Mid- and late-Holocene vegetation, surface weathering and glaciation, Fjallsjökull, southeast Iceland

Abstract

A natural section at the southern margin of Fjallsjökull in southeastern Iceland provides evidence of a mid-Holocene land-surface that has been deformed by 'Little Ice Age' glaciation. Deformation is inter preted as compression around coarse gravel core and extension along deformable silts. Restoration of the original sedimentary units reveals a succession of lake sediments and fan gravels, with pollen and wood macro fossil remains preserved in the lake silts. Vegetational and palaeogeographical reconstruction indicates that small ponds existed at the site surrounded by a mosaic of birch woodland and grassland. Radiocarbon dates spanning a period from 4200 to 3750 BP indicate that the basins were infilled rapidly over a period of about 500 years by stream sedimentation. Colour changes in the upper part of the sediment sequence and relatively high frequency dependent magnetic susceptibility values on the clay fractions of the sediments indicate that iron minerals were mobilized and oxidized in response to the weathering processes that became established on the new land surface. The 'Little Ice Age' glaciation crossed the area at the end of the nineteenth century and the site was deglacierized in 1965. This is the first record of mid-Holocene vegetation from southeast Iceland and the identification of Plantago lanceolata type pollen from the organic silts is the first pre-Landnam record of this species. Formation of the basins in which the mid-Holocene lake sediments accumulated provides indirect evidence for mid-Holocene glaciation.