Estudio petrológico de las rocas volcánicas del Pérmico de Gréixer (Pirineo catalán)

Se presenta un estudio sobre las rocas volcánicas de edad permica que afloran extensamente cerca de Greker. a lo largo del borde de la Zona Axial pirenaica. El estudio al microscopio y los análisis quimicos de las muestras recogidas, junto con los datos de campo, han proporcionado nuevos resultados sobre la datación y génesis de estas rocas, y sobre sus relaciones en el marco geológico regional y su evolución. Se pone de relieve la muy notable proporción de las ignimbritas en el material volcánico objeto de este estudio. Igualmente, la predominante composición peralcalina de este material. Las hipótesis que pueden explicar tal composición son discutidas.

Aportaciones de la prospección geofísica al estudio del subsuelo del Berguedà y Solsonés, (pre-pirineo Catalán, N.E. de la Península Ibérica)

En este trabajo se presenta la interpretaciónpor métodos geofísicos combinados de un sector del contacto entre el Pre-Pirineo y la La zona objeto del presente estudio se halla a Depresión Central Catalana...

A reappraisal of 'International Stratigraphic Lexicon' and the need for the creation named units critical catalogues

Analysis of stratigraphic terminology and classification, shows that time-related stratigraphic units, which by definition have a global extent, are the concern of international cornrnissions and committees of the intemational Union of Geological Sciences (IUGS) . In contrast, lithostratigraphic, and other closely related units, are regional in extent and are catalogued in the International Stratigraphic Lexicon (ISL), the last volume of which, was published in 1987. Tlie intemational Commission on Stratigraphy (ICS) is currently attempting to revitalize the publication of ISL, given that the information contained in published volumes has never been updated, and that there has been a significant increase in stratigraphic research in recent decades. The proliferation of named units in the South Pyrenean and Ebro Basin Paleogene is evaluated to illustrate the extent of the problem. Moreover, new approaches to stratigraphic analysis have led to the naming of genetic units according to similar guidelines followed in the naming of descnptive or lithostratigraphic units. This has led to considerable confusion. The proposal to revitalize the ISL is accepted as part of the solution, that should also include the publication of critica1 catalogues, and the creation of norms for genetic unit terminology.

Deep incision in an Aptian carbonate succession indicates major sea-level fall in the Cretaceous

Long-term relative sea-level cycles (0 5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault-controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea-level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea-level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea-level drop was in the order of tens of metres, with a duration of <1 Myr. The second stage of relative sea-level fall occurred within the Late Aptian and is recorded by an incised valley that, when restored to its pre-contractional attitude, was >2 km wide and cut 115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was back-filled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea-level drops identified fall within the glacio-eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long-term sea-level trends that are often only recognizable on larger scales (i.e. seismic) such as for the Arabian Plate.

Deep incision in an Aptian carbonate succession indicates major sea-level fall in the Cretaceous

Long-term relative sea-level cycles (0 5 to 6 Myr) have yet to be fully understood for the Cretaceous. During the Aptian, in the northern Maestrat Basin (Eastern Iberian Peninsula), fault-controlled subsidence created depositional space, but eustasy governed changes in depositional trends. Relative sea-level history was reconstructed by sequence stratigraphic analysis. Two forced regressive stages of relative sea-level were recognized within three depositional sequences. The first stage is late Early Aptian age (intra Dufrenoyia furcata Zone) and is characterized by foreshore to upper shoreface sedimentary wedges, which occur detached from a highstand carbonate platform, and were deposited above basin marls. The amplitude of relative sea-level drop was in the order of tens of metres, with a duration of <1 Myr. The second stage of relative sea-level fall occurred within the Late Aptian and is recorded by an incised valley that, when restored to its pre-contractional attitude, was >2 km wide and cut 115 m down into the underlying Aptian succession. With the subsequent transgression, the incision was back-filled with peritidal to shallow subtidal deposits. The changes in depositional trends, lithofacies evolution and geometric relation of the stratigraphic units characterized are similar to those observed in coeval rocks within the Maestrat Basin, as well as in other correlative basins elsewhere. The pace and magnitude of the two relative sea-level drops identified fall within the glacio-eustatic domain. In the Maestrat Basin, terrestrial palynological studies provide evidence that the late Early and Late Aptian climate was cooler than the earliest part of the Early Aptian and the Albian Stage, which were characterized by warmer environmental conditions. The outcrops documented here are significant because they preserve the results of Aptian long-term sea-level trends that are often only recognizable on larger scales (i.e. seismic) such as for the Arabian Plate.

The Role of Canyons in Strata Formation

This paper provides a spatial and temporal multi-scale approach of European submarine canyons. We fi rst present the long-term geologic view of European margins as related to controls on submarine canyon development. Then we discuss the extent to which submarine canyon systems resemble river systems because both essentially form drainage networks. Finally, we deal with the hortest-term, highestresolution scale to get a fl avor of the current functioning and health of modern submarine canyons in the northwestern Mediterranean Sea. Submarine canyons are unique features of the seafl oor whose existence was known by European fi shermen centuries ago, especially for those canyons that have their heads at short distance from shoreline. Popular names given to specifi c canyons in the different languages spoken in European coastal communities refer to the concepts of a"deep" or"trench." In the old times it was also common thinking that submarine canyons where so deep that nobody could measure their depth or even that they had no bottom. Submarine canyons are just one of the seven different types of seafl oor valleys identifi ed by Shepard (1973) in his pioneering morphogenetic classifi cation. Shepard (1973) defined submarine canyons as"steep-walled, sinuous valleys, with V-shaped cross sections, and relief comparable even to the largest of land canyons; tributaries are found in most of the canyons and rock outcrops abound on their walls." Canyons are features typical of continental slopes with their upper reaches and heads cut into the continental shelf.

Aportación al estudio de arcillas expansivas asociadas a las facies garumnienses de la Conca de Tremp (Prepirineo de Lleida)

Some clay levels of the garumnian facies, which surface in the southern sector of the Tremp Basin present a principal mineralogy of expansive type. The oedometer essays show that such materials present a very high grade of potencial expansivity. The swelling pressure presents values higher than 390 KN/m2. In the majority of the areas wherw this kind of clays surface the hydric erosion phenomena and the mass movements often appear to be very common and intense. The geomorphological role of the expansive clays is discussed as the triggering factor, associated to the development of these denudative processes

Métodos de reconocimiento del subsuelo

The aim of this workshop is to present the main methods of subsoil studies (namely mechanical and geophysical methods) to the Earth Sciences professorate. These methods frequently involve the use of specific material. The different methods are usually taught in the classroom where there is no real contact between the students and the equipment. Several activities, all of them taking place in surrounding areas of the university campus of Girona, will provide the assistants to the workshop with the opportunity of making measurements with different equipment. These activities will be made in the field so as to contribute to the resolution of a problem which will have been previously proposed. The problems presented are situations, most of them real, when subsoil investigation techniques are usually used. These cases have been employed as teaching-learning strategies with university and second grade students in the area of Girona. Finally, some examples of exercises involving the treatment of data obtained through subsoil investigation techniques are also presented to complement the workshop

Análisis de los acelerogramas de la serie de Adra (Almería): diciembre 1993 a enero 1994

Se analizan en este trabajo los datos acelerográficos asociados a los dos sismos principales de la denominada serie de Adra. Esta serie está constituida por un conjunto de terremotos de magnitud mb=5.0 que ocurrieron durante los meses de diciembre de 1993 y enero de 1994 en la provincia de Almería, representando el primer caso de registro de gran número de acelerogramas (terremotos principales y replicas) en España.