The Wellington Formation is an Early Permian geologic formation in Kansas and Oklahoma. The formation's Hutchinson Salt Member is more recognized by the community than the formation itself, and the salt is still mined in central Kansas. The Wellington provides a rich record of Permian insects and its beddings provide evidence for the reconstruction of tropical paleoclimates of the Icehouse Permian with the ability in cases to measure the passage of seasons. Tens of thousands of insect fossils recovered from the Wellington shales are kept in major collections at the Harvard Museum of Comparative Zoology and Yale Peabody Museum of Natural History.

Initially described as marine shales, the 500–700 feet (150–210 m) thick Wellington appears mostly as dark gray, thinly bedded soft rock, much of it terrestrial, with sediments from fresh water ponds and salt lakes. There are several variable beds of anhydrite and gypsum and the central body of most of the formation is a massive salt bed. Localized red beds and green shales indicate conditions of exposed soils with shallow freshwater tables. Marine fossils are limited to the lowest beds while the remainder features freshwater species and land life, particularly insects and reptiles.

Compared to the earlier Permian rock formations in the midcontinent, the Wellington is somewhat more restricted in range. The Wellington is identified in western Kansas, northwest Oklahoma, and the northeast corner of the Texas Panhandle, but with no identification in Nebraska (compare with relative extension of the underlying Chase Group into Nebraska and Eastern Kansas). The surface outcrop lies generally along or between the north–south highways U.S. 81 and U.S. 77. South of Salina into northern Oklahoma, the westward dipping Wellington lies under a broad, shallow valley; here, the upper Wellington has collapsed as the Hutchinson Salt member has dissolved, forming lowlands including the McPherson Valley Wetlands and the Wellington-McPherson Lowlands. West of this valley, the Wellington shales gradually slope deeper underground beneath the Ninnescah Shale, but the unit extends no further West than the western Kansas border.

At a time of extreme global glaciation, the location of the Wellington deposit was equatorial and glacier-free. The climate was generally arid but with cyclic variation in global temperatures and precipitation recorded by layers of windblown dust deposited in the basin.

The habitable environment, while initially a marine embayment, was primarily non-marine, with great many cyclic variations between dry, fresh water, brackish water, and brine.

The Wellington is not particularly rigorously divided into subunits as few easily identifiable features are consistent other than the dark shale; but certain subdivisions are recognized. Broadly, the Wellington shales are divided into an upper Wellington shale member and a lower Wellington shale member. However, these informally named divisions are based only upon the position of the Hutchinson Salt Member in the general middle of the formation, which is usually but not always present.

Some limestone beds, typically dolomite, are observed within these upper and lower shale divisions, variously ranked as members, and the otherwise unnamed adjoining shales may be classified with the named limestones. Like the salt, each is not always recognizably present.

The upper Wellington consists primarily of interbedded cycles of gray anhydritic mudrock and red mudrock, but includes limited beds of discontinuous limestone and dolomite.