Unusual biota and palynofacies of a Lower Devonian intermontane basin saline lake–playa mudflat ecosystem

The Strathpeffer–Struie Lower Devonian LORS (Lower Old Red Sandstone) deposits of the Northern Highlands of Scotland contain the decidedly unusual ‘foetid beds’. These are interpreted as being deposited in a highly saline sulphate lake and associated playa mudflat, which developed in an intermontane basin in the Caledonian Mountains of Laurussia. Palynological analysis was undertaken to investigate the biota and environments of deposition of these deposits. The sediments of the saline lake and associated playa mudflat reveal highly unusual palynofacies dominated by cyanobacterial, fungal and algal remains. Presumably the high salinity lacustrine conditions excluded grazing invertebrates and fish, enabling microbial mats and stromatolites to flourish, as is the case in modern high-altitude highly saline sulphate lakes. Dispersed spore assemblages recovered from the sequence are equated to the D–E Spore Assemblage Biozone/AP Oppel Zone (Pro Interval Zone) and suggest a latest Emsian age. The spore assemblages are depauperate compared with those from coeval lowland deposits from Laurussia, suggesting that the vegetation represents a restricted, partially endemic, upland flora. In the palynological samples, rare examples of the terrestrial fauna of the basin are represented by dispersed arthropod cuticle, including the earliest example of a scorpion pectinal tooth with peg sensilla.