A Revised Model of Weichselian Deglaciation in South and South West Iceland

Abstract

New investigations and radiocarbon dating are changing the traditional Quaternary chronology of Iceland. The Búði end moraines of southern Iceland have hitherto been regarded as the type site for the Younger Dryas glaciation. Recent radiocarbon dates now indicate that these moraines are of Preboreal age, around 9,700 B.P. Sediments from the Alleröd Interstadial have not been found in southern Iceland. This is believed to indicate a total glacial coverage of the Southern Lowlands of Iceland during the Younger Dryas stadial. The Reykjavík area is a classic locality in Icelandic geology. The shell-bearing Fossvogur sedimentary layers have long been considered to be of Interglacial age dating from the beginning of the Eemian Interglacial stage, i.e. about 120,000 years old. New radiocarbon age determinations have shown them to date back only to about 11,000 B.P. The former type locality for the Eemian Interglacial, the Fossvogur layers, now seems to be of Late Weichselian age. Consequently the till in the upper part of the Fossvogur sediments must be considered to be of Younger Dryas or Preboreal age. This till is connected to a series of end moraines, one of which is the so-called Älftanes ridge. This ridge has previously been accepted as the type locality of the Older Dryas stadial in Iceland, but must also now be considered to be of Younger Dryas or Preboreal age.

These conclusions indicate a much more extensive glaciation in Late Weichselian and Preboreal times than was previously assumed. The Younger Dryas glacier covered the whole of the Reykjavík area reaching far offshore into Faxaflói bay. Similar results can be seen by plotting radiocarbon dates from Late Weichselian and Preboreal marine shells from Iceland on a time-diagram. The dates show a rather even distribution except for a gap between 10,200–10,700 B.P. which is explained by a period of heavy glaciation during which glaciers mostly prevented deposition of marine sediments inside the present coastlines of the country. The new radiocarbon dates lead to a revision of the traditional Quaternary nomenclature of Iceland. The names Fossvogur Interglacial as a synonym for the Eemian Interglacial, the Álftanes Stadial for the Older Dryas, and Búði Stadial for the Younger Dryas cannot now be used.