The Upper Oligocene of Montgat (Catalan Coastal Ranges, Spain): new age constraints to the western Mediterranean Basin opening

The Oligocene deposits of Montgat are integrated in a small outcrop made up of Cenozoic and Mesozoic rocks located in the Garraf-Montnegre horst, close to the major Barcelona fault. The Oligocene of Montgat consists of detrital sediments of continental origin mainly deposited in alluvial fan environments; these deposits are folded and affected by thrusts and strike-slip faults. They can be divided in two lithostratigraphic units separated by a minor southwest-directed thrust: (i) the Turó de Montgat Unit composed of litharenites and lithorudites with high contents of quartz, feldspar, plutonic and limestone rock fragments; and (ii) the Pla de la Concòrdia Unit composed of calcilitharenites and calcilithorudites with high contents of dolosparite and dolomicrite rock fragments. The petrological composition of both units indicates that sediments were derived from the erosion of Triassic (Buntsandstein, Muschelkalk and Keuper facies), Jurassic and Lower Cretaceous rocks (Barremian to Aptian in age). Stratigraphic and petrological data suggest that these units correspond to two coalescent alluvial fans with a source area located northwestwards in the adjoining Collserola and Montnegre inner areas. Micromammal fossils (Archaeomys sp.) found in a mudstone layer of the Pla de la Concòrdia Unit assign a Chattian age (Late Oligocene) to the studied materials. Thus, the Montgat deposits are the youngest dated deposits affected by the contractional deformation that led to the development of the Catalan Intraplate Chain. Taking into account that the oldest syn-rift deposits in the Catalan Coastal Ranges are Aquitanian in age, this allows to precise that the change from a compressive to an extensional regime in this area took place during latest Oligocene-earliest Aquitanian times. This age indicates that the onset of crustal extension related to the opening of the western Mediterranean Basin started in southern France during latest Eocene-early Oligocene and propagated southwestward, affecting the Catalan Coastal Ranges and the northeastern part of the Valencia trough during the latest Chattian-earliest Aquitanian times.

SIMSAFADIM-CLASTIC: A new approach to mathematical 3D forward simulation modelling for terrigenous and carbonate marine sedimentation

Most sedimentary modelling programs developed in recent years focus on either terrigenous or carbonate marine sedimentation. Nevertheless, only a few programs have attempted to consider mixed terrigenous-carbonate sedimentation, and most of these are two-dimensional, which is a major restriction since geological processes take place in 3D. This paper presents the basic concepts of a new 3D mathematical forward simulation model for clastic sediments, which was developed from SIMSAFADIM, a previous 3D carbonate sedimentation model. The new extended model, SIMSAFADIM-CLASTIC, simulates processes of autochthonous marine carbonate production and accumulation, together with clastic transport and sedimentation in three dimensions of both carbonate and terrigenous sediments. Other models and modelling strategies may also provide realistic and efficient tools for prediction of stratigraphic architecture and facies distribution of sedimentary deposits. However, SIMSAFADIM-CLASTIC becomes an innovative model that attempts to simulate different sediment types using a process-based approach, therefore being a useful tool for 3D prediction of stratigraphic architecture and facies distribution in sedimentary basins. This model is applied to the neogene Vallès-Penedès half-graben (western Mediterranean, NE Spain) to show the capacity of the program when applied to a realistic geologic situation involving interactions between terrigenous clastics and carbonate sediments.

On the origin of the North Pacific arcs

We present a new hypothesis that relates global plate tectonics to the formation of marginal basins, island arcs, spreading ridges and arc-shaped mountain belts around the North Pacific Ocean. According to our model, the ellipsoidal-shaped Paleogene basins of the South China Sea, Parece-Vela Basin, Shikoku Basin, Sea of Japan and the Sea of Okhotsk in addition to those of the North American Cordillera can be attributed to the change in plate convergence direction at 42 Ma between the Indoaustralian and Eurasian plates. The new direction of convergence was parallel to the eastern continental margin of Asia and resulted in widespread extension perpendicular to this margin and to the western margin of North America. Both margins form part of a circle parallel to the Indoaustralian-Eurasian direction of convergence.

Estratigrafía del Paleógeno en la zona de tránsito entre la Cordillera Prelitoral Catalana y el Prepirineo

La serie de Eoceno y Paleoceno de El Far (provincia de Gerona), presenta un gran interés por servir de punto de enlace entre el Paleógeno de la Cordillera Prelitoral Catalana (en la zona de la Plana de Vic) y el Prepirineo. Es por ello que lieinos considerado interesante el pulilicar una serie detallada que sirva de jalón para poder correlacionar el Eoceno de la Plana de Vic con el de La Salut, Bellmunt y Puigsacalm, sobre todo en los tramos inferiores. Ambas series eocénicas poseen diferencias muy notables en su litología (cainbios laterales de facies) y potencia (aumento pogresivo hacia el surco paleógeno prepirenaico), lo que influye en la misma fauna...

Evolución tectonoestratigráfica de los Catalánides

Proposem una divisió dels Catalanids en unitats que reflecteixen un comportament paleogeografic i estratigrafic diferent durant l'etapa preorogenica (Mesozoic) i un de tectonic relativament diferenciat durant l'etapa compressiva (Paleoge). Distingim els sectors (extern, intermedi i intern) limitats per falles de sbcol longitudinals, paral.leles a la serralada, la majoria de les quals es concentra en una zona que separa els sectors extern i intern. En aquesta zona (sector intermedi) s'hi atasconen les unitats litoestratigrafiques mesozoiques. Aquest atasconament, conjuntament amb la reactivació de les fractures profundes, és el responsable, durant l'etapa compressiva, de la localització en el sector intermedi dels fronts de les principals estructures d'encavalcament. També distingim les unitats que hem anomenat domini; (septentrional, central i meridional), que estan limitades per fractures transversals a la serralada. Així, doncs, les unitats queden limitades per dos sistemes de fractures de sòcol aproximadament ortogonals.

Los sedimentos de la plataforma continental balear

El análisis sedimentológico de distintos sectores de la plataforma continental balear (Bahia de Campos, Sur de Menorca y Canal de Menorca) ha puesto de manifiesto la existencia de siete grupos de facies: A) algales, B) de bivalvos, C) de gasterpodos, D) bioclsticas, E) mixtas, F) de fragmentos liticos y G) cementadas (costras algales y calcarenitas). La distribución de estas facies sedimentarias guarda una estrecha relación con la profundidad, excepto en el Sur de Menorca, y con las comunidades bentónicas que se desarrollan en la plataforma continental. Las facies que recubren actualmente la plataforma balear se depositaron durante la fase del ascenso del nivel del mar de la transgresión Versiliense.

Las unidades litoestratigráficas del Eoceno pre-pirenaico del Ripollés oriental (prov. de Gerona y Barcelona)

En este trabajo se definen una serie de unidades litoestratigréficas para el Eoceno prepirenaico del Ripollés oriental (provincia de Gerona y Barcelona) y se da un corte general del mismo que pone de manifiesto los cambios de facies y las relaciones entre las distintas formaciones y miembros.

Nota preliminar sobre las turbiditas eocenas de los alrededores de Ripoll (Prov. de Gerona)

En este trabajo se presentan algunos resultados sobre las características sedimentológicas de las turbiditas eocenas de Ripoll, considerándose igualmente su posición y significado dentro de la cuenca de sedimentación prepirenaica.

Rasgos del Micromodelado periglaciar actual sobre zonas graníticas de los Pirineos españoles (Panticosa, Huesca y Cavaller, Lleida)

El objeto de nuestro trabajo es el estudio del micromodelado desarrollado sobre granito y su evolución postglacial en dos áreas de los Pirineos Españoles: Panticosa (valle del río Gállego) y Cavallers (valle del río Koguera de Tor). Ambas áreas presentan un modelado principalmente glacial con micro y macro-formas típicas, heredadas de la Última glaciación...

On the Upper Ordovician unconformity in the Pyrenees: New evidence from the La Cerdanya area

In recent years, contradictory reports about whether or not an unconformity exists at the base of the Upper Ordovician succession of the Pyrenees have been made. In the Cerdanya area (Central Pyrenees), good outcrop evidence for this unconformity is displayed at the base of the Rabassa conglomerates. In this area, the Upper Ordovician rocks overlie a tilted Cambro-Ordovician sequence, displaying an angular unconformity and indicating a break in the stratigraphic series. Moreover, the existence of such an unconformity is supported by the distribution of Variscan minor structures, suggesting that the Cambro-Ordovician and the Upper Ordovician strata initially had different orientations before the main Variscan folding.

Pseudo-two-girdles c-axis fabric patterns in a quartz-feldspar mylonite (Costabona granodiorite, Canigo massif)

An example of the relationship that exist between the preferred crystaliografic orientation of quartz grains and the attitude of the mylonite foliation of quartz-feldspar mylonites is described. These rocks are the result of the inhomogeneous deformation under low-grade metamorphic conditions of a late Hercynian granodiorite, intruded into the gneisses of the slopes of the Canig massif (Eastern Pyrenees). The Costabona mylonites have a quartz c-axis fabric in pseudo-twogirdles symmetrical with respect to the mylonite foliation and perpendicular to the shearband systems which produce an extensional crenulation of the mylonite foliation.

Detección por el satélite LANDSAT-4 de los efectos de la riada del 8-XI-82 en el río Segre

Por medio de técnicas de tratamiento de imágenes digitales se realiza un estudio de los efectos producidos por una inundación ocurrida a finales del año 1982 en el valle del río Segre, en Catalunya, a partir de la información multiespectral captada por el sensor TM del satélite LANDSAT-4. Utilizando un programa de clasificación no supervisada basado en la distancia euclídea, se diferencian cuatro tipos de suelo o de cubiertas en el rea de estudio (3.8 x 2.3 km). Se efecta un análisis cuantitativo de la calidad de los resultados, usando como referencia la información obtenida en un estudio de campo. Este análisis muestra un alto grado de correspondencia entre el mapa de campo (verdad terreno) y la cartografía realizada a partir de los datos multiespectrales.

New magnetotelluric data trough the boundary between the Ossa Morena and Centroiberian Zones

The south-western part of the Iberian Peninsula, including the southern branch of the Iberian Massif, has recently been the subject of several magnetotelluric (MT) studies. This area is made up of three different tectonic terranes: the South Portuguese Zone (SPZ), the Ossa Morena Zone (OMZ) and the Central Iberian Zone (CIZ). The boundaries between these zones are considered to be sutures, which appear as high electrical conductivity anomalies in the MT surveys. The OMZ is characterised by a conductive layer at middle-lower crustal levels. To investigate the continuity of this conductive layer into the CIZ, a new MT profile was carried out. This 75-km long ENE profile goes through the boundary between the OMZ and the CIZ. The results of a two-dimensional magnetotelluric inversion revealed a high-conductivity anomaly in the transition OMZ/CIZ (the so-called Central Unit), which is interpreted as due to interconnected graphite along shear planes. High-conductivity anomalies appeared in the middle crust of the CIZ, whose geometry and location are consistent with the conductive layer previously found in the OMZ, thus confirming the prolongation of the conductive layer into the CIZ. The top of this layer correlated spatially with a broad reflector detected by a seismic profile previously acquired in the same area. This, together with other geological and petrological evidence, points to a common origin for both features.

Estudi microtermomètric dels filons de quars de les Esquerdes de Rojà, Massís del Canigó, Pirineu Oriental

Els materials pre-hercinians i el granit de Costabona estan travessats per un conjunt de filons de quars de fins a 15 km de longitud, coneguts com a 'Esquerdes de Roja'. Aquests filons estan localment afectats per un sistema de bandes milonítiques i per un altre posterior de fractures. A partir de l'anilisi microtermometrica de les inclusions fluides primàries en quars, ha estat obtinguda una temperatura de formació de l'ordre de + 280 C per la major part del quars, i una temperatura de + 250 C per als monocristalls que omplen esquerdes i cavitats. Els filons s'haurien format a partir de solucions mineralitzants que contenien ~ a + C, a++, K+ i, en menor proporció, ~ g + + .fins una salinitat total de l'ordre del 20/@ en pes de la Na CI.