QUATERNARY RESEARCH 45, 245–253 (1996) ARTICLE NO. 0025 Implications for Deglaciation Chronology from New AMS Age Determinations in Central West Greenland FRANK G. M. VAN TATENHOVE 1 AND JAAP J. M. VAN DER MEER Department of Physical Geography and Soil Science, University of Amsterdam, The Netherlands Centre of Geo-Ecological Research (ICG), Nieuwe Prinsengracht 130, 1018 VZ Amsterdam, The Netherlands AND EDUARD A. KOSTER Department of Physical Geography, Utrecht University, ICG, P.O. Box 80115, 3508 TC Utrecht, The Netherlands Received May 8, 1995 der years. The latter is essential to synchronize geological New evidence has been obtained for the age of the time, ice sheet models, and new high-resolution paleocli- Umı P vı P t/Keglen and Ørkendalen moraine systems close to the pres- matic records from ice cores. The main objective of this ent ice sheet margin in central West Greenland. The study is to provide data on the deglaciation history of West Umı P vı P t/Keglen moraine system is dated at 7500 to 6500 14 C yr Greenland from radiocarbon-dated ice-marginal deposits. B.P., which is older than the previously assumed date of 7300 to Dates presented refer to core samples recovered from 6000 14 C yr B.P. The Ørkendalen system is now dated at 6200 to lakes using a slightly modified Livingstone system (UtC- 5600 14 C yr B.P. against earlier estimates of 300 to 700 14 C yr B.P. 1987 and UtC-1990) and to samples from permanently fro- The new age is based on AMS radiocarbon-dated organic material zen peat/silt deposits between moraines retrieved using a within depressions between morainic ridges belonging to the motor-driven CRREL-auger (sample UtC-2034 and UtC- Ørkendalen system. A major implication of the new age is that 2035). All other UtC-numbers mentioned in the text were ice margin positions prevailed for about 6000 years behind the present ice sheet margin. The retreat behind the present margin sampled from natural exposures. could be substantial, and in the light of deglaciation rates priorto the Ørkendalen phase, may be ca. 10’s of kilometers rather than NEW DATA kilometers. Circumstantial evidence is found forthe retreat of the ice sheet margin behind its present position during the Holocene During deglaciation in West Greenland, deposition of mo- climatic optimum. The results, placed into a time frame of deglaci- raines was fairly continuous (Fig. 2, Van Tatenhove, 1995). ation since the last glacial maximum, enable comparison with Nevertheless, clusters of moraines have been assigned names Greenland ice sheet models and ice core records.  1996 University of by Ten Brink (1975). The spatial positions of some of these Washington clusters are sometimes difficult to separate. This especially concerns the Umı P vı P t and Keglen moraine systems. Because of the short spatial distance between the Umı P vı P t and Keglen INTRODUCTION moraines, the two separate systems defined by Ten Brink (1975) are taken together in this study (Fig. 1). Although the glacial geology of the terrestrial ice-free Umı P vı P t/Keglen Moraine System area of central West Greenland has been intensively studied, several questions remained unanswered. This paper provides The Umı P vı P t/Keglen system is located near Kangerlussuaq new evidence on the age of extensive moraine deposits close (Søndre Strømfjord) harbor, Camp Lloyd (Ten Brink, 1975). to the present ice sheet margin. It also addresses the problem The age of 7300 14 C yr B.P. marks the construction of the of the position of the ice margin at the culmination of the moraines within the Umı P vı P t part of the system (Ten Brink, Holocene climatic optimum. Furthermore, it places these 1975). Formation of the system may have started several findings into a time frame of deglaciation after the last glacial centuries before 7300 14 C yr B.P. (Ten Brink, 1975). The maximum. The chronology will be given in 14 C yr and calen- retreat of the ice sheet margin from Søndre Strømfjord al- lowed the sea to invade slightly beyond the present fjord 1 E-mail: Ft@fgb.frw.uva.nl. head (Ten Brink and Weidick, 1974). The Keglen part of 245 0033-5894/96 $18.00 Copyright  1996 by the University of Washington. All rights of reproduction in any form reserved.