Lake sediments and glacial history in the High Arctic; evidence from east-central Ellesmere Island, Arctic

Deciphering glacial history in many High Arctic localities is difficult because: 1) surficial deposits are often thin or non-existent, 2) vast tracts are underlain by soft and friable bedrock, 3) the churning effects of frost action and slope processes tend to eradicate traces of glaciation, 4) cold based ice caps leave little trace of their former presence, except where marginal drainage channels form on uphill slopes, and 5) significant areas still are covered by glacier ice. Where present, striae show that an area has been glaciated, hut until a technique is devised to determine when a given set of striae was inscribed, or when a striated surface became exposed to daylight (e.g. Phillips et al. 1986: Elmore & Phillips 1987), the timing of the glacial event responsible remains an enigma. One way of approaching the problem of dating glacial events, in the High Arctic as elsewhere, is to determine the age of organic deposits associated with till or outwash. Radiocarbon dating of the basal increment from a lake sediment core or a peat deposit provides a minimum age for deglaciation and for the onset of organic accumulation. In this connection the advent of "C dating by means of accelerator mass spectrometry (AMS) has provided an extremely powerful tool for determining the timing of events more precisely. For instance, the change from marine to lacustrine conditions or, in the case of a lake above the limit of Holocene marine submergence, the onset of lacus-trine moss growth can be pin-pointed much more accurately using this technique (Blake 1985). Available basal dates on reliable organic materials from lakes in east-central Ellesmere Island, an area underlain by granites. migmatites. and associated rocks of the Canadian Shield, do not exceed 9500 radiocarbon years. The oldest age determinations, among seven lakes dated, have been obtained along the oute