Delayed Deglaciation by Downwasting of the Northeast Avalon Peninsula, Newfoundland: An Application of the Early Postglacial Pollen Record
Basal radiocarbon dates from lake sites indicate that final degiaciation began at most a few centuries before 10 ka BP on the interior plateau and proceeded by down-wasting. Comparison of the pollen record with the sequence of vegetation from the Storbreen glacier foreland, Norway, studied by the Jo...
| Published in: | Géographie physique et Quaternaire |
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| Main Author: | |
| Format: | Text |
| Language: | English |
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Les Presses de l'Université de Montréal
1996
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| Subjects: | |
| Online Access: | http://id.erudit.org/iderudit/033089ar https://doi.org/10.7202/033089ar |
| Summary: | Basal radiocarbon dates from lake sites indicate that final degiaciation began at most a few centuries before 10 ka BP on the interior plateau and proceeded by down-wasting. Comparison of the pollen record with the sequence of vegetation from the Storbreen glacier foreland, Norway, studied by the Jotunheimen Research Expeditions, indicates that pioneer herb and dwarf shrub stages gave way within 200 years to shrub-birch heath into which spruce migrated at about 8.5 ka BP. It is shown that double maxima of dwarf shrubs result from the existence of terrains of different ages within each catchment at the time when lake sediment accumulation began. An independently dated pollen record from St. John's Harbour confirms the timing and mode of degiaciation and demonstrates that the Avalon Peninsula ice cap did not extend beyond the present coast at the beginning of the Holocene. The delays in both degiaciation and the immigration of spruce are attributed to cold ocean temperatures associated with eastward discharge of meltwater from the Laurentide Ice Sheet. Les datations au radiocarbone à la base des sites lacustres laissent supposer que la déglaciation finale a commencé à peine quelques siècles avant 10 ka BP sur le plateau intérieur et s'est effectuée par fonte sur place. La comparaison entre le relevé pollinique et la séquence de la végétation enregistrée dans l'avant-pays du glacier Storbreen, en Norvège, indiquent que les premiers stades de végétation herbacée et de buissons nains ont laissé place en 200 ans à une lande de bouleaux nains où l'épinette blanche a migré vers 8,5 ka BP. Il est démontré que les deux pics de bouleaux nains enregistrés résultent de l'existence de terrains d'âges différents à l'intérieur d'un même bassin, au début de la sédimentation lacustre. Un relevé pollinique du St. John's Harbour daté de façon indépendante confirme la chronologie et le mode de déglaciation et démontre que la calotte glaciaire de la péninsule d'Avalon ne s'étendait pas au-delà de la côte actuelle, au début de ... |
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