SEDIMENTARY FACIES AND ENVIRONMENTAL HISTORY OF THE LATE-GLACIAL GLACIOMARINE FOSSVOGUR SEDIMENTS IN REYKJAVIK, ICELAND

A detailed account of facies relationships in the Late-glacial Fossvog ur beds is presented for the first time. A new interpretation in terms of sedimentary processes has been synthesized in a palaeoenvironmenta l reconstruction that incorporates the results of a recently completed , systematic C-14 dating project for the Fossvogur beds. The present s edimentological analysis has revealed three marine fossiliferous facie s and several diamictite facies. The two uppermost marine facies are s eparated by a horizon of local deformation and erosion which is ascrib ed to increased activity at a tidewater glacier margin in Fossvogur. T he fact that marine fossiliferous sediments below and above this horiz on have been confined to the Allerod chron indicates a temporary expan sion of glaciers in the Reykjavik region towards the end of. but withi n, the Allerod. The relative sea level must have been at least 20 m hi gher than at present before the expansion, and it was probably even hi gher during and after the expansion. The total absence of facies indic ating either lodgement or melt-out processes, and the abundance of dia mictites interpreted as debris-flow deposits as well as frequent errat ics in the marine mudrocks favour an interpretation based on a glaciom arine model for the Allerod deposition in Fossvogur. It is suggested t hat the relatively quiet, submarine conditions indicated by facies tow ards the top of the Fossvogur beds display continued transgression and an increased distance to the source of sediment supply during the You nger Dryas.