The mid-Carboniferous Arctic Lake Formation, northwestern Stikine terrane, British Columbia

Abstract

The Lower Devonian to Upper Permian Stikine Assemblage is well exposed in northwestern British Columbia, near the west-central margin of the Stikine terrane. The stratigraphic base of the assemblage is not exposed and the Upper Triassic Stuhini Group disconformably overlies the assemblage locally. The assemblage consists mainly of various types of volcanic rocks, and there is a large, polyphase, Devono-Mississippian sub-volcanic plutonic complex. The assemblage includes a distinctive, but laterally discontinuous mid-Carboniferous limestone named the Arctic Lake Formation. Facies are mainly locally re-worked, well-bedded skeletal wackestone, but whole fossil floatstone and intraformational olistostromal deposits are present. Stratigraphic thickness varies from 32 to 80 metres. Stratigraphic contacts with bounding Lower and Upper Carboniferous successions are conformable and intergradational, but paraconformities may also be present. The formation records weak development of disjointed carbonate ramps on volcanic highlands. Neritic faunal assemblages have warm water, open marine affinity. The formation spans the Serpukhovian-Bashkirian boundary and encompasses microfacies assigned to Global Foraminiferal zones 17, 18 and 20. Integrated foraminiferal-coralconodont biostratigraphy and uranium-lead geochronology support a circa 350 Ma age for the Tournaisian-Visean boundary, and a circa 320 Ma age for the Serpukhovian-Bashkirian (Mississippian-Pennsylvanian) boundary. RÉSUMÉLe Dévonien inférieur, jusqu'à l'assemblage de Stikine du Permien supérieur, a une bonne exposition au nord-ouest de la Colombie Britannique, près de la marge centrale-ouest du terrane de Stikine. La base stratigraphique de l'assemblage n'affleure pas, et le Groupe Stuhini du Trias supérieur recouvre localement l'assemblage de façon discordante. L'assemblage est composé principalement de types variés de roches volcaniques, et comporte un large complexe sous-volcanique plutonique polyphasé du Dévonien-Mississippien. Cet assemblage inclut un calcaire distinctif mais latéralement discontinu du médio Carbonifère appelé la Formation Arctic Lake. Localement, les faciès sont le plus souvent remaniés, et se composent de wackstones squelettiques bien stratifiés. Cependant, des floatstones contenant des fossiles entiers, ainsi que des dépôts olistostromes intraformationnels, sont présents. L'épaisseur stratigraphique varie de 32 à 80 mètres. Les contacts stratigraphiques entre les limites des successions inférieures et supérieures du Carbonifère sont

Distribution and Diversity of Carboniferous and Permian Colonial Rugose Coral Faunas in Western North America: Clues for Placement of Allochthonous Terranes

“…The greatest development of colonial rugose corals in the Mississippian of the western interior of North America (the Cordilleran miogeocline) was in the Meramecian (Viséan) [8]. For this paper the faunas of this age in the western Interior of Canada [8], Arctic Alaska [7], and the Alexander [6] and Stikine [10] terranes are compared. The Cache Creek terrane contains a completely different fauna [9].…”

“…The fauna of the Stikine terrane consists of Cystolonsdaleia, Eastonastraea, Heintzella, Lonsdaleoides and Nemistium [10]. These corals occur in strata containing zone 18 foraminifera (late Serpukhovian).…”

“…Although Cystolonsdaleia also occurs in both the Stikine terrane and the Canadian Interior, the Stikine fauna is much more diverse and contains a number of solitary and colonial coral genera of Mississippian age not present at a comparable time in cratonal North America. These genera (Dibunophyllum, Heintzella, Nemistium, and Palaeosmilia), however, occur in Euramerica and northwest Gondwana, including North Africa, where they occur at the same level [10].…”

“…Here I will first summarize knowledge on the colonial rugose coral faunas of the Mississippian, Pennsylvanian, Early Permian, and Middle Permian, and then use these data to interpret the location of the various terranes relative to one another and to the North American craton. Data on Carboniferous genera [6][7][8][9][10] are shown on Table 1 and distribution of Mississippian species is shown on Table 2. The present paper also includes information on the Late Paleozoic faunas of the North American craton [11] and that on three of the terranes, including the Stikine terrane [10] and the Eastern Klamath and Alexander terranes, the faunas of which are currently being studied.…”

“…Data on Carboniferous genera [6][7][8][9][10] are shown on Table 1 and distribution of Mississippian species is shown on Table 2. The present paper also includes information on the Late Paleozoic faunas of the North American craton [11] and that on three of the terranes, including the Stikine terrane [10] and the Eastern Klamath and Alexander terranes, the faunas of which are currently being studied. All of the Permian data have been shown on previously published tables [12].…”