Análisis de secuencias de islas barrera pleistocenas en relación con variaciones del nivel del mar, laguna de La Mata (Alicante)

En la laguna de La Mata (Alicante) se estudia un complejo de cordones litorales pleistocenos que forman el cierre de la actual laguna. Se analizan las secuencias resultantes y los posibles indicadores de variaciones del nivel del mar. Asimismo se interpretan estos depósitos en base a una curva aparente de tendencias del nivel del mar, obtenida con la suma de las componentes eustáticas cíclicas y la componente relativa debida al factor tectónico aplicado. [ABSTRACT] A complex of Pleistocene coastal barriers is studied in La Mata lagoon (Alicante). The resuting sequences are analyzed in order to establish indicators 0f sea level changes. These deposits can be correlated with an apparent curve of sea level tendencies obtained with the sum of the cyclic eustatic component and the relative component due to the tectonic factor applied

Submarine Active Faults and MorphoTectonics Around the Iberian Margins: Seismic and Tsunamis Hazards

The aim of this work is to make a synthesis at regional scale focused on the geophysical characterization of submarine faults around the Iberian margin to identify active structures and analyze their development in the framework of the present plate organization. Most of these submarine faults show seabed morphological expressions mapped with high-resolution swath bathymetry data, high-resolution parametric sub-bottom profiles and multichannel seismic profiles. Present active tectonics, deformation, seismicity, and tsunami-affected coastal areas is mainly focused on south Iberia at the Eurasian and Nubia plate boundary. Submarine active faults in these areas are represented by long strike-slip fault systems and arcuate fold-thrust systems. Their development takes place in response to present NW-SE convergence between the Eurasian and Nubia plates. We propose a strain partitioning model of the plate boundary into simple and pure shear zones to explain the distribution and mechanisms of active submarine faults along the Gulf of Cádiz, Gibraltar Arc and Alborán Sea in response to the present-day shear stress orientation. Nevertheless, deformation is also focused in the NW Iberian margin. Thus, along the Galician and Portuguese margin, several submarine faults mapped as thrust fault systems with high-seismic activity along the Iberian ocean-continent transition reflect the re-activation of former structures. We suggest that submarine active faults in the NW and W Iberia are also the response to the eastwards transfer of short-offset transform faults of the Mid Atlantic Ridge into the oceanic Iberian along a weakness as the former plate boundary between the oceanic Iberia and Eurasia domains. The distribution and activity of submarine faults mapped in this work from geophysical and bathymetric data are in good agreement with geodetic data and focal mechanisms.Versión del edito

Morfometría de montículos submarinos del talud inferior del margen continental canario (O de las Islas Canarias): Análisis basado en un MDT

We present a morphometric analysis of 41 mounded edifices located on the seafloor to the west of Canary Islands, using a 150 m resolution DEM and very high-resolution seismic profiles. In order to carry out morphometric computation a set of variables (slope, size and shape) were calculated using ArcGIS Analyst tools. A mapping cluster has been generated using Grouping Analyst ArcGIS Statistics toolset where seven differents morphometric groups have been distinguished. Four main types of edifice shapes have been identified within the seven morphometric groups. The first type is a single giant dome elevation that can be considered as an outlier mound. The second type is the most frequent and can be considered as the standard type mound on the Canary continental slope due to its intermediate morphology. They show extrusive seismic characteristics in seismic profiles. The third type is morphologically derived from type 2, representing steeper and higher mounds related with extrusive processes whereas the fourth type represents smoother and flatter mounds related to faulting. This study shows that an elaborated geomorphometry resolves between types of extrusive edifices from those under tectonic conditionsVersión del edito

Palaeoenvironments, relative sea-level changes and tectonic influence on the Quaternary seismic units of the Huelva continental shelf (Gulf of Cadiz, southwestern Iberian Peninsula)

A seismic stratigraphical study was conducted on the Huelva continental shelf (southwestern Iberian Peninsula) between the mouths of the Guadalquivir and Guadiana Rivers. Applying the basic concepts of seismic stratigraphy, 13 seismic units bound by erosive discontinuities have been identified. Two main kinds of seismic units can be distinguished: a) Units that internally show a wide variability of seismic configurations and sheet to lensoidal external shape, located in inner-to-middle shelf settings. These units are considered high-energy units (HEU), deposited during intervals of rising and highstand sea levels. They represent coastal deposits comprising two main depositional systems: coastal barriers in the form of shoreface deposits and landward lagoonal and tidal deposits. b) Units displaying low-angle oblique seismic configurations, with reflectors exhibiting good lateral continuity and amplitude. Their thickness increases seaward, with the largest depocentres located near the shelf-break, displaying therefore a typical wedge external shape. These units are located very frequently from middle shelf emplacements to outer shelf and upper slope settings, and are considered low-energy units (LEU). They are believed to have been formed during periods of falling sea level, representing the distal portions of coastal and deltaic bodies that have been preserved from erosion. The stacking pattern of the units shows three different tectonic settings: a central subsiding sector, bounded laterally by two tectonic highs, one of them structurally controlled (the western one) and the other conditioned by diapiric uplifting (the eastern one).Un análisis de estratigrafía sísmica se ha realizado en la plataforma continental de Huelva (suroeste de la península Ibérica) entre las desembocaduras de los ríos Guadiana y Guadalquivir. Aplicando los concep tos básicos de la estratigrafía sísmica, han sido identificadas 13 unidades sísmicas limitadas por discontinuidades erosivas. Dos tipos principales de unidades sísmicas han sido identificadas: a) Unidades que internamente muestran una gran variabilidad de facies sísmicas y forma externa de lámina o lenticular, localizadas en la plataforma interna-media. Estas unidades son consideradas de alta energía (high- energy units, HEU), depositadas durante intervalos de ascenso y alto nivel del mar. Se relacionan con depósitos costeros compuestos de dos sistemas deposicionales principales: barreras costeras formadas por depósitos de frente de playa y, hacia tierra, depósitos mareales y de laguna. b) Unidades caracterizadas por clinoformas progradacionales de bajo ángulo, con reflectores de alta amplitud y continuidad. Su espesor aumenta hacia el borde de plataforma, adquiriendo una forma típica de cuña. Estas unidades están localizadas frecuentemente desde la plataforma media hasta el talud superior y son consideradas como unidades de baja energía (low-energy units, LEU). Se interpreta que representan las porciones distales de cuerpos costeros y deltaicos que se han formado durante periodos de descenso relativo del nivel del mar, y que han sido preservadas de la erosión que sufrieron las capas más someras. El patrón de apilamiento de las unidades muestra tres emplazamientos tectónicos diferentes: un sector central subsidente limitado lateralmente por dos altos tectónicos, uno controlado estructuralmente (sector oeste) y otro condicionado por un levantamiento de origen diapírico (sector este).Instituto Español de Oceanografí

From hyperextended rift to convergent margin types: mapping the outer limit of the extended Continental Shelf of Spain in the Galicia area according UNCLOS Art. 76

European Geosciences Union General Assembly (2017. Viena)Spain presented on 11 May 2009 a partial submission for delimiting the extended Continental Shelf in respect to the area of Galicia to the Commission on the Limits of the Continental Shelf (CLCS). The Galicia margin represents an example of the transition between two different types of continental margins (CM): a western hyperpextended margin and a northern convergent margin in the Bay of Biscay. The western Galicia Margin (wGM 41º to 43º N) corresponds to a hyper-extended rifted margin as result of the poly-phase development of the Iberian-Newfoundland conjugate margin during the Mesozoic. Otherwise, the north Galicia Margin (nGM) is the western end of the Cenozoic subduction of the Bay of Biscay along the north Iberian Margin (NIM) linked to the Pyrenean-Mediterranean collisional belt.Instituto Geológico y Minero de España, EspañaCentro Oceanográfico de Málaga, Instituto Español de Oceanografía, EspañaInstituto Hidrográfico de la Marina, Españ

Mapping giant mass transport deposits (MTDs) for delineating the extended Continental Shelf of Spain to the West of Canary Islands according UNCLOS Art. 76

European Geosciences Union General Assembly (2017. Viena)On 19 December 2014, Spain presented a third partial submission for the delineation of the Extended Continental in the area west of the Canary Islands to the Commission on the Limits of the Continental Shelf (CLCS) according to the United Nations Convention on the Law of Sea (UNCLOS). The Canary Islands are located within a NE-SW 1,350 km long ridge of hotspot-inferred volcanic islands and seamounts (composed by more of 100, from Lars to Tropic seamounts). This submission has been documented with an extensive dataset specifically obtained for the project during ten oceanographic cruises between 2010 and 2014 aboard the Spanish research vessels Hespérides, Sarmiento de Gamboa and Miguel Oliver. This new dataset allows to investigate an area of 440,000 km2 with acoustic backscatter images and multibeam echosounder bathymetric (MBES) data (Simrad EM-12, EM-120 and EM-302, and Atlas HYDROSWEEP DS), a dense network of 65,800 km of very-high resolution (VHR) seismic lines (including chirp parametric source TOPAS PS-18 and Atlas PARASOUND P-35) and 4,471 km of multichannel seismic reflection lines (MCS) acquired with an array of air-guns yielding a total volume of 4,600 inch3 (75.38 L) and a 3,500 m long streamer composed of 280 channels.Instituto Geológico y Minero de España, EspañaInstituto Español de Oceanografía, EspañaInstituto Hidrográfico de la Marina, Españ

First evidence of a main channel generated by the Mediterranean Outflow Water after its exit from the Gibraltar Strait

An extensive terrace comprising sandy sheeted drifts characterises the proximal sector (close to the Straits of Gibraltar) of the Contourite Depositional System (CDS) of the Gulf of Cadiz and the western continental margin of Portugal. A novel morphosedimentary study over this terrace has been executed based on new multibeam echosounder data, seismic profiles, and surficial sediments samples collected during the CONTOURIBER-1 Cruise (2010). Based on that study, an impressive large channel laterally connected with the central part of the Strait of Gibraltar (Camarinal Sill) has been identified. It is associated southwestward with a huge contourite levee (sand bank), which has been generated by overflow processes related to the Mediterranean Outflow Water (MOW). In the middle to the distal part of the terrace, there are other minor channels, erosional scour alignments and depositional features. The mapping of all these features coupled with CTD data allows to further understand the pathway and deceleration of the MOW, in addition to aid the conceptual identification of contourite terrace

Características morfológicas y estructura superficial de montículos submarinos del talud inferior del margen continental canario (O de las Islas Canarias)

Extrusive edifices and structural reliefs, catalogued as mounds and located on the seafloor to the west of Canary Islands were analyzed by acoustic data obtained with multibeam and parametric echosounders during several oceanographic expeditions. They were carried out at deep waters, from 4800 to 5200 m, and they have allowed characterizing 41 newly discovered submarine structures which occur either as isolated edifices or clustered mounds. These features have circular to elongated shapes with diameters of 2-24 km and relief heights of 10 to 250 m, showing different flank slopes of 2-50°. They generally display mounded forms and show morphological elements as ridges, near-circular rock outcrops, depressions and fault scarps together with mass flow and slide deposits located at the vicinity of the edifices. Two types of extrusive features are evidenced by the morphological and seismic data analyses, the first one probably corresponds to high velocity extrusions that reach the seafloor surface and the second one is probably formed by the combination of faulted structures and low velocity extrusions that produce singular domes in the shallower sedimentary records. Based on both analyses, extrusive phenomena represent the dominant mechanism for mound field evolution in the Canary lower slope region.Versión del edito

Evidencias acústicas de procesos paralelos al talud asociados con depósitos de movimiento en masa en el talud inferior de la Isla de Madeira (Atlántico Central Oriental)

The Madeira Island lower slope has been build-up mostly by along slope-processes associated with mass movement deposits as seen in GEBCO bathymetry, multibeam bathymetry, Parasound echosounder profiles and multichannel seismic reflection profiles. A plastered contourite drift (Madeira Drift) developed on this lower slope, being composed of seismic units D1, D2 and D3. The most probable water mass responsible for its deposition is the Antarctica Bottom Water (AABW). The youngest sediments of seismic units D2 and D3 are affected by gravity-driven processes, probably slumps and debris flows, which moved downslope towards west. Parasound profiles show evidences of such mass movements on present-day seabottom (e.g. diffraction hyperbolae echoes) but also of past-events buried within the contourite sediments. These older debris flows are recognized by semitransparent/transparent acoustic facies and lenticular shape.Versión del edito

Seismic architecture of mud volcano systems in the Ceuta

Analysis of a new dataset of high-resolution seismic and swath bathymetry data acquired during the CONTOURIBER-1 cruise in the Ceuta Contourite Depositional System (Western Alborán Sea), reveals the detailed architecture of several mud volcanoes systems that comprises both surface and buried constructional edifices as well as their subsurface feeder complex which pierces the contourite deposits. Seismic characterization, distribution and interpretation of structural elements associated to the mud volcano system promotes a more comprehensive understanding of the processes involved in their genesis and evolution.El análisis de los datos batimétricos y de sísmica de alta resolución durante la campaña CONTOURIBER-1 en el Sistema Deposicional Contornítico de Ceuta (Mar de Alborán occidental) muestran la arquitectura en detalle de varios sistemas de volcanes de fango que comprenden edificios en el fondo marino y edificios enterrados, así como sus complejos de alimentación a través de los depósitos contorníticos. La caracterización sísmica, distribución e interpretación de estos elementos estructurales que componen el sistema de volcán de fango constituyen una importante ayuda para un mejor y mayor conocimiento de su génesis y evolución.Publicado