REE and Nd Isotope Stratigraphy of a Late Jurassic Carbonate Platform, Eastern Paris Basin, France

Abstract

Abstract Rare earth elements (REE) and Nd isotopes on the labile fraction of the Callovian–Oxfordian to Tithonian Jurassic carbonate platform of the eastern Paris Basin were used to reconstruct the composition of the contemporaneous waters from which the labile fraction may have originated. This sedimentary record shows a remarkable change in the manganese content between the clayey deposits at the top and bottom of the succession and the carbonate-platform deposits. The combined analyses of REE and Nd isotope ratios record the influence of emerged land and the Tethys Ocean. The REE patterns are similar to those of seawater in the middle part of the sedimentary record, suggesting REE removal by marine carbonate, while bell-shaped REE patterns are observed above and below, reflecting continent-derived REE carried by Fe–Mn coatings on detrital particles. Therefore, the REE patterns and their evolution through the sedimentary record highlight the roles played in the REE budget by Fe–Mn coatings on detrital particles and by marine carbonates. The predominant sources of Nd during platform evolution are characterized by the Nd isotope variations in the sediments; the nonradiogenic values (eNd(t) between −12 and −10) strongly suggest that the predominant source of Nd on the platform was the continental crust through weathering and river inputs, whereas some more radiogenic Nd (eNd(t) = −5) values are more typical of the Tethys seawater signature.