The Fayetteville Shale is a geologic formation of Mississippian age (354–323 million years ago) composed of tight shale within the Arkoma Basin of Arkansas and Oklahoma. It is named for the city of Fayetteville, Arkansas, and requires hydraulic fracturing to release the natural gas contained within. Nomenclature Named by Frederick Willard Simonds in 1891, Simonds recognized what is now the Fayetteville Shale as three separate formations overlying the now abandoned Wyman Sandstone: the Fayetteville Shale, the Batesville Sandstone, and the Marshall Shale. In 1904, the name "Fayetteville Shale" replaced all three of these names. The Fayetteville Shale that Simonds recognized is now considered as the lower Fayetteville Shale. Simonds' Batesville Sandstone was found to be the same as the Wyman Sandstone, and replaced the name "Wyman Sandstone", while Simonds' Batesville Sandstone became known as the "Wedington Sandstone Member" presumably after Wedington Mountain. The name Marshall Shale was abandoned and is now known as the upper Fayetteville Shale. Natural gas The formation holds natural gas in a fine-grained rock matrix which requires hydraulic fracturing to release the gas. This process became cost-effective in some shales such as the Fayetteville after years of experimentation in the Barnett Shale in North Texas, especially when combined with horizontal drilling. The Fayetteville Shale play began in July 2004 by Southwestern Energy Company in north-central Arkansas with the Thomas #1-9 vertical well in Conway County, Arkansas. In February 2005, Southwestern Energy drilled the first horizontal well, the Seeco-Vaughan #4-22H, also in Conway County. The US Energy Information Administration estimated that the shale play held 13,240 billion cubic ft (375 billion cubic meters) of unproved, technically recoverable gas. The average well was estimated to produce 1.3 billion cubic feet of gas. As of 2018, new drilling in the Fayetteville Shale had ceased and almost 1/5 of wells were abandoned. Paleontology Flora Because the Fayetteville Formation is a marine unit, most of the plants found in the black shales must have been washed into the Carboniferous sea from a landmass. However one unit within the formation, the Weddington Sandstone Member, is a series of river deposited sand beds. Fossil plants from this unit were probably deposited closer to their source. Adiantites A. minima Ankyropteris Archaeocalamites A. fayettevillensis A. gracilentus A. umbralis A. wedingtonensis Bothrodendron Carpolithus C. inquirenda Cardiopteris C. hirta Chlamidostachys C. chesterianus Lepidocystis L. chesterensis Lepidodendron L. henbesti L. occidentale L. purduei L. wedingtonense Lepidophloios Lepidophyllum L.