Misplaced Pages

Embayment Megagroup
Stratigraphic range: Eocene–Cretaceous
Type	Mega Group
Sub-units	Mounds Gravel, Grover Gravel Wilcox Formation Porters Creek Formation Clayton Formation Owl Creek Formation McNairy Formation Post Creek Formation
Thickness	upto ~1000'
Lithology
Primary	Sandstone, Clay
Other	Siltstone, Lignite
Location
Region	Alabama  Arkansas  Illinois  Kentucky  Mississippi  Missouri  Tennessee
Country	United States
Extent	Gulf Coast Plain to Southern Illinois

The Embayment Mega Group is found from the Gulf of Mexico north to southern Illinois.

Stratigraphy

Mounds Gravel

The Mounds Gravel is found in southern Illinois. It is composed of chert and quarts pebbles.

Grover Gravel

The Grover Gravel (Rubey, 1952) is found in western Illinois. Named for Grover, Missouri. It is composed of chert pebbles, quartz pebbles, as well as a matrix of quartz sand.

Willcox Formation

The Wilcox Formation is a sand formation that is part of the Embayment Megagroup. It runs from southern Illinois to the State of Mississippi. It thickens moving southward, starting at about ~20' thick in outcrops in Illinois to 250' thick in Mississippi.

Porters Creek Formation

The Porters Creek is found in southern Illinois. It is massive in nature and lacks bedding or has weak bedding surfaces. it is composed of over 80 percent montmorillonite. This clay is mined commercially in Pulaski County, Illinois.

Clayton Formation

The Clayton Formation is made up of clay. The clay is green to buff in color and is silty throughout. At the formation's base it becomes sandy with pebbles. The pebbles are made of chert and are black or white in color.

Owl Creek Formation

The Owl Creek Formation is a geologic formation ranging from Tennessee to Mississippi. It preserves fossils dating back to the Cretaceous period. Ornithomimids and ceratopsid remains are known from the formation. The ceratopsid tooth could represent a chasmosaurine.

McNairy Formation

The McNairy Formation was formed as a deltaic deposit. The upper and lower parts consists of cross-bedded white to light grey micaceous sand. The middle section is made up of grey to blackish silt, with beds of lignite. This formation is up to 450'.

Post Creek Formation

The Post Creek Formation was once called the Tuscaloosa Formation. It has been renamed due to inconsistencies with dating the formation. It is composed of chert gravel and has moderate cementations by silica or kaolinite.

Baylis Formation

The Baylis Formation is Cretaceous in age and found in the western sections of the Embayment Megagroup. It rests unconformably on Carboniferous age rock. It is composed of medium to fine grained quartz sand. The upper part of the formation is the Kiser Creek Member. It also contains lenses that may contain, clay, silt and pebbles. The lower member is the Hadley Gravel Member and contains mostly pebbles.

References

1. ^ Willman, H. B., and John C. Frye, 1970, Pleistocene Stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.
2. ^ Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.
3. Farke, Andrew A.; Phillips, George E. (2017-05-23). "The first reported ceratopsid dinosaur from eastern North America (Owl Creek Formation, Upper Cretaceous, Mississippi, USA)". PeerJ. 5: e3342. doi:10.7717/peerj.3342. ISSN 2167-8359. PMC 5444368.
4. Harrison, Richard W. and Ronald J. Litwin, 1997, Campanian coastal plain sediments in southeastern Missouri and southern Illinois— significance to the early geologic history of the northern Mississippi Embayment: Cretaceous Research 18, no. 5, p. 687-696.

Further reading

• "ILSTRAT". ilstratwiki.web.illinois.edu. Retrieved 23 March 2024.

• Cretaceous Alabama
• Cretaceous Arkansas
• Cretaceous Mississippi
• Cretaceous Missouri
• Cretaceous geology of Tennessee