Willwood Formation

Willwood Formation
Stratigraphic range: Paleocene-Eocene
~55–52 Ma
↓
Type Geological formation
Unit of Bighorn Basin
Lithology
Primary Mudstone, shale
Other Sandstone, conglomerate
Location
Region  Wyoming
Country  USA

The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene.[1] It consists of fine grained clastic rocks (mudstone and shale) interbeded 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.[2]

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.[3]

Trace fossils have been found in the Willwood Formation.[4] Fossil birds include Gastornis, Neocathartes and Paracathartes. A fossil alligatorid, namely Orthogenysuchus, was also found in this formation.

References

  1. ↑ Neasham, John W.; Vondra, Carl F. (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.
  2. ↑ "Willwood Formation". USGS.
  3. ↑ Tauxe, L., Gee, J., Gallet, Y., Pick, T., & Bown, T. (1994). Magnetostratigraphy of the Willwood Formation, Bighorn Basin, Wyoming: new constraints on the location of Paleocene/Eocene boundary. Earth and planetary science letters, 125(1), 159-172.
  4. ↑ Bown, Thomas M.; Kraus, Mary J. (31 July 1983). "Ichnofossils of the alluvial Willwood Formation (lower Eocene), Bighorn Basin, northwest Wyoming, U.S.A". Palaeogeography, Palaeoclimatology, Palaeoecology. 43 (1–2): 95–128. doi:10.1016/0031-0182(83)90050-0.
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