Sedimentología de los yesos del sector central de la Depresión del Duero

En el sector central de la Depresión del Duero afloran sedimentosneógenos, terrígenos, carbonatados y yesíferos. En los depósitos yesiferos se han diferenciado facies de yeso primario, secundario y retrabajado que junto a las facies carbonatadas se ordenan en secuencias y megasecuencias positivas y negativas. Las megasecuencias se interpretan como retracciones o expansiones del sistema lacustre. Se relacionan las secuencias con los modelos paleogeográficos establecidos y se analizan los factores que controlaron la evolución de los depósitos yesíferos en el tiempo

Análisis sedimentológico de los conglomerados de Tariego (Unidad 4, Neógeno de la depresión del Duero)

Los conglomerados de Tariego registran varios mecanismos de depósito de gravas en canales fluviales. A partir de estudios muy detallados de la geometría y relaciones laterales de facies y estructuras sedimentarias primarias, se pueden diferenciar tres tramos. El inferior con facies Gt representa el relleno de un canal por megaripple. En el intermedio, estudiado con detalle en este trabajo, se reconoce un episodio inferior con Gp/Sp debido a la migración de barras en un canal muy poco sinuoso ("recto") y otro superior, con superficies de acreción lateral y rellenos de Gp y Sp, interpretado como depósitos de barras de meandro (point bar) en un sistema meandriforme de baja sinuosidad. El tercer tramo (superior) corresponde a un episodio simple de acreción lateral de una barra de meandro

El paleógeno del sector suroccidental de la Cuenca del Duero: nueva división estratigráfica y controles sobre su sedimentación

A Paleogene four-fold stratigraphical division is proposed here as result from the detailed studies carried out during the elaboration of 22 sheets of the Geological Map of Spain (E. 1:50.000). This units (T.S.U.) are limited by regional discordances and they have a Upper Cretaceous to Oligocene ages. The previous stratigraphical schemes are rearranged due to the different stratigraphicalrelations observed between the lithostratigraphical units proPosed by other workers (Jiménez, 1970; Corrochano, 1977; Alonso, 1981 ...). An Upper Cretaceous-Paleocene age is assumed to T.S.U. MC which is mainly composed by siliciclastic sediments strongly silicified forming a FU megasequence. It is interpretated as braided streams that flowed downslope filling paleovalleys eroded onto Paleozoic materials. Mineralogical features point to a tropical climate. Lower Eocene (T.S.U. P1) is identified in the Salamanca area, where it was considered as lacking. It is composed by arkosic sediments forming a CU megasequence. Fossil faunas of this T.S.U. record a subtropical climate. It is observed a transition from high sinuosity streams to braided ones. T.S.U. P2 (Middle Eocene-Lower Oligocene) is composed of two lithostratigraphical units previously considered as bounded by a discordance (Alonso, 198 1). It has a subarkosic to lithic nature and forms a CU megasequence. This unit records a subtropical climate with short arid periods and is interpretated as braided streams showing an increasing stability and enviromental energy to the top. T.S.U. P3 (Upper Oligocene) is composed by arkosic sediments previously considered of Vallesian (Middle to Upper Miocene) age. They form a CU megasequence that records braided streams prograding basin ward from higher areas. Palinological associations and pedological features indicate an arid mediterranean climate with long arid periods and a short rainy season with strong floods. We consider that most of Lower Miocene sediments are of Paleogene age. They are afected by a widespread alteration profile developed along Lower Miocene that masked its more significative features. Sedimentological analysis of T.S.U. shows that its megasequentiality is related to the rates of tectonical uplift of source areas whereas a distensive regime developed in the sedimentation basin

North-western Cainozoic record: present knowledge and the correlation problem

Tertiary deposits of the north-western Iberian Peninsula are heterogeneous because they occur in several morpho-structural positions as isolated and dispersed basins and outerops. The quality of the palaeontological record is usually very poor and there are scarce data. Correlation depends on a wide range of criteria which arc not always equivalent: palaeontology, mineralogy and petrology, geomorphology, tectonics and comparison with better-known and better-dated facies in regions nearby. The results lack homogeneity and there arc notable discrepancie

Alpine tectonic framework of south-western Duero basin

The tectonic activity in the south-western area of the Spanish Northern Meseta (Ciudad Rodrigo and Duero basins) during most of the Tertiary was determined by u transpressive regime that reactivated Hercynian to Late-Hercynian faults. The record of the Alpine Orogeny is complex because the sedimentary record indicates a compresive regime in the sour e areas coeval with the extensionall to transpresive regime indicated by normal or strike-slip faults. This duality is due 10 the geotectonics position of this area between two compressive areas, the Cantabrian Range and the Central System, and the extensional Atlantic margin

Introducción a la estratigrafía del Terciario del SO de la Cuenca del Duero

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Reconstruction of drought episodes for central Spain from rogation ceremonies recorded at the Toledo Cathedral from 1506 to 1900: A methodological approach

Rogation (ceremonies to ask God for rain: pro-pluvia, or to stop raining: pro-serenitate) analysis is an effective method to derive information about climate extremes from documentary data. Weighted annual sum by levels has been a widespread technique to analyze such data but this analysis is liable to be biased to spring values as these ceremonies are strongly related to farming activities. The analysis of the length of propluvia periods (the time span during which rogations are carried out in relation to a drought event) and the combination of annual and seasonal information offers a more objective criterion for the analysis of the drought periods and an increase in the resolution of the study. Analysis by the pro-pluvia periods method of the rogation series from the Toledo (central Spain) Cathedral Chapter allows a good characterization of the droughts during the 1506–1900 period. Two drought maxima appear during the 1600–1675 and 1711–1775 periods, characterized by rogations during almost all the year, with a middle stage (1676–1710) when droughts were less frequent and their length shortened. Sea level pressure patterns for the instrumental and documentary periods show that droughts were mostly related to a north-eastern position of the Azores High that displaced the Atlantic lowpressure systems towards a northern position. There is a weak relation with the North Atlantic Oscillation but this fact is related to the local character of the series that increases the weight of the local factors. Comparison of rainfall/drought records around Spain and theWestern Mediterranean reveals the heterogeneity of their distribution in time and space as well as stresses the need of more and longer reconstructions. Better knowledge of drought variability would help to improve regional models of climate extremes and the understanding of the atmospheric patterns related to their development

Evolución de eventos climáticos extremos (inundaciones y sequías) para la zona central de la Península Ibérica desde el siglo XVI a partir del registro de rogativas e inundaciones históricas.

En este trabajo se presenta la evolución desde 1500 a 1900 de dos tipos de eventos climáticos extremos característicos de la Península Ibérica, las inundaciones y las sequías. Este estudio se ha llevado a cabo en la meseta sur de la Península. Aprovechando la continuidad del registro documental desde el s. XVI hasta nuestros días para la zona de estudio, hemos utilizado registros de rogativas e inundaciones históricas del rio Tajo, acaecidas en Aranjuez, Toledo y Talavera. En los cuatro siglos estudiados, parece que los periodos en los que hay una alta frecuencia de sequías también existe una alta frecuencia de inundaciones, aunque estos eventos raramente coinciden en un mismo año. En función de la frecuencia y la intensidad de los eventos, se han distinguido seis periods, dos con una alta frecuencia de eventos (1557-1623), (1717-1798), uno con frencuencia media (1624-1716), dos con frecuencias bajas (1500-1556) y (1798-1850), debido probablemente a un aumento de la presión antrópica sobre los cauces y una disminución en la frecuencia de rogativas por motivos sociopolíticos

Cenozoic lacustrine deposits in the Duero Basin (Spain)

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

South-western Duero and Ciudad Rodrigo basins: infill and dissection of a Tertiary basin

In the soult western sector of the intracontinetal Duero basin, the post-Hercynian sedimentary record consist of Upper Cretaceous to Quaternary terrestrial sediments. Climates shifted from tropical, with poorly defined seansos (end of Cretaceous), to Mediterranean (Neogene). Tertiary deposits are divided into three tectonographic completes. The Late Cretaceous-Paleocene, related to the end of the Mesozoic cycle, is caractericed by a well developed weathering profile that eroded later. The Eocene Oligocene, formed during the morpho-structural definition of the actual basin boundaries, consists of three unconformity-bounded units related to successive tectonic events of the Alpine Orogeny by the cnd of this cycle, progressive incision of the Atlantic nuvial network led to capture of the fluvial systems of the southern Duero basin and degradation (emptying) began. The Miocene-Phocene, related to and extensional tectonic regime represents the spreading of exorheik conditions to the whole basin that marked a complete hydrugraphic reorganisation. Deposition and aggradation continued in more central areas of the basin until the end of the Neogene, coeval with degradation of the south-western corner of the Duero Basin. The coexistence resulted from differential subsidence, hinge lines (uplift zones) separated sub-basins, and the dynamics of capture processes