Conference PaperPDF Available

An integrated geological-geophysical profile across northwestern Venezuela

Authors:

Figures

Content may be subject to copyright.
6th International Symposium on Andean Geodynamics (ISAG 2005, Barcelona), Extended Abstracts: 689-692
689
An integrated geological-geophysical profile across northwestern
Venezuela
Juan Carlos Sousa (1), Josmat Rodríguez (1), Carlos Giraldo (1), Inírida Rodríguez (1),
Franck Audemard (1,2), & Ricardo Alezones (1)
(1) Universidad Central de Venezuela, Cdad. Universitaria, Los Chaguaramos, Caracas, Venezuela
(2) FUNVISIS, Earth Sciences Department, Apartado Postal 76.880, Caracas 1070-A, Venezuela
E-mail addresses: jjccsspp74@cantv.net, josmatr@cantv.net , cgiraldoc@ repsolypf.com,
iniromil@yahoo.com.mx, faudemard@funvisis.org.ve, aleric@cantv.net
KEYWORDS: Surface Geology, Seismics, Gravity, Magnetics, Integrated profile, Venezuela
INTRODUCTION
The 250-km-long integrated profile here discussed is located across the northwestern part of Venezuela (Falcón
range), between Cabo San Román and Barquisimeto city, following a N15ºW direction (Figure 1). This profile
integrates surface geology, oil-prospection seismics, gravity and magnetic data. It runs north of the major active
dextral Boconó fault and south of the Colombo-Venezuelan subduction zone, crossing two different tectonic
domains (Bellizzia, et al., 1976; Stephan, 1985): the Caribbean nappes and the Oligo-Miocene Falcón basin. The
southward transport of nappes occurred from Paleocene to Eocene onto the Cretaceous-Paleocene passive
margin of northern South America, previous to a major orogenic collapse responsible for the Falcón basin. The
Falcón basin anticlinorium, inverted from the Middle Miocene, follows an ENE-WSW direction, perpendicular
to the maximum horizontal stress (1). In addition, the Oca-Ancón fault –a major activ e east-west dextral fault
running from the Colombian border and joining the San Sebastian fault to the east–, crosses the Falcón range,
offsetting its axis in as much as 33 km and presenting a “transtensional jog” geometry in the central part of the
Falcón range (Audemard, 1993; Audemard et al., 1994).
The Falcón basin depositional history started during the late Eocene, being older units lying above the
Caribbean allochthonous, and contemporary to a main extensional period responsible for a “horst and graben”
generalised geometry (Audemard, 1993). Muessig (1984) suggests that this geometry could be associated to a
“pull-apart” deformation related to the Oligocene Oca-Ancón fault activity. However, Audemard (1993) and
Audemard and Giraldo (1997) conclude that dextral deformation occurred only during the last 17-15 Ma, during
compressive phases such as the one currently active.
Since a “rifting” period has preceeded during Oligocene-Early Miocene time to compressive phases
(Audemard, 1995), very important variations in thickness and paleo-geographic conditions (Paraiso, Pecaya, San
Luis and Churuguara Formations) during this extensional episode have been well documented (González de
Juana et al., 1980). Besides, basaltic intrusions of Early-to-Middle Miocene age have been interpreted as derived
from the upper mantle/continental lithosphere boundary (McMahon, 2001) and associated to this intraplate
“extensional” process responsible for the early structuration of the Falcón basin (Audemard, 1993). The northern
part of the profile images WSW-ENE-trending “horsts” and “grabens”, interpreted from seismic lines, affecting
both the Caribbean allochthonous and the Miocene sediments.
6th International Symposium on Andean Geodynamics (ISAG 2005, Barcelona), Extended Abstracts: 689-692
690
BOUGUER ANOMALY AND MAGNETIC DATA
The database comprises 1833 gravity and 491 magnetic measures, of which 205 and 299 were acquired for this
study (Rodríguez and Sousa, 2003). The Bouguer anomaly map shows a preferential N70°E direction ranging
between - 40 and 60 miligals. This last value correlates well with the ultramafic rocks outcropping in the
northern edge of the profile (Cerro de Santa Ana). In the central part a maximun value of 45 mgal can be
correlated with the Early Miocene intrusions. The value of -30 mgal in the southern part can correlate with the
Siquisique Ophiolitic Complex (pillowlavas and metagrabros; Bartok et al., 1985).
The magnetic field ranges from 34,200 to 35,500 gamma. The maximun values are located in the northern edge
(Cerro de Santa Ana ultramafic rocks) and in the central part of the Falcón basin (35,500 gamma) correlating
well to the Miocene intrusions and also suggesting a thinned crust. The minimum value of 34,200 gamma –
between the Oca-Ancón and Boconó faults, in the southern part of the section- has been correlated with the
metamorphic rocks of the Caribbean allochthonous.
DISCUSSION
The Falcón range can be interpreted as part of a much longer Oligocene basin, later inverted during Middle
Miocene to Holocene times. According to geophysical modelling, the thickest part of the basin corresponds to a
dramatic crustal thinning from 40 km to 20 km, located in the central part of the profile coinciding with the
Miocene intrusions alignment (Figure 2). From several attempts of gravimetric and magnetic modelling along
the entire profile, the best-fit model that integrates available geological-geophysical data corresponds to a
shallow (incipient) flat subduction having a south vergence (Figure 3). Therefore, this is partly in agreement
with the flat slab subduction model of anomalously thick oceanic Caribbean plate under South American plate,
proposed by Van der Hilst and Mann (1994), although differing in the amount of slab subducted.
References
Audemard, F. A., 1993, Neotectonique, Sismotectonique et Aléa Sismique du Nord-ouest du Vénézuéla
(Système de failles d’Oca-Ancón). PhD Thesis, Université Montpellier II, 369 pp.
Audemard, F. A., 1995, La Cuenca Terciaria de Falcón, Venezuela Noroccidental: Síntesis Estratigráfica,
Génesis e Inversión Tectónica. Proceedings IX Congreso Latinoamericano de Geología, Caracas, Venezuela
(on Diskette).
Audemard, F. A. and Giraldo, C., 1997, Desplazamientos dextrales a lo largo de la frontera meridional de la
placa Caribe, Venezuela septentrional. Proceedings VIII Congreso Geológico Venezolano, Porlamar, 1, 101-
108.
Audemard, F. A., Singer, A., Rodríguez, J. A. & Beltran, C., 1994, Definición de la traza activa del sistema de
fallas de Oca-Ancón, Noroccidente de Venezuela. Proceedings VII Congreso Venezolano Geofísica, Caracas,
Venezuela, 43-51.
Bartok, P.; Renz, O., and Westermann, E., 1985, The Siquisique ophiolites, northern Lara state, Venezuela; a
discussion on their middle Jurassic ammonites and tectonic implications. Geological Society of America
Bulletin 96(8), 1050-1055.
Bellizzia, A., Pimentel, N. and Bajo, R., 1976. Mapa geológico-estructural de Venezuela. Scale 1:500,000.
Ministerio de Energia y Minas, Ed. Foninves, Caracas.
González de Juana, C., Iturralde de Arozena, M. y Picard Cadillat, X., 1980, Geología de Venezuela y de sus
cuencas Petrolíferas, Ed. Foninves, 2 vols.
McMahon, C., 2000. Evaluation of the effects of oblique collision between the Caribbean and South American
plates using geochemistry from igneous and metamorphic bodies of northern Venezuela. Ph.D. thesis,
University of Notre Dame, USA, 227 pp.
6th International Symposium on Andean Geodynamics (ISAG 2005, Barcelona), Extended Abstracts: 689-692
691
Muessig, K., 1984, Structure and Cenozoic tectonics of the Falcon basin, Venezuela, and adjacent areas: Memoir
Geological Society of America, 162: 217-230.
Rodríguez, J. and Sousa, J. C., 2003, Estudio geológico-estructural y geofísico de la sección cabo San Román-
Barquisimeto, estados Falcón y Lara. Trabajo Especial de Grado. Universidad Central de Venezuela.
Venezuela.
Stephan, J-F., 1985. Andes et chaîne caraïbe sur la transversale de Barquisimeto (Vénézuela). Evolution
géodinamique. Proceedings Symposium Géodynamique des Caraïbes, Paris, 505-529.
Van der Hilst, R. and Mann, P. (1994) Tectonic implication of tomographic images of subducted lithosphere
beneath northwestern South América. Geology, 22, 451-454.
Figure 1. Profile location (Rodriguez and Sousa, 2003)
6th International Symposium on Andean Geodynamics (ISAG 2005, Barcelona), Extended Abstracts: 689-692
692
Figure 2. Integrated profile (Rodriguez and Sousa, 2003)
Figure 3. Geophysical modeling (Best fit = Shallow subduction -left-, Rodriguez and Sousa, 2003)
... Once the structural evolution of the region was established and Cenozoic rocks were documented as the source, oil burial history diagrams and thermal calibration of six wells (five drilled and one pseudowell) were modelled using %Ro values and T max from Rock Eval pyrolysis (Figs 18-24). The structural model indicates that the Falcón Basin formed as a result of a tectonic collapse since the Late Eocene, coeval with an important crustal thinning as proposed by Sousa et al. (2005). This tectonic event was accompanied by an anomalous increase in the heat flow of the region due to mantle upwelling (incipient delamination process?) that played an important role in the source rock maturation as will be explained later. ...
... The idea of incipient Caribbean Plate flat slab subduction (dip angle ,20 8S) is consistent with recent gravimetric results (Sousa et al. 2005). These authors proposed that the frontal part of the slab is currently below the Paraguaná Península at about 15 km depth (Fig. 36), which is where the bulk of the seismicity occurs. ...
... Gravimetric model for the subduction in northwestern Venezuela (AfterSousa et al. 2005). ...
... Once the structural evolution of the region was established and Cenozoic rocks were documented as the source, oil burial history diagrams and thermal calibration of six wells (five drilled and one pseudowell) were modelled using %Ro values and T max from Rock Eval pyrolysis (Figs 18-24). The structural model indicates that the Falcón Basin formed as a result of a tectonic collapse since the Late Eocene, coeval with an important crustal thinning as proposed by Sousa et al. (2005). This tectonic event was accompanied by an anomalous increase in the heat flow of the region due to mantle upwelling (incipient delamination process?) that played an important role in the source rock maturation as will be explained later. ...
... The idea of incipient Caribbean Plate flat slab subduction (dip angle ,20 8S) is consistent with recent gravimetric results (Sousa et al. 2005). These authors proposed that the frontal part of the slab is currently below the Paraguaná Península at about 15 km depth (Fig. 36), which is where the bulk of the seismicity occurs. ...
... Gravimetric model for the subduction in northwestern Venezuela (AfterSousa et al. 2005). ...
Book
Full-text available
A multi-event tectonic episode that affected the Caribbean and South American Plate boundaries as well as Cenozoic oil generation is based on new structural and geochemical data from the western Falcon Basin, Venezuela. It involves Late Cretaceous to Middle Eocene emplacement of the Lara Nappes followed by Late Eocene to Early Miocene tectonic collapse and graben formation, Middle Miocene inversion and out of sequence thrusting. Oil-source rock correlation of seeps in the northern part of the basin suggests a Cenozoic siliciclastic source rock deposited under suboxic to anoxic conditions. Potential Cenozoic source rocks and Late Cretaceous La Luna Formation were used to evaluate the generation conditions using one-and two-dimensional thermal modelling. A heat flow of c. 190 mW m(-2) was reached during the Oligocene-Early Miocene in the central part of the basin. As a result the Cretaceous source rock is overmature, while the primary Cenozoic source rocks are in the oil window. The thermal modelling also suggests that hydrocarbon accumulations are mainly located on the flanks of the graben, with small amounts possible in the centre, due to erosion during basin inversion. This modelling is highly consistent with the proposed polyphase tectonic model.
... The Falcó n Basin is included in a complex geological setting influenced by tectonic processes driven by the junction between the Caribbean, Nazca and South America plates (Audemard, 2001;Bezada et al., 2007;among others). Likewise, outcrops of intrusive igneous bodies occur along the axis of the Falcó n Basin and have been associated with crustal thinning during Late Eocene-Early Miocene times (Sousa et al., 2005;Bezada et al., 2007). This tectonic event was accompanied by an abnormal increment of the heat flow (w190 mW m À2 ) of the region that significantly affected the maturation of the source rocks in the Falcó n Basin (Baquero et al., 2009). ...
... This implies that: (1) the geothermal gradient was normal during and after the deposition of the Pedregoso Formation, (2) the OM maturation in this unit is due to the sedimentary burial. Therefore, if an increase of the geothermal gradient occurred in the Falcó n Basin (Sousa et al., 2005;Bezada et al., 2007), this increase occurred before the Pedregoso Formation was deposited, and/or the thermal anomaly did not reach the study area. Similar results are reported in relation to the Pecaya Formation in the central part of the Falcó n Basin (Baquero et al., 2009). ...
Article
The early Miocene Pedregoso Formation is one of the numerous formations rich in organic matter within the stratigraphic record of the Urumaco Trough, in the central area of the Falcón Basin. Due to its lithological characteristics and stratigraphic position, this formation is of great interest regarding the basin's petroliferous systems. The evaluation of various inorganic and organic geochemical parameters indicates that the organic matter is primarily of marine origin, deposited in a marine carbonate environment typical of reefal systems, under oxic-to-dysoxic conditions. The low variability in the TOC concentrations and in the distributions of the biomarkers extracted from the samples suggests that the paleoenvironmental conditions and the organic-matter supply remained approximately constant throughout the sedimentation of this unit. The Pedregoso type-II organic matter (marine origin) and initial organic richness value (∼1.8%) suggest that this unit has probably generated hydrocarbons within the Urumaco Trough. However, present-day thermal maturity parameters reveal that the Pedregoso organic matter is overmature (dry gas window), indicating that this unit is only capable to generate gas. In addition, the geothermal gradient, maturity parameters, and the maximum paleotemperature estimated in this study suggest that the Pedregoso Formation reached a maximum burial depth the ∼6.5 km, consistent with the value obtained from data of stratigraphic thickness in the Urumaco Trough. This implies that the thermal anomaly that affected the basin during the Late Eocene–Early Miocene did not reach the central part of the basin, and therefore, the organic matter maturation in this unit is due to the sedimentary burial.
... Based on the existence of basaltic intrusions along the axis of the basin, it has been proposed that crustal thinning occurred as the basin opened from the Late Eocene to Late Oligocene (Muessig, 1978(Muessig, , 1984. A 2D model based on potential field methods and surface geology incorporated a thinning of the crust under the Falcón Basin to explain the positive gravity anomaly in the area (Rodríguez and Sousa, 2003;Sousa et al., 2005). Up to the present, however, no seismic evidence of such thinning existed. ...
... It is important to note that the reflections on the thinned crust correspond to only one, unreversed shot, thus reducing our ability to constrain the geometry of the thinning. Nonetheless, the existence of this feature is supported by preceding interpretations based on surface geology and is corroborated by the gravity model presented in this contribution as well as earlier work (Rodríguez and Sousa, 2003;Sousa et al., 2005). Gravity modeling carried out as part of this study complements the seismic model and shows that the P-wave velocity structure obtained is consistent with independent gravity observations. ...
Article
The Falcon Basin in northwestern Venezuela has a complex geological history driven by the interactions between the South American and Caribbean plates. Igneous intrusive bodies that outcrop along the axis of the basin have been associated with crustal thinning, and gravity modeling has shown evidence for a significantly thinned crust beneath the basin. In this study, crustal scale seismic refraction/wide-angle reflection data derived from onshore/offshore active seismic experiments are interpreted and forward-modeled to generate a P-wave velocity model for a approximately 450 km long profile. The final model shows thinning of the crust beneath the Falcon Basin where depth to Moho decreases to 27km from a value of 40 km about 100 km to the south. A deeper reflected phase on the offshore section is interpreted to be derived from the downgoing Caribbean slab. Velocity values were converted to density and the resulting gravimetric response was shown to be consistent with the regional gravity anomaly. The crustal thinning proposed here supports a rift origin for the Falcon Basin.
... A lo largo del perfil Andes Norte el espesor cortical oscila alrededor de 40 km, con una disminución en la cuenca de Falcón de valores de ~30 km que puede ser vista como una extensión del adelgazamiento cortical identificado en el este y por debajo de la cuenca de Falcón a lo largo de la extensión occidental del sistema de fallas Oca-Ancón, que ha sido interpretada como una cuenca extensiva de Trasarco (e.g. Sousa et al., 2005;Bezada et al., 2008 Las velocidades sísmicas de las ondas P (Vp) en el perfil sísmico Andes Norte (Figura 7), varían entre 3,2 a 5,75 km/s para la cobertura sedimentaria y 5,5 a 6,3 km/s para las rocas Paleozoicas, Mesozoicas y Cenozoicas del orógeno Andino. Vp de la corteza superior varía entre 6,15 y 6,55 km/s, y de la corteza inferior, zona de transición del "Moho" y el manto superior entre 6,75 y 8,3 km/s. ...
Article
Full-text available
The northwestern region of the South American continent is one of the main active tectonic zones in the world, due to the convergence of the plates of South America, the Caribbean and Nazca. These displacements and regimes of compressive efforts formed diverse orogenic structures such as of The Santa Marta-Perijá Mountain range, The Mérida Andes and The Basements of Maracaibo Lake, Barinas-Apure and Falcón. Some scientific works have partially explained its geotectonic evolution of the region; however, none has reached a specific result. the geologic history of the Mérida Andes and its relationship with the surrounding structures has not been clarified yet. In order to these conditions into consideration, the Venezuelan Foundation for Seismological Research (FUNVISIS) has carried out the Integral Geoscience research project of The Mérida Andes (GIAME), which has among its objectives to study the geodynamic and tectonic evolution of the northwestern region of Venezuela, in addition to the nearby geological structures, and to estimate the depth of the basement and the thickness of the sediments, All these objectives will be fundamental for the creation of a model of the crust of the Andes of Mérida, which will complement the structural information and its relationship with the gravimetric root of the orogen.
... A low velocity zone appears between 20 km and 40 km in depth ( Fig. 9.b, 9.c and 9.d; from -70 • to -68 • , from 10N • to 11.5N • ); and it seems to be coupled to the shortening found in the Northeastern Falcón Basin extending from the lower crust (Sousa et al., 2005, Guedez, 2007Niu et al., 2007;Bezada et al., 2008, Mazuera et al., 2019 to the lithosphere-asthenosphere boundary (LAB; Masy et al., 2015). This lithospheric thinning is thought to be the expression of a failed continental rifting stage in the Eocene-Early Oligocene in a back-arc setting (e.g. ...
Article
We explore the shear-wave lithospheric velocity structure of the Eastern Caribbean and Northern Venezuela using ambient noise tomography with stations deployed around the study area. We construct cross-correlation functions from continuous seismic records, and measure phase velocities of fundamental-mode Rayleigh waves. These velocities are further projected onto 0.6°x0.6° phase velocity grids for each period between 5 s and 50 s. The pseudo-dispersion curve at each grid point is inverted for 1D shear velocity profiles by using a Markov Chain Monte Carlo scheme. The interpolated 3D velocity model shows that the mean shear velocity of the Eastern Caribbean lithospheric mantle is lower than the global average, which is in agreement with values reported in other large igneous provinces. We interpret that low velocities in the lithospheric keel are associated with an anomalous composition and/or an elevated thermal state; this gives the Caribbean plate a high buoyancy that determines the subduction polarities in the region. The results also indicate that: (a) the mantle beneath Northern Venezuela retains compositional anomalies related to extension processes of different ages; (b) the overriding of the Caribbean plate by the Great Antilles arc seems to be much slower than previously suggested; and (c) the localized volcanism in the center of the Lesser Antilles arc is related to asthenospheric flow through the tear induced on the subducted slab by major strike-slip faults.
... Evidences of a thinned crust are well documented from geophysics studies. A crustal thinning ranging between~20 and~30 km was proposed from gravity/deep-seismic observations and modeling Guedez, 2007;Orihuela-Guevara et al., 2011;Rodríguez & Graterol, 1975;Rodríguez & Sousa, 2003;Sánchez-Rojas et al., 2010;Sousa et al., 2005) about 100 km further east. This thinned crust coincides with the aligned, maximum observed satellite gravity anomalies ( Figure 3) and results from recent gravity and seismic studies (Calderón et al., 2016;Cisneros et al., 2016;Ramírez et al., 2014;Yegres et al., 2018) along the same location of the Northern Andes profile. ...
Article
Full-text available
Northwestern Venezuela is located in the complex deformation zone between the Caribbean and South American plates. Several models regarding the lithospheric structure of the Merida Andes have been proposed. Nevertheless, they lack relevant structural information in order to support the interpretation of deeper structures. Therefore, a 560-km-long refraction profile across the northern part of Mérida Andes, oriented in a NNW direction, covering areas from the Proterozoic basement in the south, to both Paleozoic and Meso-Cenozoic terranes of northwestern Venezuela to the north, is analyzed in this contribution. Thirteen land shots were recorded by 545 short-deployment seismometers, constraining P-wave velocity models from first-arrival seismic tomography and layer-based inversion covering the whole crust in detail, with some hints to upper mantle structures. The most prominent features imaged are: absence of a crustal root associated to the Mérida Andes, as the Northern Andes profile is located marginal to the Andean crustal domain, and low-angle subduction of the Caribbean oceanic slab (~10-20°) beneath northwestern South America. Further crustal structures identified in the profile are: (a) crustal thinning beneath the Falcón Basin along the western extension of the Oca-Ancón fault system interpreted as a back-arc basin, (b) suture zones between both the Proterozoic and Paleozoic provinces (Ouachita-Marathon-related suture?), and Paleozoic and Meso-Cenozoic terranes (peri-Caribbean suture) interpreted from lateral changes in seismic velocity, (c) evidence of a deep Paleozoic(?) extensional basin, underlying thick Mesozoic and Cenozoic sequences (beneath the Guárico area).
... Basado en el análisis de las reflexiones del Moho (PmP) observadas en las secciones sísmicas correspondientes a la cuenca de Falcón (ejemplo ver figura 5), se estiman espesores corticales en el orden de 30 km (Flores et al. 2015), considerando que esta discontinuidad importante corresponde a Moho. Esto implicaría, que el adelgazamiento cortical identificado en la parte oriental de Falcón (Sousa et al. 2005;Bezada et al. 2008), se extiende hacia el occidente de la cuenca de Falcón. Sin embargo, del análisis de las primeras llegadas (Pg y Pn; figura 6) deriva una discontinuidad más profunda (entre 40 y 50 km de profundidad) debajo del perfil Andes Norte. ...
Conference Paper
Full-text available
En el marco del proyecto Geociencia Integral de Los Andes de Mérida (GIAME) se desarrollan estudios geofísicos interdisciplinarias para determinar la estructura litosférica de Los Andes de Mérida. Desde el año 2013 se realizaron mediciones geofísicas a diferentes escalas cubriendo gran parte del occidente de Venezuela. Las investigaciones se enfocan a lo largo de tres perfiles que cruzan Los Andes en el norte por Barquisimeto, en el centro por Valera y al sur de Mérida. Las mediciones gravimétricas en los perfiles se complementaron con mediciones espaciales entre la costa de Falcón y Los Llanos centrales, así como mediciones en los ríos del estado Amazonas y mediciones de gravedad absoluta para el amarre de todas las bases. Se realizó el control de calidad de la base de datos, y los primeros modelos estructurales permiten ver la geometría de la raíz de Los Andes. También se finalizaron las mediciones magnetotelúricas a lo largo de los perfiles central y sur con 96 estaciones medidas, que se encuentran en la fase de procesamiento. Las mediciones sísmicas profundas de gran ángulo se enfocaron a lo largo de los tres perfiles con longitudes entre 350 y 550 km, así como un perfil perpendicular en Falcón de 300 km. Se realizaron en una primera etapa registros de 40 disparos con cargas de explosivo entre 110 y 1600 kg, así como de los sismos ocurridos en la zona, en un total de 1050 equipos de registro en 4 instalaciones. Los primeros modelos confirman el desfase de la raíz de Los Andes unos 40 km hacía el noroeste respecto al perfil topográfico con una profundidad del Moho de hasta 55 km, aproximadamente. En el perfil sur se complementará la información con registros sísmicos de reflexión entre el Vigía y Santa Bárbara de Barinas. En las cuencas sedimentarias adyacentes se realizaron mediciones de ruido sísmico con el fin de determinar los períodos de vibración del suelo y correlacionarlos con las estructuras provenientes de la exploración petrolera. El registro de las deformaciones en superficie se realiza mediante campañas de observación GNSS en 30 sitios, medidos a finales de 2011 e inicio 2013, y próximamente a comienzos de 2016, y cuyos resultados demuestran la complejidad de las deformaciones en la región. Para las estructuras profundas se contempla en el marco del proyecto MAPS (Merida Andes – Perija Santa Marta) la instalación de 40 estaciones sismológicas de banda ancha en el occidente de Venezuela, en conjunto con 20 estaciones en el oriente de Colombia con énfasis en el rol de la losa de subducción del Caribe en la dinámica de la región. Estas estaciones se complementan con 13 estaciones a lo largo del perfil sur.
... La cuenca de Los Roques se observa como una sucesión de máximos y mínimos valores de gradientes. Se resaltan muy bien los gradientes positivos asociados al adelgazamiento cortical del norte de Falcón (Sousa et al. 2005, Bezada et al. 2008) y se observa la anomalía de gradientes positivos que se prolonga desde la isla de Margarita hacia el arco de las Antillas Menores. ...
Article
We made a gravimetric study using the satellital gravity database of the northern region of Venezuela in order to delimitated the intra-plate margin and characterize the crustal structures of the interaction zone between oceanic, transitional and continental regimes located between the south Caribbean deformed belt and venezuelan frontal thrust. The results clearly show cortical differentiation between oceanic and transitional crust identifiable by the gravimetric signature. The limit between both types of crust is located at the South Caribbean Deformed Belt, and its extension reaches up to 64º W, 250 km farther west than had been previously reported. On the other hand, the separation between transitional and continental crust to the south is less clear in the gravimetric signature. We interpret that the transitional crust is a overthrusted and sutured block to South America, and the San Sebastian-El Pilar fault system may represent the suture zone.
... The 30 km CPD contour in northwestern and north central Venezuela (Fig. 5) marks a limit that appears in the Moho depth map from receiver functions (Niu et al., 2007) and in the estimation from seismic refraction . Within this region, a crustal shortening congruent with the formation of the Falcon Basin has been reported Sousa et al., 2005). The heat flow data of 3 μcal cm −2 s −1 reveals a system with a strong thermal component that surely affects the magnetic response of the crust. ...
Thesis
Full-text available
L'aléa sismique du Nord-Ouest vénézuélien a été estimé au moyen d'une approche néotectonique et sismotectonique par suite de I'existence d'une faible sismicité caractérisée par des séismes de magnitude faible a modérée, connue pendant une periode de temps historique réduite (depuis 1492). Cette étude a permis de reconnaitre de nombreux accidents actifs couns (quelques dizaines de kilometres) et a faible vitesse de déplacement (~ 0,4 mrn/an), qui sont capables de générer des séismes de magnitude modérée (6 ~ Ms ~ 7) et a longue période de retour (> 1500 ans), supérieure a la période de connaissance de la sismicité. Mais cette région (en Colombie et au Vénézuéla) est traversée d' Est en Ouest par le systeme de failles d'Oca-Ancón, sur une longueur de I'ordre de 600 km. L'activité de ce systeme a été précisée au moyen de deux tranchées de recherche paléosismique qui ont permis d'établir I'occurrence de séismes de magnitude (Ms) 7 ,4 a 7 ,5 et d'estimer la vitesse du systeme a 2 mrn/an. La récurrence de ces événements sismiques est de 1752.:t. 133 ans pour la faille d'Ancón et de 4300 .:t. 1000 ans pour la faille d'Oca. Par ailleurs, deux séismes de magnitude (mb) 5 et 5, 7 appanenant a une crise sismique de plus de 2000 séismes enregistrée au large de la cóte orientale falconienne pendant le deuxieme trimestre de 1989, ont produit des phénomenes de liquéfaction que nous avons étudié au moyen de tranchées. Cette étude a confirmé que des séismes de magnitude 5 sont capables d'induire des phénomenes de liquéfaction dans un rayon de 30 km. De plus, nous avons pu réaliser la cane macrosismique d'un autre séisme qui a eu lieu au voisinage de Churuguara (centre de la zone d'étude) le 24- 11-90. Pour cette région, nous avons réétudié cenains séismes associés au systeme d'Oca-Ancón, pour lesquels nous proposons des mécanismes au foyer cohérents avec la cinématique du systeme et le champ de contraintes actuel. D'autre pan, nous nous sommes intéressés a l'évolution tectonique du bassin de Falcón depuis sa formation a l'Éocene supérieur-Oligocene, afin de mieux comprendre le contexte tectonique des déformations les plus récentes. Ceci nous a conduit a modéliser de fayon analogique deux problemes tectoniques: I'existence a grande échelle de zones de transfert le long du chevauchement de Guadalupe- Taima Taima, et l'inversion tectonique du bassin de Falcón a plus petite échelle, permettant ainsi de mieux comprendre deux des traits tectoniques majeurs de cette région. En dernier lieu, nous proposons un modele d'évolution cénozorque de la fa~ade sud-américaine du domaine caraibe qui tient compte des résultats généraux de notre étude et en paniculier de l'existence d'une phase distensive généralisée de cette fa~ade pendant l'Oligocene, responsable de la formation du bassin de Falcón. Nous concevons la formation du bassin dans un contexte d'arriere-arc.
Chapter
The Falcon Basin in NW Venezuela and adjacent offshore basins developed within a zone of extensional tectonics during Oligocene and Miocene times. Extension resulted from right-lateral motion along offset, E-W-trending, transcurrent faults, including the Oca fault in W Venezuela, the Cuiza fault in N Colombia, and the San Sebastian fault along the coastal areas of central Venezuela. Evidence of Oligocene magmatic activity is found in the central part of the Falcon basin where volcanic rocks and hypabyssal intrusions are exposed. These rocks are similar to other suites of continental igneous rocks typically associated with rifting environments. A similar Tertiary tectonic regime is postulated for the larger area of the Bonaire Crustal Block, a block that includes the Falcon and Bonaire basins. -from Author
Article
Ammonites from the pillow basalt associations of the Siquisique ophiolites located in west-central Venezuela indicate a minimum Bajocian to early Bathonian age for emplacement of the complex. The ammonites have been identified as ?Stephanoceras (Skirroceras) cf. macrum (Quenstedt), ?Emileia ex gr. multiformis (Gottsche) et quenstedti Westermann, and ?Parkinsonia sp. This association of cosmopolitan Pacific and Tethyan elements aids in the location of the western end of the Middle Jurassic seaway set between the Tethys and the Pacific Oceans (Hispanic Corridor). The apparent age of the ammonites indicates that some of the Sisquisique sediments, pillow basalts, and serpentines are the oceanic remnants of an arrested early phase of rifting between North and South America. -Authors
Article
We used seismic tomography to investigate the complex structure of the upper mantle below northwestern South America. Images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted Caribbean-Pacific litho sphere beneath the study area. Beneath western Venezuela and Colombia we distinguish two slabs: a Maracaibo and a (redefined) Bucaramanga slab. The Maracaibo slab, coinciding with most of the Bucaramanga slab previously defined by W. D. Pennington, dips in a direction of 150° at an angle of 17° to a depth of 275 km and correlates to the subducted Late Cretaceous oceanic plateau of the Caribbean plate. Farther south, a second slab dips at an angle of 50° in a direction of 125° to a depth of at least 500 km and correlates to the subducted oceanic crust of the Nazca plate and the downdip extension of the Panama island arc. We refer to this slab as the redefined Bucaramanga slab, because it is different from the Bucaramanga slab segment defined by Pennington. The area of the South American plate overriding both slabs is characterized by the absence of an active volcanic are, an anomalouslywide topographically uplifted and tectonically active area, and the northward escape of the Maracaibo block along active strike-slip faults. In support of earlier studies, we attribute this to the underthrusting of the Caribbean oceanic plateau (our shallowly dipping Maracaibo slab) along the base of the South American lithosphere and to the recent collision of the Panama island arc rafted in on more steeply dipping crust of the Nazca plate (our redefined Bucaramanga slab).
Andes et chaîne caraïbe sur la transversale de Barquisimeto (Vénézuela) Evolution géodinamique
  • Venezuela
  • J- F Stephan
Venezuela. Stephan, J-F., 1985. Andes et chaîne caraïbe sur la transversale de Barquisimeto (Vénézuela). Evolution géodinamique. Proceedings Symposium Géodynamique des Caraïbes, Paris, 505-529
Mapa geológico-estructural de Venezuela Ministerio de Energia y Minas
  • A Bellizzia
  • N Pimentel
  • R Bajo
Bellizzia, A., Pimentel, N. and Bajo, R., 1976. Mapa geológico-estructural de Venezuela. Scale 1:500,000. Ministerio de Energia y Minas, Ed. Foninves, Caracas
Evaluation of the effects of oblique collision between the Caribbean and South American plates using geochemistry from igneous and metamorphic bodies of northern Venezuela Extended Abstracts: 689-692 691 Muessig Structure and Cenozoic tectonics of the Falcon basin, Venezuela, and adjacent areas
  • C K Mcmahon
McMahon, C., 2000. Evaluation of the effects of oblique collision between the Caribbean and South American plates using geochemistry from igneous and metamorphic bodies of northern Venezuela. Ph.D. thesis, University of Notre Dame, USA, 227 pp. r6th International Symposium on Andean Geodynamics (ISAG 2005, Barcelona), Extended Abstracts: 689-692 691 Muessig, K., 1984, Structure and Cenozoic tectonics of the Falcon basin, Venezuela, and adjacent areas: Memoir Geological Society of America, 162: 217-230
Geología de Venezuela y de sus cuencas Petrolíferas
  • C González De Juana
  • M Y Iturralde De Arozena
  • X Picard Cadillat
González de Juana, C., Iturralde de Arozena, M. y Picard Cadillat, X., 1980, Geología de Venezuela y de sus cuencas Petrolíferas, Ed. Foninves, 2 vols.