Marcel-lí Farran

The Ebro continental shelf: Quaternary seismic stratigraphy and growth patterns

Abstract Single-channel seismic-reflection profiles on the Ebro shelf and upper slope between Cap Salou and the Columbretes Islands have been interpreted to outline the Quarternary shelf evolution in this deltaic area. Three types of unconformity surfaces can be differentiated in the seismic records, type 1 and 2 unconformities, and toplap surfaces. These surfaces are the stratigraphic expression of the difference between rate of eustatic sea-level fall and subsidence on the outer shelf: a type 1 unconformity forms if the rate of eustatic sea-level fall is the more rapid, a type 2 unconformity forms if subsidence is faster, and toplap forms if subsidence and eustatic sea-level fall are equal. Thirteen stratigraphic units can be differentiated on the basis of unconformities. Based on their relative location on the shelf, these units are subdivided into inner and outer units. The inner units occur on the inner and middle shelf and are characterized by an underlying transgressive surface, while the outer units extend onto the middle to outer shelf and upper slope and show unconformities at their bases. The inner units are interpreted to be stacked transgressive and highstand systems tracts bounded by a maximum flooding surface. The outer units correspond to shelf deltas and shelf margin deltas that prograded southward and seaward over an unconformity in relatively stable water depths when sea-level fall was compensated for by subsidence. The progradation of these units ends with an episode of generalized erosion of the shelf and canyon cutting across the new shelf edge. The growth pattern of the northern Ebro shelf is characterized by important hiatuses, condensed stratigraphic sections, and units which are older than those on the southern shelf. The depositional processes were mainly controlled by eustatic sea-level oscillations, subsidence and changes in sediment supply. The subsidence during the Late Pleistocene was sufficient to compensate for the sea-level falls and allow the development of shelf deltas and shelf-margin deltas on the middle and outer shelf during low sea-level stands.

Pleistocene progradational growth pattern of the northern Catalonia continental shelf (northwestern Mediterranean)

The Pleistocene sedimentary growth pattern of the northern Catalonia continental shelf is characterized by the vertical stacking of seaward downlapping regressive deposits. These deposits are characterized by a progradational development, with oblique clinoforms of low angle in the middle continental shelf, that become more inclined seaward in the outer continental shelf and shelfbreak. Eustatic sea level fluctuations controlled the development of this sedimentary pattern, whereas sediment supply conditioned the nonuniform progradation along the continental shelf and subsidence due to both sediment loading and tectonics controlled its preservation through and along the continental shelf.

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.

Late Pleistocene-Holocene sedimentary evolution of the northern Catalonia continental shelf (northwestern Mediterranean Sea)

Abstract The late Pleistocene-Holocene sedimentary evolution of the northern Catalonia continental shelf is interpreted as transgressive and highstand systems tracts, separated by an unconformity that seismically represents the coincidence between the ravinement surface and maximum flooding surface. During the transgressive stage, the shoreface erosion prevailed over sedimentation, leading to the development of palimpsest and relict facies. During the highstand stage, accumulation occurred only in areas with a steady supply of sediment, favouring the development of a depositional mound and the Fluvia-Muga and Ter prodeltas. Their distribution resulted from southward geostrophic current flow and the physiographic configuration 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 (

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.

Oligocene to Recent Processes on the Agadir Continental Margin and Basin (Central Eastern Atlantic)

The Atlantic continental margin off NW Africa connects with the Agadir Basin at 4275 m water depth (Fig. 1),The largest downslope feature in the Agadir continental margin and basin is the Agadir turbidite system (Oligocene to Recent in age) (Ercilla et al. 1998). This system is part of the submarine drainage system linking back to the Atlas mountains through the Agadir Canyon (400 km long) and Channel (75 km long) (Fig. 1). This work is based on the interpretation of high-resolution seismic records (airgun profiles) and ultra-high resolution seismic profiles (TOPAS, TOpographic PArametric Sonar). Open image in new window Fig. 1. Location map of the study area on the Agadir continental margin and basin showing the recent architectural elements of the Agadir turbidite system and also the seamounts, sediments waves and contourite deposits