Paleontological and chronostratigraphic correlations of the mid-Cretaceous Wayan-Vaughn depositional system of southwestern Montana and southeastern Idaho

ABSTRACT

The Mussentuchit Member of the Cedar Mountain Formation of eastern Utah represents the best source of data on Cenomanian vertebrate assemblages from North America. However, increasing data has recently been forthcoming from the late Albian to Cenomanian Wayan Formation of Idaho and Vaughn Member of the Blackleaf Formation of Montana, which are both at least partially coeval with the Mussentuchit Member. While the paleontological assemblages of the Wayan Formation and Vaughn Member are fragmentary, numerous vertebrate forms are represented, with the small burrowing neornithischian Oryctodromeus cubicularis dominating these assemblages. The differences between the Wayan Formation and Vaughn Member assemblages, the Mussentuchit and few other mid-Cretaceous assemblages are likely a result of some combination of preservational biases, paleogeography, and paleoenvironmental differences. The chronostratigraphy, fossil content, bracketing facies, and ages of the Wayan Formation and Vaughn Member suggest these sediments represent the same depositional system prior to disruption by subsequent tectonic and volcanic events. This assemblage from the Wayan Formation and Vaughn Member is here termed the Wayan-Vaughn Assemblage (WVA). Continued work in the WVA, particularly with microvertebrate materials, may reveal additional shared taxa between the WVA and other coeval units.

KEYWORDS:

• Idaho
• Montana
• Wayan Formation
• Vaughn Member
• Albian
• Cenomanian

Acknowledgments

Sincere thanks to the reviewers for the comments and critiques they provided that greatly increased the value of this report. Appreciation is expressed to Ted Dyman for field experience in the Vaughn Member and discussions of its possible relationship to the Wayan Formation. Thanks to Jim Kirkland and Dave Varricchio for providing images that were used in this report. Chase Brownstein and Ashley Ferguson critiqued initial versions of this report, Brooks Britt, Rod Scheetz, and the late William Tidwell assisted with the Wayan Formation foliage specimens. Thanks to Robert Simon for personal contributions that have supported this fieldwork.

Disclosure statement

No potential conflict of interest was reported by the author.