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

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

Stratigraphy

Mounds Gravel

The Mounds Gravel is found in southern Illinois. It is composed of chert and quarts pebbles.Willman, H. B., and John C. Frye, 1970, Pleistocene Stratigraphy of Illinois: Illinois State Geological Survey Bulletin 94, 204 p.

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.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.

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 Montmorillonite is a very soft phyllosilicate group of minerals that form when they precipitate from water solution as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite grou ...

. This clay is mined commercially in

Pulaski County, Illinois Pulaski County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 5,193. Its county seat is Mound City. Its largest city is Mounds. It is located along the Ohio River in the southwestern po ...

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 A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

ranging from

Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...

to Mississippi. It preserves marine

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dating back to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

. Shark teeth and

mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains wer ...

remains are common.

Ornithomimid Ornithomimidae (meaning "bird-mimics") is an extinct family of theropod dinosaurs which bore a superficial resemblance to modern ostriches. Ornithomimids were fast, omnivorous or herbivorous dinosaurs known mainly from the Late Cretaceous Period ...

and

ceratopsid Ceratopsidae (sometimes spelled Ceratopidae) is a family of ceratopsian dinosaurs including ''Triceratops'', '' Centrosaurus'', and '' Styracosaurus''. All known species were quadrupedal herbivores from the Upper Cretaceous. All but one species are ...

remains are known from the formation. The ceratopsid tooth could represent a

chasmosaurine Chasmosaurinae is a subfamily of ceratopsid dinosaurs. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non- avian dinosaurs, during ...

McNairy Formation

The McNairy Formation was formed as a

deltaic A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creati ...

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 Lignite (derived from Latin ''lignum'' meaning 'wood'), often referred to as brown coal, is a soft, brown, combustible sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35% and is considered the lowest ...

. 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 Kaolinite ( ; also called kaolin) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina () ...

.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.

Baylis Formation

The Baylis Formation is

in age and found in the western sections of the Embayment Megagroup. It rests unconformably on

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

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.