Deglaciation of Chilliwack River valley, British Columbia

Abstract

Quaternary sediments and landforms in Chilliwack River valley, southwestern British Columbia, provide a detailed record of déglaciation of this area between 12 000 and 11 000 years BP. Stratigraphic, sedimentological, and radiocarbon data show that a large glacier in eastern Fraser Lowland (part of the Cordilleran Ice Sheet) blocked the mouth of Chilliwack valley at a time when the middle reaches of the valley were ice free. A lake existed between the ice dam in the lower part of the valley and a delta – sandur complex, west of Chilliwack Lake, in the upper part of the valley. Two relatively minor advances of the Fraser Lowland ice lobe into lower Chilliwack valley occurred about 11 500 and 11 200 years BP. These were separated by a brief period of recession during which tephra was deposited and a coniferous forest and soil developed on freshly deglaciated terrain. Shortly after 11 200 years BP, a glacial lake formed in Cultus Lake basin; two sets of terraces in lower Chilliwack valley are graded to different levels of this lake. The glacier dam at the mouth of Chilliwack valley disappeared about 11 000 years BP, and déglaciation of Fraser Lowland was complete less than 100 years later.

Deglaciation of the Cordillera of Western Canada at the end of the Pleistocene

“…At least one of these advances happened during or before the Older Dryas interval; another may have happened during an intra-Allerød cold interval; and a third likely dates to the Younger Dryas interval. Two of these events are also recorded in Chilliwack River valley, where a lobe of the Cordilleran Ice Sheet in nearby Fraser Lowland advanced at least twice over forest in the lower reach of the valley and impounded a lake upstream (Saunders et al, 1987). Similarly, Clague (2002a, 2002b) provided stratigraphic and geomorphic evidence for an advance of a lobe of the Cordilleran Ice sheet in the Cheakamus River valley north of Vancouver during the Younger Dryas chronozone.…”

Deglaciation of the North Cascade Range, Washington and British Columbia, from the Last Glacial Maximum to the Holocene

“…On the north side of the lower Fraser River a Marion Lake sediment core yielded a macrofossil age of 13.7 ka, the same age for deglaciation of the lower Chilliwack and Nooksack (Table 2; Fig. 5C; Mathewes, 1973;Saunders et al, 1987). Deep Kettle Bog in the lower South Fork of the Nooksack River was deglaciated about 14.5 ka (Kovanen and Easterbrook 2001).…”

“…1; Mathewes et al, 1972;Saunders et al, 1987;Dragovitch et al, 1999;Kovanen and Easterbook, 2001). On the north side of the lower Fraser River a Marion Lake sediment core yielded a macrofossil age of 13.7 ka, the same age for deglaciation of the lower Chilliwack and Nooksack (Table 2; Fig.…”

“…The lower and middle reaches of the valley were ice-free by 13.7 ka, but the lower valley was inundated during three or more re-advances of ice from Fraser Lowland ( Fig. 5C; Saunders et al, 1987;Clague et al, 1997). Re-advances of the CIS occurred from 13.6 to 13.3 ka, and from 12.9 to 12.0 ka (Kovanen, 2002).…”

“…5C; Saunders et al 1987). In the middle Chilliwack valley, the outwash train extends from the Chilliwack Lake moraine and grades into lacustrine deposits in the lower valley Dansgaard et al, 2003), alpine glacier ELAs (red; Porter et al, 1983;Riedel et al, 2010) (Clague and Luternauer, 1982).…”