The timing of coalification in relation to structural events in the Grande Cache area, Alberta, Canada

Abstract

Lower Cretaceous coals from the inner Foothills of the Rocky Mountains were sampled for a study of the relationships between coal rank and folding and faulting. The coals were collected from laterally continuous seams in a highly folded and faulted area near Grdnde Cache, Alberta. Rank of the coals as determined by measuring mean maxinlum vitrinite reflectances ranges from medium-to low-volatile bituminous.The results indicate that the degree of coalitication was established during burial from Albian to Late Paleocene times, before folding and faulting started. "Isoreflectance" lines run parallel to the bcdding of thc folded strata, and there are no significant changes in reflectances in the same seam from one thrust sheet to the other. However, in the footwall of the Mason Thrust, the mean maximum reflectances and biretlectances are locally increased above regional values.Regionally there appears to be a trend to slightly lower reflectances in the southeast of the study area. It is suggested that the lower reflectances are related to a somewhat lesser former depth of burial of the coals, probably of the order of 50 rn.Les charbons du CrktacC infkrieur des Foothills internes des Rocheuses ont kt@ kchantillonnCs pour Ctudier les relations entre la catkgorie du ckarbon et les plis et failles. Les Cchantillons de charbon ont Ct C prklevks dans des veines d'extension latkrale continue dans une rkgion, intenskment plissee et faillke, prks de Grande Cache, en Alberta. La catCgorie de charbon telle que dkterminCe par la moyenne des rnesures maximales de la rktlectance de la vitrinite varie de houilles contenant des matikres volatiles en quantitk faible a moyenne.Les resultats rkvklent que le degrk de la carbonification fut ktabli durdnt l'enfouissement qui a pris place entre 19Albien et le Palkockne supkrieur, avant le dChut de la dkformation responsable des plis et failles. Les lignes d'isorkflectance se maintiennent pamllkleinent au litage des strdtes plisskes, et il n'existe pas de ckangements significatifs des rkflectances au sein d'une veine donnke appardissant dans une nappe de chamage ou une autre. Les valeurs moyennes des rkflectances et birktlectanees maximales sont plus klevCes que les valeurs rkgionales uniquement en certains emplacements sur la lkvre inferieure de la faille Mason.Dans la partie sud-est de la rkgion CtudiCe appariit une tendance regionale d'une diminution faible des rktlectances. Nous cnjyons que cette attknuation des ktlectances est due i un enfouissement des charbons plus faible profondeur. possiblement de l'ordre de 50 m.[Traduit par la r e~u e ]Can.

Environmental Aspects of Trace Elements in Coal

“…Samples were collected very closely, when possible, to monitor the variation of B content (Table 4.5). Boron content of these seams is in the range of 10-40 ppm, in agreement with freshwater depositional environment (Kalkreuth and Langenberg, 1986), indicating a stable depositional environment during formation of the coal seams. The coals with brackish setting (B: > 110 ppm) are mainly in the western areas indicating the direction of brackish water intrusion into the coal forming area.…”

Burial and temperature evolution in thrust belt systems: Sedimentary and thrust sheet loading in the SE Canadian Cordillera

“…[34] Finally, the importance of tectonic loading is also documented by England and Bustin [1986a], Kalkreuth and Langenberg [1986], Kalkreuth et al [1989], and Langenberg et al [1998] with clear examples of higher OMRs in some footwall blocks of significant thrusts in the area. We thus conclude that simple correlation to stratigraphic depth, as from organic maturation by sedimentary burial, does not fit with the OMR distribution in these highly imbricated thrust sheet stacks.…”