Sm-Nd isotope systematics in deep-sea sediments: clay-size versus coarser fractions

Sm-Nd studies were carried out on Last Glacial and Holocene sediments from the Labrador Sea. Three grain-size fractions were analyzed for each sediment: the clay-size fraction (<2 μm), the fine cohesive silts (2-10 μm) and the coarse silts (10-63 μm). In most cases, Sm-Nd signatures are different from one grain-size to another. In addition, different Sm-Nd signatures are derived from the clay-size fractions compared to the cohesive silt fraction, indicating that the cohesive fraction is heterogeneous and that distinct origins in terms of source-areas are implied. Silt fractions record the influence of supplies from the North American Precambrian Shield, whereas clay-size fractions (<2 μm) are more sensitive to sedimentary input from the Eastern Basins, in relation with deep currents. Coupling Sm-Nd studies on silt and clay fractions may be a powerful tool to unravel the evolution of deep circulations versus detrital supplies.