Miocene to recent Cariaco basin, offshore Venezuela: Structure, tectonosequences, and basin-forming mechanisms     

Alejandro Escalona  Paul Mann 《Marine and Petroleum Geology》2011,28(1):177-199

The Cariaco basin, located ∼40 km off the central part of the coast of Venezuela, is the largest (∼4000 km²) and bathymetrically deepest (1400 m BSL) Neogene fault-bounded basin within the right-lateral strike-slip plate boundary zone that separates the Caribbean and South American plates. Using subsurface geophysical data, we test two previously proposed tectonic models for the age, distribution and nature of east-west-striking, strike-slip faults, and basin-forming mechanism for the two main depocenters of the Cariaco basin. The earliest interpretation for the opening of the twin Cariaco depocenters by Schubert (1982) proposes that both depocenters formed synchronously by extension along transverse (north-south) normal faults at a ∼30-km-wide rhomboidally-shaped pull-apart basin between the right-lateral, east-west-striking, and parallel San Sebastian and El Pilar fault zones. A later model by Ben-Avraham and Zoback (1992) proposes that both depocenters formed synchronously by a process of ”transform-normal parallel extension”, or rifting in a north-south direction orthogonal to the east-west-striking and parallel strike-slip faults.We use more than 4000 km of 2D single- and multi-channel seismic data tied to 11 wells to map 5 tectono-stratigraphic sequences and to produce a series of structural and isopach maps showing how the faults that controlled both Cariaco depocenters evolved from Paleogene to the present. Comparison of fault and isopach maps for dated horizons from Paleogene to late Neogene in age show three main phases in basin development: 1) from middle Miocene to Pliocene, the West Cariaco basin formed as a rhomboidally-shaped pull-apart at a 30-km-wide stepover between the northern branch of the San Sebastian fault and the El Pilar fault zone; 2) during the early Pliocene, a new strike-slip fault transected the West Cariaco basin (southern branch of the San Sebastian fault) and caused extension to cease; and 3) during the early Pliocene to recent, a “lazy-Z” shaped pull-apart formed along the curving connection between the southern branch of the San Sebastian and El Pilar fault zones.  相似文献   

Tectonostratigraphic evolution of the Morichito piggyback basin, Eastern Venezuelan Basin     

Migdalys SalazarLorena Moscardelli  William FisherMaria Antonieta Lorente 《Marine and Petroleum Geology》2011,28(1):109-125

The Morichito piggyback basin (MPB) is a SW-NE-oriented depocenter in the Eastern Venezuelan Foreland Basin (EVFB). This piggyback basin formed by overlying the Pirital thrust during the middle to late Miocene as a result of oblique collision between the Caribbean and South-American Plates. The MPB covers an area encompassing approximately 1000 km² between the Serrania del Interior range and the Pirital high, which is a hanging wall uplift along the Pirital thrust that acts as a confining barrier on the southern boundary of the MPB. Previous studies have tried to address the tectonostratigraphic significance of the MPB, but new biostratigraphic information and recently acquired 3D seismic data have allowed us to expand the understanding of this basin. The MPB occupies a relatively small area of the EVFB; however, the MPB contains a valuable stratigraphic record that can be used to unveil the timing of the main deformational events that took place in the EVFB.This work presents the tectonostratigraphic evolution of the MPB by defining four tectonostratigraphic sequences (T1-T4). Each sequence was defined on the basis of integration of well logs, biostratigraphy, and seismic geomorphological interpretations. T1 (24-16 Ma) (late Oligocene to middle Miocene), which was deposited in shallow-marine environments, extends to the south of the Pirital high beyond the boundaries of the MPB. T1 is equivalent to the early foredeep stage of the EVFB, having been formed when structural deformation and uplifting were already occurring to the north on the proto-Serrania del Interior range (∼24-16 Ma) and the Pirital thrust was active (∼22 Ma). T2 (16-11 Ma) (middle to late Miocene) is composed of alluvial-fan deposits derived from the proto-Serrania del Interior range. The geometry and internal configuration of T2 indicate that during this time the basin was transitioning from an open-foreland basin to a confined piggyback basin. During deposition of T2, the Pirital fault was active as an out-of-sequence thrusting event (16-∼11 ma). T3 (late Miocene) and T4 (early Pliocene to Recent), composed of shallow-marine and fluvial deposits, were deposited in an already restricted piggyback basin. The Pirital high was already in place during deposition of T3 (∼11-9.3 ma). T3 and T4 represent the final phases of MPB infilling, when tectonic activity and subsidence were at their lowest rates. MPB sedimentary infilling dates the activity of thrusting events in the proto-Serrania del Interior (∼24-16 Ma), timing of maximum deformation associated with the Pirital out-of-sequence thrusting event (16-∼11 Ma), timing of final emplacement of the Pirital high (∼11-9.3 Ma), and the beginning of tectonic quiescence (<5.2 Ma).  相似文献   

Role of the shale tectonics on the evolution of the Eastern Venezuelan Cenozoic thrust and fold belt     

Leo Duerto  Ken McClay 《Marine and Petroleum Geology》2011,28(1):81-108

This paper presents a structural and stratigraphic analysis of the foreland-fold-belt of the Eastern Venezuelan Basin and the main conclusions about shale tectonic mechanisms in the area. The deformation of the foreland-fold-belt has been investigated analyzing the growth strata architecture preserved on the structure fold limbs. Three contractional episodes are proposed for the Eastern Venezuelan Basin: 1) Oligocene to middle Miocene, 2) late Miocene to Pliocene and 3) Pleistocene. The first episode produced contractional listric faults inside the shale and long displacement blind thrusts in the underlying Cretaceous units. The second episode produced the deformation of the Cenozoic strata into overlapping east-west-trending, convex northward anticlines that covers more than 200 kilometers in length and 40 kilometers wide, break-through normal faults product of a high sedimentary load that overcomes contraction and the formation of short-displacement blind thrusts in the underlying Cretaceous units. The last episode is related to an oblique compression and the formation of high angle extensional faults with dextral movement and NW-SE strike. The role of the shale tectonics in the evolution implies that shale deforms in two stages: 1) folding and 2) normal faulting of the crest of the anticline (Break through normal faulting). Folding controlled the sediment distribution during most of the Neogene strata, while the normal faulting of the anticlines represent basin potential for hydrocarbon. The best potential hydrocarbon plays in the basin are related to oblique-collision restricted basins and controlled by break-through normal faults and the presence of NW-SE strike faults that connect the HC source with the reservoirs. Results from this research imply that the role of sedimentation is fundamental for the overburden sand distribution and tectonic constrain of the folds.  相似文献   

STRUCTURAL TENSION,MIGRATION, AND DEVELOPMENT: A CASE STUDY OF VENEZUELA*     

Victoria A. Lawson  Lawrence A. Brown 《The Professional geographer》1987,39(2):179-188

Mismatch of labor demand and supply, resulting from economic growth, is referred to here as structural tension. Spatial variations in structural tension are identified for Venezuelan states in 1971. Positive tension, indicating overutilization of human resources, prevails in urban areas. By contrast, rural locales exhibit underutilization due to rapid labor force growth without parallel increases in employment opportunities. Influence of structural tension, coupled with other migration determinants, upon destination choice by economically active immigrants is explored. Structural tension emerges as strongly significant for the total sample, displacing wages from the model. This is consistent with our contention that wages are a less precise indicator of labor supply and demand.  相似文献   

Human and environmental factors in the increasing incidence of dengue fever: a case study from Venezuela     

M.I. Brightmer  M.G. Fantato 《GeoJournal》1998,44(2):103-109

Dengue and its more serious form, Dengue Haemorrhagic Fever, is an acute vector-borne disease, endemic in more than 100 countries in the tropics and sub-tropics. It is increasing as a public health problem with approximately two billion people at risk. The disease is transmitted by the mosquito Aedes aegypti which is highly domesticated. During the 1980s the mosquito recolonised areas in the Americas from where it had previously been eradicated and the incidence of dengue increased dramatically, affecting places where the disease had hitherto been unknown. It was identified as a global priority by the World Health Organisation in 1993. Venezuela experienced major dengue epidemics in 1989 and 1995 and further outbreaks throughout the 1990s. In this paper the macro-economic issues as well as human behavioural characteristics in the occurrence of epidemic dengue are discussed in the Venezuelan context using the results of a survey in Caracas, and their significance is compared with climatic factors. Given that the vector's eradication is improbable in the near future and that no cure or vaccines are yet available, prevention is the only strategy for disease control. Vector control programmes are the current priority, but have had little success. It is argued that there is a need for individual and community participation in programmes but this will require more information as to the knowledge, attitudes and practices of the populations at risk, which suggests a role for social scientists. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Neotropical vegetation response to rapid climate changes during the last glacial period: Palynological evidence from the Cariaco Basin     

Catalina González  Lydie M. Dupont 《Quaternary Research》2008,69(2):217-230

We present new palynological information from the anoxic Cariaco Basin, off Venezuela, that provides insight into the response of northernmost South American vegetation to rapid climate changes between 68 and 28 ka, specifically during North Atlantic Heinrich events (HEs) and Dansgaard/Oeschger cycles. We defined three different vegetation modes: (1) an interstadial mode characterized by the highest pollen concentration and the maximum extension of semi-deciduous and evergreen forests; (2) a stadial mode characterized by increases of salt marshes, herbs, and montane forests; and (3) a Heinrich event mode characterized by the lowest pollen concentrations, abrupt increases of salt marshes, and decreased forest abundance. Similarly, indices of C4/C3 plants show increases during stadials with clear peaks during the onset of HEs, though grasslands did not become dominant during these periods. We alternatively propose that these expansions of C4 plants are associated with the expansion of coastal salt marshes. Our vegetation record suggests the prevalence of humid conditions during interstadials, dry and cold conditions during stadials, and dry and cold conditions together with changes in sea level during HEs. This new palynological evidence supports previous interpretations that main environmental changes in northernmost South America were driven by latitudinal displacements of the Intertropical Convergence Zone and sea-level changes.  相似文献   

委内瑞拉马拉开波盆地构造演化对油气的控制   总被引：2，自引：1，他引：1  

汪伟光  喻莲  宋成鹏  琚亮 《现代地质》2012,26(1):131-138

委内瑞拉马拉开波盆地自中生代以来经历了裂谷、被动大陆边缘、前陆盆地和马拉开波向斜4个演化阶段,对油气的生成运移聚集起到了重要的控制作用。从石油地质条件对构造作用的地质响应出发,探讨了构造演化对盆地烃源岩、储层、圈闭类型以及油气运聚的控制作用。受构造作用影响,烃源岩发育南薄北厚,沉积中心也发生迁移,形成3个向不同方向增厚的碎屑岩楔体,构成了马拉开波盆地的主要储层,并引起烃源岩埋深的变化,导致生烃条件的多期变化。同时,构造作用还控制了不同层系主要的圈闭类型,而早期与裂谷作用相关的断层在后期构造作用下的复活或反转,为油气提供了主要的运移通道。此外,盆地区域性的倾斜也为油气的运移提供了大的构造格局。  相似文献   

Preliminary results from U-Th dating of glacial-interglacial deposition cycles in a silica speleothem from Venezuela     

J. Lundberg  C. Brewer-Carias 《Quaternary Research》2010,74(1):113-365

Recent explorations in Cueva Charles Brewer, a large cave in a sandstone tepui, SE Venezuela, have revealed silica biospeleothems of unprecedented size and diversity. Study of one — a sub-spherical mass of opaline silica — reveals a complex, laminated internal structure consisting of three narrow dark bands alternating with two wider light bands. Uranium-thorium dating has produced 3 stratigraphically correct dates on the light bands from 298 ± 6 (MIS 9) to 390 ± 33 ka (MIS 11). U concentration is only 30-110 ppb. Initial ²³⁴U/²³⁸U ratios are high and increase over time from 1.8 to 5.3. Growth rate is very low, the fastest, at 0.37 ± 0.23 mm/ka, in MIS 9. Trace element and heavy metal content of the dark bands is distinctly higher than that of the light bands. It is hypothesized that the dark and light bands correlate with drier/glacial and wetter/interglacial periods, respectively, and that this sample probably began to grow in MIS 13. The cave is in a region that straddles a regionally important ecotone: the speleothem isotopic and trace element variations may preserve a useful paleoclimatic signal. This is the first published suite of U-Th dates from a single silica speleothem and the longest Quaternary record for this region.  相似文献   

Reviewing the Guayana project: Lifetime migration to and from Bolivar state,Venezuela, 1950–2001     

Evelyn D. Ravuri 《Singapore journal of tropical geography》2011,32(2):253-266

By the mid‐twentieth century the population and economic resources in many developing economies had become concentrated in the capital city. Planned industrial cities became an important mechanism to encourage more balanced urban systems as well as development in peripheralized regions. Venezuela boasts one of the most impressive planned industrial cities, Ciudad Guayana, constructed in 1959 in the resource rich but inaccessible Bolivar state in the southeast. This paper summarizes the lifetime migration to and from Bolivar state for the years 1950, 1971 and 2001. Whereas the majority of lifetime migrants originated from the neighbouring northeast region in 1950 and 1971, by 2001 more migrants arrived from the capital region. For lifetime outmigrants, the destination states became more diverse and less focused on the capital region. Gender ratios of lifetime migrants to and from Bolivar became more equitable as women became more prominent in migration flows. The level of urban primacy in Venezuela declined substantially after 1971 as the country became more internally integrated, although this more equitable distribution of the country's population may not have been solely a result of the creation of the growth pole, but a result of wider economic development.  相似文献   

A probabilistic model for the prediction of meteorological droughts in Venezuela     

F.J. Paredes  E. Guevara 《Atmósfera》2013,26(3):311-323

Droughts occur when rainfalls diminish or cease for several days, months or years. In the last five years several meteorological droughts have occurred in Venezuela, impacting negatively water supply, hydro-power and agriculture sectors. In order to provide institutions with tools to manage the water resources, a probabilistic model has been developed and validated to predict in advance the occurrence of meteorological droughts in the country using monthly series of 632 rainfall stations. The standardized precipitation index (SPI) was used to identify dry events of each rainfall series. A principal component analysis associated to a geographic information system was used to define geographically continuous homogeneous sub-regions (HS) for the values of SPI. For each HS a representative station was selected (reference station, RS). A lagged correlation analysis was applied to the SPI series of the RS and the corresponding series of anomaly indices of 10 macroclimatic variables (MV). The four MV with higher correlation in each RS were organized into three levels (-1, 0 and +1), using the quartiles Q₂ and Q₄ as values of truncation. The SPI series are expressed in four ranges: non-dry, moderately dry, severely dry and extremely dry. The conditional probability of occurrence of the four ranges of SPI was determined in every combination that can occur in the four VM best correlated. The resulting model in each RS was validated using the SPI series from 20 meteorological stations operated by the Servicio de Meteorología de la Fuerza Aérea Venezolana (Meteorological Service of the Venezuelan Air Force) which were not used in the development of the models. Results indicate that models detected the occurrence of ES with an accuracy ranging from 85.19 to 100%; the success is directly proportional to the length of records used in the development of the model. This methodology could be applied in any country that has long, continuous and homogeneous rainfall series.  相似文献