Sistemas polimórficos de la Cerdanya y su relación con los del País Vasco

En este trabajo se ha caracterizado la población autóctona de La Cerdanya mediante el estudio serológico de los sistemas MNSs, Kell, Duffy y HLA (loci A y B), y, se ha comparado con la población vasca. Los resultados obtenidos únicamente muestran diferencias para algunos sistemas en determinadas poblaciones comparadas, lo cual parece indicar que, en el País Vasco, no existe uniformidad genética para todos los marcadores. Las características serológicas que presenta la población autóctona de la Cerdanya no demuestran una proximidad genética, como cabría esperar "a priori" dados sus antecedentes históricos y, de haber existido este patrimonio genético, debió haber sido "diluido" por la influencia de invasiones posteriores.Pour mener ce travail, nous avons voulu caractériser la Cerdagne par une étude séro-anthropologique de la population autochtone parce que les caractères sérologiques sont sous le contrôle direct du génotype et échappent totalement aux conditions du milieu. Comme cela n'avait pas encore été fait du côté sud, et du côté français, la population a été étudiée en tenant compte de l'ensemble des Pyrénées Orientales. D'autre part, l'étude des caractères morphologiques, les seuls longtemps utilisés pour caractériser les populations, avait déjà été realisée par le Dr. Alcobé, bien que la population n'était pas totalement autochtone, que ces caractères dépendent d'une herédité polymorphique et qu'ils sont influencés par le milieu.La Cerdagne est un territoire de 1.129 Km2 situé dans une vallée des Pyrénées Orientales. Elle est formée par le haut bassin du Segre et elle est entourée par des chaînes montagneuses qui atteignent presque 3.000 m. d'altitude. Cette région a été partagée de NW en SE par la frontière franco-espagnole au traité des Pyrénées, en 1660, entre Louis XIV de France et Felipe IV de Castilla, et elle a été utilisée par des peuples pré et indoeuropéens comme lieu de passage pour entrer dans la Péninsule Ibérique. A la fin de l'époque mégalithique et après pendant l'Âge du Bronze, des populations brachycéphales sont venues du Centre de l'Europe vers les Pyrénées et ont pénétré par la Cerdagne dans la Péninsule Ibérique influant sur les populations autochtones qui avaient un élément dolichocéphale. Les événements de ces époques associés à des études de toponymies semblent indiquer que le peuple primitif de la Cerdagne pourrait avoir des affinités avec les peuples franco-cantabriques, lesquels parlaient une langue commune pré-indoeuropéenne de type basque, comme l'indique un grand nombre de noms de villages de type basque qui existent en Cerdagne: Das, Êller, Urtx, Urús, Ur, Ix, Er, Naüja, etc. En même temps, les anciens cerdagniens sont rapportés, par des romains, comme des "Kerretani". Ce mot provient du mot basque "Kerr", ou "xerri". Ces faits nous amenent à considérer si des analogies possibles existent entre la population basque et celle de la Cerdagne ou bien, au contraire, si tous les deux différent génétiquement. Le présent travail a été réalisé dans la Basse Cerdagne (côté sud) qui a 603.36 Km2 , dont la densité de population atteint seulement 22 hab/km2 et la population autochtone n'atteint pas 30%. Les marqueurs sérologiques (systèmes érythrocytaires Duffy, Kell, MNSs et le système lymphocytaire HLA -loci A, B-) ont étéanalysés sur 140 individus autochtones, sans apparentement connu jusqu'a 1/8. Les résultats obtenus témoignent, en général, d'une conduite inégale à l'ègard des différentes populations basques avec lesquelles nous les avons comparés. Il faut tenir compte du travail présenté par Malgosa à ce congrès intitulé: "Êtude des systèmes sanguins ABO, Lewis, P et Rh dans la population autochtone de la Cerdagne. Relation avec la population basque"

El Canal de Diego Cao y sus depresiones morfológicas (margen del Banco del Guadalquivir, Golfo de Cádiz). Implicaciones oceanográficas y sedimentológicas

The Diego Cao channel is located on the central-north middle slope of the Gulf of Cadiz. It separates the Bartolomeu Dias and Faro sheeted drift plateaus to the north of the Guadalquivir Bank margin uplift. A striking linear series of circular depressions occur parallel to the channel on the Bartolomeu Dias sheeted drift (western channel flank), while a remarkable amphitheater-shaped escarpment affects the channel eastern flank. Their morphological and high- and medium-resolution stratigraphic analysis allows inferring their origin as the result of a complex interplay between oceanographic (bottom currents), mass-wasting and tectonic processes. All features seem to have a common origin, related to an especially active tectonic phase during the Mid-Pleistocene, probably related to adjustments of the deep structural features. Since then, the action of the bottom currents and the local influence of structural processes have shaped the present-day topography. The Diego Cao channel is re-interpreted as a contourite moat associated to a complex mounded, separated drift that includes the circular depressions. They result from contourite deposition over the erosional surface originated by widespread mass-wasting events during the Mid-Pleistocene.Versión del edito

Origin of morphological depressions on the Guadalquivir Bank uplifted area (Gulf of Cadiz middle slope)

We have investigated the origin of morphological depressions (circular-elliptical depressions, amphitheatre-shaped escarpments and valleys) on the Guadalquivir Bank uplifted area (Gulf of Cadiz middle slope). This work is based on swath bathymetry and high- and mid-resolution reflection seismic datasets. Depressions occur on the distal (depositional) sector of the Gulf of Cadiz Contourite Depositional System, which has been developed under the influence of the Mediterranean Outflow Water (MOW). The Guadalquivir Bank is a NE-oriented relief that was uplifted along the Neogene and Quaternary. It forms the southern limit of the Bartolomeu Dias and Faro Sheeted Drift (SD) plateaus that are separated by the NW-trending Diego Cao Contourite Channel. Circular-elliptical depressions occur on the Bartolomeu Dias SD plateau, aligned parallel to the rim of the Diego Cao Channel. Irregular, crescent-shaped depressions occur to the SE of the study area and a valley surrounds the Guadalquivir Bank. The origin of these features is interpreted as the result of the interplay between oceanographic, mass-wasting, tectonic and fluid-escape processes. Four stages define the development of these features: 1) Onset of a contourite mounded drift associated with a proto-Diego Cao moat originated by a weak MOW circulation as it interacted with the structural features of the Guadalquivir Bank during the Lower Pliocene; 2) Evolution to a more complex multi-crest drift and moat system, probably as a result of an enhanced MOW and increased deformation of the underlying structures during the Upper Pliocene-Early Quaternary; 3) Event of enhanced tectonic activity that provoked widespread mass-wasting events along middle slope sheeted drift plateaus during the Mid Pleistocene. It was recorded in a prominent erosive surface under the present-day Diego Cao channel western rim and numerous slide scars displaying amphitheatre shapes on the limits of the plateaus; 4) Final stage (Late Quaternary) when the Mediterranean Intermediate Branch started flowing towards the N-NW along the deep gateway that was opened as a result of the mass-wasting event and/or structural adjustments. The contourite system evolved, due to tectonic events, to the present-day channel and a complex separated drift that includes circular depressions. They result from the interaction between the bottom current and the irregular basal surface created by the slide scars. During this phase, crescent-shaped depressions were created, probably by the interplay between bottom currents and fluid escape processes, and the marginal valley around the Guadalquivir Bank resulted from current reworking of the irregular topography of contouritic deposits affected by slide scars

Oblique basin inversion and strain partitioning in back-arc context: example from the Moroccan Alboran Margin (Western Mediterranean)

EUROPEAN GEOPHYSICAL UNIO

Tsunami generation potential of a strike slip fault tip in the westernmost Mediterranean

Tsunamis are triggered by sudden seafloor displacements, and usually originate from seismic activity at faults. Nevertheless, strike-slip faults are usually disregarded as major triggers, as they are thought to be capable of generating only moderate seafloor deformation; accordingly, the tsunamigenic potential of the vertical throw at the tips of strike-slip faults is not thought to be significant. We found the active dextral NW–SE Averroes Fault in the central Alboran Sea (westernmost Mediterranean) has a historical vertical throw of up to 5.4 m at its northwestern tip corresponding to an earthquake of Mw 7.0. We modelled the tsunamigenic potential of this seafloor deformation by Tsunami-HySEA software using the Coulomb 3.3 code. Waves propagating on two main branches reach highly populated sectors of the Iberian coast with maximum arrival heights of 6 m within 21 and 35 min, which is too quick for current early-warning systems to operate successfully. These findings suggest that the tsunamigenic potential of strike-slip faults is more important than previously thought, and should be taken into account for the re-evaluation of tsunami early-warning systems.Versión del edito

Formation of Mass Transport Deposits on the Submarine Bank of Portimão (Gulf of Cadiz, SW Iberia)

European Geosciences Union General Assembly (2017. Viena)The development of submarine mass transport deposits (MTDs) plays an important geo-hazards role along continental margins. Accordingly, their identification and characterization is crucial to understand their sources, dynamics, frequency and spatial distribution. In this work a piston core located at the slope (2876 m water depth) of the southern flank of Portimao Bank (Portugal, Gulf of Cadiz, SW Iberia) underwent detailed magnetic (fabric and rock magnetism) and sedimentological (grain-size, carbonates, organic matter) analyses complemented by AMS 14C dating. Such multidisciplinary study identified about one meter of sediments that is unconformable with the ages obtained above and below this layer. Its magnetic fabric, as determined by anisotropy of magnetic susceptibility, indicates sharply changes from oblate to neutral shape, decrease of the anisotropy and preferred orientation of the magnetic susceptibility ellipsoid. Such layer is also individualized by sedimentary parameters, especially in its upper part by a lighter colour and decrease of the mean grain size than the rest of the core. Based on these results it is possible to conclude that the sedimentary column analyzed here shows evidence of an on-going development of a slide, which is well individualized and characterized by magnetic fabric studies.Instituto Dom Luiz, University of Lisbon, PortugalInstituto Superior de Engenharia de Lisboa, PortugalEstrutura de Missão para a Extensão da Plataforma Continental, PortugalInstituto Português do Mar e da Atmosfera, PortugalInstituto de Ciencias del Mar, Consejo Superior de Investigaciones Científicas, EspañaCentro Oceanográfico de Málaga, Instituto Español de Oceanografía, EspañaInstituto Geológico y Minero de España, Españ

The role of late Quaternary tectonic activity and sea-level changes on sedimentary processes interaction in the Gulf of Cadiz upper and middle continental slope (SW Iberia)

A morphological and seismic-stratigraphic analysis of the Gulf of Cadiz area near the Strait of Gibraltar is presented in this work, focused on the sedimentary evolution of the upper and proximal middle-continental slope since the Mid-Pleistocene. Based on the analysis of seismic reflection profiles and swath bathymetry data, this work analyses the close influence of the activity of buried and outcropping diapiric ridges and late Quaternary sea-level changes on the evolution of contouritic features related to the Mediterranean Outflow Water (MOW) and Eastern North Atlantic Central Water (ENACW), gravitational features and fluid-escape structures. The stratigraphic architecture reveals that, under active diapiric deformation, the upper slope plastered drift grew during low sea-level stages, when sediment supply was high and the ENACW swept the upper slope, contrasting with the present-day highstand situation dominated by northwest-trending MOW flow. The south-estward ENACW flow forced asymmetry and lateral migration of gullies incised in the plastered drift. Two evolutionary stages have been established: 1) After the Mid Pleistocene, activity of diapirs with a NE trend determined the location of the deepest depressions which were infilled by plastered contouritic drifts; 2) Between Late Quaternary and present, a drastic change of buried diapirs growth pattern and orientation to a NW trend enhanced slope-derived gravitational processes affecting the bottom current dynamics. Adjustments to tectonic changes led to a phase of plastered drift growth on the upper slope during which depocenters varied their distribution and orientation. In a long-term the structural control on sedimentation shows a northwestward displacement of deformation, resulting in an overall extension of the contourite depositional system to the NW. In a short-term, sea-level changes favored drift deposition, gullies incision and the strengthening of water masses. This work evidences the importance of tectonic deformation in sedimentation at recent time scales, and the twodirectional interplay between recent tectonic activity and bottom current dynamics.Versión del edito