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

Evidencia de fuertes erosiones por abrasión hídrica en el Estrecho de Gibraltar: aspectos morfométricos

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Estudio morfometrico comparativo entre las ondulaciones de los prodeltas de los rios de Andalucia Oriental

A partir de un estudio detallado de datos de batimetría multihaz se ha realizado el análisis morfométrico de 8 campos de ondulaciones desarrollados sobre prodeltas ubicados en la plataforma continental del margen norte del Mar de Alborán. Los parámetros morfológicos obtenidos se han relacionado con el régimen hídrico asociado a los sistemas fluviales estudiados, caracterizado por un patrón estacional influenciado por el clima regional. Los resultados indican que existe una clara relación entre las ondulaciones y la localización de los cauces fluviales, lo cual indicaría una influencia directa de las descargas fluviales en la generación de las ondas. Por otro lado, se ha comprobado que las ondulaciones asociadas a los ríos con mayor longitud y cuenca de drenaje alcanzan un mayor desarrollo que aquellas identificadas sobre cuerpos prodeltaicos asociados a ríos pequeños y ramblas, posiblemente indicando la existencia de diferentes tasas de aporte sedimentario en la plataforma continental.Publicado

New records of rare fish species for the Gulf of Cádiz

Comunicación a congresoThe Gulf of Cádiz represents an area with a high faunistic biodiversity due to the coexistence of species from different biogeografical regions (Lusitanian, Mediterranean, Mauritanian). The natural distribution of these species includes latitudinal (African and north Atlantic species) or longitudinal gradients (Mediterranean and anfiatlantic species). Information on the distribution/presence of species in the Gulf of Cádiz is scarce for deep-sea ones and it is of interest for biodiversity studies and further monitoring of global warming effects (colonization of species from lower latitudes), among others. During the scientific surveys INDEMARES/CHICA 0211 and ARSA 0311, carried out by the IEO on board R/V Cornide de Saavedra, some rare fish species were caught using diferent fishing gears such as otter-trawl and beam-trawl. Some of them represents first records for the Gulf of Cádiz area or the European margin

Evidencias de actividad tectónica contemporánea en el sector oriental de la plataforma continental y talud superior del Golfo de Cádiz (SO de la Península Ibérica)

La interpretación de una serie de registros de sísmica de muy alta resolución con ecosonda paramétrica TOPAS obtenidos en las campañas CADHYS0713, INDEMARES/CHICA1011 y ARSA 0313 en el sector oriental de la plataforma continental y talud superior del Golfo de Cádiz entre los 50 y los 400 m de profundidad, ha permitido identificar una serie de estructuras tectónicas que deforman tanto los depósitos de edad Holoceno y Pleistoceno Superior, como la superficie del fondo . Estas unidades estratigráficas se han identificado sobre la Superficie Transgresiva Posglacial, datada en 18 ka. Las principales estructuras identificadas son fallas normales y fallas inversas, cuya actividad se ha relacionado con fases de elevación de estructuras diapíricas de naturaleza salina que se extienden desde zonas emergidas hasta zonas distales del margen continental del Golfo de Cádiz.Very high resolution parametric echosounder (TOPAS) data interpretation obtained during CADHYS0713, INDEMARES/CHICA1011 and ARSA0313 cruises along the middle, external shelf and upper slope of the eastern Gulf of Cadiz between 50 and 400 m depth has allowed us the identification of several active tectonic structures acting since the Holocene. To date this activiy, it have been identified along the study area three postglacial discontinuities, Postglacial Trangressive Surface (TS) of 18 ky BP; the maximum flooding surface (MFS) of 6.5 ky; and the 3.5 ky Mid highstand deposits surface (MHS). Active normal and reverse faults have been identified whose recent activity is closely linked to the uplift episodes of salt diapirs structures from onshore to distal areas of the continental margin.Versión del edito

Informe de Campaña INDEMARES-CHICA 0211

Informe de la campaña oceanográfica INDEMARES CHICA 0211, realizada a bordo del Cornide de Saavedra entre febrero y marzo de 2011. En esta campaña hemos centrado nuestra actividad en la zona del Caladero de pesca del Laberinto, al norte, frente a Cádiz, y en la zona de los Volcanes de Fango del campo Hespérides, al sur, frente al Estrecho de Gibraltar.Las zonas de trabajo se sitúan en el talud continental del margen del Golfo de Cádiz, frente a las localidades de Chipiona y Cádiz, para el Caladero de pesca del Laberinto, y frente a Barbate y Tarifa para la zona de Volcanes de Fango del campo Hespérides

Episodios de construcción de un delta mediterráneo: Cambio climático y modificaciones antropogénicas en el delta del río Adra

The evolutionary stages of the submarine delta off the Adra River are investigated in this study, under the context of climatic fluctuations entangled with increasing human activities and interventions in the drainage basins and adjacent shores during the Middle to Late Holocene. To achieve that goal, we used an extensive database comprising a set of bathymetric data covering different time slices, a dense grid of high-resolution seismic data and several sediment cores collected in the two submarine lobes of the Adra River delta. Two main evolutionary phases can be identified. The first one extended through most of the construction history and was mediated by major climatic events at the Mediterranean scale; this phase included three major progradational events occurring during the Mid Holocene, the Roman time and the Little Ice Age. The most recent phase is strongly determined by human modifications of the fluvial channels, and resulted in a drastic transformation of the submarine sedimentary environment.Versión del edito

The role played by the slope and the fluvial discharge on deltaic built-up processes off mountainous seasonal rivers

The construction and evolution of submarine deltaic deposits are influenced by a combination of allogenic and autogenic factors. Numerical simulation of turbidity currents are used to propose a morphodynamic model that quantifies the effect of the slope and river input variations on delta development/construction for the case of mountainous rivers subjected to a seasonal Mediterranean climate, such as those located in the northern shelf of the Alboran Sea. These simulations were performed by using both constant and variable rates of fluvial flows. Both theoretical and real bathymetric profiles were used in the simulations. The results indicate that both the river flow and the depositional basin slope are key features for the development of morphostratigraphic features of submarine deltas at different spatial scales.Versión del edito

Multidisciplinary study of mud volcanoes and diapirs and their relationship to seepages and bottom currents in the Gulf of Cádiz continental slope (northeastern sector)

The seabed morphology, type of sediments, and dominant benthic species on eleven mud volcanoes and diapirs located on the northern sector of the Gulf of Cádiz continental slope have been studied. The morphological characteristics were grouped as: (i) fluid-escape-related features, (ii) bottom current features, (iii) mass movement features, (iv) tectonic features and (v) biogenic-related features. The dominant benthic species associated with fluid escape, hard substrates or soft bottoms, have also been mapped. A bottom current velocity analysis allowed, the morphological features to be correlated with the benthic habitats and the different sedimentary and oceanographic characteristics. The major factors controlling these features and the benthic habitats are mud flows and fluid-escape-related processes, as well as the interaction of deep water masses with the seafloor topography. Mud volcano eruptions give rise to mud flows and/or aqueous fluid seepage. These processes sustain chemosynthesis-based communities, closely associated with fluid seepage. Large depressions in the nearby area are influenced by collapse-related phenomena, where active fluid escape and the erosive effect of bottom currents have been identified. When the extrusion activity of the mud volcano is low and the seepage is diffuse, authigenic carbonates form within the edifice sediments. The bottom current sweeps the seafloor from the SE to the NW. When the velocity is moderate, sedimentary contourite processes take place on both sides of the edifices. At high velocities, the authigenic carbonates may be exhumed and colonised by species associated with hard substrates. Small carbonate mounds are found at the summits of some volcanoes and diapirs. Living corals have been found on the tops of the shallowest mud volcanoes, revealing different oceanographic conditions and strong bottom currents that favour the availability of nutrients and organic particles. The edifices affected by very high current velocities are located in the channels where erosive processes dominate.Postprint2,517