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TitreThe hydrogeological characteristics of the Upper Cretaceous De Courcy Formation (Nanaimo Group), from a subsurface core, groundwater observation well, Cedar, British Columbia
TéléchargerTéléchargements
AuteurHamblin, A P; McCartneny, T
SourceCommission géologique du Canada, Dossier public 7628, 2014, 30 pages, https://doi.org/10.4095/294859
Année2014
ÉditeurRessources naturelles Canada
Documentdossier public
Lang.anglais
DOIhttps://doi.org/10.4095/294859
Mediaen ligne; numérique
Formatspdf
ProvinceColombie-Britannique
SNRC92B/13; 92F/01; 92F/08; 92G/04
Lat/Long OENS-124.6667 -123.5000 49.5000 48.7500
SujetsCrétacé supérieur; eau souterraine; ressources en eau souterraine; régimes des eaux souterraines; aquifères du substratum rocheux; aquifères; milieu sédimentaire; antecedents de sedimentation; cadre tectonique; roches sédimentaires; grès; conglomérats; Formation de De Courcy ; Groupe de Nanaimo ; Formation de Comox ; Formation d'Haslam ; Formation d'Extension ; Formation de Pender ; Formation de Protection ; Formation de Cedar District ; Formation de Northumberland ; Formation de Geoffrey ; Formation de Spray ; Formation de Gabriola ; hydrogéologie; sédimentologie; Mésozoïque; Crétacé
Illustrationslocation maps; cross-sections; stratigraphic columns; photographs
Consultation
Endroit
 
Bibliothèque de Ressources naturelles Canada - Ottawa (Sciences de la Terre)
 
ProgrammeAquifer Assessment & support to mapping, Géoscience des eaux souterraines
Diffusé2014 07 15
Résumé(disponible en anglais seulement)
A new inquiry into the groundwater potential of the Nanaimo Lowlands was jointly undertaken by concerned municipal, provincial and federal agencies because rapid population growth and expanding industrial development are, and will continue to, put pressure on the limited groundwater resources. The bedrock component of the project focused on the characterization of the aquifer potential of the Upper Cretaceous Nanaimo Group, as a likely target of importance. This unit is a thick succession of 11 intertonguing sandstone-dominated and shale-dominated formations, of which only the lower 8 are present in the defined study area. As one step in the analysis, a 112.5 m core was obtained as part of the drilling of a Groundwater Observation Well in the Cedar area of Vancouver Island, about 10 km SE of Nanaimo City centre. The entire length of the core comprises the mid-Nanaimo Group, sandstone-dominated (potential aquifer zone) De Courcy Formation, the uppermost coarse grained formation in the study area. The De Courcy Formation present in the studied core is characterized by stacked, thick bedded medium to coarse grained arkosic sandstone separated by units of bioturbated sandy siltstone with thin finer grained sandstone. It includes two main facies: 1) thick bedded, grey medium to coarse grained sandstone interpreted as high-energy density current and turbidity flow deposits emplaced in a moderately deep marine setting on the surface of, and in channels on, a northwestward-sloping submarine fan system, with minor thin beds of bioturbated siltstone, and 2) thinly interbedded dark grey bioturbated siltstone to sandy siltstone interpreted as lower-energy, background sedimentation on the surface of the submarine fan systems, and very fine to medium grained sandstone, interpreted to represent slower, more distal, higher-energy density current turbidity flow events which occasionally punctuated that quiet background sedimentation. The thick bedded sandstone facies represents about 65% of the strata in the core, and has porosity ranging 2.0 to 10.2 %, averaging 6.8 %, and permeability ranging 2.8 to 105.0 mD, averaging 24.4 mD. In thin section, these sandstones are predominantly feldspathic litharenites and lithic arkoses with abundant plagioclase, volcanic rock fragments, quartz and chert, in a clay matrix. Multiple, laterally-extensive units of thick, porous and permeable sandstone, up to 6 m thick, likely represent significant aquifer horizons within the De Courcy Formation. The interbedded siltstone and thin sandstone facies occupies about 35% of the core strata and has porosity ranging 4.0 to 9.7 %, averaging 7.4 %, and overall permeability ranging 1.8 to 40.0 mD, averaging 12.7 mD. However, within this facies, the thin sandstone beds have an average permeability of 15.4 mD, whereas the bioturbated siltstones have average permeability of only 5.4 mD. Multiple, laterally-extensive units of interbedded siltstone and thin sandstone, up to 6 m thick, may represent significant aquitard horizons within the De Courcy Formation. These results, although derived from the De Courcy Formation only, may display comparative analogies to the characteristics of the other (uncored) potential aquifer zones present lower in the Nanaimo Group; the Comox, Extension and Protection formations.
Résumé(Résumé en langage clair et simple, non publié)
Dans le cadre des travaux sur le potentiel des eaux souterraines des unités du groupe de Nanaimo, une carotte de forage de 112,5 m de longueur a été obtenue d'un puits d'observation près du village de Cedar, sur l'île de Vancouver. L'ensemble de la carotte est dominé par les grès (aquifère potentiel) de la formation de De Courcy et se caractérise par d'épais lits gréseux, grains de moyens à grossiers (65 % de la carotte) avec des unités interstratifiées de siltstone. Les grès ont une perméabilité et une porosité décente et peuvent former des aquifères souterrains, tandis que les siltstones ont une porosité et une perméabilité plus faible et peuvent former des barrières à l'écoulement des eaux souterraines. Plus important encore, les caractéristiques affichées dans cette carotte servent d'analogues pour les couches en profondeur qui pourraient contenir d'autres aquifères potentiels en profondeur au sein du groupe de Nanaimo (Comox, Extension, formations de Protection), pour lesquels nous n'avons aucune données.
GEOSCAN ID294859