Nature
The Willwood Formation is a sedimentary unit in Wyoming underlying parts of the Bighorn Basin, deposited from the late Paleocene into the early Eocene about 55 to 52 million years ago, with the Paleocene-Eocene boundary near its base. Composed chiefly of fine-grained clastic rocks including mudstone and shale, with interbedded sandstone and occasional conglomerates, it has been dated through radiometric analysis of volcanic tuffs and magnetostratigraphic correlation. Its rich fossil record includes trace fossils, birds such as Gastornis, Neocathartes, and Paracathartes, the alligatorid Orthogenysuchus, and many mammals, making it crucial for studying faunal change in the Bighorn Basin across this transition.
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Wyoming · United States