The Djibouti Drift is an elongated separated contourite drift located at the southwestern foot of the Djibouti Ville Seamount just at the outer edge of the Motril Marginal Plateau (northern Alboran Sea). The core Sagas K-3 (up to 4.60 m) was recovered at 713 m water depth from the drift deposits formed by the interaction of intermediate and deep Mediterranean water masses with the seafloor. The objective of this work is to study the sediment dynamics of these drift deposits and infer changes in bottom current intensities and fluctuations in water mass depths which could be related to climate changes in the SW Mediterranean Sea. Sedimentological and geochemical data have been used for this study. Grain-size analysis was measured for the total and carbonate-free fraction. The median (MD), sortable silt (SS, 10-63 μm) and silt/clay ratios (S/C) of the carbonate-free fraction were used as proxies for bottom current variability. Major elements were determined by X-ray fluorescence analysis (XRF). Selected element (Ca, Fe, Ti) and Si/Si+Al, Zr/Al ratios have been used as proxies for detrital input fluctuations whereas Ca/Ca+Fe, Br/Al, and S/Al ratios are used to infer changes in marine productivity. The stratigraphy for the Sagas K3 core is based on: i) two radiocarbon dates in the upper section of the core (10.9 ka at 22.5 cm and 29.8 ka at 87.5 cm), and ii) the correlation of the down-core Ca intensity curve with the stacked SPECMAP isotope curve. We are currently performing stable oxygen isotope analyses on Sagas K3 to infer alternating warm and cool periods in the Alboran Sea. According to this preliminary age model, the core could span the last 300 ka back to end of glacial MIS 8, which shows low sedimentation rates for this core (1.5 cm/1000 yr in average). However, this result is supported by the low sedimentation rates calculated between the two C-14 dated samples (3.4 cm/1000 yr) and those calculated on the basis of the last 450 ka (MIS 12) (2 cm/1000 yr) from the chronostratigraphy of high resolution seismic profiles from the Motril Marginal Plateau. This low sedimentation rate differs from the values recorded in previous work on the Alboran Sea. This can probably be attributed to the specific morpho-structural setting of the Sagas K-3 core, the outer edge of the Motril Marginal Plateau which is an isolated area far from fluvial sediment sources, and related to a seamount. The grain size records of the bulk fraction reveal that the drift deposits are essentially poorly sorted muds (3.5-5 μm MD) and poorly and moderated sorted clayey-silts (7-10.5 μm MD). The down-core trend in MD of the free-carbonate fraction displays up to 10 peaks (7-10.5 μm) which correlate with the higher values of SS and S/C. These peaks are related to faster flows and probably better-oxygenated deep waters as reflected by increasing values of marine productivity proxies. Thus, geochemical proxies show similar down-core trends of the grain-size parameters to concomitant high values of MD, SS and silt/clay ratio as well as high values of Ca/Ca+Fe, Si/Si+Al, Zr/Al. [...]

30th IAS Meeting of Sedimentology, 2-5 September 2013, Manchester.

Peer reviewed