Repositorio Institucional Universidad EAFIT ::Examinando por Materia "South America"

Examinando por Materia "South America"

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A Classification System for Colombian Wetlands: an Essential Step Forward in Open Environmental Policy-Making
(Springer Netherlands, 2019-01-01) Ricaurte L.F.; Patiño J.E.; Zambrano D.F.R.; Arias-G J.C.; Acevedo O.; Aponte C.; Medina R.; González M.; Rojas S.; Flórez C.; Estupinan-Suarez L.M.; Jaramillo Ú.; Santos A.C.; Lasso C.A.; Nivia A.A.D.; Calle S.R.; Vélez J.I.; Acosta J.H.C.; Duque S.R.; Núñez-Avellaneda M.; Correa I.D.; Rodríguez-Rodríguez J.A.; Vilardy Q S.P.; Prieto-C A.; Rudas-Ll A.; Cleef A.M.; Finlayson C.M.; Junk W.J.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
Knowledge about the distribution and diversity of wetlands has become an essential tool for environmental management and policy-making. Yet, while recent estimates indicate that 27% of the area of Colombia is covered by wetlands and despite a number of regional studies, information about the diversity of wetlands nationally is scarce. In response, we present a national wetland classification system that is based on an ecological approach, from the perspective of wetland scientists, and which builds upon the assumptions underlying the flood pulse concept and hydrogeomorphic approach. Thus, the approach and structure of the Brazilian wetland classification system are used, with geomorphological adjustments made according to Colombia’s topography. The classification is hierarchical, multi-scale, functional, and organized according to four levels (system, macroregion, subsystem, and class), with the wetland diversity of Colombia represented nationally by 89 macrohabitats across marine-coastal, inland, and anthropogenic systems. The primary purpose of this classification is to provide integrated and organized information on the distribution and diversity of Colombian wetlands that will serve as a baseline for transparent environmental policy-making. © 2019, Society of Wetland Scientists.
Effects of realistic topography on the ground motion of the Colombian Andes - A case study at the Aburra Valley, Antioquia
(OXFORD UNIV PRESS, 2016-03-01) Restrepo, D.; Bielak, J.; Serrano, R.; Gómez, J.; Jaramillo, J.; Mecánica Aplicada
This paper presents a set of deterministic 3-D ground motion simulations for the greater metropolitan area of Medellin in the Aburra Valley, an earthquake-prone region of the Colombian Andes that exhibits moderate-to-strong topographic irregularities. We created the velocity model of the Aburra Valley region (version 1) using the geological structures as a basis for determining the shear wave velocity. The irregular surficial topography is considered by means of a fictitious domain strategy. The simulations cover a 50 x 50 x 25 km(3) volume, and four M-w = 5 rupture scenarios along a segment of the Romeral fault, a significant source of seismic activity in Colombia. In order to examine the sensitivity of ground motion to the irregular topography and the 3-D effects of the valley, each earthquake scenario was simulated with three different models: (i) realistic 3-D velocity structure plus realistic topography, (ii) realistic 3-D velocity structure without topography, and (iii) homogeneous half-space with realistic topography. Our results show how surface topography affects the ground response. In particular, our findings highlight the importance of the combined interaction between source-effects, source-directivity, focusing, soft-soil conditions, and 3-D topography. We provide quantitative evidence of this interaction and show that topographic amplification factors can be as high as 500 per cent at some locations. In other areas within the valley, the topographic effects result in relative reductions, but these lie in the 0-150 per cent range.
Estimating the Impacts of Bolivia’s Protected Areas on Poverty
(Elsevier, 2013) Canavire-Bacarreza, Gustavo; Hanaueronly, Merlin M.; Universidad EAFIT, Medellin, Colombia; Sonoma State University, Rohnert Park, USA; Escuela de Economía y Finanzas; Economía; Estudios en Economía y Empresa
Bolivia has experienced a rapid proliferation of protected areas over the past several decades. Using rich biophysical and socioeconomic data, we estimate the impacts of Bolivia’s protected areas on poverty between 1992 and 2001. We find no evidence that the establishment of protected areas exacerbated poverty. In fact, we provide robust estimates indicating that communities affected by protected areas exhibited differentially greater levels of poverty reduction as compared to similar unaffected communities. Our results add to the growing body of evidence that environmental conservation does not necessarily come at the expense of local communities.
The Evolution of Security in South America: a Comparative Analysis Between Colombia and Brazil
(Facultad de Relaciones Internacionales, Estrategia y Seguridad, 2015-06-01) Luis F. Vargas-Alzate; Sosa, S.; Héctor José Galeano David
This article studies the evolution of security in South America by comparing the advances of two of its most characteristic cases, Colombia and Brazil, in their transition from traditional security models to the application of the concept of human...
Fission-track datings and geomorphic evidences for long-term stability in the Central Cordillera highlands, Colombia
(Gebruder Borntraeger Verlagsbuchhandlung, 2006-01-01) Toro, G.; Hermelin, M.; Schwabe, E.; Posada, B.O.; Silva, D.; Poupeau, G.; Toro, G.; Hermelin, M.; Schwabe, E.; Posada, B.O.; Silva, D.; Poupeau, G.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y Tectónica
Age of weathered andesitic volcanic ash layers, which cover most of the landscape in the Central Cordillera northern massif plateaus in Colombia, were determined through the use of fission track counting in volcanic zircon crystals. A stoneline, exposed in many outcrops, which corresponds to the lower limit of younger tephras, gave ages between 350 ka and 440 ka. Andosols lying above the stoneline could not be dated. Paleolake deposits in the study area and surroundings were dated at about 2 Ma; older ashes deposited on the Rio Negro erosion surface (SII) below the stoneline level gave ages between 3.4 and 5.4 Ma. The study area is located about 150 km from the volcanic center. The ash layers decrease in thickness only slightly with distance, as perceived from profiles sampled in flat areas. We conclude that the only noticeable erosional event in the region was the emplacement of the stone-line. This erosion event which was relatively short and mild in intensity, as part of the underlying soil derived from quartzdiorite was preserved. This soil formed above a saprolite with a thickness which may reach 150 m, a fact which supports the inference that the plateaus have been stable for millions of years, in contrast to the high erosion rates observed in the surrounding steep slopes and canyons. © 2006 Gebrüder Borntraeger.
Human induced discharge diversion in a tropical delta and its environmental implications: The Patía River, Colombia
(ELSEVIER SCIENCE BV, 2012-03-06) Restrepo, Juan D.; Kettner, Albert; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
The Patía River, the number one in terms of sediment yield ~1500tkm -2yr -1 draining the western South America, has the most extensive and well developed delta on the Pacific coast, measuring 1700km 2. During the Holocene, nature forced the Patía delta to the south; however, a major water diversion, starting in 1972, diverted the Patía flow to the Sanguianga River, the latter, a small stream draining internal lakes from the Pacific lowlands. This human induced discharge diversion shifted the active delta plain back to the north and changed the northern estuarine system into an active delta plain. Overall, major environmental consequences of this discharge diversion in terms of morphological changes along the delta coast and distributary channels, are evidenced by: (1) coastal retreat along the abandoned delta lobe; 63% of the southern shoreline is retreating at maximum rates of 7myr -1, with a corresponding coastal land loss of 106myr -1; (2) transgressive barrier islands with exposed peat soils in the surf zone; (3) abandonment of former active distributaries in the southern delta plain with associated closing of inlets and formation of ebb tidal deltas; (4) breaching events on barrier islands; and (5) distributary channel accretion in the northern delta plain by morphological processes such as sedimentation (also in crevasses), overbank flow, increasing width of levees, interdistributary channel fill, and colonization of pioneer mangrove. The Sanguianga Mangrove National Park (SMNP), the largest mangrove reserve in Colombia, measuring 800km 2, lies in this former estuary, where major hydrologic and sedimentation changes are occurring. Observed environmental changes in the SMNP, include (1) seaward advance of the sub-aqueous delta front at the Sanquianga inlet evidenced by an increase in tidal flat area from 5.4Mm 2 in 1986 to 14Mm 2 in 2001; (2) freshening conditions in the Sanguianga distributary channel, a hydrologic change that has shifted the upper estuarine region (salinity <1psu) downstream; (3) downstream advance of freshwater vegetation, which is invading channel banks in the lower and mixing estuarine zones; (4) die-off of approximately 5200ha of mangrove near the delta apex at Bocas de Satinga; and (5) recurrent periods of mangrove defoliation due to a warm plague. Further analysis indicate that during the past two decades, processes such as mangrove erosion in the delta shore, are the result of a short-term relative sea-level rise of 5.1mmyr -1 for the 1984-2006yr-period, after the devastating tsunami of 1979. In the Patía catchment, erosion rates have been more pronounced during the 1970-1980 and 1990-2000 decades, as a result of land degradation and deforestation. Preliminary results indicate that relative resent anthropogenic influences on the Patía River drainage basin have altered the deltaic environment and beyond significantly. © 2011 Elsevier B.V.
Late Quaternary vegetation and climate change in the Panama Basin: Palynological evidence from marine cores ODP 677B and TR 163-38
(ELSEVIER SCIENCE BV, 2006-05-03) Gonzalez, C; Urrego, LE; Martinez, JI; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
The Late Quaternary paleoenvironmental history from Pacific slopes of the western Andes is reconstructed by pollen analysis of 32 samples from two marine sediment cores from the Panama Basin, eastern equatorial Pacific: core ODP 677B (83°44.2200' W, 1°12.1440' N, 3473 m water depth) is 185 cm long and spans the last 39,410 years, core TR 163-38 (81.583° W, 1.337° N, 2200 m water depth) is 103 cm long and covers the last 17,380 years. Six ecological groups were established: mangrove, brackish and fresh water swamps, terra firma lowland forests, broad range taxa, Andean forests, and open vegetation. A good correspondence was found between the changes of these ecological groups in the two cores. The records evidence the continuous presence of all vegetation types during the last 39,410 years and specially the uninterrupted occurrence of tropical rain forest. They record a development from: (1) a cold and humid phase (39,410-28,120 yr cal BP) with moderately high sea levels, (2) the coldest and driest phase in the record (28,120-14,500 yr cal BP) accompanied by the lowest sea levels, (3) a transitional phase when sea level rose and humid conditions dominated, (4) a stage (11,300-5600 yr cal BP) of the highest sea levels and moisture conditions including a drier period ~7000 yr BP, to (5) a final period (5600 yr cal BP-Present) when sea level reached its present height, humidity persisted, and indicators of disturbance expanded. Peaks in pollen and spore concentration, associated with high river discharge periods, indicate periods of higher precipitation around 33,500, 28,000 and 12,000-9000 yr cal BP. Although main vegetation responses seem to reflect rainfall and moisture variations, a good correspondence was found between d18O values and percentages of Andean and lowland pollen, suggesting that vegetation also responded to tempearture changes. © 2005 Elsevier B.V. All rights reserved.
Paleoceanographic conditions in the western Caribbean Sea for the last 560 kyr as inferred from planktonic foraminifera
(ELSEVIER SCIENCE BV, 2007-09-14) Martinez, J. Ignacio; Mora, German; Barrows, Timothy T.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
Faunal analyses of planktonic foraminifera and upper-water temperature reconstructions with the modern analog technique are studied and compared to the magnetic susceptibility and gamma ray logs of ODP Core 999A (western Caribbean) for the past 560 kyr in order to explore changes in paleoceanographic conditions in the western Caribbean Sea. Long-term trends in the percentage abundance of planktonic foraminifera in ODP Core 999A suggest two hydrographic scenarios: before and after 480 ka. High percentage abundances of Neogloboquadrina pachyderma and Globorotalia inflata, low abundances of Globorotalia menardii and Globorotalia truncatulinoides, low diversity, and sea-surface temperatures (SST) under 24 °C are typical characteristics occurring from 480 to 560 ka. These characteristics suggest a "shallow" well-oxygenated upper thermocline and the influx of nutrients by either seasonal upwelling plumes and/or eddy-mediated entrainment. The second scenario occurred after 480 ka, and it is characterized by high and fluctuating percentage abundances of Neogloboquadrina dutertrei, G. truncatulinoides, G. menardii, Globigerinita glutinata, Globigerinella siphonifera, and Globigerinoides ruber; a declining trend in diversity; and large SSTs. These characteristics suggest a steady change from conditions characterized by a "shallow" thermocline and chlorophyll maximum to conditions characterized by a "deep" thermocline (mainly during glacial stages) and by more oligotrophic conditions. The influence of the subtropical North Atlantic on the upper thermocline was apparently larger during glacial stages, thus favoring a deepening of the thermocline, an increase in sea-surface salinity, and a dramatic reduction of nutrients in the Guajira upwelling system. During interglacial stages, the influx of nutrients from the Magdalena River is stronger, thus resulting in a deep chlorophyll maximum and a fresher upper ocean. The eddy entrainment of nutrients is the probable mechanism responsible of transport from the Guajira upwelling and Magdalena River plumes into ODP 999A site. © 2007 Elsevier B.V. All rights reserved.
Prediction of landslide occurrence in urban areas located on volcanic ash soils in Pereira, Colombia
(Springer Verlag, 2004-01-01) Rios, D.A.; Hermelin, M.; Rios, D.A.; Hermelin, M.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y Tectónica
As a result of the 25 January 1999 Armenia earthquake, the city of Pereira (400,000 inhabitants), located on a volcanic ash-covered alluvial fan in the western limit of the Central Cordillera (Colombia), suffered 250 slope movements. After a complete inventory, a monitoring process of unstable areas was designed, based on repeated topographic surveys, soil pore saturation levels and visual inspections. The participation of the communities was crucial and permitted the prediction of slope movements between 2 weeks and 3 months in advance and the evacuation of the inhabitants. Three specific examples are discussed. The method could be improved by excavating observation trenches and observing in detail local rainfall. In all cases, the strong involvement of the community was considered indispensable for the success of the process. © Springer-Verlag 2004.
Quantitative biostratigraphic model for the tertiary of the lower Magdalena Basin, Colombian Caribbean
(Ecopetrol, 2006-01-01) Cuartas, C.; Jaramillo, C.; Martínez, J.-I.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
The reinterpretation of biostratigraphic information by new models and quantitative correlation techniques substantially improves its resolution and its correlative potential, thus minimizing oil exploration risks. With this aim, biostratigraphic information, i.e. first (FO) and last (LO) occurrence events of benthonic and planktonic foraminifera was analysed from sixteen wells from the Lower Magdalena Valley (LMV). The inconsistencies found in the biostratigraphic record, i.e. varying successions of first and last appearances of species from well to well as a result of several factors such incomplete sampling and preservation, true variation in the distribution of fosil taxa, etc., and the great amount of biostratigraphic data makes it practically impossible to accurately constrain basin history from biostratigraphic information by unaided visual inspection. This motivates the treatment of biostratigraphic information with new quantitative approaches, such as constrained optimization (CONOP9 software) and graphic correlation concepts (GraphCor 3,0) and the comparative method approach of Cooper et al. (2001). The succession of biostratigraphic events found through the application of each technique was statistically filtered and compared with Kendall tau coefficients whose values were 0,8. An optimal biostratigraphic succession of LOs was found and calibrated with the Berggren et al. (1995) global time scale by a LOESS regression model for the middle Eocene-Pliocene interval, thus revealing three major changes in sediment accumulation rates for the basin during this time interval: (1) middle Eocene to Oligocene, with low accumulation rates, (2) early Miocene to middle Miocene, with high accumulation rates and (3) late Miocene to Pliocene, with lower accumulation rates. The calibrated composite succession enabled the construction of age-well depth plots, which indicate periods of local deposition and accumulation rates, and periods of erosion, no deposition or very low accumulation rates (unconformities). The best plots were used to build a model for the correlation of unconformities, which shows that they are heterochronous, lasted at least 2,5 Ma, and are of limited extent. Finally, a correlation model was proposed that includes: (1) a time-calibrated succession of biostratigraphic events, and (2) a Haq curve that shows how each geologic period is recorded in each well.
The rock coast of South and Central America
(Geological Society of London, 2014-05-24) Blanco-Chao, R.; Pedoja, K.; Witt, C.; Martinod, J.; Husson, L.; Regard, V.; Audin, L.; Nexer, M.; Delcaillau, B.; Saillard, M.; Melnick, D.; Dumont, J.F.; Santana, E.; Navarrete, E.; Martillo, C.; Pappalardo, M.; Ayala, L.; Araya, J.F.; Feal-Pérez, A.; Correa, D.; Arozarena-Llopis, I.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
The great variety of climatic conditions, tidal ranges and wave regimes of South and Central America act on a complex geology and tectonic framework. Many of the rock and cliffed coasts of South America are strongly controlled by the occurrence of extensive Cenozoic and Pleistocene sediments that crop out at the coast. Geology and the different uplift rates are a major factor in the whole coastal geomorphology of South and Central America, and consequently are a very important control of the processes and landforms of rock coasts. This chapter covers several aspects of the rock coast of South and Central America, with special attention to the combination of tectonic movements and Quaternary Pleistocene-Holocene sea-level changes. © The Geological Society of London 2014.
Sedimentary metal ratios in the Colombia Basin as indicators for water balance change in northern South America during the past 400,000 years
(AMER GEOPHYSICAL UNION, 2005-11-15) Mora, Germán; Martínez, J.; Universidad EAFIT. Departamento de Geología; Ciencias del Mar
Recent paleoclimate reconstructions for northern South America suggest changes in moisture balance interpreted to result from shifts in the mean latitudinal position of the Intertropical Convergence Zone (ITCZ). Because most of these records only extend back to the last glacial interval, we measured metal abundances in sediments from Ocean Drilling Program Core 999A in the Caribbean Sea spanning the last 400 kyr to evaluate glacial/interglacial fluctuations in the water balance of northern South America. Variations in sedimentary Al/Ti, K/Ti, Fe/Ti, and Fe/Al ratios are interpreted to reflect changes in riverine input through the Magdalena River. The measured metal ratios show a strong 100-kyr cyclicity, which could reflect changes in sedimentation related to sea level fluctuations or to climate. Although the variability in Fe/ Ti and Fe/Al ratios points to rainfall-induced changes in the mineralogy of the terrigenous fraction, shelf erosion induced by sea level fluctuations cannot completely be ruled out. If climate accounted for changes in the nature of the terrigenous components, then the strong 100-kyr fluctuations in the measured metal ratios would point to the influence of high-latitude climate on the local hydrological balance of northern South America with ice volume growth forcing a southward displacement of the ITCZ. Copyright 2005 by the American Geophysical Union.
Tectonic and climate driven fluctuations in the stratigraphic base level of a Cenozoic continental coal basin, northwestern Andes
(PERGAMON-ELSEVIER SCIENCE LTD, 2008-12-01) Tamayo, J. C. Silva; Sierra, G. M.; Correa, L. G.; Tamayo, J. C. Silva; Sierra, G. M.; Correa, L. G.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y Tectónica
Changes in the sedimentologic and stratigraphic characteristics of the coal-bearing middle Oligocene-late Miocene siliciclastic Amagá Formation, northwestern Colombia, reflect major fluctuations in the stratigraphic base level within the Amagá Basin, which paralleled three major stages of evolution of the middle Cenozoic Andean Orogeny. These stages, which are also traceable by the changes in the compositional modes of sandstones, controlled the occurrence of important coal deposits. The initial stage of evolution of the Amagá Basin was related to the initial uplift of the Central Cordillera of Colombia around 25 Ma, which promoted moderate subsidence rates and high rates of sediment supply into the basin. This allowed the development of aggradational braided rivers and widespread channel amalgamation resulting in poor preservation of both, low energy facies and geomorphic elements. The presence of poorly preserved Alfisols within the scarce flood plains and the absence of swamp deposits suggest arid climate during this stage. The compositional modes of sandstones suggest sediment supply from uplifted basement-cored blocks. The second stage of evolution was related to the late Oligocene eastward migration of the Pre-Andean tholeitic magmatic arc from the Western Cordillera towards the Cauca depression. This generated extensional movements along the Amagá Basin, enhancing the subsidence and increasing the accommodation space along the basin. As a result of the enhanced subsidence rates, meandering rivers developed, allowing the formation of extensive swamps deposits (currently coal beds). The excellent preservation of Entisols and Alfisols within the flood plain deposits suggests rapid channels migration and a humid climate during deposition. Moderate to highly mature channel sandstones support this contention, and point out the Central Cordillera of Colombia as the main source of sediment. Enhanced subsidence during this stage also prevented channels amalgamation and promoted both, high preservation of geomorphic elements and high diversity of sedimentary facies. This resulted in the most symmetric stratigraphic cycles of the entire Amagá Formation. The final stage of evolution of the Amagá Basin was related to the early stage of development of the late Miocene northwestern Andes tholeitic volcanism (from ~10 to ~8 Ma). The extensive thrusting and folding associated to this volcanism reduced the subsidence rates along the basin and thus the accommodation space. This permitted the development of highly aggradational braided rivers and promoted channels amalgamation. Little preservation of low energy facies, poor preservation of the geomorphic elements and a complete obliteration of important swamp deposits (coal beds) within the basin are reflected by the most asymmetric stratigraphic cycles of the whole formation. The presence of greenish/reddish flood plain deposits and Alfisols suggests a dry climate during this depositional stage. The presence of channel sandstones with high contents of volcanic rock fragments supports a dry climate, and suggests an incipient phase of the Combia tholeiitic magmatism present during deposition of the Amagá Formation. The subsequent eastward migration of the NW Andes magmatic arc (after ~8 Ma) may have produced basin inversion and suppressed deposition along the Amagá Basin. © 2008 Elsevier Ltd. All rights reserved.

Examinando por Materia "South America"

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