Évolution postglaciaire des hauts sommets alpins et subalpins de la Gaspésie

Abstract

The stratigraphy of surficial deposits located in a snow-patch site, at an altitude of 1200 m in the Mount Jacques-Cartier area, provides evidence of a Late Glacial to mid-Holocene deglaciation. During the Late Glacial, or at the beginning of the Holocene, the diamictons on the high summits of the McGerrigle Mountains were affected by a severe periglacial climate, responsible for the formation of most of the periglacial landforms, such as sorted polygons, sorted stripes, stone-banked lobes, and block fields. During the Holocene, these landforms were fossilized by vegetation, and podzolic soil profiles developed within the stony deposits. After the Hypsithermal, a cooling trend was registered in snow-patch sites, where gelifluction was active after ca. 5200, 3470 – 3340, 2500, 2100, 1860, 1490, and 650 BP. Subalpine meadows followed the opening of the forest, at least since 2200 BP, and were due to neoglacial cooling. Within the alpine belt, the coniferous cover regression is registered at least since 1400 BP. During the so-called Little Ice Age of the past centuries, conifers retracted because of periglacial activity, which was followed by the formation of sorted stripes and gelifluction lobes. The extinction of tree species in the alpine tundra is related to periglacial activity, an ecological situation rather specific to the high summits of Gaspé.