The Weberg and Warm Spring members of the Snowshoe Formation in Suplee area, Oregon: Lithofacies and Aalenian-early Bajocian ammonoid zonation

This paper documents the stratigraphic information upon which an ammonoid zonation from the lower part of the Snowshoe Formation in the Suplee area was originally established (Taylor, 1988). Ammonoid ranges from 22 measured stratigraphic sections reveal about 60 ammonoid species distributed among eight zones encompassing the late Aalenian and part of the early Bajocian stages. The sediments are dominantly volcaniclastic and, as a result, there are numerous tuff beds in the succession. As noted in Taylor (1982) the principal tuff beds (herein designated as units A through F) can be used jointly with the ammonite sequence to give precise correlations from section to section. Utilizing the ammonoids, tuff beds, and facies in combination gives a graphic representation of the westward transgression of the Snowshoe Formation as it enveloped an irregular topography, and lapped onto the topographically high Grindstone High to the west. The ammonoid zonation is significant in that it gives a standard of reference for the biochronology of the late Aalenian and early Bajocian ammonoids in the North American Western Cordillera.