Glacio-isostatic rebound rates from in-situ cosmogenic chlorine-36 dating of raised marine beaches in Makinson inlet, eastern Ellesmere island

Abstract

Ellesmere Island, in the Canadian Arctic, and adjacent sea were covered by ice during the Last Glacial Maximum (LGM, 20-10 ky ago). Postglacial rebound rates, indic ative of ice sheet configuration, glacial and deglacial chronologies, and rheologic proper ties of the underlying mantle, were determined for Makinson Inlet using a new approach based on in-situ accumulation of cosmogenic 36Cl. Surface and subsurface gravel samples were collected from fourteen paleobeaches at elevations between the sea level and the Holocene marine limit at ca. 105 m a.s.l. Apparent 36Cl ages range from ca. 4 to 13 ky and corrected 36Cl ages (in calendar years) range from 10 ky to recent. Corrected 36Cl ages agree with 14C ages of organic material from the same paleobeach sequence. Instantaneous uplift rates decrease from the high of 42 m ky- 1 at the beginning of emergence 10 ky ago, to less than I m ky- 1 today. These results show the applicability of the cosmogenic 36CI exposure dating method in studies of postglacial emergence. The ability to date inorganic surficial materi als has two main advantages: (1) the approach may be used on any material, such as rocks and sediments, that has been exposed at the surface due to isostatic rebound; and (2) an arbitrarily large number of samples can be collected at the same location, thereby provid ing the means of constructing a high-resolution record of exposure and isostatic emer gence.