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41.
Elvin Delgado 《社会与自然资源》2017,30(7):797-811
ABSTRACTThis article provides a critical analysis of the process involved in transforming small-scale artisanal production of solar salt into large-scale industrial production by Produsal in Los Olivitos Wildlife Refuge and Fishing Reserve in Lake Maracaibo, Venezuela. In doing so, it highlights the socioecological impacts resulting from this process in the wetland and the fishing community of Ancón de Iturre. Using political economy of nature as a theoretical framework, especially notions of the formal subsumption of nature, materiality of natural resources, and the commodification of nature, this article explores how the biophysical characteristic of salt and the ecosystem where it is contained present a specific set of natural obstacles for its production; the different strategies used by Produsal to overcome these obstacles; and the social and ecological contradictions embedded in the process. 相似文献
42.
This paper presents a compilation of 16 present-day stress tensors along the southern Caribbean plate boundary zone (PBZ), and particularly in western and along northern Venezuela. As a trial, these new stress tensors along PBZ have been calculated from inversion of 125 focal mechanism solutions (FMS) by applying the Angelier & Mechler's dihedral method, which were originally gathered by the first author and published in 2005. These new tensors are compared to those 59 tensors inverted from fault-slip data measured only in Plio-Quaternary sedimentary rocks, compiled in Audemard et al. (2005), which were originally calculated by several researchers through the inversion methods developed by Angelier and Mechler or Etchecopar et al.The two sets of stress tensors, one derived from geological data and the other one from seismological data, compare very well throughout the PBZ in terms of both stress orientation and shape of the stress tensor. This region is characterized by a compressive strike-slip (transpressional senso lato), occasionally compressional, regime from the southern Mérida Andes on the southwest to the gulf of Paria in the east. Significant changes in direction of the maximum horizontal stress (σH = σ1) can be established along it though. The σ1 direction varies progressively from nearly east-west in the southern Andes (SW Venezuela) to between NW-SE and NNW-SSE in northwestern Venezuela; this direction remaining constant across northern Venezuela, from Colombia to Trinidad. In addition, the σV defined by inversion of focal mechanisms or by the shape of the stress ellipsoid derived from the Etchecopar et al.'s method better characterize whether the stress regime is transpressional or compressional, or even very rarely trantensional at local scale.The orientation and space variation of this regional stress field in western Venezuela results from the addition of the two major neighbouring interplate maximum horizontal stress orientations (σH): roughly east-west trending stress across the Nazca-South America type-B subduction along the pacific coast of Colombia and NNW-SSE oriented one across the southern Caribbean PBZ. Meanwhile, northern Venezuela, although dextral strike-slip (SS) is the dominant process, NW-SE to NNW-SSE compression is also taking place, which are both also supported by recent GPS results. 相似文献
43.
About 7 Mt of high volatile bituminous coal are produced annually from the four coal zones of the Upper Paleocene Marcelina Formation at the Paso Diablo open-pit mine of western Venezuela. As part of an ongoing coal quality study, we have characterized twenty-two coal channel samples from the mine using organic petrology techniques. Samples also were analyzed for proximate–ultimate parameters, forms of sulfur, free swelling index, ash fusion temperatures, and calorific value.Six of the samples represent incremental benches across the 12–13 m thick No. 4 bed, the stratigraphically lowest mined coal, which is also mined at the 10 km distant Mina Norte open-pit. Organic content of the No. 4 bed indicates an upward increase of woody vegetation and/or greater preservation of organic material throughout the life of the original mire(s). An upward increase in telovitrinite and corresponding decrease in detrovitrinite and inertinite illustrate this trend. In contrast, stratigraphically higher coal groups generally exhibit a ‘dulling upward’ trend.The generally high inertinite content, and low ash yield and sulfur content, suggest that the Paso Diablo coals were deposited in rain-fed raised mires, protected from clastic input and subjected to frequent oxidation and/or moisture stress. However, the two thinnest coal beds (both 0.7 m thick) are each characterized by lower inertinite and higher telovitrinite content relative to the rest of Paso Diablo coal beds, indicative of less well-established raised mire environments prior to drowning.Foreland basin Paleocene coals of western Venezuela, including the Paso Diablo deposit and time-correlative coal deposits of the Táchira and Mérida Andes, are characterized by high inertinite and consistently lower ash and sulfur relative to Eocene and younger coals of the area. We interpret these age-delimited coal quality characteristics to be due to water availability as a function of the tectonic control of subsidence rate. It is postulated that slower subsidence rates dominated during the Paleocene while greater foreland basin subsidence rates during the Eocene–Miocene resulted from the loading of nappe thrust sheets as part of the main construction phases of the Andean orogen. South-southeastward advance and emplacement of the Lara nappes during the oblique transpressive collision of the Caribbean and South American tectonic plates in the Paleocene was further removed from the sites of peat deposition, resulting in slower subsidence rates. Slower subsidence in the Paleocene may have favored the growth of raised mires, generating higher inertinite concentrations through more frequent moisture stress. Consistently low ash yield and sulfur content would be due to the protection from clastic input in raised mires, in addition to the leaching of mineral matter by rainfall and the development of acidic conditions preventing fixation of sulfur. In contrast, peat mires of Eocene–Miocene age encountered rapid subsidence due to the proximity of nappe emplacement, resulting in lower inertinite content, higher and more variable sulfur content, and higher ash yield. 相似文献
44.
Felix V. Kaminsky Sergei M. Sablukov Ludmila I. Sablukova Dominic M.DeR. Channer 《Lithos》2004,76(1-4):565-590
In Venezuela, kimberlites have so far only been found in the Guaniamo region, where they occur as high diamond grade sheets in massive to steeply foliated Paleoproterozoic granitoid rocks. The emplacement age of the Guaniamo kimberlites is 712±6 Ma, i.e., Neoproterozoic. The Guaniamo kimberlites contain a high abundance of mantle minerals, with greater than 30% olivine macrocrysts. The principal kimberlite indicator minerals found are pyrope garnet and chromian spinel, with the overwhelming majority of the garnets being of the peridotite association. Chrome-diopside is rare, and picroilmenite is uncommon. Chemically, the Guaniamo kimberlites are characterized by high MgO contents, with low Al2O3 and TiO2 contents and higher than average FeO and K2O contents. These rocks have above average Ni, Cr, Co, Th, Nb, Ta, Sr and LREE concentrations and very low P, Y and, particularly, Zr and Hf contents. The Nb/Zr ratio is very distinctive and is similar to that of the Aries, Australia kimberlite. The Guaniamo kimberlites are similar in petrography, mineralogy and mantle mineral content to ilmenite-free Group 2 mica kimberlites of South Africa. The Nd-Sr isotopic characteristics of Guaniamo kimberlites are distinct from both kimberlite Group 1 and Group 2, being more similar to transitional type kimberlites, and in particular to diamondiferous kimberlites of the Arkhangelsk Diamond Province, Russia. The Guaniamo kimberlites form part of a compositional spectrum between other standard kimberlite reference groups. They formed from metasomatised subcontinental lithospheric mantle and it is likely that subduction of oceanic crust was the source of this metasomatised material, and also of the eclogitic component, which is dominant in Guaniamo diamonds. 相似文献
45.
委内瑞拉1999年特大泥石流灾害 总被引：10，自引：2，他引：8
受娜尼拉现象的影响,１９９９－１２－１５～１６委内拉北部阿维拉册区加勒比海沿岸的８个州连降特大暴雨,造成山体大面积滑塌,数十条沟谷同时暴发大规模的泥石流。泥石流造成３万人死亡、经济损失高达１００亿美元,成为本基纪最严重的泥石流灾害,这次泥石汉灾害具有群发性、规模大、低频率和直接入海等特点,对这类泥石流进行泥石流成因、活动规律、预测预报、泥石流与异常气候现象关系和直接入海型泥石流运动规律,沉积特征、 相似文献
46.
The world’s present demand for oil and gas is still in a rapid growth period, and traditional oil and gas resources account for more than 60% of the global oil and gas supply. The Americas is the world’s second largest production and consumption center of liquid fuel, and is also the world’s largest natural gas producer. In 2016, the Americas had 85.3 billion tons of proven oil reserves and 18.7 trillion m3 of proven natural gas reserves, which account for 35.4% and 10.0% of world’s total reserves, respectively. It produced 1267.1 Mt of oil and 1125.4 billion m3 of natural gas, which account for 28.9% and 31.7% of the world’s total production, respectively. The crude oil and natural gas reserves are mainly distributed in the U.S., Canada and Venezuela. The U.S. is the earliest and most successful country in shale gas exploration and development, and its shale gas is concentrated in the southern, central and eastern U.S., including the Marcellcus shale, Barnett shale, EagleFord shale, Bakken shale, Fayettevis shale, Haynsvill shale, Woodford shale and Monterey/Santos shale. The potential oil and gas resources in the Americas are mainly concentrated in the anticline and stratigraphic traps in the Middle-Upper Jurassic slope deposition of the North Slope Basin, the Paleozoic Madsion group dolomite and limestone in the Williston Basin, dominant stratigraphic traps and few structural traps in the Western Canada Sedimentary Basin, the Eocene structural-stratigraphic hydrocarbon combination, structural-unconformity traps and structural hydrocarbon combination, and the Upper Miocene stratigraphic-structural hydrocarbon combination in the Maracaibo Basin of Venezuela, the stratigraphic-structural traps and fault horst, tilting faulted blocks and anticlines related to subsalt structure and basement activity in the Campos Basin, the subsalt central low-uplift belt and supra-salt central low-uplift belt in the Santos Basin of Brazil, and the structural-stratigraphic traps in the Neuquen Basin of Argentina. In addition, the breakthrough of seismic subsalt imaging technology makes the subsalt deepwater sea area of eastern Barzil an important oil and gas potential area. 相似文献
47.
Quartz microtextures and microstructures owing to deformation of glaciolacustrine sediments in the northern Venezuelan Andes 总被引：1，自引：0，他引：1
W. C. Mahaney R. W. Dirszowsky M. W. Milner J. Menzies A. Stewart V. Kalm M. Bezada 《第四纪科学杂志》2004,19(1):23-33
Glaciolacustrine sediments, ranging in age from Early to Late Mérida (Wisconsinan) in sections in the northern Venezuelan Andes near Pedregal, were studied to assess the effect of small‐scale folding and faulting on the surface microtextures of individual grains. At site PED5, faulting of sediments beneath 35 m of Middle to Late Mérida glaciolacustrine, glaciofluvial and probable till deposits, has resulted in a maximum displacement of 1 m and many crushed sand grains are found along the shear zone. These dominantly quartz particles are typically smoothed and/or faceted with surface skins split from parent grains to produce adhering blade or wafer‐shaped coarse silts. Faulting with displacement of< 40 cm occurs in Late Mérida glaciolacustrine beds at sites PED13 and PED11, beneath ca. 1–5 m of sediment and is thought to result from the removal of lateral support during valley erosion and possibly seismic disturbance. Associated sediments exhibit a greater incidence of small‐scale fold structures and convoluted bedding but with similar numbers and types of crushed grains. All of the fault traces examined exhibit microstructural modifications, including microfaulting, folding and multiple domains associated with fluidisation and liquefaction. The microtextures described are distinct from those produced by glacial or glaciofluvial transport processes and potentially may be used to infer glaciotectonic or other post‐depositional disturbance of sediments. Rare euhedral quartz grains with distorted crystallographic axes may derive from the shear zone of the regional transform Boconó Fault, although many of these grains appear to be overprinted by glacial and/or recent deformation processes. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
48.
The major features of the crustal structure in north-eastern Venezuela from deep wide-angle seismic observations and gravity modelling 总被引：2，自引：0，他引：2
Venezuela is located on the plate boundary zone between the South American continent and the Caribbean plate. A relative movement of 2 cm/year is accommodated by a system of strike–slip faults running from the Andes to the Gulf of Paria. The Interior Range, a moderate-height mountain range, separates the Oriental Basin from the Caribbean. To the south, predominantly Precambrian rocks are outcropping in the Guayana Shield south of the Orinoco River. Results of deep wide-angle seismic measurements for the region were obtained during field campaigns in 1998 (ECOGUAY) for the Guayana Shield and in 2001 (ECCO) for the Oriental Basin. The total crustal thickness decreases from 45 km beneath the Guayana Shield, to 39 km at the Orinoco River, and 36 km close to El Tigre, in the center of the Oriental Basin. The average crustal velocity decreases in the same sense from 6.5 to 5.95 km/s. Detailed information was obtained on the velocity distribution within the Oriental Basin. Velocities are as low as 2.2 km/s for the uppermost 2 km, 4.5 km/s down to 4 km in depth, and a maximum depth of 13 km was derived for material with seismic velocities up to 5.9 km/s, interpreted as the base of the sedimentary basin. A gravimetric model confirms the structures derived from the seismic data. Discrete increases in sedimentary thickness along the basin may be associated to extension processes during the passive margin phase in the Cretaceous, or during earlier extension phases. 相似文献