Analyse macrofossile d'une palse subarctique (Québec nordique)

Abstract

Plant and animal macrofossils (vascular plant, moss, fungus, bryozoan, cladoceran and coleoptera remains) were analyzed to reconstitute the development of a palsa peat located at the northwestern forest limit of subarctic Quebec (57°45′N., 76°15′W.) and to detect any black spruce (Picea mariana) remains older than the presumed time of arrival of the species in the study area (4560 BP), after the deglaciation. The oldest peat deposits were formed in a fen with many shallow pools between 5850 and 4500 BP. The flora was mainly composed of aquatic taxa (Ranunculus trichophyllus, Potamogeton spp., Hippuris vulgaris). Around 4500 BP, there was a shift from a very wet fen to a sedge fen with Potentilla palustris and Menyanthes trifoliata. From 3700 to 1950 BP, most plant remains were wood fragments of dwarf birch (Betula glandulosa). The formation of the palsa occurred after 1950 BP. The development of this peatland is similar to that of other palsa peatlands of subarctic Quebec, except that it is characterized by the presence of a thick peat layer composed of Betula glandulosa fragments at the top of the palsa. There were no black spruce remains older than 4560 BP. Three peaks of coleoptera abundance were identified at 4400, 3800, and 2700 BP, respectively. Most of the coleoptera taxa being hygrophilous, it was not possible to infer structural changes in the peatland from their fragments. Key words: palsa peatland, macrofossil analysis, subarctic Quebec, Betula glandulosa, Picea mariana, beetles.