REVISION OF THE EARLY HOLOCENE LAKE SEDIMENT BASED CHRONOLOGY AND EVENT STRATIGRAPHY ON HOCHSTETTER FORLAND, NE GREENLAND

The previously established and often debated lake sediment based chron ology and event stratigraphy from Hochstetter Forland, NE Greenland, h as been re-examined. These new studies show that the last deglaciation of the coastal area is several thousand years younger than previously described. The main reason behind the difference is the fact that the older chronology was based on C-14 datings of bulk sediment samples, which are now shown to contain enough coal fragments to produce errone ous ages. The re-examination was performed on sediments from two lakes located within the Nanok moraine system: one is situated at or slight ly above the marine limit around 65 m, the other at 21-22 m a.s.l. The combined stratigraphy from the two lakes shows that the area was degl aciated before 9000 BP, after which followed deposition of glaciomarin e sediments, fining upwards. The first vegetation seems to have been d ominated by grasses, Lycopodium and Polypodiaceae. At c. 8000 BP the l imnic production increased significantly and a pioneer vegetation char acterized the area. At this time the 'Artemisia' grains appear. A shor t but distinct climatic cooling occurs at c. 7500 BP causing a signifi cant drop in lake productivity and possibly also producing coarser sed iments in the (glacio)marine environment. About 200 years later the la ke productivity again increased, very rapidly, and the marine sediment s became finer and more rich in molluscs, as a response to the beginni ng of the climatic optimum. Because of the time-lag between climate an d vegetation response it took another 300 years before Betula nana imm igrated, at the same time as the 'Artemisia' grains disappeared, and a nother several hundred years before a real dwarf-shrub vegetation deve loped in these parts of Hochstetter Forland. Before the lower lake was isolated from the sea at c. 6000 BP, coarse wave-washed sediments, fo llowed by a typical isolation sequence, were deposited in it.