Ferran Estrada

Catastrophic flood of the Mediterranean after the Messinian salinity crisis

The Mediterranean Sea became disconnected from the world’s oceans and mostly desiccated by evaporation about 5.6 million years ago during the Messinian salinity crisis. The Atlantic waters found a way through the present Gibraltar Strait and rapidly refilled the Mediterranean 5.33 million years ago in an event known as the Zanclean flood. The nature, abruptness and evolution of this flood remain poorly constrained. Borehole and seismic data show incisions over 250 m deep on both sides of the Gibraltar Strait that have previously been attributed to fluvial erosion during the desiccation. Here we show the continuity of this 200-km-long channel across the strait and explain its morphology as the result of erosion by the flooding waters, adopting an incision model validated in mountain rivers. This model in turn allows us to estimate the duration of the flood. Although the available data are limited, our findings suggest that the feedback between water flow and incision in the early stages of flooding imply discharges of about 108 m3 s-1 (three orders of magnitude larger than the present Amazon River) and incision rates above 0.4 m per day. Although the flood started at low water discharges that may have lasted for up to several thousand years, our results suggest that 90 per cent of the water was transferred in a short period ranging from a few months to two years. This extremely abrupt flood may have involved peak rates of sea level rise in the Mediterranean of more than ten metres per day.

Sediment drifts and deep-sea channel systems, Antarctic Peninsula Pacific Margin

Abstract Twelve sedimentary mounds are identified on the upper continental rise of the Pacific Margin of the Antarctic Peninsula. All these mounds are produced by a varying degree of interaction of along-slope bottom water flow with down-slope turbidity currents. These mounds provide a complete range of intermediates between two end members: the sediment drift and the channel levee. Surface sediments on drift 7 suggest that the mechanisms for the supply and transport of sediment include entrainment of material from turbidity currents within ambient bottom currents, and pelagic settling from the sea surface, including biogenic and glacially derived material. The long-lasting activity of these mechanisms is documented by the data provided by four DSDP and ODP drill sites. Bathymetric and seismic data, both at a large, comprehensive scale and at a small, detailed scale, show the geometry of the sedimentary mounds and their relationships with the adjacent turbidity current channel systems. These data allow the determination of some diagnostic criteria to identify the sediment drifts.

The Ceuta Drift, Alboran Sea, southwestern Mediterranean

Abstract The Ceuta Drift is an elongated-terrace feature (up to 100 km long, 28 km wide, 400 m relief, and 700 ms thick) located in the southwestern Alboran Sea, close to the Gibraltar Strait. It extends between 200 and 700 m water depth, parallel to the Moroccan slope. The drift stratigraphy is defined by the vertical stacking of at least five seismic units bounded by discontinuities: onlap and downlap surfaces at the bottom, and erosive surfaces at the top. Sedimentologically, the most recent deposits are defined by the vertical succesion, from bottom to top, of contouritic sandy muds, muds, and silty clays. The Ceuta Drift began to develop during the early Quaternary, when the pre-existing sea-floor morphology favoured the formation of an offshoot current system from the Mediterranean water masses. The action of this current together with sea-level changes have controlled the growth pattern of this drift.

The Magdalena Turbidite System (Caribbean Sea): present-day morphology and architecture model

Abstract A detailed analysis of the modern morphology, acoustic facies and architecture of the eastern Magdalena Turbidite System has been based on multibeam bathymetry and backscatter data. In spite of the fact that the Magdalena Turbidite System developed in a tectonically active setting, its present architecture model is comprised of two tecto-sedimentary provinces: deformed-constructional and undeformed-erosive. The deformed province occurs where the deformed prism developed. This prism is characterised by structural highs and associated small-scale ridges and scarps. In this province, the Magdalena Turbidite System is constructional because sediment coming from the Colombian hinterland (via the Magdalena River and from coastal erosion) and sediment remobilised from the walls of the structural highs are transported trough canyons and gullies, and emplaced as gravity deposits into the deformed prism. In the undeformed province, by contrast, the Magdalena Turbidite System displays an architecture model similar to a passive continental margin, and is characterised by large-scale mass-flow deposits, leveed channel complexes, scars of slumps, and sediment waves. This province is presently erosive because the existing leveed channels are partially or totally destroyed and cannibalised by mass-flow deposits, cut by small-scale scars of slumps, and their morphology is subdued or modified by the formation of a sediment wave field.

Origin, sedimentary processes and depositional evolution of the Agadir turbidite system, central eastern Atlantic

The Oligocene to Recent Agadir turbidite system occurs in the Agadir Basin, abutting against the continental margin off South Morocco (central eastern Atlantic). This system is part of the submarine drainage system linking back to the Anti- and High Atlas mountains through the Agadir Canyon, and its sedimentary evolution is shown to comprise lateral shifts of canyon, channel, overbank and lobe deposits, governed by local topography (draped palaeorelief, seamounts, and a contourite ridge) and channel avulsions. In addition, the turbidite system shows an overall retrogradational stacking (migrating about 60 km upslope). This probably reflects a decrease in gradient on the continental margin, gradual basin filling, and/or a progressive decrease in energy and load of the sediment gravity flows that fed the system. The latter change in sediment flux could result from the interplay between the progressive denudation of the source areas, together with the climatic change which led to the present arid/desertic conditions in the hinterland. The seismic features observed with new ultra-high resolution seismic tools allow the recognition of the present-day sedimentary activity within the Agadir turbidite system, and this is related, among other factors, to the active seismicity of the area.

New high-resolution acoustic data from the 'braided system' of the Orinoco deep-sea fan

Abstract The interpretation of approximately 100 km of EM12 multibeam bathymetry and backscatter data together with high resolution TOPAS profiles obtained during a transit over the Orinoco deep-sea fan, near the Barbados accretionary prism, shows that the braided drainage pattern seen on GLORIA images by Belderson et al. (1984) corresponds to wide (∼10 km), low relief (

Massive accumulation of highly polluted sedimentary deposits by river damming.

Uncontrolled dumping of anthropogenic waste in rivers regulated by dams has created contaminated deposits in reservoirs that have remained unidentified for decades. The Flix Reservoir is located in the Ebro River, the second largest river flowing into the NW Mediterranean, has been affected by residue dumping from a chlor-alkali electrochemical plant for decades. High-resolution seismic profiles, bathymetric data, surficial sediment samples and sediment cores were obtained in the Flix Reservoir to study the characteristics of the deposit accumulated by this dumping. These data were used to reconstruct the waste deposit history. Since the construction of the Flix Dam in 1948, more than 3.6×10(5) t of industrial waste has accumulated in the reservoir generating a delta-like deposit formed by three sediment lobes of fine-grained material highly contaminated by Hg, Cd, Zn and Cr (max: 640, 26, 420 and 750 mg kg(-1), respectively). This contamination was associated with the Hg that was used for the cathode in the electrochemical plant from 1949 and with the production of phosphorite derivatives from 1973. After the construction of two large dams only a few kilometres upstream during the 1960s, the solids discharged from the industrial complex became the main sediment source to the Flix Reservoir. The deposit has remained in the reservoir forming a delta that obstructs about 50% of the river water section. Its stability only depended on the flow retention by the Flix Dam. At present, this contaminated waste deposit is being removed from the water reservoir as it is a cause of concern for the environment and for human health downriver.

Physical and Geotechnical Properties and Assessment of Sediment Stability on the Continental Slope and Basin of the Bransfield Basin (Antarctica Peninsula)

Our investigation is centred on the continental slope of the Antarctic Peninsula and adjacent basin. Type of sediments, sedimentary stratigraphy, and physical and geotechnical characterization of the sediments have been integrated. Four different types of sediments have been defined: diamictons, silty and muddy turbidites, muddy, silty and muddy matrix embedded clast contourites. There is a close correspondence between the physical properties (density, magnetic susceptibility and p-wave velocity) and the texture and/or fabric as laminations and stratification. From a quantitative point of view, only a few statistical correlations between textural and physical properties have been found. Within the geotechnical properties, only water content is most influenced by texture. This slope, with a maximum gradient observed (20°), is stable, according to the stability under gravitational loading concepts, and the maximum stable slope that would range from 22° to 29°. Nevertheless, different instability features have been observed. Volcanic activity, bottom currents, glacial loading-unloading or earthquakes can be considered as potential mechanisms to induce instability in this area.

Quaternary Mass-Transport Deposits on the North-Eastern Alboran Seamounts (SW Mediterranean Sea)

The Quaternary stratigraphic architecture of seamounts and surrounding deposits in the eastern Alboran Sea reveals at least 53 stacked MTDs in the Pollux Bank, Sabinar Bank (Sabinar Platform and Western Sabinar), Maimonides Ridge, and Adra Ridge. These MTDs are grouped into two types based on their size: small-scale MTDs (length 5 km and thickness >18 ms). The study of these deposits has allowed us to define a close relationship between size (thickness-length) and source area gradients. The frequency of MTD events has varied between 40 and 373 kyr throughout the Quaternary (1.8 Ma to present). Correlation between individual MTDs is difficult but could be done for at least one local MTD event between Sabinar Platform and Western Sabinar (Sabinar Bank); in addition, one regional MTD event has been recognized around all of the studied seamounts. These failure events could have been triggered by tectonically controlled seismicity at both regional and local scale.

Quaternary tectonics influence on the Adra Continental slope morphology (Northern Alboran Sea)

Vazquez, J. T. ... et. al.-- Inciativa Iberica para el Estudio de las Fallas Activas, Segunda Reunion Iberica sobre Fallas Activas y PaleosismologiaI IBERFAULT 2014, 22-24 de octubre de 2014, Lorca, Espana.-- 4 pages, 4 figures, 1 table