Yellow Cat Member
| Cedar Mountain Formation Stratigraphic range: Early Cretaceous |
|
|---|---|
| Type | Geological formation |
| Sub-units | See text |
| Underlies | Naturita Formation |
| Overlies | Morrison Formation |
| Thickness | 0–410 ft (0–125 m) |
| Lithology | |
| Primary | Conglomerate, sandstone, mudstone |
| Location | |
| Region | Utah |
| Country | United States |
| Type section | |
| Named for | Cedar Mountain |
The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah. The formation was named for Cedar Mountain in northern Emery County, Utah, where William Lee Stokes first studied the exposures in 1944.
The formation occurs between the underlying Morrison Formation and overlying Naturita Formation (sometimes formerly called the Dakota Formation).
It is composed of non-marine sediments, that is, sediments deposited in rivers, lakes and on flood plains. Based on various fossils and radiometric dates, the Cedar Mountain Formation was deposited during the last half of the Early Cretaceous Epoch, about 127 - 98 million years ago (mya).
It has lithography similar to the Burro Canyon Formation in the region.
Dinosaur fossils occur throughout the formation, but their study has only occurred since the early 1990s. The dinosaurs in the lower part of the formation differ from those in the upper part. These two dinosaur assemblages, characterized by distinct dinosaurs, show the replacement of older, European-like dinosaurs with younger, Asian-like dinosaurs as the North American Continental Plate drifted westward. A middle dinosaur assemblage may be present, but the fossil record is not clear.
The Cedar Mountain Formation is sandwiched between the Morrison Formation below and the Naturita Formation and Mancos Shale above. The youngest date for Morrison just below the Cedar Mountain Formation is 148.1 ± 0.5 Ma . or lower Tithonian. Typically, the Jurassic-Cretaceous boundary in western North America is marked by an unconformity of variable length, and typically signifies 10-49 million years of missing geologic time. This boundary between the Morrison and Cedar Mountain is commonly marked by a horizon of carbonate nodules or by highly polished pebbles that are allegedly gastroliths.
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Wikipedia