Rare earth element geochemistry of upper Ordovician cherts from the Southern Uplands of Scotland

Caradoc and Ashgill radiolarian cherts and siliceous mudstones from the Southern Uplands preserve primary rare earth element (REE) signatures which are comparable to those of more recent deposits from continental margin settings. This is incompatible with the widely held view of these rocks as open ocean deposits incorporated in an accretionary prism and reinforces the model of deposition on an extensional continental margin. The REE signatures can be used as fingerprints to differentiate between some of the fault-bounded formations within the area. They indicate the provenance of the mud grade siliciclastic material in these distal hemipelagites and are comparable with published REE data on grey wackes in the same successions. This detailed analysis of the REE patterns in Lower Palaeozoic cherts demonstrates the usefulness of this approach in ancient orogens.