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 sedimen t: the clay-size fraction (<2 mu m), the fine cohesive silts (2-10 mu m) an d the coarse silts (10-63 mu m) In most cases, Sm-Nd signatures are differe nt from one grain-size to another. In addition, different Sm-Nd signatures are derived from the clay-size fractions compared to the cohesive silt frac tion, indicating that the cohesive fraction is heterogeneous and that disti nct 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 mu m) 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. (C) 2000 Elsevier Science B. V. All rights reserved.