La Formación Areniscas de Ciudad Rodrigo: Ejemplo de sedimentación controlada por paleorrelieves (Eoceno, fosa de Ciudad Rodrigo)

[ES] Se define formalmente como Formación Areniscas de Ciudad Rodrigo a la Unidad litoestratigráfica comprendida entre los relieves paleozoicos de las Sierras de Torralba, Camaces, Peronilla y Carazo y los bordes del sureste de la Fosa de Ciudad Rodrigo. Esta Formación es el resultado del desmantelamiento de áreas madres metamórficas y granitoides ubicadas al NO, O y SE. La disposición convergente de las paleocorrientes y la existencia de paleorrelieves al NE, señalan la configuración paleogeográfica de una cuenca endorreica. Esta cuenca fue rellenándose por los sedimentos arrastrados por sistemas de abanicos aluviales. La ordenación actual de los depósitos, hace suponer que el desarrollo del sistema sedimentario estuvo controlado por paleorrelieves que cerraban al borde NE de la cuenca durante el Eoceno.[EN] In the southeastern Ciudad Rodrigo there is a conspicuous sandstone unit that has been usually refered to as «Serie» de Ciudad Rodrigo. The purpose of this paper is to define this Lithostratigraphic Unit: Ciudad Rodrigo Sanstone Formation. This Unit consist of clastic sediments derived from the weathered metamorphic and plutonic rocks placed in NW, SW and S of the basin. Paleocurrent measurement reveal a convergent pattern which coupled with the existent paleo reliefs towards the NE, suggest and endorheic basin that was progresively filled up by alluvials fans sediments. From the analysis of the present day distribution of deposits it is proposed that the development of alluvials fans was controlled by the paleo-reliefs that closed the Noreastern edge of the basin during Eocene times

Introduction to the analysis of flood hazards on the margins of estuarine areas: The case of the towns adjacent to the Ría de Huelva (SW Spain)

Floods are natural events that occur in depressed areas. These phenomena can be related with extreme river discharges in fluvial valleys or with wave surges in coastal areas. In estuarine areas, both causes can coincide during stormy periods. The Ría de Huelva is the common estuary of Tinto and Odiel rivers, which are extremely irregular because of their pluvial character. The slatey-quartzitic character of the drainage area induces an immediate response of the fluvial flow to the rains. This estuary is submitted to a mesotidal regime, with a mean tidal range of 2.0 metres, but with extreme equinox high waters that can reach 1.7 metres over the mean tide level (74 cm. over the mean high waters). Meteorologic surges caused by low pressures and winds blowing from the south to the coast can increment the water level near to 1 m. over the tidal level. Strong rains and meteorologic surges occur at same time during Atlantic storms. When these storm coincide with equinox high tides the towns located at the margins of the estuary are normally floode

Karstic processes in the calcarenite formation of Niebla (Huelva, SW Spain)

4 páginas, 2 figuras, 1 fotografía, 10 referencias.-- 21ª Sesión Científica, Huelva, 1996.The development of a covered karst in the Miocene calcarenite formation in the N area of Niebla (Huelva) has been studied. The cover consists of sediments of Quaternary terraces of the River tinto (T9, T8, T7 and T6), and to a lesser degree, fragments of Mio-Pliocene clays ("blue marls"). Solution if the calcarenite has originated vertical pipes of varying size evolving in the top to form funnerl-shaped channels of preferential solution.Peer reviewe

Estructuras post-sedimentarias en el margen noroccidental de la cuenca del Guadalquivir (Niebla, Candón, Valverde del Camino), SO de España

Description of deformational structures in tertiary sediments, which have been interprerted as a result of a fluids migration process, along with the presence of preferential structural directions of fracture planes developed in the substratum. This fracture net could have been recently reactivated, so leading to the development of the described structures

Shoreline changes and recenf erosion-sedimentation rates on the south Iberían Atlantic coast (SW Spain)

3 páginas,2 figuras, 6 referencias.-- 21ª Sesión Científica, Huelva, 1996.[EN]: Following the maximum Flandrian Transgression (6,900 yr. B.P.), the original coastline, with wide promontories and estuaries, underwent considerable straightening out. This was due mainly to the intense littoral dynamics, causing retreat of the capes and progradation in the inlets. Measurement of recent rates of coastal advance-retreat have been possible thanks to the number of XVIth-XVIIth century watchtowers situated on the shoreline, and to geomorphological mapping and radiometric dating of the littoral sedimentary formations (Doñana). An area of maximum retreat has been identified (at the Asperillo tower) averaging around 1.2 m/yr in the last 240 years, and an area of maximum progradation (Doñana), averaging up to 2-4 m/yr for the last 1,800 years and 1.05 m/year in the last 200 years. The natural evolution of this coastal stretch shows a tendency for the erosive-sedimentary poínt of inflexion to move eastwards, as shown by the different erosive and sedimentar y landforms of the area.[ES]: A partir del inicio de la transgresión Flandriense hasta la actualidad, en todo el ámbito del Golfo de Cádiz, ha tenido lugar una importante e intensa retrogradación costera en los salientes continentales así como una fuerte progradación en los entrantes. Los estudios morfosedimentarios más recientes, realizados en las costas españolas, demuestran que un porcentaje significativo de estas tasas de erosión-depósito litorales están controladas, a largo plazo, por el factor tectónico y, a corto plazo, por la dinámica marina (Zazo et al., 1990). Siendo especialmente, en los últimos siglos, la actividad antrópica un factor esencial.Este trabajo ha sido subvencionado por el proyecto de la DGICYT PB94-1090-C03-01 y por el II Plan Propio de Investigación de la Universidad de Huelva. Es una contribución al proyecto 367 del IGCP.Peer reviewe

Evolucion de la costa atlántica onubense (so España) desde el máximo flandriense a la actualidad

The maximum Holocene Transgression, dated as around 6,900 years BP, gave rise initially, in this area of the Iberian south Atlantic coast, to an irregular coastline with wide inlets (estuaries) and prominent continental capes. These estuarine areas would become the lower stretches of the main fluvial systems (Guadiana, Piedras, Tinto-Odiel and Guadalquivir). The relative stability of the sea level (which continues today) has aided the straightening out of the coastline, with retreat of the continental promontories and the formation of cliffs. Littoral accumulative landforms have developed in the estuarine areas, prograding in the direction of the prevailing drift current (eastwards). Since the Guadalquivir mouth shows the most extensive and best conserved sedimentary formations, we can establish there with the greatest chronological accuracy the different Holocene cycles of progradation and retrogradation, with geomorphological corroboration from the other estuaries. Thanks basically to geomorphological mapping, 14C dating, and archaeological evidences, a series of prograding phases can be established for this coastal area. The first of these must have taken place 6,900-4,500 years BP, although there are not yet reliable data. The second phase was between 4,200 and 2,600 years BP, the third between 2,300 and 1,100 years BP, and the fourth - and last - between 1,000 and the present. There were separations of successive erosional phases between 4,500-4,200 years BP, 2,600-2,300 years BP, and 1,100-1,000 years BP. A progradation rate of 2-4 m/yr for the last 1,800 years has been established for the littoral spit of Donan̄a. In the prograding phases, sea level was stable or decreased slightly, with domination of the fluvial medium and greater filling with sediments, so restricting estuarine geometry. During the retrograding phases, sea level increased slightly, implying marine domination in the estuary, and greater erosive activity on the cliffs.Peer Reviewe

Evolución holocena de las formaciones litorales de la costa de Huelva

7 páginas, 3 figuras, 25 referencias.-- IV Reunión del Cuaternario Ibérico.-- Asociación Española para el Estudio del Cuaternario (AEQUA, Huelva, 1997.La posición actual del nivel del mar en la costa suratlántica ibérica es el resultado de la transgresión holocena (Flandriense), que mantiene su estabilidad desde hace unos 6.000 años. En este tiempo, los procesos de regularización marina, cambios climáticos e intervención humana, han favorecido períodos alternos de progradación y erosión costera, que han modificado sensiblemente la configuración de la línea de costa. Los sedimentos resultantes de este trasiego energético se localizan rellenando los estuarios fluviales y tapizando la plataforma continental submarina. De las cuatro fases de progradación, definidas a nivel regional, sólo se tienen evidencias directas de las tres últimas. De la primera, comprendida entre el máximo flandriense y los 4.500 años B.P., tan solo existen evidencias indirectas; la segunda se sitúa entre 4.200-2.600 años B.P.; la tercera entre 2.350-800 años B.P.; y la cuarta entre 500 años B.P. y la actualidad. Sucesivas fases de no progradación y/o erosión se localizan entre ellas, entre 4.500-4.200 años B.P., 2.600-2.350 años B.P. y 800-500 años B.P. Las sucesivas fases de avance o retroceso costero se acompañan con migraciones de mantos eólicos hacia el interior del continente. Dos son las grandes secuencias de predominio de la morfogénesis eólica que pueden establecerse: una antigua, de edad Tardiglacial-Holoceno, y otra reciente, de carácter eminentemente histórico.Subvenciones recibidas por la DGICYT, mediante los proyectos PB91-0622-C03-01 y PB94-1090-C03-01, y el Plan Propio de la Universidad de Huelva. Este trabajo es una contribución al IGCP-367.Peer reviewe

Quaternary phases of chemical sedimentation in los Covachos cave (Almadén de la Plata, Seville)

The geological and geomorphological studies in Los Covachos cave reveal a wide collection of speleothems and a thick archaeological stratigraphies. Both isotopie dating of speleothems C^ThP^U) and charcoal layers C4C), in chemical and terrigenous sediments, show a Quaternary sequence of palaeoenvironmental evolution related with an alternating phases of biostatic and rhexistatic genesis. The first ones are partially situated in a warm and wet isotopie stages (7, 5, 3, and 1) and the others in a wider warm and dry stages (6, 4 and 2

Isotopie dating of continental carbonates in thè Upper Pleistocene of Chafarinas lslands (N Africa, Spain)

Las islas volcánicas de Chafarinas guardan un amplio registro sedimentario del Pleistoceno superior continental. El análisis radiomètrico de las muestras de calcretas y gasterópodos fósiles, presentes en la serie de la isla del Rey Francisco I, por medio de isótopos de Uranio y Carbono, nos ha servido para fechar este registro entre 100 y 20 ka BP.Chafarinas Islands are a volcanic outcrop in the North edge of Africa, with an Upper Miocene-Pliocene age. The present cliffed landform result of an intensive marine action that has eroded the previous volcanic relief. Quaternary deposits and calcrete formations cover the most part of the planated surface of the islands, mainly in Rey Francisco I isle. Here we studied a wide geological section with 18 m of detritic and calcrete layers. Isotopie dating (230Th/234U and 14C) of these continental deposits (calcretes and shells) and their geological interpretation show a palaeoclimatic fluctuations along the Late Quaternary (100-20 ky BP)