Yazoo Clay

{{Short description|Geologic formation in the United States}}

{{Infobox rockunit

| name = Yazoo Clay

| image =

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| type = Formation

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| prilithology = clay

| otherlithology = sand, marl

| namedfor = Yazoo River

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| region = {{Flag|Alabama}}, {{Flag|Louisiana}}, and {{Flag|Mississippi}}

| country = United States

| coordinates =

| unitof = Jackson Group

| subunits = North Twistwood Creek Member, Cocoa Sand Member, Pachuta Marl Member, and Shubuta Member

| underlies =

| overlies = Moodys Branch Formation

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}}

Yazoo Clay is a clay geologic formation in Alabama, Louisiana, and Mississippi. It was named after a bluff along the Yazoo River at Yazoo City, Mississippi.{{cite journal |last1=Monroe |first1=Watson H. |title=Geology of the Jackson Area Mississippi |journal=United States Geological Survey Bulletin |date=1954 |volume=986 |pages=56–62 |url=https://pubs.usgs.gov/bul/0986/report.pdf |access-date=27 June 2018}} It contains is a type of clay known as montmorillonite, making it a poor foundation material due to the fact that moisture causes extreme changes in volume. Sand, pyrite, and marl have all been noted in the formation. It preserves fossils from the Eocene, including the prehistoric cetaceans Basilosaurus and Zygorhiza, and the marine snake Pterosphenus.{{cite journal |last1=Breard |first1=Sylvester Q. |last2=Stringer |first2=Gary L. |date=1995 |title=Paleoenvironment of a Diverse Marine Vertebrate Fauna from the Yazoo Clay (Late Eocene) at Copenhagen, Caldwell Parish, Louisiana |url=https://w2.vetmed.auburn.edu/drw0004/Whale%20papers/Breard_Stringer_1995_GCAGSv45_VertFaunaYazoo_Copenhagen0077.pdf |journal=Gulf Coast Association of Geological Societies Transactions |volume=45}} Sharks, rays, eels, and fish have also been found from the formation.https://www.mdeq.ms.gov/wp-content/uploads/2017/06/Circular_1.pdf