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TitreThe last 9,000 years in lake records from the NWT: time constraints from 14C dating, age-depth modeling, and a new occurrence of the White River Ash
AuteurCrann, C; Patterson, R T; Macumber, A L; Galloway, J M; Roe, H M; Falck, H
SourceNorthwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume 2013, 2013 p. 1
LiensOnline - En ligne
Année2013
Séries alt.Secteur des sciences de la Terre, Contribution externe 20130444
Documentpublication en série
Lang.anglais
Mediapapier; en ligne; numérique
Formatspdf
ProvinceTerritoires du Nord-Ouest
Sujetspaléoclimats; Holocène; sediments lacustres; carottes de sediments lacustres; datations au C-14; isotopes de carbone; paléontologie; géochronologie; Cénozoïque; Quaternaire
Programmeadaptation et impacts sur l'environnement, environnement du nord, Géosciences de l'environnement
Résumé(disponible en anglais seulement)
As part of a multidisciplinary paleoclimate project aimed at assessing the future viability of the Tibbitt to Contwoyto Winter Road (TCWR) in the central Northwest Territories, we examined late Holocene sedimentary records from lake cores transecting boreal forest, treeline, and tundra zones. Before undertaking paleoclimate and paleoenvironmental studies on the cores, radiocarbon based age-depth models were constructed to ensure the sedimentary record covers at least the last 3,500 years and there are no major hiatuses in deposition.

Chronologies are fundamental to interpreting the timing and rates of past environmental changes. Significant advancements have been made during the last decade in the methods of age-depth modeling and the calibration of radiocarbon dates. Traditionally, linear regression linear interpolation models were used to estimate the ages of depths between a few dated horizons. While the classic approach is sufficient at a coarse scale, our study requires much higher precision in order to resolve paleoclimate shifts on a multi-decadal scale. In addition to improving the dating resolution by adding more 14C dates than have been traditionally used for cores in the region, the age-depth models for sedimentary successions retrieved as part of this study are constructed using a probabilistic/Bayesian approach involving multiple simulations. Such chronologies are essential in high-resolution paleoclimate and paleoenvironmental studies.

Thus far, over 130 14C dates have been obtained, primarily on bulk sediment, from 19 sediment cores obtained from 11 lakes along a latitudinal gradient spanning from boreal forest near Yellowknife to tundra sites near Lac de Gras. There are between four to twenty-five 14C dates per core, some of which extend back as far as 9,000 years before present. In two sediment cores obtained from Pocket Lake near Yellowknife, a visible tephra is geochemically fingerprinted as the White River Ash (WRA). The WRA is from a Plinian-type eruption of Mount Churchill in Alaska that occurred ca. 1,200 years ago. The timing of the eruption is best constrained by radiocarbon dates from the outer rings of trees that were buried in coarse tephra and a pyroclastic flow near the source vents (Clague et al., 1995). The occurrence of the WRA in the Pocket Lake cores is, to the best of our knowledge, the furthest east it is recognized as a visible tephra. Because the timing of the WRA is well constrained, its occurrence in Pocket Lake is incorporated into the age-depth models for cores obtained from this site. This is important validation of the 14C based age-depth models.
Résumé(Résumé en langage clair et simple, non publié)
Cette recherche fait partie d'un projet pluridisciplinaire plus vaste ayant pour but d'évaluer la viabilité future de la route d'hiver qui relie Tibbitt à Contwoyto, la seule route terrestre qui dessert les mines du centre des Territoires du Nord-Ouest. L'analyse à haute résolution des sédiments des lacs qui vont des environs de Yellowknife au lac de Gras sera utilisée pour mieux comprendre la variabilité du climat dans cette région. Les relations entre l'âge et la profondeur sont au coeur de la reconstitution du paléoclimat. Cette contribution établit des chronologies pour les sédiments lacustres étudiés au moyen de la géochronologie au radiocarbone, de la modélisation âge-profondeur et de l'analyse du téphra. Plus de 130 datations établies au radiocarbone ont été tirées de 19 carottes de sédiments lacustres. Il y a de quatre à 25 datations établies au radiocarbone par carotte, surtout dans les sédiments en vrac. Deux carottes de sédiments obtenues du lac Pocket, près de Yellowknife, contenaient un téphra visible identifié du point de vue géochimique comme étant des cendres de la rivière White dont l'origine présumée est l'éruption du mont Churchill en Alaska qui a eu lieu il y a environ 1 200 ans. Jamais encore ce téphra n'avait été découvert si loin à l'est.
GEOSCAN ID293587