizado de la estructuración profunda de este orógeno. En el marco del proyecto de investigación GIAME (Geociencia Integral de Los Andes de Mérida), se intentarán resolver las interrogantes sobre la estructuración litosférica y para ello, en primer lugar se adquirieron datos sísmicos de gran ángulo a lo largo de varios perfiles realizados en el occidente del país. En este caso particular, se presenta el modelado bidimensional del perfil denominado Andes Norte, sobre cuya extensión de aproximadamente 560 km, se detonaron cargas de explosivos sísmicos de entre 200 y 1000 kg, en 13 sitios diferentes, y cuya información fue grabada por aproximadamente 600 equipos de registro portátil (Texan), facilitados en su mayoría por el IRIS-PASSCAL Instrument Centre (EE.UU.), y por Funvisis. El espaciamiento entre éstos Texan varió de 0,5 a 1 km. Se han construido diferentes secciones con la rutina Seisplot (Arnaiz et al., 2014), en donde se ha reconocido la energía sísmica con llegadas para la fase “Pg” en distancias de hasta 188 km; para las llegadas “Pn”, entre 125 y 545 km; las fases “PmP” y “Pi”, han permitido modelar la discontinuidad del “Moho”, e intracorticales, respectivamente, en profundidades variables entre 40 y 50 km (Moho), aplicando una inversión tomográfica con los métodos de ZB92 (Zelt y Smith, 1992) y ZB98 (Zelt y Barton, 1998). La estructura de velocidades de ondas “P”, revela variaciones de 3,2 a 5,75 km/s para los sedimentos; de 6,15 a 6,55 km/s para la corteza superior, y de 6,75 a 8,3 km/s para la corteza inferior, zona de transición del “Moho” y el manto superior. A partir del análisis tomográfico se han evidenciado estructuras de alta velocidad asociadas al núcleo de la cordillera andina, y las rocas Precámbricas y Paleozoicas del macizo El Baúl.
... As mentioned earlier, strain partitioning is taking place throughout the MA. Thus, significant thrusting occurs subparallel to the RLSS Boconó fault on both sides of the MA, accommodating a rather large amount of shortening across the chain (González de Juana, 1952;Rod, 1956b;Hospers and Van Wijnen, 1959;Schubert, 1968;Kellogg and Bonini, 1982;Henneberg, 1983;Soulas, 1985;Audemard, 1991;De Toni and Kellogg, 1993;Jácome, 1994;Sánchez et al., 1994;Colletta et al., 1996;Audemard, 1997b;Colletta et al., 1997;Duerto et al., 1998). A good knowledge of the sub-surface structure of both foothills has been acquired due to the large set of geophysical surveys performed in the Maracaibo and Barinas-Apure basins by the oil industry in the last two decades, but most of the deep structure of the chain remains unknown except for the Moho depth in certain areas (29 km for the Maracaibo crust by Padrón and Izarra, 1996) and the general mass distribution that may be derived from gravimetric profiles and surveys (e.g., Hospers and Van Wijnen, 1959;Bonini et al., 1977). ...
Conference Paper
Full-text available
This International Workshop is a contribution to the INQUA Project 0511, entitled “The geomorphic and geologic signature of active blind dip-slip faulting”, as well as to the following projects: FONACIT 0001002492, “Historia Sísmica y segmentación sismogenética de la Falla de Boconó con base en el análisis geológico de sedimentos recientes deformados (por vía de trincheras y núcleos continuos)”; FONACIT-ECOS Nord PI-2003000090 “Estudio integrado, sedimentológico y sismotectónico, de la amenaza sísmica a lo largo de la frontera sur del Caribe”; FONACIT G-2002000478 “Geodinámica reciente del límite norte de la Placa Sudamericana (estudio de la corteza y el manto superior mediante métodos geofísicos y geológicos)” y FONACIT-BID 200400738 "Microzonificación Sísmica en las ciudades de Caracas y Barquisimeto".
Article
Full-text available
The main purpose of this research is to generate gravimetric/crustal models for Western Venezuela, based on the flexure of the lithosphere theory and using data extracted from the Red Gravimetrica Nacional, wells and seismicity Statistical and geostatistical controls were applied to the gravimetric data, and Bouguer anomaly and free air anomaly maps were interpreted. The depth of the crustal interfaces was estimated using power spectra of the anomalies, and deep gravimetric sources were interpreted from upward field continuation with the purpose of modelling the crustal structures of the area. It is concluded that: a)flexure of Barinas-Apure basin is mainly generated by the Merida Andes; b) flexure of Maracaibo block is not controlled by the Andean load, but by the load distribution along this tectonic feature; c) the estimated crustal thickness for the South American plate is 40 km, and for Maracaibo block is 36 km; the elastic thickness estimated for the South American plate is 24 kin, and for Maracaibo block is 16 km; d) the upper crust-lower crust discontinuity is about 19 km deep; e) the contact between both plates resembles a type A subduction with NW strike, in which South America underlays the Maracaibo block, although the existence and polarity of this subduction remains uncertain.
Article
Full-text available
The main purpose of this research is to generate gravimetric/crustal models for Western Venezuela, based on the flexure of the lithosphere theory and using data extracted from the Red Gravimétrica Nacional, wells and seismicity. Statistical and geostatistical controls were applied to the gravimetric data, and Bouguer anomaly and free air anomaly maps were interpreted. The depth of the crustal interfaces was estimated using power spectra of the anomalies, and deep gravimetric sources were interpreted from upward field continuation with the purpose of modelling the crustal structures of the area. It is concluded that: a) flexure of Barinas–Apure basin is mainly generated by the Mérida Andes; b) flexure of Maracaibo block is not controlled by the Andean load, but by the load distribution along this tectonic feature; c) the estimated crustal thickness for the South American plate is 40 km, and for Maracaibo block is 36 km; the elastic thickness estimated for the South American plate is 24 km, and for Maracaibo block is 16 km; d) the upper crust–lower crust discontinuity is about 19 km deep; e) the contact between both plates resembles a type A subduction with NW strike, in which South America underlays the Maracaibo block, although the existence and polarity of this subduction remains uncertain.
Article
Deposition of organic carbon-rich intervals of the La Luna and Navay formations of northwestern Venezuela was governed by the development of key paleobathymetric barriers (Santa Marta and Santander massifs, Paraguana Block, and ancestral Merida Andes). These enhanced the development of anoxia in the 'La Luna Sea' by causing poor circulation and limited ventilation. Anoxia was also promoted by high evaporation and low precipitation rates (high salinity bottom water), and high levels of marine algal productivity (high organic matter flux). Nutrient supply was augmented by infrequent fluvial sources. Bottom water oxygen levels increased from the Late Santonian through the end of the Cretaceous. Ventilation of anoxic bottom waters may have been enhanced by more frequent or intense seasonal upwelling (caused by higher wind stress) and catastrophic overturn, as well as the removal of a key paleobathymetric barrier. Common byproducts of overturn events were massive phytoplankton blooms, which produced red tides. Fish and marine reptile bone beds within the Tres Esquinas Member (La Luna Formation) are attributed to massive mortality during these events, and are correlative with similar Campanian units in eastern Colombia. During the Maastrichtian, increasing ventilation, combined with siliciclastic dilution, ultimately produced sediments with lower total organic carbon (TOC) content.
Article
The end of the Early Cretaceous in northern South America was marked by regional palaeoceanographic change. In western Venezuela, this change was highlighted near the end of the Albian by drowning of the Maraca Formation shallow-water carbonate platform. Regional marine transgression continued during the Cenomanian and Turonian in western Venezuela with drowning of the more southerly Guayacan Member (Capacho and Escandalosa formations) carbonate platform. Deposition of organic carbon-rich intervals of the La Luna and Navay formations occurred unconformably on Maraca Formation and Guayacan Member shallow-water carbonates and continued through the early Santonian. During this interval, the Maracaibo and Barinas/Apure basins were characterized by low-oxygen or anoxic bottom-water conditions away from the basin margins. Deposition of organic carbon-lean upper La Luna and Navay formation strata show that bottom-water oxygen content increased from the late Santonian through the end of the Cretaceous. The siliceous and phosphatic late Santonian to early Maastrichtian Tres Esquinas Member, and the glauconitic late Campanian to early Maastrichtian Socuy Member (both of the La Luna Formation) represent the final phase of La Luna deposition in the Maracaibo Basin. Tectonic uplift in eastern Colombia during the Campanian and Maastrichtian caused progradation of the Colón, Mito Juan, and Burgüita Formation deltas, and eventual infilling of the Maracaibo and Barinas/Apure basins.
Article
The Bocono fault is a major NE–SW-trending, dextral fault that extends for about 500 km along the backbone of the Venezuelan Andes. Several large historical earthquakes in this region have been attributed to the Bocono fault, and some of these have been recently associated with specific parts through paleoseismologic investigations. A new trench study has been performed, 60 km to the northeast of Merida in the central Venezuelan Andes, where the fault forms a releasing bend, comprising two conspicuous late Holocene fault strands that are about 1 km apart. The southern and northern strands carry about 70% and 30% (respectively) of the 7–10 mm=yr net slip rate measured in this sector, which is based on a 40 vs. 85–100 m right-lateral offset of the Late Pleistocene Los Zerpa moraines. A trench excavated on the northern strand of the fault (near Morros de los Hoyos, slightly northeast of Apartaderos) across a twin shutter ridge and related sag pond exposed two main fault zones cutting Late Pleistocene alluvial and Holocene peat deposits. Each zone forms a shutter ridge with peat deposits ponded against the uplifted block. The paleoearthquake reconstruction derived from this trench allows us to propose the occurrence of at least 6–8 earthquakes in the past 9000 yr, yielding a maximum average recurrence interval of about 1100–1500 yr. Based on the northern strands average slip rate (2.6 mm=yr), such an earthquake sequence should have accommodated about 23 m of slip since 9 ka, suggesting that the maximum slip per event ranges between 3 and 4 m. No direct evidence for the large 1812 earthquake has been found in the trench, although this earthquake may have ruptured this section of the fault. Further paleoseismic studies will investigate the possibility that this event occurred on the Bocono fault, but ruptured mainly its southern strand in this region.
Article
Full-text available
The main purpose of this research is to generate gravimetric/crustal models for Western Venezuela, based on the flexure of the lithosphere theory and using data extracted from the Red Gravimétrica Nacional, wells and seismicity. Statistical and geostatistical controls were applied to the gravimetric data, and Bouguer anomaly and free air anomaly maps were interpreted. The depth of the crustal interfaces was estimated using power spectra of the anomalies, and deep gravimetric sources were interpreted from upward field continuation with the purpose of modelling the crustal structures of the area. It is concluded that: a) flexure of Barinas-Apure basin is mainly generated by the Mérida Andes; b) flexure of Maracaibo block is not controlled by the Andean load, but by the load distribution along this tectonic feature; c) the estimated crustal thickness for the South American plate is 40 km, and for Maracaibo block is 36 km; the elastic thickness estimated for the South American plate is 24 km, and for Maracaibo block is 16 km; d) the upper crust-lower crust discontinuity is about 19 km deep; e) the contact between both plates resembles a type A subduction with NW strike, in which South America underlays the Maracaibo block, although the existence and polarity of this subduction remains uncertain.
ResearchGate has not been able to resolve any references for this publication.