An ammonite zonation for the lower Jurassic of Canada and the United States - The Pliensbachian

This is the first in a series of papers intended to establish a Lower Jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the North American succession. Its development has been spurred by the need for high-resolution correlation between allochthonous terranes and the need for a standard to which microfossil sequences may be coupled.In North America the lower boundary of the Pliensbachian is drawn above the last echioceratids. The lower Pliensbachian is divided into, in ascending order, the Imlayi, Whiteavesi, and Freboldi zones; the upper Pliensbachian, into the Kunae and Carlottense zones. The Fannin Bay section in the Queen Charlotte Islands is designated the stratotype for the Whiteavesi, Freboldi, and Kunae zones; ideal stratotypes for the Imlayi and Carlottense zones are not presently known. Reference sections former illustrating the faunal associations that characterize all the zones are designated in western Nevada (the Sunrise Formation), northeastern Oregon (the Hurwal Formation), and northern British Columbia (the Spatsizi Group and Takwahoni Formation).The Polymorphitidae and Eoderoceratidae furnish the most important zonal indicators for the lower Pliensbachian; Oxynoticeratidae (Fanninoceras) and Hildoceratidae, for the upper Pliensbachian. Pseudoskirroceras imlayi and Acanthopleuroceras whiteavesi are described as new species. The presence of amaltheids in the northern parts of the allochthonous terranes permits a comparison with the northwest European succession at this level. Furthermore, the association in North America of typically east Pacific, Mediterranean, and northeast Asian species, as well as northwest European forms, emphasizes the critical importance of the North American Pliensbachian in achieving global correlations. </jats:p

Jurassic foraminifera from the Queen Charlotte Islands, British Columbia, Canada: Biostratigraphy, paleoenvironments and paleogeographic implications

Lower and Middle Jurassic (Sinemurian to Callovian) foraminifera were examined from 66 localities of the Queen Charlotte Islands, British Columbia, Canada. Over 200 species of well preserved benthic calcareous and agglutinated taxa belonging to 50 genera were identified. Foraminifera from the Lower Jurassic are represented by an abundant and diverse, Tethyan-derived calcareous assemblage, with Boreally derived agglutinated taxa becoming gradually more dominant in the upper Lower Jurassic to lower Middle Jurassic. Sedimentary strata and their faunal components and position of hiatuses correlate approximately with the Jurassic eustatic sea-level curve. Sea-level changes have resulted in a variety of depositional environments ranging from deep-water euxinic shales with abundant tuff beds, characterized by small pyritized foraminifera, to a well oxygenated outer shelf setting, characterized by a major faunal increase, to shoreface sandstones and conglomerates with absent to rare benthic foraminifera. A gradual shallowing from a slope- to a shelf-dominated deposition, with a magmatic arc provenance, is suggested for the Lower Jurassic, changing in the Middle Jurassic to an inner shelf to upper shoreface setting dominated by sedimentary strata of volcaniclastic origin. A marked faunal turnover is observed in the Lower Jurassic Whiteaves Formation (middle Toarcian) with the extinction of several earlier species and the appearance of a new diverse assemblage of 225 taxa. This turnover is also observed in the ammonite and radiolarian assemblages of the Queen Charlotte Islands. In comparison to the dominantly Tethyan-derived taxa of pre-middle Toarcian age, many of the species from the middle Toarcian are found in northern latitudes such as on the northern slope of Alaska, Arctic Islands and the Northwest Territories. Hence, foraminifera, in conjunction wit

Geology, Geochronology, Lithogeochemistry and Metamorphism of the Mahatta Creek Area, Northern Vancouver Island

BC Ministry of Energy and Mines, Geoscience Map 2011-3, 1:50 000 scale