YOUNGER DRYAS AND PREBOREAL END MORAINES, READVANCES, AND RECESSION RATES, WESTERN CANADIAN ARCTIC

Between 11 and 9.6 14C ka BP, the Amundsen Lobe of the Laurentide Ice Sheet and its successors the Prince Albert Lobe and the Dolphin and Union Lobe constructed a broad, complex belt of hummocky and ridged end moraine on western Victoria Island and on the adjacent arctic mainland. The most prominent and continuous end moraine ridges within the belt display cross-cutting relationships with older ridges and are correlated with drumlin and fluting sets that are superimposed on older bedforms in different orientations. Readvances and moraine construction occurred throughout Younger Dryas and early Preboreal time. The largest readvance occurred 9.8-9.6 14C ka BP, forming the Colville moraine on Victoria Island and the Stapylton Bay moraine on the mainland. Although this event may represent delayed response to Younger Dryas cooling, the suggestion by Fisher et al. (2002; QSR) that Preboreal cooling may have been triggered by the diversion of Lake Agassiz outflow from the Atlantic to the Arctic Ocean invites the interpretation that Preboreal cooling was particularly strong in the Beaufort Sea region and that the NW Laurentide ice margin responded to that cooling almost immediately, because the equilibrium line fell close to the margin. Net recession during the interval 11 and 9.6 14C ka BP was much slower than average recession rates of the northwestern Laurentide margin during the interval 13-7 14C ka BP. If mass loss due to calving in wide marine channels is ignored, mass balance during the period of moraine construction was close to zero, if not positive. Ages referred to here are on marine molluscs using a reservoir correction of 740 years.