Resumen de Tesis Doctoral: Evolución tectonosedimentaria de la cuenca Terciaria de As Pontes (NW de España)

The oligo-miocene As Pontes strike-slip basin (Galicia, NW Spain) is a first order coal-field in the Iberian Peninsula. Their structural and sedimentary features are genetically related to the evolution of a NW-SE dextral strike-slip fault system located in NW Galicia. This contribution deals with the analysis of structural evolution, stratigraphic framework and tectonics-sedimentation relationships in the basin. The structural evolution recorded in the basin is characterised by two evolutionary stages. The sedimentation began in two sub-basins located in a compressive relay of two main strike-slip faults, and their conve rgence led to a second stage characterised by a restraining bend strike-slip fault geometry. The preserved basin fill records syntectonic activity during 7,4 My, between 29,8 My (near the Rupelian-Chattian boundary) to 22,4 My (Aquitanian). A sequence stratigraphy subdivision of the basin fill has been carried out in order to set up a hierarchy of genetic stratigraphic units. The subdivision is based on the spreading-retreat trends affecting the palustrine-lacustrine systems. These stratigraphic units can be either simple (elemental sequences) or complex (composite sequences, macrosequences and megasequences). Tectonics was the main control on the sequence arrangement recorded in the basin, and acted in an ensemble of diverse overlapped spatial and temporal scales, controlling subsidence and uplift rates, that in its turn influenced sediment and water inputs. These factors altogether caused the alluvial-fan progradation-retrogradation trends, and also the spreading-retreat trends of the lacustrine-palustrine systems. Autogenic controls (differential compaction, alluvial fan dynamics) and climate represent minor controls, and probably their effects were partially concealed by tectonic effects, even in the elemental sequences order

Magnetocronología de las sucesiones cenozoicas de la cuenca de As Pontes (La Coruña, Noroeste de España)

The Terciary Basin of As Pontes (Northwest Spain) is associated with an onshore NW-SE dextral strike-slip fault system. A total of 900 specimens from the sedimentary infill have been demagnetized, using thermal and alternating field demagnetization procedures. Paleomagnetic data indicate that the duration of sedimentation in the basin was about 6,2 My, lasting from the latest Early Oligocene until the Early Miocene. The magnetostratigraphy of the basin successions allows us to establish a very precise chronological correlation within the basin. In addition, the overall pattern of declinations shows a clockwise rotation (9º±4º in the sedimentary infill) with respect to the Oligocene-Miocene reference declination, coherent with a NW-SE dextral strike-slip faults system. The dating of the sedimentary infilling of the As Pontes basin establishes that the NW-SE dextral strike-slip faults system of NW Iberian Plate were highly active from the uppermost Early Oligocene to the Early Miocene. This implies that the end of the main tectonic activity in both NW Iberian offshore and onshore took place during the same time span

Magnetochronology of the cenozoic successions of the As Pontes basin (La Coruña, Northwestern Spain)

Este trabajo resume los resultados de la Tesis de Licenciatura del primer firmante (A.H.), presentada en la Universitat de Barcelona. Los autores expresan su agradecimiento al Dr. Pere Santanach por realizar una revisión crítica de este trabajo. A la dirección y a la sección de Geología de ENDESA Mina As Pontes.[ES] La cuenca terciaria de As Pontes (Noroeste de España), asociada a un corredor de fallas transcurrentes de dirección NW-SE, ha sido datada mediante magnetoestratigrafia, para lo cual se han estudiado un total de cuatro sucesiones magnetoestratigráficas. Las litologías estudiadas han sido sobre todo arcillas aluviales y palustres-lacustres, con un contenido variable de materia orgánica. En total se han desmagnetizado unos 900 especímenes, mediante desmagnetización térmica y por campos alternantes. Los minerales responsables de la magnetización en las rocas estudiadas son la magnetita y los sulfuros de hierro. A partir de los datos paleomagnéticos, se puede establecer que la sedimentación en la cuenca comenzó en el cron 10r (parte alta del Starnpiense) y se prolongó, como mínimo, hasta el subcron 6AAr.2n (Aquitaniense superior). Así, la duración de la sedimentación en la cuenca fue de unos 6,2 Ma, abarcando desde la última parte del Oligoceno temprano hasta el Mioceno temprano. La correlación magnetoestratigráfica de las diferentes sucesiones de la cuenca ha permitido establecer una correlación cronológica muy precisa a escala de cuenca, determinando la casi total isocronía de la mayor parte de los diferentes niveles de lignito y de las unidades litoestratigráficas de la cuenca. Por otro lado, las declinaciones medias muestran una rotación de 9"+4" para el relleno sedimentario de la cuenca de As Pontes, en sentido horario con respecto a la declinación del Oligoceno-Mioceno, coherente con el movimiento dextrógiro del corredor de fallas transcurrentes de dirección NW-SE. La datación del registro sedimentario de la cuenca de As Pontes permite establecer que los sistemas de fallas transcurrentes de orientación NW-SE del noroeste de la Península Ibérica fueron fuertemente activos desde la última parte del Oligoceno temprano hasta el Mioceno temprano. La finalización del movimiento principal de estos sistemas de fallas coincidió con el fin de actividad del margen entre la microplaca Ibérica y la placa Europea. Esto implicaría que el final de la actividad tectónica principal coincide en el ofshore y en el onshore del NW peninsular.c[EN] The Terciary Basin of As Pontes (Northwest Spain) is associated with an onshore NW-SE dextral strike-slip fault system. A total of 900 specimens from the sedimentary infill have been demagnetized, using thermal and alternating field demagnetization procedures. Paleomagnetic data indicate that the duration of sedimentation in the basin was about 6,2 My, lasting from the latest Early Oligocene until the Early Miocene. The magnetostratigraphy of the basin successions allows us to establish a very precise chronological correlation within the basin. In addition, the overall pattern of declinations shows a clockwise rotation (g0k4O in the sedimentary infill) with respect to the Oligocene-Miocene reference declination, coherent with a NW-SE dextral strike-slip faults system. The dating of the sedimentary infilling of the As Pontes basin establishes that the NW-SE dextral strike-slip faults system of NW Iberian Plate were highly active from the uppermost Early Oligocene to the Early Miocene. This implies that the end of the main tectonic activity in both NW Iberian offshore and onshore took place during the same time span.Este trabajo se ha realizado bajo amparo de los proyectos AMB92-311, PB091-96 y PB94-826 con la colaboración y soporte de ENDESA, Mina As Pontes, a través de un convenio de colaboración Universidad-Empresa de la Fundación Bosc i Gimpera. La investigación necesaria para desarrollar este trabajo ha sido parcialmente financiada con el soporte del "Comissionat per Universitats i Recerca de la Generalitat de Catalunya", grup de qualitat GRQ97 SGR-73.Peer reviewe