Chapter 9: Upper Jurassic To Paleogene Assemblages

Yorath, C J; Stott, D F; Dixon, J; Gabrielse, H; Anderson, R G; Souther, J G; Woodsworth, G J; Tipper, H W; Monger, J W H; Brown, A. Sutherland; Campbell, R B; Dodds, C J

doi:10.4095/134093

Cited by 3 publications

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“…The only preserved Cretaceous strata in the Mackenzie Mountains are found in a fault‐bounded outlier in the hanging wall of the Plateau Fault [ Blusson , ]. These strata have a minimum thickness of 1300 m [ Turner et al ., ], and the repetitive sandstone, conglomerate and coal successions are proposed to represent nonmarine deposition from meandering streams [ Yorath , ]. Analysis of pollen in the strata indicate that the lower 700 m of the section has a post‐Barremian to late Albian age, and a poorly defined plant fossil assemblage in the upper 600 m suggests a youngest age of Coniacian to Campanian [ Turner et al ., ].…”

Section: Discussionmentioning

confidence: 99%

“…Analysis of pollen in the strata indicate that the lower 700 m of the section has a post‐Barremian to late Albian age, and a poorly defined plant fossil assemblage in the upper 600 m suggests a youngest age of Coniacian to Campanian [ Turner et al ., ]. Some authors have suggested that deposition of this Cretaceous succession occurred in an intermontane setting [ Dixon , ]; however, our model results support the interpretation of these fluvial deposits filling an Aptian foredeep in front of the emerging Mackenzie Mountains to the southwest, possibly developing into an intermontane basin as the Mackenzie Mountains evolved throughout the Late Cretaceous [ Gabrielse , ; Yorath , ; Gordey et al ., ]. We are hesitant to predict exactly how far this Early Cretaceous system may have extended over the Mackenzie Mountains, as the source for the Albian strata 150 km to the northeast in the Mackenzie Plains is almost certainly from the craton to the east [ Yorath and Cook , ; Thomson et al ., ].…”

Section: Discussionmentioning

confidence: 99%

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Zircon (U‐Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

et al. 2016

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Sedimentary strata of the Neoproterozoic Mackenzie Mountains Supergroup (MMSG) and Windermere Supergroup (WSG) occupy the cores of anticlines in the Mackenzie Mountains of the Canadian Cordilleran Foreland Belt. Stratigraphic and structural evidence suggest that these rocks have undergone several episodes of burial and unroofing relatively intact. We report single‐grain detrital muscovite 40Ar/39Ar and zircon (U‐Th)/He (ZHe) data from a suite of samples across the fold‐thrust belt and the Neoproterozoic stratigraphic record. The strata have not reached high enough temperatures to reset the muscovite 40Ar/39Ar system, and instead our detrital muscovite data refine Tonian‐Cryogenian depositional ages. Single‐crystal ZHe dates range from 432 ± 35 to 46 ± 4 Ma, indicating that MMSG and WSG strata have not been heated sufficiently to fully reset the ZHe system. These factors make the Neoproterozoic strata an attractive natural laboratory to test the utility of the zircon radiation damage and annealing model on the quantification of thermal histories from detrital zircon populations that have accumulated radiation damage over long geologic timescales. Thermal modeling reveals that (1) a substantial sedimentary package was deposited following the Devonian and removed during Permo‐Triassic cooling, and (2) the Cordilleran deformation front propagated through the study area from the Albian to the Paleocene, with a moderate increase in cooling rates between 75–67 Ma in the southwest and 60–55 Ma at the deformation front. Ultimately, relationships between radiation damage and helium diffusion kinetics in zircon explain substantial ZHe date dispersion and elucidate the temperature‐time history of the northern Canadian Cordillera.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Zircon (U‐Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

et al. 2016

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“…At Late Cretaceous initiation of Nanaimo Group deposition, Wrangellia Terrane had accreted to the west coast of North America and was bordered to the west by the accretionary complex related to subduction of the Kula or Farallon ocean plate (Yorath 1991). The centre of coeval plutonism is located approximately 150 km to the east of the present location of the Nanaimo Group and at least twice that distance from the western edge of the Wrangellia Terrane, which had become the leading edge of the North American plate (Friedman et al 1995).…”

Section: Geologic Settingmentioning

confidence: 99%

The basal unconformity of the Nanaimo Group, southwestern British Columbia: a Late Cretaceous storm-swept rocky shoreline

2006

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The Turonian to Santonian Comox Formation forms the basal unit of the Nanaimo Group. In the southern Gulf Islands of British Columbia, the Comox Formation nonconformably overlies Devonian metavolcanic and Jurassic intrusive rocks and is interpreted to reflect a rocky foreshore reworked by waves and ultimately drowned during transgression. The nonconformity displays a relief of metres to tens of metres. Basal deposits vary in thickness, as does the facies character along the several kilometres of paleoshoreline studied. In the study area, three distinct but related environments are expressed, typical of a complex rocky shoreline with headlands and protected coves. Crudely stratified conglomerates represent gravel-dominated fans characterized by debris-flow processes, building out from local coastal cliffs and gullies directly onto the rocky shoreline. Fine-grained basal units represent shoreline environments protected from higher energy shoreline processes, presumably in small embayments. Sandstone facies associations reflect stormdominated shoreface environments. The unusual thickness and coarseness of these shoreface intervals suggest a combination of increasing accommodation space, proximal and high sediment supply, and high frequency and energy of storm activity. This, in turn, suggests that the majority of the shoreline was exposed to the full effects of large, openocean storms. This interpretation differs from most previous models for the lower Nanaimo Group, which suggest that deposition occurred in more sheltered strait or bay environments.Résumé : La Formation de Comox (Turonien à Santorien) comprend l'unité de base du Groupe de Nanaimo. Dans les îles du sud du golfe de la Colombie-Britannique, la Formation de Comox repose en discordance sur des roches méta-volcaniques dévoniennes et sur des roches intrusives du Jurassique; cette formation est interprétée comme le reflet d'un estran rocailleux retravaillé par les vagues et finalement submergé au cours d'une transgression. La discordance pré-sente un relief de mètres à des dizaines de mètres. Les dépôts à la base et le faciès ont une épaisseur variable le long des kilomètres de paléorivage étudié. Dans la région à l'étude, trois environnements distincts mais reliés sont définis; ils sont typiques d'un rivage rocailleux complexe avec des caps et des anses protégées. Des conglomérats à stratifications mal définies représentent des éventails de gravier caractérisés par des écoulements de débris; ils sont construits à partir de falaises côtières et de ravins, directement sur le rivage rocailleux. Les unités basales à grain fin représentent des environnements de rivage protégés contre des processus de rivage à énergie plus élevée, probablement dans de petites baies. Les faciès associés au grès reflètent des environnements d'avant-plage dominés par des tempêtes. L'épaisseur et la grosseur inhabituelles des sédiments de ces intervalles d'avant-plage suggèrent plus d'espace, un approvisionnement proximal et abondant de sédiments et une grande fréquence de tempêtes...

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“…Extensional tectonics dominated the region in the Eocene prior to the widespread EoceneNeogene volcanism (Riddell 2011). All the rock sequences underwent mid-Cretaceous compression and Late Cretaceous to Paleocene transcurrent faulting (Yorath 1991). Widespread Eocene volcanic sequences and Miocene flood basalts overlie Mesozoic sedimentary and volcanic sequences.…”

Section: Introductionmentioning

confidence: 99%

Mapping crustal structure of the Nechako–Chilcotin plateau using teleseismic receiver function analysis^,

et al. 2014

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This paper presents results of a passive-source seismic mapping study in the Nechako-Chilcotin plateau of central British Columbia, with the ultimate goal of contributing to assessments of hydrocarbon and mineral potential of the region. For the present study, an array of nine seismic stations was deployed in 2006-2007 to sample a wide area of the Nechako-Chilcotin plateau. The specific goal was to map the thickness of the sediments and volcanic cover, and the overall crustal thickness and structural geometry beneath the study area. This study utilizes recordings of about 40 distant earthquakes from 2006 to 2008 to calculate receiver functions, and constructs S-wave velocity models for each station using the Neighbourhood Algorithm inversion. The surface sediments are found to range in thickness from about 0.8 to 2.7 km, and the underlying volcanic layer from 1.8 to 4.7 km. Both sediments and volcanic cover are thickest in the central portion of the study area. The crustal thickness ranges from 22 to 36 km, with an average crustal thickness of about 30-34 km. A consistent feature observed in this study is a low-velocity zone at the base of the crust. This study complements other recent studies in this area, including active-source seismic studies and magnetotelluric measurements, by providing site-specific images of the crustal structure down to the Moho and detailed constraints on the S-wave velocity structure.Résumé : Cet article présente les résultats d'une étude de cartographie sismique, de sources passives, dans le plateau de Nechako-Chilcotin, au centre de la Colombie-Britannique; le but ultime de l'étude est de contribuer aux évaluations du potentiel d'hydrocarbures et de minéraux de la région. Pour cette étude, un réseau de neuf stations sismiques a été déployé en 2006-2007 pour échantillonner un vaste secteur du plateau de Nechako-Chilcotin. Le but spécifique était de cartographier l'épaisseur des sédiments et de la couverture volcanique, ainsi que l'épaisseur en général de la croûte et sa structure géométrique sous le secteur à l'étude. L'étude utilise des enregistrements d'environ 40 séismes éloignés entre 2006 et 2008 pour calculer les fonctions de réception; elle construit des modèles de vitesse pour l'onde S pour chaque station au moyen de l'inversion de l'algorithme de voisinage. Les sédiments à la surface ont une épaisseur de 0,8 à 2,7 km et celle de la couche volcanique sous-jacente est de 1,8 à 4,7 km. Les sédiments et la couverture volcanique atteignent leur épaisseur maximale dans la portion centrale du secteur à l'étude. L'épaisseur de la croûte varie de 22 à 36 km, avec une épaisseur moyenne d'environ 30 à 34 km. Une caractéristique constante observée dans cette étude est la zone à faible vitesse à la base de la croûte. La présente étude s'ajoute aux autres études récentes dans ce secteur, dont les études sismiques de sources actives et les mesures magnétotelluriques; elle fournit des images, spécifiques aux sites, de la structure de la croûte jusqu'à la profondeur du Moho, et encadre, de ma...

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Chapter 9: Upper Jurassic To Paleogene Assemblages

Cited by 3 publications

References 0 publications

Zircon (U‐Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

Zircon (U‐Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

The basal unconformity of the Nanaimo Group, southwestern British Columbia: a Late Cretaceous storm-swept rocky shoreline

Mapping crustal structure of the Nechako–Chilcotin plateau using teleseismic receiver function analysis^,

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Chapter 9: Upper Jurassic To Paleogene Assemblages

Cited by 3 publications

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Zircon (U‐Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

Zircon (U‐Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

The basal unconformity of the Nanaimo Group, southwestern British Columbia: a Late Cretaceous storm-swept rocky shoreline

Mapping crustal structure of the Nechako–Chilcotin plateau using teleseismic receiver function analysis,

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Mapping crustal structure of the Nechako–Chilcotin plateau using teleseismic receiver function analysis^,