The El Masnou Infralittoral sedimentary environment (Barcelona province, NW Mediterranean Sea): morphology and Holocene seismic stratigraphy

A detailed analysis of the morphology and the Holocene seismic and sequence stratigraphy and architecture of the infralittoral sedimentary environment of the El Masnou coast (Catalonia, NW Mediterranean Sea) was carried out using multibeam bathymetry and GeoPulse seismic data. This environment extends down to 26-30 m water depth, and is defined morphologically by two depositional wedges whose seafloor is affected by erosive furrows, slides, fields of large- and small-scale wavy bedforms, and dredging trenches and pits. Erosive terraces are also identified in the transition domain toward the inner continental shelf. The Holocene stratigraphy of the infralittoral environment is defined by two major seismic sequences (lower and upper), each one formed by internal seismic units. The sequences and units are characterised by downlapping surfaces made up of deposits formed by progradation of coastal lithosomes. The stratigraphy and stratal architecture, displaying a retrogradational arrangement with progradational patterns of minor order, were controlled by different sea-level positions. The stratigraphic division represents the coastal response to the last fourth-order transgressive and highstand conditions, modulated by small-scale sea-level oscillations (≈1-2 m) of fith to sixth order. This study also highlights the advantage of an integrated analysis using acoustic/seismic methods for practical assessment of the anthropogenic effects on infralittoral domains based on the association of marine geological observations

Glacial to Holocene climate changes in the SE Pacific. The Raraku Lake sedimentary record (Easter Island, 27ºS)

Easter Island (SE Pacific, 27ºS) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Climates in the mid- to lowlatitude region of the eastern South Pacific Ocean are controlled by fluctuations in the Westerlies winds, the South Pacific Convergence Zone and the South Pacific Anticyclone. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34000 years based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 to 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest in the watershed during the Glacial period and a cold and relatively humid climate. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major floods due to the erosion of littoral sediments. Deglaciation (Termination 1) between 17.3 and 12.5 cal kyr BP was characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels, dominance of organic deposition and algal lamination. The timing and duration of deglaciation events in Easter Island broadly agree with other mid- and low latitude circum South Pacific terrestrial records. The transition to the Holocene was characterized by lower lake levels. The lake level dropped during the early Holocene (ca. 9.5 cal kyr BP) and peatbog and shallow lake conditions dominated till mid Holocene, partially favored by the colmatation of the lacustrine basin. During the mid to late Holocene drought phases led to periods of persistent low water table, subaerial exposure and erosion, generating a sedimentary hiatus in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The human colonization of the island coincides with a new humid episode that started 800 yrs ago. The palm deforestation of the Easter Island, attributed to the human impact could have started earlier, during the 4.2 to 0.8 cal kyr BP sedimentary gap. Changes in land uses (farming, intensive cattle) during the last century had a large impact in the hydrology and limnology (eutrophication) of the lake

New discoveries of mud volcanoes on the Moroccan Atlantic continental margin (Gulf of Cádiz): morpho-structural characterization

10th International Conference on Gas in Marine Sediments, 6-11 September 2010, Listvyanka, RussiaDuring the MVSEIS-08 cruise of 2008, ten new mud volcanoes (MVs) were discovered on the offshore Moroccan continental margin (Gulf of Cádiz) at water depths between 750 and 1,600 m, using multibeam bathymetry, backscatter imagery, high-resolution seismic and gravity core data. Mud breccias were recovered in all cases, attesting to the nature of extrusion of these cones. The mud volcanoes are located in two fields: the MVSEIS, Moundforce, Pixie, Las Negras, Madrid, Guadix, Almanzor and El Cid MVs in the western Moroccan field, where mud volcanoes have long been suspected but to date not identified, and the Boabdil and Al Gacel MVs in the middle Moroccan field. Three main morphologies were observed: asymmetric, sub-circular and flat-topped cone-shaped types, this being the first report of asymmetric morphologies in the Gulf of Cádiz. Based on morpho-structural analysis, the features are interpreted to result from (1) repeated constructive (expulsion of fluid mud mixtures) and destructive (gravity-induced collapse and submarine landsliding) episodes and (2) interaction with bottom currentsDivisión de Geología Marina, Instituto Geológico y Minero de España, EspañaCentro Oceanográfico de Málaga, Instituto Español de Oceanografía, EspañaFacultad de Ciencias del Mar, Universidad de Cádiz, EspañaFacultad de Ciencias Geológicas, Universidad Complutense de Madrid, Españ

Identificación de riesgos geoambientales y su valoración en la zona de hundimiento del buque Prestige

Potential geological hazard assessment has been carried out in the area where the Prestige vessel was sunk using a broad database that comprises: multibeam, high and ultra-high resolution seismic profiles, gravity cores, onland seismicity stations and Ocean Bottom Seismometers (OBS). The main results of this study indicate that among the geologic factors that can be considered as potential hazards, four main categories can be differentiated based on their origin: morphologic, sedimentary, tectonic, and seismicity. Hazards of morphologic origin include steep gradients; the morphologic features suggest the occurrence of mass-wasting instabilities. Hazards of sedimentary origin also includes the occurrence of slope instability processes in form of single slides and a great variety of erosive and depositional gravity flows (debris and turbidity flows). Hazards of tectonic and seismic origin are important because the sinking area straddles the Calida Bank which is a structural seamount with a moderate tectonic activity that results in a latent seismicity of low to moderate magnitude. The interaction of these factors leads to consider to the risk as medium, and the degree of exposure of the bow and stern as high. Several general and specific recommendations are made in order to increase the geological and geophysics knowledgement in the Prestige sinking area and Spanish continental margins and deep sea areas. These recommendations also should be used to elaborate the options for reducing the hazard and loss

Caracterización sedimentológica de un 'debris flow' reciente en el margen continental del Ebro

Results from sedimentological and mass-physical properties of seven piston cores recovered on the youngest major landslide in the Ebro continental slope and base-of-slope, Northwestern Mediterranean Sea, are presented

Caracterización sedimentológica de un 'debris flow' reciente en el margen continental del Ebro

Results from sedimentological and mass-physical properties of seven piston cores recovered on the youngest major landslide in the Ebro continental slope and base-of-slope, Northwestern Mediterranean Sea, are presented

Tectonic activity evolution of the Scotia-Antarctic Plate boundary from mass transport deposit analysis

The spatial distribution and temporal occurrence of mass transport deposits (MTDs) in the sedimentary infill of basins and submerged banks near the Scotia-Antarctic plate boundary allowed us to decode the evolution of the tectonic activity of the relevant structures in the region from the Oligocene to present day. The 1020 MTDs identified in the available data set of multichannel seismic reflection profiles in the region are subdivided according to the geographic and chronological distributions of these features. Their spatial distribution reveals a preferential location along the eastern margins of the eastern basins. This reflects local deformation due to the evolution of the Scotia-Antarctic transcurrent plate boundary and the impact of oceanic spreading along the East Scotia Ridge (ESR). The vertical distribution of the MTDs in the sedimentary record evidences intensified regional tectonic deformation from the middle Miocene to Quaternary. Intensified deformation started at about 15 Ma, when the ESR progressively replaces the West Scotia Ridge (WSR) as the main oceanic spreading center in the Scotia Sea. Coevally with the WSR demise at about 6.5 Ma, increased spreading rates of the ESR and numerous MTDs were formed. The high frequency of MTDs during the Pliocene, mainly along the western basins, is also related to greater tectonic activity due to uplift of the Shackleton Fracture Zone by tectonic inversion and extinction of the Antarctic-Phoenix Ridge and involved changes at late Pliocene. The presence of MTDs in the southern Scotia Sea basins is a relevant indicator of the interplay between sedimentary instability and regional tectonics.Geophysical Department, Geological Survey of Denmark and Greenland, DinamarcaInstituto Geológico y Minero de España, EspañaDepartment of Earth Sciences, Royal Holloway University of London, Reino UnidoInstituto Andaluz de Ciencias de la Tierra, Universidad de Granada, EspañaInstituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, EspañaDepartamento de Geodinámica, Universidad de Granada, Españ

Structural and palaeoclimatic implications of submarine gullies on the Gulf of Cadiz upper slope from high and very high resolution seismic stratigraphic studies

Deep-Water Circulation Conference: Multidisciplinary Perspective (3º. 2017. Wuhan, China)The Gulf of Cadiz upper slope records the interplay between mass movement processes, mostly channelized flows along downslope-trending submarine gullies, and the action of bottom currents, in an area where paleoclimatic changes may have led to important variations of the oceanographic conditions, especially between glacial and interglacial periods. This work investigates the evolution of downslope-trending gullies in the upper slope of the Gulf of Cadiz, based on the analysis of high and very high resolution seismic record (Parasound and airgun profiles) and their correlation with regional stratigraphic interpretations. The gullies can be identified in the present-day seafloor as parallel downslope-trending features (10-15 km long, 1-1.5 km wide, up to 50 m deep). Their heads lie below the continental shelf-break and they terminate abruptly at the base of the upper slope, where they meet the Cadiz Contourite Channel along the middle slope. A seismic stratigraphic correlation allows identifying gully-like depressions in the seismic record from the Middle Pleistocene. Their high spatial and temporal variability can be related to the activity of the deep structures (particularly diapiric ridges) and in some cases to fluid escape processes that affect the region. The evolution of the gullies since the Mid Pleistocene can be established in order to infer the effect of climatic and structural changes that affect the circulation patters in the Gulf of Cadiz (i.e., changes in the trend, depth and velocity of the Mediterranean Outflow Water and other water masses such as the Eastern North Atlantic Central Water and the Superficial Atlantic Water but also changes affecting the interfases between water masses) from the variations in the sedimentation processes of the upper slopeInstituto Geológico y Minero de España, EspañaConsejo Superior de Investigaciones Científicas, EspañaPeer reviewe