A Submerged Late-Quaternary Deposit at Roddans Port on the North-East Coast of Ireland

Recent coastal erosion has cut into the filling of a former inter-drumlin lake and exposed an excellent sequence of Late-glacial deposits. These have been investigated by pollen analyses, identification of seeds, Mollusca, ostracods, and Algae; by stratigraphic studies and by radiocarbon dating. The coincidence of all this evidence strongly confirms that the greater part of the depositional sequence embraces the north-west European Late-glacial stages of the Older and Younger Dryas or Salix herbacea clays, with the intervening milder Allerod oscillation. This sequence is overlain by a small thickness of Post-glacial peat. The Late- and Post-glacial filling is shown to be sandwiched between deposits laid down during two phases of marine submergence; the earlier transgression is represented by a red marine clay which had a widespread occurrence on the Co. Down coast, and the later transgression is represented by the local development of the Post-glacial raised beach. The pollen analyses from the close sampling of the organic Allerd phase muds have yielded unusually detailed data on vegetational conditions in the Late-glacial period. The radiocarbon dates, while fully confirming the age attribution, have not enough precision to give a close measure of the duration of the Allerd phase. The pollen evidence on vegetation and climate is augmented and clarified by identifications of seeds, shells, ostracods and Algae. The ostracods confirm the marine character of the early red clay, and freshwater shells were found in the overlying Allerd mud. The algal species from the Late-glacial layers have been compared with recent algal floras from Ireland, and with those found in Late- and Inter-glacial sediments elsewhere. The most notable feature is the prominence of species representative of a base-rich habitat.