Émersion des terres et développement des sols bien drainés au lac Guillaume-Delisle, Québec subarctique

Abstract

Dans la région du lac Guillaume-Delisle, au Québec subarctique, des cônes de déjection d’âge et d’altitude variables se sont déposés tout au cours de l’Holocène sur des plages soulevées, offrant ainsi la possibilité d’étudier une chronoséquence holocène de sols. Le cadre temporel a été établi par la datation radiocarbone de 38 horizons organiques enfouis et la mise à jour de la courbe d’émersion des terres pour la région. L’émersion se serait effectuée selon un taux moyen de 5,6 m/siècle entre 8500 et 4500 années cal. BP et de 1,2 m/siècle après 4500 années cal. BP. Les analyses morphologiques et chimiques ont montré que les sols et paléosols subarctiques sableux, bien drainés et soustraits à l’influence des combes à neige, sont formés principalement par l’accumulation dans l’horizon B de matière organique humifiée combinée à de l’aluminium et du fer (podzolisation). L’enrichissement de l’horizon B en fer et en aluminium se fait lentement en suivant une fonction linéaire. La durée de pédogenèse requise pour obtenir le seuil minimal (Fep+Alp) de 0,4 % pour l’horizon Bf fixé par le Système canadien de classification des sols serait d’environ 12 400 années. Bien que théorique, cette durée indique à quel point les conditions nécessaires à la formation des podzols sont difficiles à réunir dans les sols subarctiques où la végétation demeure basse et le couvert nival peu épais.In the Lake Guillaume-Delisle area, alluvial fans of various ages and elevations were deposited throughout the Holocene over raised beach deposits, which allowed the studying of a subarctic soil chronosequence. The temporal framework is based on 38 14C dates obtained from buried organic soil horizons, and on an update of the Lake Guillaume-Delisle emersion curve. Postglacial uplift due to glacio-isostatic rebound occurred at a mean rate of 5.6 m/century from 8500 to 4500 cal. yr BP, and of 1.2 m/century after 4500 cal. yr BP. Soil morphology and chemistry showed that well-drained sandy soil and paleosoil development, when not influenced by late-lying snowpatches and snowmelt, is characterized by B horizons having a dominant accumulation product of amorphous material composed mainly of humified organic matter combined with Al and Fe (podzolisation). However, pedogenic development is weak and would take about 12 400 years to reach the minimum values of (Fep+Alp) ≥0,4% required for meeting the criteria of a Bf horizon in the Canadian system of soil classification, according to a linear function. Although theoretical, this value indicates that conditions required for Podzol formation are hard to reach in subarctic soils with low vegetation and thin snow cover

Primary succession of subarctic vegetation and soil on the fast‐rising coast of eastern Hudson Bay, Canada

“…To estimate the age of the soil surface at the time of white spruce establishment, a mean emergence rate of 1.2 m century −1 was used, based on published vertical uplift curves (Hillaire‐Marcel, 1976; Allard & Tremblay, 1983; Bégin et al. , 1993; Lafortune et al. , 2006; Lavoie, 2006).…”

“…The current emersion rate of the Hudson Bay coast is estimated to be between 1.1 and 1.3 m century −1 (Hillaire‐Marcel, 1976; Allard & Tremblay, 1983; Bégin et al. , 1993; Lafortune et al. , 2006; Lavoie, 2006).…”

Deglaciation landforms and C-14 chronology of the Lac Guillaume-Delisle area, eastern Hudson Bay: A report on field evidence

“…the slope of the RSL curve) at the time of deglaciation, even more as measurement errors of a few meters in elevations or a few hundreds of meters in distance do not significantly affect the results. The plot of the upper segment of the RSL curve, from estimated slope value, falls on the three available beach-Mytilus C-14 dates, between 205 and 138 m asl, and on the mixed shells date (7814-7557 cal BP; 7340 ± 60 14 C BP; Beta-144405) found in a raised beach at 218 m asl (Lafortune et al, 2006a). By projecting the slope upward to the marine limit at 271 m, the RSL curve indicates a deglaciation age of ca.…”

“…A small number of previous studies on-land have provided a series of snapshots on the geomorphological history of the Lac GuillaumeDelisle area, including the marine limits and postglacial emergence (Stanley, 1939;Lee, 1960;Hillaire-Marcel, 1976, 1980Allard and Seguin, 1985;Daigneault, 2001;Lafortune et al, 2006a), raised beaches (Stanley, 1939;Lee, 1960;Hillaire-Marcel, 1976) and alluvial fan activity (Lafortune et al, 2006b). The east coast of Hudson Bay is mainly known for having the largest and fastest postglacial isostatic uplift in the World.…”

Periphytic diatom community structure in thermokarst ecosystems of Nunavik (Québec, Canada)

“…This deglaciation was followed by a marine transgression episode (postglacial Tyrrell Sea), which covered the landscape with marine (silt-clay) and coastal (sand) deposits that are widespread today in topographic depressions (Saulnier-Talbot et al 2003;Lavoie et al 2008a). Following ice retreat, strong isostatic rebound (up to 9 m per century) affected the landscape, resulting in marine regression (Allard and Séguin 1987;Lafortune et al 2006). The exposure of fine-grained sediments to the cold climate conditions of the late Holocene, especially during the Little Ice Age, gave way to permafrost inception and development in the region (Fig.…”