M. Druet

Bedforms in the Southern Submarine Canyons of the Balearic Islands (Western Mediterranean) Interpreted as Cyclic Steps

Multibeam bathymetric data collected along the Menorca Channel (Balearic Islands) for a depth range of 70–850 m revealed the occurrence of bedforms along some of the submarine canyons of the Balearic southern slope. The four main canyons presented in this study display a linear to sinuous geometry, incising the slope for up to 170 m and carving the shelf-edge at a depth of 110 m. Bedforms along these canyons are more developed along the two northernmost canyons, particularly within the 300–700 m depth range. The crescentic shape of the bedforms and their wavelengths of between 120 and 210 m resemble the morphology of bedforms found in other submarine channels and canyons. In line with these previously observed bedforms, we here explore the possibility that the bedforms in the canyons could be interpreted as cyclic steps formed by supercritical turbidity currents. Assuming this interpretation holds, then some simple modelling would allow us to give rough estimates of velocity and thickness of the flows that formed the cyclic steps.

Sedimentary Bedforms in the Menorca Channel Region, Balearic Islands (Western Mediterranean)

A variety of sedimentary bedforms have been identified on the continental shelf between Mallorca and Menorca (Menorca Channel). The bedforms consist of different grain sizes, ranging from very fine to coarse, predominantly bioclastic sands, and include rippled scour depressions in association with fine sand patches, sand waves, sand ridges, ribbons and furrows. The morphology and acoustic appearance of these bedforms are documented in a number of maps generated on the basis of detailed multibeam bathymetric datasets, side-scan sonar images and high-resolution reflection seismic profiles (TOPAS).

New Survey Explores the Northern Hispaniola Offshore Margin

The highly oblique convergence between the North American and Caribbean plates has yielded that the thickened crust of Bahamas banks impinges into northern Hispaniola developing a narrow band of compressive deformation (northern Hispaniola margin) and a thick foreland basin (Hispaniola-Caicos basin). Approximately 280 km of 2D MCS profiles and 17000 km2 of high-resolution, systematic swath bathymetry data were recorded in the northern Hispaniola offshore margin in November-December of 2013 (NORCARIBE cruise). This is the first time that this region is explored systematically with high-resolution multibeam bathymetry. Using new multibeam bathymetry and MCS data, combined we have studied the along- and across-strike variations of the shallower structure along a 330 km-long segment of the northern Hispaniola margin. Pronounced along-strike changes in structural style observed in the northern Hispaniola margin and Hispaniola-Caicos basin are associated with the active oblique underthrusting/indentation of the irregular boundary of the southernmost slope of the Mouchouir and Silver banks. The upper slope of the northern Hispaniola margin exhibits good economic potential associated to thick slope basins and terraces where is observable a continuous and prominent BSR. Preliminary results provide well- defined targets to carry out future exploration studies.

Submarine Mass Movements Along a Sediment Starved Margin: The Menorca Channel (Balearic Islands – Western Mediterranean)

Sediment starved passive margins, particularly those of insular slopes, display significant mass transport activity despite the absence of environmental stresses from high sedimentation rates. The “Menorca Channel” represents the up to 120 m deep shelf sector connecting the Menorca and Mallorca Islands (Balearic Islands – Western Mediterranean). South of the Menorca Channel submarine gravitational processes have been mapped and interpreted from swath-bathymetry, TOPAS parametric echosounder and deep-towed videos. The shelf-break is located at an average depth of 140 m, and sediment instability is a widespread phenomenon. The slope region south the Menorca Channel shows a number of submarine canyons disrupting the outer shelf. The north-easternmost canyon is the more active feature, with an incised axis and scars shaping the flanks up to their edges. Headwall scarps, between 140 and 700 m depth, are up to 20 m high. The shallower scarps producing slab-type failures have carved the outer edges of planar sedimentary bodies interpreted as formed in shallow environments during previous glacial stages. Results show that a variety of sediment instability processes extensively shape the southern upper slope of the Menorca Channel. Submarine canyons develop on the Emile Bodout Escarpment (EBE), a passive tectonic feature which bounds the slope region of the study area. A number of knickpoints within the canyons suggest backward erosion control on mass wasting and, at the same time, that slope failure is one of the main drivers for canyon upslope migration. Steep gradients of the upper slope, the presence of weak layers and the action of major storms during lowstand stages are additional factors likely to influence the distribution and frequency of mass wasting processes in this area.