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The AAPG/Datapages Combined Publications Database
CSPG Bulletin
Abstract
Stratigraphy of the Lower Part of the Belt-Purcell Supergroup (Middle Proterozoic) in the Lewis Thrust Sheet of Southern Alberta and British Columbia
ABSTRACT
Detailed mapping in the northern part of the Clark Range salient of the Lewis thrust sheet has led to a revision of stratigraphic correlations across the width of the thrust sheet, and has shown that marked facies changes occur within formations near the base of the Lewis thrust sheet. Strata immediately above the Lewis thrust, exposed around two windows through the Lewis thrust sheet in southeastern British Columbia, previously were correlated with the Waterton Formation, which had been considered the lowest unit within the thrust sheet. The strata immediately above the Lewis thrust are now shown to occupy a stratigraphic position below the Waterton Formation. Two new units, the Haig Brook Formation and the Tombstone Mountain Formation, are proposed for the stratigraphic interval between the Lewis thrust and the redefined base of the Waterton Formation. Strata in the hangingwall of the Lewis thrust that were penetrated by the Pacific-Atlantic Flathead No. 1 well, 20 km southeast of the windows, represent new units that are stratigraphically lower than the Tombstone Mountain and Haig Brook Formations, and comprise the lowest stratigraphic units known from the Clark Range salient of the Lewis thrust sheet.
STRATIGRAPHIE DE LA BASE DU SUPER-GROUPE BELT-PURCELL (PROTEROZOIQUE MOYEN) DANS LA NAPPE LEWIS DU SUD ALBERTA ET DE LA COLOMBIE BRITANNIQUE
RESUME
Dans la nappe Lewis, la cartographie detaillee de la partie nord du segment de la chaine de Clark a conduit a reviser les correlations stratigraphiques a l'interieur de la nappe, et a permis de montrer que d'importants changements de facies lateraux existent vers sa base. Dans le Sud-Est de la Colombie Britannique, les strates situees immediatement au-dessus du contact de base sont exposees autour de deux fenetres structurales. Ces strates, qui etaient precedemment correlees avec la formation Waterton, consideree comme l'unite la plus inferieure de la nappe, apparaissent maintenant localisees sous cette formation. Deux nouvelles unites, la formation Haig Brook et la formation Tombstone Mountain, sont proposees pour cet interval stratigraphique entre le chevauchement et la base redefinie de la formation Waterton. Vingt km au Sud-Est des fenetres structurales, les strates qui furent traversees par le forage Pacific-Atlantic Flathead No. 1 a la base de la nappe sont aussi de nouvelles unites, stratigraphiquement inferieures aux formations Tombstone Mountain et Haig Brook.
Traduit par B. Collot
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