Luminescence dating of Holocene geomorphic activity on Ammassalik Island, SE Greenland

Abstract

A geomorphological investigation of nival, aeolian and littoral landforms, based on sedimentological and stratigraphical analyses combined with eight optically stimulated luminescence (OSL) and two 14C accelerator mass spectrometry (AMS) dates, are presented from the Mittivakkat area, western Ammassalik Island, SE Greenland. As the sediments are liable to annual freezing, the modern average annual water content has been modelled, and used in the calculation of the luminescence ages. The OSL technique gaves ages as young as 500 years, and is considered useful for dating the relatively young sediments of this arctic environment. By combining the results of the investigations of the individual landforms, a first attempt towards a reconstruction of the geoenvironment, primarily during the Late Holocene becomes possible. Enhanced geomorphological activity during the Little Ice Age is evidenced by increased snowdrift and aeolian activity from about 900 years ago. The prevalent wind direction has been from N and NE since at least about 2800±300 years ago, as nivation activity has taken place at least since then, and avalanche slopes have been active since about 3900±560 years ago. Sediments in the Mittivakkat Delta have been deposited at least since 1300±400 years ago, indicating sea level to have been close to the present level by that time. An aeolian sand sheet started to accumulate around 500±40 years ago on the beach south of the Mittivakkat Delta, providing further evidence for a sea level close to the present. Two dates for sediment from raised littoral terraces at 10 and 40 m asl. clearly postdate general sea level activity at these levels. Average Late Holocene terrestrial sedimentation rates from 0.06 to 1.69 mm y -1 have been determined for the different landforms.