No abstract

Analysis of the distribution of coral taxa, principally genera and subgenera, in the Mississippian of the Western Interior Province of Canada and the conterminous United States permits recognition of a system of coral zones and subzones useful for correlating stratigraphic units throughout an area extending from the southwestern District of Mackenzie in the Northwest Territories of Canada to southern California in the United States. The zonation comprises six Oppel zones, four of which are divided into locally useful subzones. Coral Zone I corresponds approximately to the Kinderhookian Provincial Series and is divided into Subzones A, B, and C. Coral Zone II corresponds approximately to the Osagean Provincial Series and is divided into Subzones A and B. The Tournaisian Stage of western Europe is represented by Coral Zones I and II. Coral Zone III corresponds approximately to the lower and middle parts of the Meramecian Provincial Series and is divided into Subzones A, B, C, and D. Coral Zone IV corresponds approximately to the upper part of the Meramecian and is not divided. Coral Zone V corresponds approximately to the lower and middle parts of the Chesterian Provincial Series and is divided into Subzones A and B. Coral Zone VI corresponds approximately to the upper part of the Chesterian and is not divided. The Visean Stage of western Europe is represented by Coral Zones III and IV and Subzone VA. The lower part of the Namurian Stage of western Europe is represented by Coral Subzone VB and Zone VI. Deep-water and shallow-water coral biofacies are discussed and integrated into the zonation system. The coral zones are correlated with foraminifer and conodont zones, which provide the primary bases for establishing ranges of coral taxa. Forty-five coral genera and subgenera used in the zonation are diagnosed, discussed, and illustrated. Correlations of Mississippian formations in the Western United States and Western Canada are presented as examples of the utility of the coral zonation.

Conodonts, radiolarians, foraminiferids, and corals provide constraints on the geology and tectonics of the Nechako region. They also support the notion that the Cache Creek Terrane is allochthonous with respect to the North American craton. The 177 conodont collections, assigned to 20 faunas, range in age from Bashkirian (Late Carboniferous) to Norian (Late Triassic); 70 radiolarian collections representing 12 zones range from Gzhelian (Late Carboniferous) to Toarcian (Early Jurassic); 335 collections assigned to 11 fusulinacean assemblages (with associated foram-algal associations) range from Bashkirian to Wordian (Middle Permian); and two coral faunas are of Bashkirian and Wordian age. The fossils document a long but sporadic history of sedimentary events within the Cache Creek Complex that included two major carbonate buildups in the Late Carboniferous (Pope limestone) and Middle Permian (Copley limestone), punctuated by intervening Early Permian deepening; basaltic eruptions during the mid Carboniferous and mid Permian; the onset of oceanic chert sedimentation close to the Carboniferous–Permian boundary and its persistence through the Late Triassic (Sowchea succession); latest Permian and Early Triassic mixed clastics and volcanics (Kloch Lake succession); Middle and Late Triassic reworking of carbonates (Whitefish limestone), including cavity fill in older limestones (Necoslie breccia), and fine-grained clastic sedimentation extending into the Early Jurassic (Tezzeron succession). Tethyan, eastern Pacific, and (or) low-latitude biogeographic attributes of the faunas are noted in the Gzhelian (fusulines), Artinskian (conodonts, fusulines), Wordian (fusulines, corals, conodonts), and Ladinian (conodonts, radiolarians). The Cache Creek Terrane lay far to the west of the North American continent during these times.

Regional stratigraphic and fauna distribution data from 5 surface stratigraphic sections and 37 subsurface sections indicate the following ages and stratigraphic relationships within the Lower Carboniferous succession of the area. The Banff Formation (Early? and Middle Tournaisian, Plains), which consists of shale with minor amounts of siltstone and limestone, passes westward into equivalent shale and chert of the Besa River Formation. The Pekisko Formation (Middle Tournaisian, Plains), composed of skeletal limestone and wackestone, and the "Shunda'' Formation (Late Tournaisian, Plains), comprising argillaceous limestone, calcareous shale and minor amounts of skeletal and pelletoid limestone, change facies westward, near the eastern edge of the disturbed belt, into the upper Besa River Formation and Member A of the Prophet Formation, and are equivalent to the upper Clausen and lower Flett formations to the north (southern Mackenzie Mountains). The lower member of the Debolt Formation (Early and Early Middle Visean, Plains), composed of micritic and skeletal limestone, wackestone and calcareous shale, grades westward into the cherty dolomite and limestone of Member B of the Prophet Formation and is correlated with the limestone and calcareous shale of the middle Flett Formation. The upper member of the Debolt Formation (Late Middle and Early Late Yisean, Plains) consists of pelletoid, micritic, argillaceous and skeletal limestone with minor amounts of calcareous shale and dolomite, and is correlative with the cherty, skeletal limestone of Member C and the upper part of Member B of the Prophet Formation, and with the skeletal limestone and calcareous shale of the upper Flett Formation. The cherty carbonates of the Prophet Formation(Late? Tournaisian to Early Late Yisean) occur in the outcrop belt and westernmost plains of northeastern British Columbia and change facies into the Besa River Formation by a progressive increase in shale and chert from base to top toward the west. The Stoddart Group (Early Late Vi sean to Pennsylvanian), which consists of terrigenous elastics and carbonates, occurs in the plains and outcrop belt of northeastern British Columbia, and grades northward into the coarse-grained, partly continental elastics of the Mattson Formation, and westward into the shale of the Besa River Formation. Eleven Middle Tournaisian to Late Yisean foraminiferal zones within the area correspond to zones previously established for the North American Cordillera, and correlate with the original Lower Carboniferous stratigraphic sequence of Eurasia. There is a consistent relationship between the vertical and lateral distribution of foraminiferal zones and associated macro faunal assemblages. With minor exceptions, the combined fauna succession of this area matches that in southwestern Alberta and western United States and forms part of a consistent biostratigraphic scheme applicable to Lower Carboniferous rocks throughout western North America.

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