Structure of recent sedimentary units in the Galician continental shelf

[Resumen] Los 'perfiles·· de sísmica de reflexión de alta resolución en la plataforma continental gallega nos permiten conocer la estratigrafía de los sedimentos holocenos. De techo a muro se distinguen: - Un nivel superior de limos holocenos marinos con interestratificaciones de arena. - Un reflector basal que aflora hacia~·ra zona Inedia y externa de la plataforma continental y formado por varias superficies erosionales debidas a lo reducido de los aportes sedimentarios en ese punto. - Un basamento acústico de naturaleza ígnea y metamórfica con una fuerte respuesta sísmica. La plataforma se caracteriza por el desarrollo de dos cuerpos de arena limosa que se extiende hacia mar abierto desde la zona interior de plataforma hacia el sur y una superficie de progradaci6n en la zona externa de la plataforma. El mapa de isopacas demuestra que los sedimentos marinos holocenos forman ... generalmente un lecho contínuo que alcanza su máximo espesor delante de las rías.[Abstract] High-resolution seismic reflection profiles of Galician Continental Shelf show the shallow seismic stratigraphy of Holocene sediments. Three acoustic units can be distinguished from top bottom: - a continuous upper layer of Holocene marine muds with interstratifications of sand. - a basal reflector which outcrops towards the middle and outer continental shelf, forming several erosional surfaces due to reduced sediment supply. - an acoustic basement, of igneous and metarnorphic nature; with strong seismic response. The shelf is characterized by the development of two bodies of sandy mud that extends offshore from the inner shelf toward the south and a progradation surface on the outer shelf. The isopac map shows that the Holocene marine sediments generally form a continuous layer that reachs a maximum thickness in front of the «rias»

Enhanced Parallel Generation of Tree Structures for the Recognition of 3D Images

Segmentations of a digital object based on a connectivity criterion at n-xel or sub-n-xel level are useful tools in image topological analysis and recognition. Working with cell complex analogous of digital objects, an example of this kind of segmentation is that obtained from the combinatorial representation so called Homological Spanning Forest (HSF, for short) which, informally, classifies the cells of the complex as belonging to regions containing the maximal number of cells sharing the same homological (algebraic homology with coefficient in a field) information. We design here a parallel method for computing a HSF (using homology with coefficients in Z/2Z) of a 3D digital object. If this object is included in a 3D image of m1 × m2 × m3 voxels, its theoretical time complexity order is near O(log(m1 + m2 + m3)), under the assumption that a processing element is available for each voxel. A prototype implementation validating our results has been written and several synthetic, random and medical tridimensional images have been used for testing. The experiments allow us to assert that the number of iterations in which the homological information is found varies only to a small extent from the theoretical computational time.Ministerio de Economía y Competitividad MTM2016-81030-

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

Relationship between the offlap-break location of Holocene prograding wedges on wave climate in southeastern Iberian Peninsula

Wave climate exerts a significant influence on the development of Holocene sedimentary prograding wedges. This is demonstrated by the fact that near-bed orbital velocities between 0.10 and 0.14 m/s (threshold for resuspension) occur in the vicinity of the infralittoral prograding wedges (IPW) offlap-breaks during storm-weather conditions, but during medium wave energy conditions in the case of prodeltaic wedges

Submarine deltaic geometries linked to steep, mountainous drainage basins in the northern shelf of the Alboran Sea: Filling the gaps in the spectrum of deltaic deposition

A comprehensive analysis of small deltaic environments linked to short, mountainous, and seasonal fluvial systems in the northern shelf of the Alboran Sea was undertaken in order to define the controlling parameters of the geomorphological variability. The database includes multibeam and backscatter imagery, surficial sediment samples, and high-resolution seismic profiles. Additionally, geomorphological and hydrodynamic modeling and statistical analysis (principal component and cluster analysis) of hydrological and physiographic variables were performed.Most of the studied deltaic systems have high-gradient, coarse-grained deposits with preferential development of the submarine portions to the detriment of the deltaic plains. The geomorphological analysis identified three basic types of plan-viewdistributions according to the length-to-width ratios: elongate, linguoid and lobate. Cross-slope profiles evidence dominant concave-upward geometries, fewer occurrences of planar geometries, and no sigmoid profiles. Sediment depocenters are extremely thick in proximal locations, but thin out rapidly seawards. The geometric distribution patterns of the deltaic systems are characterized by a predictable pattern in plan-view according to the type of fluvial system, ranging from a relatively large river to ephemeral creeks. Prevailing concave and secondary planar profiles support strong sediment progradation in the submarine realmand lowsediment retention in the emerged deltaic environment. Two different types of systems are distinguished: (1) larger rivers,where deltaic deposition is largely controlled by basin dimensions, ultimately dictating themagnitude of water and sediment discharges; and (2) smaller rivers and creeks,where deltaic geometries are related to the basin slopes. The influence of hydrodynamic variables on defining the submarine deltaic geometry has been observed in the case of concave-upward geometries, where geomorphological boundaries are defined by medium- and high-energy wave conditions.Versión del editor2,520

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

Seabed morphology and bottom water masses related to benthic habitats at the Cristóbal Colón diapir (NW of the Guadalquivir ridge, Gulf of Cádiz)

The seabed morphology and the sub-superficial characteristics of the Cristóbal Colón diapir located on the continental slope of the Gulf of Cadiz have been analysed from data obtained in the framework of the LIFE+INDEMARES/CHICA project. The aim of this study is to recognize the morphological features and the geological processes generated by the bottom water masses and their influence on the habitats and associated benthic communities. The NACW affects the generation of morphological features on the summit, revealing that different oceanographic conditions favoured the carbonate mound growth in the past. The interface between the NACW and the MOW sweeps the bottom from the SE to the NW and the presence of benthic communities dominated by filter feeders on the contouritic drift indicates that this current is strong enough to favour the availability of nutrients and organic particles and to develop both the contouritic deposits on the SE flank and the moats on the N and W flanks.Versión del edito

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

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

Versión de edito