The relative influence of Laurentide and local ice sheets during the last glacial maximum in the eastern Chic-Chocs Range, northern Gaspé Peninsula, Quebec

Abstract

Geochemical signatures, erratic dispersal, and striae indicate glacial flows in the north-central Gaspé Peninsula exclusively from Appalachian sources, except for the coastal fringe. During the last glacial maximum (LGM), ice from the Monts McGerrigle flowed northward and northwestward over the summits of the eastern Chic-Chocs Range and the coastal plateau to the Gulf of St. Lawrence. Lesser flows also occurred to the north from Mont Albert and the western Chic-Chocs Range. Where intersecting striae were noted, the older flows are associated with a locally developed ice cap. The rare occurrences of striae and erratics, and morphometric and lithological characteristics of summit diamictons, imply limited basal erosion by both local and regional ice caps. This is postulated to result from early protection of rock surfaces by the initial buildup of thin, frozen-based ice in the eastern Chic-Chocs Range. A compact till mantle in the cols and on the coastal plateau and striae parallel to col directions indicate a downslope transition to wet-based ice. Occasional gneiss boulders above the marine limit between Cap-Chat and Sainte-Anne-des-Monts indicate a slight onlap of the Laurentide Ice Sheet (LIS), but the latter was excluded from the interior of the peninsula east of Cap-Chat. Whole-rock geochemistry from three granitoid erratics on Chic-Chocs summits and one in the York River basin indicates a local Devonian rather than a Precambrian Canadian Shield source. The absence of southward downwarping of synchronous postglacial marine limits across the Gaspé Peninsula corroborates this view for the LGM.Résumé : Les signatures géochimiques, la dispersion des blocs erratiques et les stries dans le centre nord de la Péninsule gaspésienne indiquent que l'écoulement glaciaire provenait uniquement de sources appalachiennes, sauf pour la bordure côtière. Durant le dernier maximum glaciaire, la glace des monts McGerrigle s'écoulait vers le nord et le nord-ouest pardessus les sommets de la chaîne orientale des monts Chic-Chocs et le plateau côtier vers le Golfe du Saint-Laurent. Il s'est aussi produit des écoulements secondaires vers le nord, en provenance du Mont Albert et de la chaîne occidentale des monts Chic-Chocs. Là où les stries s'entrecoupent, les plus anciens écoulements sont associés à une calotte glaciaire formée localement. Les rares occurrences de stries et de blocs erratiques ainsi que les caractéristiques morphométriques et lithologiques de diamictons de sommets impliquent une érosion basale par les calottes glaciaires régionales et locales. Cela découlerait de la protection précoce des surfaces rocheuses par l'accumulation de glace mince figée à la base des calottes glaciaires dans la chaîne orientale des monts Chic-Chocs. Un manteau compact de till dans les cols et sur le plateau côtier, avec des stries parallèles aux directions des cols, indique une transition dans le sens de la pente vers de la glace avec présence d'eau à la base. Les blocs occasionnels de gneiss au-dessus de la limite marine, entre Cap-Chat e...

Early subduction dynamics recorded by the metamorphic sole of the Mt. Albert ophiolitic complex (Gaspé, Quebec)

“…Sirois and Grandtner, 1992;Martin and Germain, 2016) contrasting with the generally dense forest cover found over most of the amphibolite du diable. Exposure of the metamorphic sole is further restrained by the presence of numerous boulders of both local and remote origin related to the last glacial maximum (see Olejczyk and Gray, 2007). Consequently, exposed sections through the metamorphic sole are not continuous over scales of hundreds of metres as in Oman, complicating the study of mineralogical changes with distance to the contact of the peridotite, as folding and possible late faulting cannot be rigorously evaluated.…”

Late Holocene sea-level changes in eastern Québec and potential drivers

“…The Baie des Chaleurs was marine inundated by 12,600 ±200 cal yrs BP (Olejczyk and Gray, 2007) following deglaciation and retreat of the Gaspesie (Olejczyk and Grey, 2007) and Escuminac ice caps (Pronk et al, 1989;Bail, 1985) and the eastern limit of the LIS. After reaching a postglacial marine limit of 45 to 55 m on the north shore of the Baie des Chaleurs (Veillette and Cloutier, 1993), RSL dropped below the present-day level around 12,000 cal yrs BP (Thomas et al, 1973).…”

The Chic-Choc Mountains are the last southern refuge for Arctic lichens in eastern North America

“…Hétu and Gray (1985) suggested that the plateaus could have been exposed during the Wisconsin glaciation as well because they only found slight traces of glacial erosion and the age of these erosion events cannot be determined accurately because of the lack of correlative deposits. However, the nunatak hypothesis is controversial (Wynne-Edwards 1937;Marie-Victorin 1938;Griggs 1940;Scoggan 1950;Rousseau 1974;Olejczyk and Gray 2007). For example, Olejczyk and Gray (2007) postulated that the sparse striae and erratics on the plateaus may have been due to protection from the glaciers by an initial buildup of ice.…”

“…However, the nunatak hypothesis is controversial (Wynne-Edwards 1937;Marie-Victorin 1938;Griggs 1940;Scoggan 1950;Rousseau 1974;Olejczyk and Gray 2007). For example, Olejczyk and Gray (2007) postulated that the sparse striae and erratics on the plateaus may have been due to protection from the glaciers by an initial buildup of ice. Although it is uncertain if the Chic-Chocs were nunataks, they still contain numerous endemic and disjunct populations of vascular plants (Fernald 1925), lichens (Macoun 1902;Dodge 1926;Sirois et al 1988;McMullin et al 2014), and moss (Belland 1987a(Belland , 1987b(Belland , 2015, many of which typically occur in the Arctic and the western mountains of North America.…”