Sr-Nd isotope signatures of surficial sediments from the Portuguese continental shelf

Abstract

This study focus on the Sr-Nd isotope signatures of detrital and carbonate fractions of seven samples from surficial sediments deposited in the Portuguese continental shelf. 87Sr/86Sr and 143Nd/144Nd isotope compositions of the lithic component are used to constrain potential endmember contributions and determine sediment provenance. The 87Sr/86Sr ratios measured in the acid leachates of the seven sediment samples (carbonate fraction) lie within the range 0.7088 – 0.7092, close to the value for modern seawater (0.7091 – 0.7092), suggesting a dominant biogenic origin for this component. In contrast, the Sr isotope signatures for acid-leached silicate residues (lithic fraction) from the same samples are widely variable (87Sr/86Sr = 0.7179 to 0.7346) reflecting the input of terrigenous particles from three distinct sources (northern Iberian Variscan crust, southern Iberian Variscan crust and North African aerosols). The narrow range of ƐNd(0) values displayed by these samples (-8.5 to -10.6) does not allow effective discrimination between the different endmembers.