Lower triassic stages and ammonoid zones of Arctic Canada

Nine ammonoid zones are recognized in an unusually complete section of marine Lower Triassic rocks exposed on Ellesmere and Axel Heiberg Islands. These zones are grouped into four new stages, named, in ascending order, Griesbachian, Dienerian, Smithian and Spathian. The Spathian strata a r e followed conformably by beds with early Anisian (Middle Triassic) ammonoids . The Lower Triassic rocks of Western Canada are dated in terms of these stages. The stages may fill a need for named sub divisions within the Lower Triassic and provide a standard for rocks of this age throughout the world. Comparison with alternative classifications shows the need for the new subdivisions.