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Communication Dans Un Congrès Année : 2017

Global and local forcings on sediment distribution of the SW Gulf of Lions (NW Mediterranean)

Résumé

The SW termination of the Gulf of Lions (GoL) is characterized by a narrowing shelf (from 80 km in the central part to ca. 20 km at the French/Spanish border), increased hydrodynamic processes and lowered sediment supply. It has been the target of a relatively large number of high-resolution seismic and acoustic investigations, as well as grab sampling, but few long cores are presently available because relatively low sedimentation rates (compared to the central GoL) did not attract the interest for paleo-environmental studies. In preparation of a map of surficial sediments in this area, a compilation of available data was undergone. In dip section, beyond the littoral prism, 4 distinct morpho-sedimentary units are at the origin of submarine landscapes. From W to E, they include: (1) between -20 and -60 m, a (2) between 60 and -75 m, a relict, 2 to 5 m-thick mud wedge, highly eroded, that can be assigned to the Younger Dryas by analogy with similar, thicker features described and well-dated further to the east; (3) between ca. -75 m and -100 m, a set of stacked thickening seaward forced-regressed Systems Tracts linked to 100 ky and 40 ky glacio-eustatic cycles. They consist of over-consolidated muds from paleo-prodeltas and lower shorefaces, and to sand bodies reworked into large dunes, drapped by a veneer of recent muds. These sands are locally cemented and form elongated reliefs at the position of paleo-shorelines (beachrocks). A characteristic of unit 3 in that part of the GoL is that, because of important reworking by hydrodynamic processes, sequences assigned to Marine Isotope Stages (MIS) 6.2, 6.4 and 7.6 are outcropping at some places, in contrast with the central GoL where they are buried underneath a 20-50 m interval of MIS 3-MIS 2 sediments. (4) between ca. -100 m and the shelf edge (that ranges between -110 and -170 m depending on the distance from canyon heads), normally consolidated offshore muds forming a wedge up to 150 m where accommodation is sufficient (infilled canyon heads). In summary, the distribution of surficial sediments in the GoL is, in general, largely controlled by the history of sea-level changes and the position of point sources. More specifically, the western termination of the GoL exemplifies the major role of hydrodynamic processes in modifying the position and water depth of boundaries between different sedimentary units and sequences.
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Dates et versions

hal-01929207 , version 1 (21-11-2018)

Identifiants

  • HAL Id : hal-01929207 , version 1

Citer

Elise Grenard-Grand, Serge S. Berné, Grégory Agin, Yoann Alonso, Maria-Angela Bassetti, et al.. Global and local forcings on sediment distribution of the SW Gulf of Lions (NW Mediterranean). International Meeting of Sedimentology, Oct 2017, Toulouse, France. ⟨hal-01929207⟩
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