A candidate for the last interglacial record in northern Iceland: the Sydra formation. Stratigraphy and sedimentology

The Sydra Formation is a widespread interglacial complex in the North Volca nic Zone, Iceland, from the sector of the Askja volcano down to Oxarfjordur at the north coast. It probably corresponds to OIS 5e, 5d and 5c. Subseque ntly, the region was covered by the Weichselian ice cap. It is significant as well for the understanding of the OIS 6 deglaciation and its relations t o volcanism as also for the erosional budget of the Saalian, warm based and Weichselian, cold based, glaciations. A topographic bulge linked with a ra pid glacio-isostatic rebound, downstream of the Jokulsa a Fjolum river, is responsible for the development of the Sydra lacustrine deposits. An early abrupt event (Sy2), the Sydra ash probably corresponds to ash zone B as on the northern Iceland shelf and possibly an abrupt cooling. It presents no s imilarity with the Fossvogur formation in the Reykjavik district. The meani ng of the formation is significant in term of rift activity and of palaeocl imate for OIS 5. (C) 2001 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.