Wayan Formation
| Wayan Formation Stratigraphic range: Early Cretaceous - Late Cretaceous |
|
|---|---|
| Type | Geological formation |
| Underlies | Sage Junction Formation |
| Overlies | Smiths Formation |
| Thickness | 1,344 meters in western Tincup Canyon area, Caribou County |
| Location | |
| Region | North America |
The Wayan Formation is a geological formation in Idaho whose strata date back to the latest Early Cretaceous and the earliest Late Cretaceous. Dinosaur, other reptile, mammal, and micro and macro-floral remains are among the fossils that have been recovered from the formation. The lack of extensive outcrops, limited geographic extent, and extreme structural deformation have limited paleontological explorations of the Wayan.
The Wayan occurs in the Caribou Mountains of eastern Idaho. Sediments are dominantly floodplain mudstones (many having undergone extensive pedogenic processes) with some fluvial sandstones and minor conglomerates, limestones, and tuffs. Carbonate nodules in pedogenic mudstones suggest a semi-arid, seasonal climate during deposition. Radiometric U-Pb dates from detrital zircons indicate a latest Albian to early to middle Cenomanian age. Detrital zircon U-Pb dating within one stratigraphic meter of an Oryctodromeus locality yielded an age of 99.1 +1.5/-1.3 Ma showing proximity to the Albian/Cenomanian stage boundary.
The Wayan is equivalent to the upper Cedar Mountain Formation of Utah, the Aspen Shale of Wyoming, and the Vaughn member of the Blackleaf Formation of Montana.
The vertebrate fauna is dominated by the small basal ornithopod Oryctodromeus, which dominates the vertebrate assemblage and is known from several partial skeletons. An ankylosaur, a Tenontosaurus-like iguanodontid, a hadrosaurid, dromaeosaurs, a tyrannosauroid, a possible neovenatorid allosauroid, a giant oviraptorosaur (represented by eggshell of the oogenus Macroelongatoolithus carleylei), indeterminate small theropods, possible neoceratopsians, large and small crocodilians, turtles, a variety of small mammals, and semionotid fish are known from very fragmentary remains.
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