Nd isotope composition and rare earth element distribution in early Paleozoic biogenic apatite from Baltoscandia: A signature of Iapetus ocean water

Analyses of the Nd isotopic composition and REE distribution in biogenic ap atite (organophosphatic brachiopods and conodont elements) from the Cambria n and Ordovician sequences of the Baltic plate give new insights into the d evelopment of the southeastern segment of the continental margin bounding t he Iapetus ocean. The Nd isotope analyses show epsilon(Nd(t)) of similar to -8.0 for the Cambrian, indicating that the main source of the sedimentary d eposition came from weathered sedimentary rocks of Vendian and Cambrian age . The increase of epsilon(Nd(t)) to similar to-5.0 for the Early Ordovician indicates the appearance of a new source of radiogenic Nd in the surroundi ng area-most likely a volcanic are along the western borderland of Baltic p late from Arenigian time. Samples of Cambrian biogenic apatite show signifi cantly lower total amounts of REE than do the Ordovician samples, and this is probably due to a shorter exposure to seawater before burial during Ordo vician sedimentary accumulation in Baltoscandia. These preliminary results suggest that biogenic apatite from the Baltoscandian basin preserves geoche mical signatures of the water masses that will be important for understandi ng the evolution of the Iapetus ocean during the early Paleozoic.