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 Volcanic 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. Subsequently, 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 to volcanism as also for the erosional budget of the Saalian, warm based and Weichselian, cold based, glaciations. A topographic bulge linked with a rapid 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 similarity with the Fossvogur formation in the Reykjavik district. The meaning of the formation is significant in term of rift activity and of palaeoclimate for OIS 5.