Toarcian (Lower Jurassic) ammonite biostratigraphy and ammonite fauna of North America ...

• Main Author: Jakobs
• Format: Text
• Language: English
• Published: University of British Columbia 2008
• Subjects: Arctic; Alaska; Siberia; Yukon
• Online Access: https://dx.doi.org/10.14288/1.0052892; https://doi.library.ubc.ca/10.14288/1.0052892

Toarcian ammonite collections from British Columbia, Nevada, Oregon, the Yukon, and Alaska form the basis of a detailed taxonomic study. Fifty-seven species are described, allocated to 27 genera, one of which is new ( Yakounia). Nine new species are introduced: Yakouma yakounensis, Y. pacifica, Y. freboldi, Y. silvae, Pleydellia maudensis, P.crassiornata, Phymatoceras hillebrandti, Leukadiella n. sp. A, and Leukadiella n. sp. B. Measured sections from the Queen Charlotte Islands and other key areas in western North America were used to distinguish six successive assemblage zones: Kanense, Levisoni, lonica, Crassicosta, Hillebrandti, and Yakounensis. All six zones, which can be recognized from southern Alaska to Nevada, are defined here for the first time. The Arctic basins (Sverdrup and Brooks-MacKenzie) have a low diversity ammonite faunal sequence similar to that of Siberia and the zonation developed there can be used in Arctic North America. The Toarcian of western North America is most commonly ...