The Bolling-age Blomvag Beds, western Norway: implications for the Older Dryas glacial re-advance and the age of the deglaciation

Foreshore marine sediments, named the Blomvag Beds and now dated to the Bolling-Allerod from 14.8 to 13.3 cal. ka BP, contain the richest Lateglacial bone fauna in Norway, numerous mollusc shells, driftwood, and flint that some archaeologists consider as the oldest traces of humans in Norway. The main theme of this paper is that the Blomvag Beds are overlain by a compact diamicton, named the Ulvoy Diamicton, which was interpreted previously as a basal till deposited during a glacial re-advance into the ocean during the Older Dryas (c. 14 cal. ka BP). Sediment sections of the Blomvag Beds and the Ulvoy Diamicton were exposed in ditches in a cemetery that was constructed in 1941-42 and have subsequently not been accessible. A number of radiocarbon and cosmogenic 10Be exposure ages demonstrate that the diamicton is not likely to be a till because minimum deglaciation ages (14.8-14.5 cal. ka BP) from the vicinity pre-date the Ulvoy Diamicton. We now consider that sea ice and icebergs formed the Ulvoy Diamicton during the Younger Dryas. The Scandinavian Ice Sheet margin was located on the outermost coastal islands between at least c. 18.5 and 14.8 cal. ka BP; however, no ice-marginal deposits have been found offshore from this long period. The Older Dryas ice margin in this area was located slightly inside the Younger Dryas margin, whereas farther south it was located slightly beyond the Younger Dryas margin.