Cenozoic studies in northernmost Chile     

Dr. Cedric Mortimer Santiago  Nicolás Sarič Rendic 《International Journal of Earth Sciences》1975,64(1):395-420

The Cordillera de la Costa is constructed from a block-faulted Paleogene landscape. The range is cut by canyons and bordered by a high cliff and a zone of marine terraces. To the east the longitudinal depression is infilled by Neogene deposits which were laid-down over the Paleogene surface and have since been locally structurally disturbed. In the Andes stratovolcanoes rise above the Andean plateau and are surrounded by internal drainage basins.In northernmost Chile subsidence of the submarine continental margin has been complemented by uplift of the Andes. Ingestion of sial and sima in the trench area seems to have led to magma production, and there has been an eastward movement in both igneous and structural events. The present plate motions have produced a compressive tectonism, but local distension has occurred at the edge of the continental plate. The longitudinal depression is believed to be a tectonically neutral zone west of the eastward-dipping reverse faulting of the Andean region. Wave-action on a subsiding coast is considered responsible for carving the high cliff, whereas littoral terraces reflect a recent zonally-atypical uplift phase.N-S strike-slip faulting is attributed to ancient plate-closure patterns. Problematic approximately E-W faults could reflect the adjustment of the continental margin to the stresses generated during recent relative plate motions.Early Tertiary erosion produced a Paleogene pediplain. The resulting large quantities of Paleogene sediment are considered to have been subducted during plate convergence. Tectonic movements formed the longitudinal depression and other smaller basins in the late Oligocene. Towards the south, Neogene planation has eroded the Paleogene pediplain, although major pediplanation and aggradation had everywhere ceased by the Upper Miocene when canyon formation commenced. Ignimbritic eruption waned in the Upper Miocene, and gave way to andesitic stratovolcano production that modified the Altiplano internal drainage. Post-Miocene capture of some of this drainage has occurred by headward erosion along Andean flank channels. Canyons across the coastal mountains were established at about the same time, although some of the long channels in the south are of greater antiquity.

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Zusammenfassung Die Küstenkordillere Nordchiles stellt eine paleogene Landschaft mit Blockverwerfungen dar. Das Gebirge ist von Canyons zerlegt und im Westen von einem hohen Cliff und marinen Terrassen begrenzt. Ostwärts befindet sich der Längstalgraben, gefüllt mit neogenen Ablagerungen. Die neogenen Formationen sind lokal gestört. In den Hochanden haben sich Stratovulkane auf dem andinen Plateau gebildet.Im nördlichsten Chile ist das Abtauchen des submarinen Kontinentalrandes vom Aufstieg der Anden begleitet. Sial und Sima, die im Grabenbereich verschwanden, haben wahrscheinlich eine Magmaproduktion hervorgerufen. Die magmatischen und strukturellen Vorgänge bewegen sich dort ostwärts. Die Plattenbewegungen hatten eine kompressive Tektonik zur Folge, aber lokale Dehnung hat am Rande der kontinentalen Platte stattgefunden. Die Längstaldepression ist als eine tektonisch neutrale Zone westlich der ostwärts fallenden Aufschiebung der Anden zu betrachten. Die Küstenterrassen stellen eine rezente, für die Zone atypische Hebungsphase dar.Horizontale N-S-Verwerfungen sind alten Plattenverschiebungen zuzusprechen. Problematische, ungefähr E-W verlaufende Verwerfungen könnten die Einordnung der Kontinentalränder zu dem durch rezente relative Plattenbewegungen hervorgerufenen Stre\ darstellen.Frühtertiäre Erosion hat eine paleogene Landschaft geformt. Die dadurch verursachten gro\en Mengen paleogener Sedimente sind wohl während der Plattenkonvergenz verschluckt worden. Tektonische Bewegungen im späten Pliozän haben die Längstal- und andere kleinere Depressionen gebildet. Im Süden hat die neogene Erosion die paleogene Landschaft geformt, aber zur Zeit des oberen Miozäns hat jede wichtigere Pediplanation und Aggradierung aufgehört und die Bildung der Canyons eingesetzt. Im oberen Miozän haben die Ignimbritergüsse aufgehört, während die Produktion der andesitischen Stratovulkane einsetzte, die das interne Abflu\system des Altiplano modifizierte. Die rückwirkende Erosion in den Kanälen längs der Anden hat einige dieser Flu\systeme nach dem Miozän eingefangen. Die Canyons durch das Küstengebirge waren auch zu ungefähr dieser Zeit etabliert, aber einige der längeren Kanäle im Süden sind älter.

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Résumé La Cordillère cotière du Nord du Chili apparaÎt comme un horst découpant une surface morphologique paleogène. La chaÎne est entaillée par des canyons et domine en falaise une étroite bande de terrasses marines. La dépression longitudinale qui la limite à l'Est est remplie de dépÔts néogènes qui ensevelissent la surface paléogène faiblement deformée.Dans les Andes, des stratovolcans parsèment le plateau andin.Dans l'extrÊme Nord du Chili, la subsidence de la marge continentale sous-marine a été accompagnée par le soulèvement des Andes. L'ingestion de sial au niveau de la fosse semble responsable de la gènèse des magmas et de la migration vers l'Est des manifestations ignées et structurales.L'actuel mouvement de plaques a produit une tectonique en compression avec des distensions locales sur la marge de la plaque continentale. La dépression longitudinale est interpretée comme une zone tectonique neutre à l'Ouest de la faille à plongement Est remontant la zone andine.L'abrasion marine sur la cÔte en voie de subsidence est rendue responsable de la mégafalaise cotière bien que les terrasses littorales témoignent d'une phase de soulèvement local.Les décrochements Nord-Sud représenteraient des mouvements différentiels au sein de la plaque. Le système de failles E-W répondrait au réajustement de la marge continentale. La pédiplaine paléogène résulterait de la phase d'érosion du début du tertiaire. Les produits d'érosion auraient été entraÎnés dans la subduction durant la convergence des plaques. Les mouvements tectoniques de la fin de l'oligocène for mèrent la dépression longitudinale et d'autres petits bassins. Vers le Sud la pénéplanation néogène a érodé les restes de la pédiplaine paléogène; enfin toute érosion planaire a cessé à la fin du Miocène avec la formation des canyons. Le volcanisme ignimbritique s'est achevé à la fin du Miocène supérieur et a été relayé par le volcanisme central andésitique qui modifia le drainage de l'Altiplano. La capture post-miocène par érosion regressive de quelques-uns de ces réseaux a été effectuée par les cours d'eau du flanc occidental de la Cordillère. Les canyons qui entraillent la Cordillère cotière furent creusés à la mÊme époque, bien que certains au Sud semblent plus anciens.

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Environmental assessment of a large industrial marine complex based on a community of benthic filter-feeders     

Carballo JL  Naranjo S 《Marine pollution bulletin》2002,44(7):605-610

Biological quality in a bay affected by man's activities was evaluated by means of the composition of assemblages of sponges and ascidians. Our results showed that the structure of these two groups of filter-feeders aided in discriminating between undisturbed and disturbed areas, establishing different "environmental health categories" from moderately to strongly disturbed areas, and in ascertaining the extension of the area of each "health category". We were able to divide the bay into four zones based on type of disturbance or anthropogenic source: (1) stations free of any source of disturbance, (2) stations under moderate disturbance, located close to industrial ports, millworks, etc., (3) stations that are under the direct influence of industrial wastes such as a power station and oil refinery, and (4) stations near strongly disturbed areas, influenced directly by harmful steelworks activities. We differentiated clearly between four large species assemblages, and related the composition of these assemblages to different kinds of disturbances. Thus, these species could be used to manage the marine environment in this bay by comparing the observed fauna, with expected fauna in an unstressed site. Moreover, the joint presence of the sponge Cliona vastifica and tunicate Policitor adriaticum seems always to indicate a more or less pristine environmental situation, functioning as bioindicators of normal conditions. We think that the use of specific bioindicators for monitoring disturbance is a valid tool to establish baselines to predict impacts associated with industrial development in many marine ecosystems. The advantages to monitoring communities on hard rocks versus sandy or muddy bottoms are also commented upon.  相似文献   

Deforestation of water‐repellent soils in Galicia (NW Spain): effects on surface runoff and erosion under simulated rainfall     

E. Benito  J.L. Santiago  E. de Blas  M.E. Varela 《地球表面变化过程与地形》2003,28(2):145-155

At three adjacent sites in steeply sloping woodland in Galicia (NW Spain), surface runoff and associated erosion under simulated rainfall (64 mm h^?1) were measured on five occasions between June 1998 and July 1999. Two of the three sites had recently been deforested and topsoil added, and one of these two had been sown with grass, which was germinating at the onset of the study. Deforestation greatly increased runoff and erosion rates, and the recovery of plant cover reduced erosion. All three soils were very hydrophobic due to high levels of poorly humified organic matter, which led to higher runoff rates than expected, especially during dry periods. However, great structural stability prevented there being a significant correlation between runoff rate and soil erosion. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Geomorphology and geochronology of sackung features (uphill-facing scarps) in the Central Spanish Pyrenees   总被引：4，自引：1，他引：4  

F. Gutirrez-Santolalla  Enrique Acosta  Santiago Ríos  Jesús Guerrero  Pedro Lucha 《Geomorphology》2005,69(1-4):298-314

The paper analyses uphill-facing scarps and associated troughs developed in the oversteepened slopes of two neighbouring glacial valleys in the central Spanish Pyrenees. Previous studies of sackung landforms in the Pyrenees have argued for deglacial unloading as the genetic mechanism, but this causal and temporal relationship has not been proved due to the lack of chronological data. The antislope scarps in the two studied locations, Vallibierna and Estós, are developed in Palaeozoic metasedimentary rocks (parallel to the contour lines and the structural grain), occur in the intermediate sector of the hillslope, and are up to 0.5 km long and several meters high. A trench was excavated in a sackung trough fill in each of the valleys in order to gain information about their chronology and genesis. Charcoal from the lowermost unit in Vallibierna provided an age of 5.9 cal. ka for the sackung and extrapolation of the three dates obtained in Estós indicates that the trough formed ca. 7.6–7.8 cal. ka. Deglaciation of the studied sectors of the valleys occurred between 16 and 13 ka. The time lag of >5 ka suggests that glacial erosion and the subsequent debutressing of the oversteepened valley walls created slopes predisposed to sackung development, but did not initiate the movement. Seismic shaking is proposed as a probable triggering factor. This hypothesis, although supported by the sudden deformation event recorded by a failure plane exposed in Vallibierna trench, and by the seismic and neotectonic activity of the area, cannot be proved due to the lack of chronological information about paleoearthquakes.  相似文献   

Damage analysis of simulated I-880 structures under the Loma Prieta Earthquake   总被引：1，自引：0，他引：1  

Santiago Rodríguez-GmezAhmet . akmak  Masanobu Shinozuka 《Soil Dynamics and Earthquake Engineering》1995,14(4)

This paper analyzes the collapse of the Cypress portion of the Nimitz freeway in Oakland, California, during the Loma Prieta Earthquake of 17 October 1989. The most important bent configuration is chosen to carry out a nonlinear dynamic analysis and damage evaluation using the program SARCF-III. The acceleration history recorded at a nearby location with similar soil properties is used as the input ground motion. In order to cover the uncertainty about the structural properties and reinforcing details six different structures models are utilized. The maximum dynamic internal forces are compared to the structural capacity. It is investigated whether the collapse can be explained using a simplified structural model and one of the available computer codes.  相似文献   

Nutrient,heavy metal and organic pollutant composition of suspended and bed sediments in the Rhone River     

S. Santiago  R. L. Thomas  G. Larbaigt  C. Corvi  D. Rossel  J. Tarradellas  D. J. Gregor  L. McCarthy  J. P. Vernet 《Aquatic Sciences - Research Across Boundaries》1994,56(3):220-242

The environmental quality of the Rhone River (Switzerland-France) has been assessed with a geochemical survey of the pollutants bound to suspended sediments. Ten samples were collected between Lake Geneva and the Mediterranean Sea in Nobember 1989 by continuous flow centrifugation and analysed for grain size distribution, carbonate, organic C, N, forms of particulate P, trace metals, and organic compounds (chlorobenzenes, organochlorine pesticides, PCBs, and PAHs). Four bed sediment samples were also studied for comparative purposes. The suspended solids provide lower variance by parameter than the bed sediments and are clearly most suitable for synoptic monitoring.The Upper Rhone River carries a glacial derived sediment with a low nutrient content, the stretch from Geneva to Lyon provides a sediment dominated by carbonate, and in the Lower Rhone the organic matter and phosphorus are relatively increased, mainly due to wastewater effluents and to an industrial P source. High concentrations of metals and organic micropollutants downstream of Lyon indicate a multiple contamination in the Lower Rhone, whereas more specific inputs are located downstream of Geneva and Arles.The comparison with data from other polluted major systems, the Rhine, the Niagara and the Detroit rivers, shows on overall similarity confirming that the Rhone quality is degraded downstream of Lyon. The levels of particular concern are for Hg, DDT metabolites which reveal a recent release in the basin, PCBs with a likely high chlorine content, and PAHs.The statistical evaluation of the compositional variables indicates a limited number of well defined associations, suggesting that the contamination of the suspended sediments results from the combination of numerous and intermittent point and diffuse sources in the Rhone River basin.  相似文献   

CFD simulation of airflow over a regular array of cubes. Part I: Three-dimensional simulation of the flow and validation with wind-tunnel measurements     

Jose Luis Santiago  Alberto Martilli  Fernando Martín 《Boundary-Layer Meteorology》2007,122(3):609-634

Air flow inside an array of cubes is simulated. Cubes (edge length 0.15 m) are arranged in a regular array, separated by 0.15 m in the streamwise and spanwise directions. Numerical simulations are performed based on Reynolds-averaged Navier–Stokes equations (RANS), solved in a computational fluid dynamics model (CFD), with standard k–ε turbulent closure (two prognostic equations are solved for the turbulent kinetic energy k and its dissipation ε, respectively). Simulations are validated against wind-tunnel data using a technique based on hit-rate calculations, and calculated statistical parameters. The results show that the horizontal velocity is very well modelled, and despite some discrepancies, the model that fulfils the hit-rate test criteria gives useful results that are used to investigate three-dimensional (3-D) flow structures. The 3-D analysis of the flow shows interesting patterns: the centre of the canyon vortex is at 3/4 of the canyon height, and stronger downward than upward motions are present within the canyon. Such behaviour is explained by the presence of a compensation flow through the side of the canyon, which enters the canyon from the upper part and exits from the lower part. This complex 3-D structure affects the tracer dispersion, and is responsible for pollutant transport and diffusion.  相似文献   

Trace metal concentrations in the aquatic environment of Albay Gulf in the Philippines after a reported mine tailings spill     

Santiago EC  Africa CR 《Marine pollution bulletin》2008,56(9):1657-1663

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Paleomagnetic and gravimetrical reconnaissance of Cretaceous volcanic rocks from the Western Colombian Andes: paleogeographic connections with the Caribbean Plate     

Santiago Hincapié-Gómez  Agustín Cardona  Giovanny Jiménez  Gaspar Monsalve  León Ramírez-Hoyos  Germán Bayona 《Studia Geophysica et Geodaetica》2018,62(3):485-511

The reconstruction of the tectonic evolution of the oceanic crust, including the recognition of ancient oceanic plumes and the differentiation between multiple and single oceanic arcs, relies on the paleogeographic analysis of accreted oceanic fragments found in orogenic belts. Here we present paleomagnetic and gravity data from Cretaceous oceanic basaltic and gabbroic rocks, the continental metamorphic basement, and their associated cover from northwestern Colombia. Based on regional scale tectonic reconstructions and geochemical constraints, such rocks have been interpreted as remnants of an oceanic large igneous province formed in southern latitudes, which was accreted to the sialic continental margin during the Late Cretaceous. Gravity analyses suggest the existence of a coherent high density segment separated by major suture zones from a lower density material related to the continental crust and/or thick sedimentary sequences trapped during collision. A characteristic paleomagnetic direction in Early and Late Cretaceous oceanic volcano-plutonic rocks, revealing a southeastern declination (D) and a negative inclination (I), may be interpreted in two different ways: (1a primary magnetization (tilt-corrected direction D = 130.3°, I = -23.3°, k = 23.4, α₉₅ = 26.4°), suggesting clockwise rotation around 130°, and magnetization acquired in southern latitudes (range of 4°S to 21°S); or (2) a remagnetization event during a reverse interval of the Earth’s magnetic field in the Cenozoic (in situ direction D = 128.7°, I = -6.2°, k = 23.1, α₉₅ = 26.1°), suggesting a counter-clockwise rotation around 50°. The first scenario seems more plausible, as it is consistent with previous paleomagnetic studies at other localities; it is compatible with a southern paleogeography for this block, and when integrated with other regional geological and paleomagnetic studies, supports a southern Pacific origin of a major oceanic block, formed as a part of a broader Cretaceous plateau that may have extended south or southwest of Galapagos. After its initial accretion, this block was subsequently fragmented due to the oblique SW-NE approach to the continental margin during the Late Cretaceous.  相似文献   

A multi-wavelength study of the 2009 impact on Jupiter: Comparison of high resolution images from Gemini,Keck and HST     

Imke de Pater  Leigh N. Fletcher  Santiago Pérez-Hoyos  Heidi B. Hammel  Glenn S. Orton  Michael H. Wong  Statia Luszcz-Cook  Agustin Sánchez-Lavega  Mark Boslough 《Icarus》2010,210(2):722-741

Within several days of A. Wesley’s announcement that Jupiter was hit by an object on UT 19 July 2009, we observed the impact site with (1) the Hubble Space Telescope (HST) at UV through visible (225–924 nm) wavelengths, (2) the 10-m W.M. Keck II telescope in the near-infrared (1–5 μm), and (3) the 8-m Gemini-North telescope in the mid-infrared (7.7–18 μm). All observations reported here were obtained between 22 and 25 July 2009. Observations at visible and near-infrared wavelengths show that large (～0.75-μm radius) dark (imaginary index of refraction m_i ～ 0.01–0.1) particulates were deposited at atmospheric pressures between 10 and 200–300 mbar; analysis of HST-UV data reveals that in addition smaller-sized (～0.1 μm radius) material must have been deposited at the highest altitudes (～10 mbar). Differences in morphology between the UV and visible/near-IR images suggest three-dimensional variations in particle size and density across the impact site, which probably were induced during the explosion and associated events. At mid-infrared wavelengths the brightness temperature increased due to both an enhancement in the stratospheric NH₃ gas abundance and the physical temperature of the atmosphere. This high brightness temperature coincides with the center part of the impact site as seen with HST. This observation, combined with (published) numerical simulations of the Shoemaker-Levy 9 impacts on Jupiter and the Tunguska airburst on Earth, suggests that the downward jet from the terminal explosion probably penetrated down to the ～700-mbar level.  相似文献