Devonian miospores have been discovered in the previously poorly dated Old Red Sandstone volcanic sequence of Papa Stour. They occur at two sites in minor sedimentary deposits between the lavas, and fossil fish remains are also present. The age range of the miospores is mid Eifelian to early Givetian, probably more specifically late Eifelian and from a position close to the Achanarras horizon. This allows a correlation of the Papa Stour volcanic sequence with that of the Upper Stromness Flags of Orkney and not the tuffaceous horizons in the Eday Sandstones. The good preservation and composition of the miospores indicate a close similarity to other Orcadian Basin sediments and support the view that the Old Red Sandstone sequences W of the Melby Fault have affinities with the Orkney and Caithness successions rather than with Shetland. The age of the volcanic sequence also provides a valuable datum point for plate tectonic models based on the geochemistry of Old Red Sandstone lavas.
