Caracterización y procedencia de las areniscas del Paleógeno del sector Norte de la cuenca del Tajo

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Petrographic characterization of coeval carbonate grains in recent fluvial sands (Serranía de Cuenca, Spain)

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Sedimentación lacustre (Carbonatado-salina) en las facies autuniense de la Cordillera Ibérica

The aim of this paper is the better understanding of the carbonate and evaporite sedimentation of the upper unit of the Autunian facies in the "Sierra de Aragoncillo". Also the diagenetic evolution of these sediments in their reactions with the interbedded ryolitic-dacitic tuffs and ashes, have reen studied. The petrographic features of these carbonates are indicative of an early process of dolomitization in a hypersaline environment. The source of magnesium could be the sorroun ding volcanic rocks close to the lacustrine basin. Other common diagenetic minerals are: Zeolites, K-feldspar, quartz and clay minerals. The authigenesis of these minerals are reported to be the result of the reaction of tuffaceous rocks with interstitial waters trapped during sedimentation in a saline-alkaline lake. Considering the above data, we can establish that the lacustrine sedimentation at the end ofthe Autunian took place in a closed basin with arid climate

Detrital modes in sedimenticlastic sands from low-order streams in the Iberian Range, Spain: the potential for sand generation by different sedimentary rocks

The composition of modern stream sands derived from sedimentary source rocks in the Iberian Range has been analyzed in order to evaluate the contributions of the different bedrock types (mainly sandstones, limestones and dolostones). Temperate to subhumid climate and short transport conditions promote a weathering-limited denudation regime. As expected, sand composition proved to be essentially quartzolithic, with variable amounts of penecontemporaneous carbonates. Sand compositional data were compared with the exposure areas of the different bedrocks in the drainage sub-basins considered for semi-quantitative assessment of the sand generation potential of each bedrock type. Siliciclastic formations (sandstones) appear to be by far the most significant sand producers, with Sand Generation Indices (SGIs) in the medium sand fraction ranging from 4 to 20; i.e., 4 to 20 times greater than the SGI of carbonate rocks. Composition and texture are the main factors controlling carbonate sand generation. Sparitic limestones yield higher SGIs (2.8 to 20) when source terrains are constituted exclusively by carbonate rocks. High sparite grain content in the sands is enhanced by supplies from additional sources, such as calcitized dolostones. Dolomicrite sources are strongly under-represented in the sands analyzed (very low SGI), whereas the proportion of micritic limestone grains tends to be an accurate reflection of that bedrock at the source. Even though the results presented here refer to the first stage of sand generation with negligible transport effects, we think they may be helpful in the analysis and reconstruction of source terrains in ancient sedimenticlastic deposit

Diagenetic paths in a low subsident Triassic Basin: NW zone of Iberian Range Spain.

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Evolution of sandstone composititon in a continental foreland basin. Loranca Basin, Spain.

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

La porosidad en las areniscas triásicas (Rama Aragonesa de la Cordillera Ibérica)

Se estudia la porosidad en las areniscas triásicas (facies Buntsandstein y Muschelkalk) de la Rama Aragonesa de la Cordillera Ibérica, partiendo del cálculo estimativo de la porosidad primaria del sedimento, para posteriormente analizar los distintos procesos diagenéticos que han intervenido en su destrucción (compactación mecánica, compactación química y cementación). La caracterización textural y genética de los poros en dichas areniscas pennite establecer la existencia de procesos generadores de porosidad secundaria (disolución y fractura). La disolución del feldespato potásico, cemento carbonático y de baritina se relaciona con flujos de aguas meteóricas ligadas a discordancias intramesozoicas, mientras que la porosidad de fractura se asocia a la estructuración terciaria de la Cordillera Ibérica. Por último, se concluye que la cantidad de porosidad secundaria en las areniscas estudiadas depende fundamentalmente de la composición original de los depósitos, así como de la geoquímica del ambiente de sedimentación que controla las primeras etapas diagenéticas (eo-diagénesis). Este hecho se traduce a lo largo de las series estudiadas en una variabilidad, tanto en la cantidad como en los tipos de porosidad. [ABSTRACT] Triassic sandstone's porosity (Buntsandstein and Muschelkalk facies) from the Aragonesa Branch of the Iberian Range are studied, firstIy at the sediment primary porosity calculation and secondly tbe porosity-reducing processes are analyzed. Processes creating secondary sandstone porosity can be established (dissolution and fracturing) by the textural and genetic caracterization of the sandstone's voids. The dissolution of potassium feldspar, carbonate cement and barite cement, is related with meteoric pore-water flow alloys to intramesozoic unconformities. Fracturing porosity is related to Iberian Range tertiary structuration. Finally, we conc1uded that the amount of the sandstone's secondary porosity depends mainly on the original composition of the sediments and also on the geochemical sedimentary environments that control the first diagenetic stages (eo-diagenesis). This faot manifests itself in tbe amount and types of variating porosities along the stratigraphic section

Source area versus detrital products: a geographical information system approach.

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Base litoestratigráfica de las facies Buntsandstein y Muschelkalk en la Rama Aragonesa de la Cordillera Ibérica (Zona norte)

En este trabajo se realiza una descripción de la litoestratigrafía de las facies Buntsandstein y Muschelkalk en la rama aragonesa de la Cordillera Ibérica, con el fin de cubrir un vacío bibliográfico de gran importancia en el contexto global del Trías de l a Cordillera Ibérica. Se han definido informalmente cuatro unidades litoestratigráficas correspondientes a las facies Buntsandstem y dos a las facies Muschelkalk. La presencia de dos litotipos triásicos (mediterráneo e ibérico) en la zona de estudio, permite analizar en detalle las relaciones litológicas entre ellos. Por último, se realiza un intento de correlación entre las unidades definidas informalmente en este trabajo con las definidas por Ramos (1979) en las proximidades de Molina de Aragón, con el fin de relacionar el Trías de las dos ramas de la Cordillera Ibérica. [ABSTRACT] In order to complete the information about the Triassic in the Iberian Range, a description of Buntsandstein and Muschelkalk facies lithostratigraphy of the aragonesa branch has been made. In tbis way we have inforrnaly defined six lithostratigraphic units. The presence of two Triassic lithotypes (Iberian Triassic and Mediterranean Triassic) in the study area aIlows us to analyse the lithologic relationships between both of thern. Finally. a first attempt of correlation be:tween the informal units mentioned above and the Ramos (1979) units of the Molina de Aragón area has been made. This correlation permits us to relate the Triassic of both branches in the Iberian Range

Características petrológicas de las areniscas del Carbonífero de facies Culm de la isla de Menorca.

Las facies Culm (Viseense Terminal o Namuriense Inferior) de la isla de Menorca son el resultado de la sedimentación. de más de 4.000 m. de potencia, de depósitos turbidíticos. Estos depósitos están formados por cuerpos canaliformes de areniscas de grano grueso y conglomerados de cantos de tamaño fino, e intercalados entre depósitos dominantemente lutíticos (thin beds turbidites), interpretados como producto del desbordamiento de los canales cuando eran activos. Los depósitos arenosos que rellenan los canales son grauvacas con una matriz de origen diagenético producto de la deformación y disgregación de fragmentos lábiles. No obstante, la composición original de dichos depósitos sería más litoarenítica (065 F10 F R2s1. Del análisis de los contenidos de los distintos componentes del esqueleto se deducen unas áreas fuentes fundamentalmente epicrustales (rocas metamórficas de bajo grado y sedimentarias), junto con un aporte de rocas ígneas granudas y volcánicas espilitizadas. Con respecto al volcanismo, se concluye que fue anterior a la sedimentación de las facies Culm. La constancia de la composición de las areniscas a lo largo de la serie estratigráfica, así como la gran madurez composicional y textural de las mismas, hace pensar en un retrabajamiento y homogeneización de los depósitos en etapas previas a su sedimentación, por lo que se infiere la existencia de una plataforma siliciclástica que nutrió a las facies Culm. [ABSTRACT] The Culm facies (youngest Visean or early Namurian) of the Island of Minorca is represented by more than 4.000 m. of turbidite deposits. They consist of microconglomeratic sandstones interbedded in thin-bedded turbidites interpreted to represent overbank deposits of active channels. The sandstones of the channels are greywackes with a diagenetic matrix produced by the deformation and desintegration of labile fragments. Therefore the original composition of these deposits has been more lithoarenitic (065 FlO RF2s]. Optical analysis of different framework components indicate esentially epicrustal source areas (low-grade metamorphic racks and sedimentary rocks) tagether with a contribution of granitic igneous and spilitized volcanic rocks. The volcanic activity was probably prior to the depositian af the Culm facies. A significant reworking and homogenizatian previaus depositian is deduced by the high monatony of sandstone campositian and maturity of these deposits. This may indicate the existen ce of a siliciclastic platform which acted as source area for the Culm facies