Trace element distribution in Neoproterozoic carbonates as palaeoenvironmental indicator

A first study of REE + Y distribution in a variety of Neoproterozoic (Cryogenian and Ediacaran) carbonates from different settings in the Saldania, Gariep, Damara and West Congo Belts in southwestern and central Africa revealed systematic differences that can be explained by varying palaeoenvironmental factors. The majority of samples display relatively unfractionated, flat shale-normalised REE + Y patterns that cannot be ascribed solely to shale contamination but are interpreted as resulting from the incorporation of near-shore colloids, possibly related to Fe-oxihydroxide scavenging. Only few carbonate units yielded trace element distributions that conform to a typical seawater composition. Those carbonates that were affected by stratiform, syn-sedimentary hydrothermal mineralisation are distinguished by Eu anomalies. Considering the similarity in residence time between REE and carbon, the strong influence of river-born particles on the REE + Y distribution in the analysed carbonates casts considerable doubt over the usefulness of these carbonates for stratigraphic correlation of Neoproterozoic sediment successions based on carbon isotopes.