MID-HOLOCENE AND LATE-HOLOCENE VEGETATION, SURFACE WEATHERING AND GLACIATION, FJALLSJOKULL, SOUTHEAST ICELAND

A natural section at the southern margin of Fjallsjokull in southeaste rn Iceland provides evidence of a mid-Holocene land-surface that has b een deformed by 'Little Ice Age' glaciation. Deformation is interprete d as compression around coarse gravel core and extension along deforma ble silts. Restoration of the original sedimentary units reveals a suc cession of lake sediments and fan gravels, with pollen and wood macrof ossil remains preserved in the lake silts. Vegetational and palaeogeog raphical reconstruction indicates that small ponds existed at the site surrounded by a mosaic of birch woodland and grassland. Radiocarbon d ates spanning a period from 4200 to 3750 BP indicate that the basins w ere infilled rapidly over a period of about 500 years by stream sedime ntation. 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 be came established on the new land surface. The 'Little Ice Age' glaciat ion 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 v egetation from southeast Iceland and the identification of Plantago la nceolata type pollen from the organic silts is the first pre-Landnam r ecord of this species. Formation of the basins in which the mid-Holoce ne lake sediments accumulated provides indirect evidence for mid-Holoc ene glaciation.