Willwood Formation

Willwood Formation Stratigraphic range: Thanetian-Ypresian (Clarkforkian-Bridgerian) ~56–48 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Geological formation
Sub-units	Gray Bull beds, Sand Coulee beds, Sand Creek Facies, Wa-1 Zone
Lithology
Primary	Mudstone, shale
Other	Sandstone, conglomerate
Location
Coordinates	44°30′N 108°00′W / 44.5°N 108.0°W / 44.5; -108.0Coordinates: 44°30′N 108°00′W / 44.5°N 108.0°W / 44.5; -108.0
Approximate paleocoordinates	49°12′N 90°48′W / 49.2°N 90.8°W / 49.2; -90.8
Region	Wyoming
Country	USA
Extent	Bighorn Basin
Type section
Named for	Shale, mudstone, limestone
Willwood Formation (the United States) Willwood Formation (Wyoming) Show map of the United StatesShow map of WyomingShow all

The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or Clarkforkian, Wasatchian and Bridgerian in the NALMA classification.^[1][2]

Description[]

It consists of fine grained clastic rocks (mudstone and shale) interbedded with medium grained clastic rocks (sandstone) and sporadic conglomerates. The formation underlies portions of the Bighorn Basin of Big Horn, Hot Springs, Park and Washakie counties of Wyoming.^[3]

Dating[]

Radiometric dating of volcanic tuffs, combined with comparisons with other formations using magnetostratigraphy, using numerous samples from various levels of the formation suggest an age range of 55 - 52 million years ago, placing the Paleocene-Eocene boundary near the base of the formation.^[4]

Fossil content[]

Trace fossils have been found in the Willwood Formation.^[5] Fossil birds include Gastornis, Neocathartes and Paracathartes. A fossil alligatorid, namely Orthogenysuchus, was also found in this formation.

Wasatchian correlations[]

Wasatchian correlations in North America

Formation	Wasatch	DeBeque	Claron	Indian Meadows	Pass Peak	Tatman	Willwood	Golden Valley	Coldwater	Allenby			Margaret	Nanjemoy	Hatchetigbee	Tetas de Cabra	Hannold Hill	Coalmont	Cuchara	Galisteo	San Jose	Ypresian (IUCS) • Itaboraian (SALMA) Bumbanian (ALMA) • Mangaorapan (NZ)
Basin	Powder River Uinta Piceance Colorado Plateau Wind River Green River Bighorn	Piceance	Colorado Plateau	Wind River	Green River	Bighorn		Williston	Okanagan								Rio Grande	North Park	Raton	Galisteo	San Juan	Willwood Formation (North America)
Country	United States								Canada					United States		Mexico	United States
Copelemur
Coryphodon
Diacodexis
Homogalax
Oxyaena
Paramys
Primates
Birds
Reptiles
Fish
Insects
Flora
Environments	Alluvial-fluvio-lacustrine	Fluvial				Fluvial	Fluvio-lacustrine	Fluvial	Lacustrine		Fluvio-lacustrine		Deltaic-paludal	Shallow marine		Fluvial	Shallow marine	Fluvial		Fluvial		Wasatchian volcanoclastics Wasatchian fauna Wasatchian flora
Volcanic	Yes	No							Yes	No	Yes	No	Yes	No						Yes	No

See also[]

References[]

Bibliography[]

• Strait, S. G. 2001. New Wa-0 mammalian fauna from Castle Gardens in the southeastern Bighorn Basin. 33. 127–143.
• Clyde, W. C. 1997. Stratigraphy and mammalian paleontology of the McCullough Peaks, northern Bighorn Basin, Wyoming: Implications for biochronology, basin development, and community reorganization across the Paleocene-Eocene boundary - PhD thesis, .. University of Michigan.
• Polly, P. D. 1997. Ancestry and Species Definition in Paleontology: A Stratocladistic Analysis of Paleocene-Eocene Viverravidae (Mammalia, Carnivora) from Wyoming. 30. 1–53.
• Redline, A. D. 1997. Revision of the Wind River faunas, early Eocene of central Wyoming. Part 13. Systematics and phylogenetic pattern of early Eocene Hyopsodus (Mammalia: Condylarthra). Annals of Carnegie Museum 66. 1–81.
• Maas, M. C., and M. O'Leary. 1996. Evolution of molar enamel microstructure in North American Notharctidae (primates). Journal of Human Evolution 31. ..
• O'Leary, M. A., and K. D. Rose. 1995. New mesonychian dentitions from the Paleocene of the Bighorn Basin, Wyoming. Annals of Carnegie Museum 64. 147–172.
• Wing, S. L.; J. Alroy, and L. J. Hickey. 1995. Plant and mammal diversity in the Paleocene to Early Eocene of the Bighorn Basin. Palaeogeography, Palaeoclimatology, Palaeoecology 115. 117–155.
• Bown, T. M.; K. D. Rose; E. L. Simons, and S. L. Wing. 1994. Distribution and stratigraphic correlation of upper Paleocene and lower Eocene fossil mammal and plant localities of the Fort Union, Willwood, and Tatman formations, southern Bighorn Basin, Wyoming. 1540. 1–103.
• Tauxe, L.; J. Gee; Y. Gallet; T. Pick, and T. Bown. 1994. Magnetostratigraphy of the Willwood Formation, Bighorn Basin, Wyoming: new constraints on the location of Paleocene/Eocene boundary. Earth and Planetary Science Letters 125. 159–172.
• Gunnell, G. F., and P. D. Gingerich. 1991. Systematics and Evolution of Late Paleocene and Early Eocene Oxyaenidae (Mammalia, Creodonta) in the Clarks Fork Basin, Wyoming. 28. 141–180.
• Zhou, X., and P. D. Gingerich. 1991. New Species of Hapalodectes (Mammalia, Mesonychia) from the Early Wasatchian, Early Eocene of Northwestern Wyoming. 28. 215–220.
• Ivy, L. D. 1990. Systematics of Late Paleocene and Early Eocene Rodentia (Mammalia) from the Clarks Fork Basin, Wyoming. 28. 21–70.
• Gingerich, P. D., and H. A. Deutsch. 1989. Systematics and Evolution of Early Eocene Hyaenodontidae (Mammalia, Creodonta) in the Clarks Fork Basin, Wyoming. 27. 327–391.
• Thewissen, J. G. M., and P. D. Gingerich. 1989. Skull and Endocranial Cast of Eoructes melanus, a New Palaeoryctid (Mammalia: Insectivora) from the Early Eocene of Western North America. Journal of Vertebrate Paleontology 9. 459–470.
• Bown, T. M., and K. D. Rose. 1987. Patterns of Dental Evolution in Early Eocene Anaptomorphine Primates (Omomyidae) from the Bighorn Basin, Wyoming. 23. 1–162.
• Gingerich, P. D. 1987. Early Eocene bats (Mammalia, Chiroptera) and other vertebrates in freshwater limestones of the Willlwood Formation, Clark's Fork Basin, Wyoming. 27. 275–320.
• Gunnell, G. F. 1985. Systematics of Early Eocene Microsyopinae (Mammalia, Primates) in the Clark's Fork Basin, Wyoming. 27. 51–71.
• Bown, Thomas M., and Mary J. Kraus. 1983. Ichnofossils of the alluvial Willwood Formation (lower Eocene), Bighorn Basin, northwest Wyoming, U.S.A. Palaeogeography, Palaeoclimatology, Palaeoecology 43. 95–128. doi:10.1016/0031-0182(83)90050-0
• Winkler, D. A. 1983. Paleoecology of an Early Eocene mammalian fauna from paleosols in the Clarks Fork Basin, northwestern Wyoming (U.S.A.).. Palaeogeography, Palaeoclimatology, Palaeoecology 43. 261–298.
• Krause, D. W. 1982. Multituberculates from the Wasatchian Land-Mammal Age, Early Eocene, of Western North America. Journal of Paleontology 56. 271–294.
• Rose, K. D. 1981. The Clarkforkian Land-Mammal Age and Mammalian Faunal Composition Across the Paleocene-Eocene Boundary. 26. 1–197.
• Bown, Thomas M. 1979. New Omomyid Primates (Haplorhini, Tarsiiformes) from Middle Eocene Rocks of West-Central Hot Springs County, Wyoming. Folia Primatologica 31. ..
• Harrison, C. J. O. 1979. A new cathartid vulture from the lower Eocene of Wyoming. In C. J. O Harrison, C. A. Walker (eds.), 7–10. Studies in Tertiary Avian Palaeontology.
• Neasham, John W., and Carl F. Vondra. 1972. Stratigraphy and Petrology of the Lower Eocene Willwood Formation, Bighorn Basin, Wyoming. . _. .. doi:10.1130/0016-7606(1972)83[267:SAPOTL]2.0.CO;2