Late Wisconsinan deglaciation and glacial lake development in the Appalachians of southeastern Québec

Abstract

Late Wisconsinan deglaciation in southeastern Québec was preceded by a northward ice-flow reversal that was recorded in the northeastern part of the region. The reversal event was generated by flow convergence toward the St. Lawrence Ice Stream, a northeastward-flowing ice stream which formed in the St. Lawrence estuary prior to 13 000 years BP and lasted until at least 12 400 years BP. In the Bois-Francs uplands, the flow reversal event led to the formation of a semi-detached ice mass that underwent widespread stagnation and downwasting. In the southwestern region, northward retreat of the margin of the Laurentide Ice Sheet was marked by the formation of a series of discontinuous recessional moraines and by the development of ice-dammed lakes in the main valleys. The level of these lakes fell as progressively lower outlets became ice-free. The main episodes are (1) the Sherbrooke Phase of Glacial Lake Memphremagog, (2) an unnamed transitional lake and (3) Glacial Lake Candona, a large lake which had expanded northeastward from the deglaciated regions of the Upper St. Lawrence (Lake Iroquois) and Ottawa valleys to the Lake Champlain (Glacial Lake Vermont) basin. As recorded by the Danville Varves, Lake Candona lasted about 100 years following deposition of the Ulverton-Tingwick Moraine. Subsequent ice retreat along the Appalachian piedmont led to final drainage of Lake Candona and allowed Champlain Sea waters to invade much of these glaciolacustrine terrains about 12 000 years BP. On the basis of the Danville Varves record, a regional rate of ice retreat of about 200 m·a -1 is inferred. The age of the earliest moraine, the Frontier Moraine, is thus about 12 550 years BP, while the ages of the subsequent Dixville, Cherry River-East-Angus, Mont Ham and Ulverton-Tingwick moraines are estimated at 12 500, 12 325, 12 200 et 12 100 years BP, respectively.La déglaciation du Wisconsinien supérieur a été précédée d'une inversion d'écoulement glaciaire vers le nord. Cette inversion, enregistrée dans le nordest de la région, résulte de la convergence des glaces vers le Courant glaciaire du Saint-Laurent, lequel s'était formé dans l'estuaire du Saint-Lau- rent avant 13 000 ans BP et a duré au moins jusque vers 12 400 ans BP. Dans les hautes-terres des Bois-Francs, cette inversion d'écoulement a mené à l'isolement d'une masse glaciaire partiellement détachée et qui se dissipa tardivement. Dans le secteur sud-ouest, le retrait de l'Inlandsis est ponctué par la mise en place d'ensembles morainiques discontinus et par le développement de lacs proglaciaires barrés dans les vallées principales. Le niveau de ces lacs chutait à mesure que le retrait glaciaire libérait des cols de plus en plus bas. Les principaux épisodes sont : la Phase Sherbrooke du Lac glaciaire Memphrémagog ; un lac de transition ; le Lac glaciaire Candona, formé de la coalescence des lacs glaciaires endigués dans les vallées du haut Saint-Laurent, des Outaouais, du lac Champlain (Lac Vermont) et du Saint-François. Le Lac Candona a subsisté quelque ...

The Saint-Narcisse morainic complex and early Younger Dryas events on the southeastern margin of the Laurentide Ice Sheet

“…Datable material have been sampled from glaciomarine diamictons associated with morainic complexes, from marine silts in front or immediately on top of the moraine, from peat and gyttja close to the moraine, and from reworked deposits. The significance of 14 C ages from marine shells in the Champlain-Goldthwait Seas has been thoroughly debated (Hillaire-Marcel, 1979, 1981Rodrigues, 1992;Rodrigues and Vilks, 1994;Parent and Occhietti, 1999;Dyke et al, 2003;Occhietti and Richard, 2003;Richard and Occhietti, 2005). In this paper, mean-oceanic-reservoir corrected ages from marine shells will be used, with an estimated value of ␦ 13 C = 0‰ (reservoir correction of -410 years with regard to conventional ages) (Stuiver and Reimer, 1993; Table I).…”

“…Between the northernmost moraines in the Appalachians of southern Québec (LaSalle et al, 1977a(LaSalle et al, , 1977bParent and Occhietti, 1999) and the outer limit of the Saint-Narcisse morainic complex, ice-marginal features are rarely observed and not continuous. This is related to a rapid ice retreat with phases of calving ice in Champlain Sea.…”

“…mostly to a previously increased ablation process resulting from converging ice flow towards the St. Lawrence Estuary. The pre-Saint-Narcisse west-east ice flow in Charlevoix (Rondot, 1974;Govare, 1995;Lanoie, 1995;Fournier, 1998;Occhietti, 2001) represented the northern converging side of the St. Lawrence Ice Stream which drained the LIS ice in the St. Lawrence Estuary and Gulf (Parent and Occhietti, 1999;Occhietti et al, 2001b).…”

“…Nevertheless, younger ages were obtained in the Lake Champlain basin and the onset time would be comprised between 13.1 and 12.7 cal ka (Cronin et al, 2008). If the same mean ice-retreat rate of 250 m/yr as in the Appalachians is applied (Parent and Occhietti, 1999), deglaciation of the central St. Lawrence Valley, from the Appalachian piedmont to the position of the Saint-Narcisse Moraine in the Saint-Maurice Valley, would have lasted about 260 calendar years for 65 km. The early YD ice-retreat slowdown would have been compensated by a calving ablation.…”

First recognition of a Laurentide Ice Stream : Robert Bell on Hudson Strait

“…Between 18 000 and 10 000 yr BP, the LIS reconstruction of Dyke and Prest (1987b) showed narrowly confined ice-flows, presumed or argued to have been basally lubricated, fast-flowing, often, but not exclusively, located over linear topographic lows. Examples later more fully studied include the St. Lawrence Valley (Parent and Occhietti, 1999), basins flooded by the Great Lakes (Breemer et al, 2002), and Hudson Strait (Laymon, 1992 ;Manley, 1996), all now recognized as ice-streams.…”