Quaternary stratigraphy, paleoecology, and glacial geology, Îles de la Madeleine, Quebec

Abstract

On the Îles de la Madeleine, a rock platform as much as 20 m asl, locally with clam borings, is correlated to the regional interglacial surface at 2–8 m; its anomalous height may be a consequence of salt tectonics. Overlying lagoonal and paludal organic beds, one with Th/U ages of 89–101 ka, record the Sangamonian climatic optimum (substage 5e), which culminated in forest more thermophilous than that of the Holocene optimum. Overlying littoral gravel and sand, considered analogous to sediments in present-day tombolos, and organic beds with less temperate pollen types were deposited during the marine transgressive climax of substage 5e and thus indicate that sea level remained high after the thermal optimum, as in Holocene time. Cold-based Early Wisconsinan ice, probably centred on the Magdalen Shelf, tectonized bedrock and interglacial beds and deposited till upon them. Periglacial features indicate a subsequent long cold period. An organic bed dating from 11.3 to 10.6 ka records a warm interval followed by cooling. Buried peat, a submerged fossil sea cliff, and barrier beaches record a marine transgression during the late Holocene.

The Laurentide and Innuitian ice sheets during the Last Glacial Maximum

“…Gratton et al (1984) argued that ice did not override Middle Wisconsinan marine sediments on Anticosti Island in the northern Gulf of St. Lawrence. Only ancient glaciation was recognized on the Magdalen Islands in the western part of the gulf and the presence there of surficial organic deposits dating from the Sangamonian (isotopic stage 5) suggested an absence of Late Wisconsinan ice cover (Prest et al, 1977;Dredge et al, 1992). Limited Laurentide ice was also indicated by a general preclusion of Laurentide (Canadian Shield) erratics from the Gaps!…”

The Drift des Demoiselles on the Magdalen Islands (Québec, Canada): sedimentological and micromorphological evidence of a Late Wisconsinan glacial diamict

“…The question of whether the Magdalen archipelago was glaciated during the Wisconsinan has been a topic of research since the beginning of the last century (Richardson 1881;Chalmers 1895;Clarke 1911;Goldthwait 1915;Coleman 1919;Alcock 1941;Hamelin 1959;Prest et al 1976;Dredge and Grant 1987;Parent and Dubois 1988;Dredge et al 1992). Past studies do not agree on whether the Magdalen Islands were glaciated (Fig.…”

“…Parent and Dubois (1988) divided it into two glacial facies and named the deposit Till de Havre-Aubert. Dredge and Grant (1987), Dredge et al (1992), and Parent and Dubois (1988) proposed that the Magdalen archipelago was glaciated during the Early Wisconsinan but unglaciated during the Last Glacial Maximum (LGM). During the Middle Wisconsinan, the ice would have retreated to the north of Anticosti Island (Gratton et al 1984), leaving the Magdalen Islands ice-free (Dyke et al 2002).…”

“…During the Middle Wisconsinan, the ice would have retreated to the north of Anticosti Island (Gratton et al 1984), leaving the Magdalen Islands ice-free (Dyke et al 2002). During the LGM, Dredge et al (1992) suggested that the archipelago was affected by periglacial processes during a lower sea level. In contrast to prior considerations that were unable to account for the Magdalen Islands remaining ice-free, all recent glacier modelling has assumed that the Islands were glaciated during the Late Wisconsinan, either by the Laurentide Ice Sheet (Dyke et al 2002;Dyke 2004) or by the Appalachian Glacier Complex (Stea et al 1998(Stea et al , 2011Josenhans and Lehman 1999;Stea 2004;Shaw et al 2006;Josenhans, 2007) (Fig.…”

Sandy barriers, climate change and long-term planning of strategic coastal infrastructures, Îles-de-la-Madeleine, Gulf of St. Lawrence (Québec, Canada)

“…Geological evidence suggest that this trend started 9000-6500 years BP, at a mean rate of 1 mm/year (Dredge et al, 1992;Grenier and Dubois, 1992). Present RSL rise is estimated to vary between 2 and 3.5 mm/year in the Maritime Provinces and southern Gulf of St. Lawrence (D. Bérubé, New Brunswick Department of Natural Resources, pers.…”