Tennessee's Geology: Landscapes and Sedimentary Rocks

The state of Tennessee is very diverse. This is characterized by the variety of landscapes in the area. Tennessee landscape is majorly made up of these landforms; river valley plains, highlands and basins, and mountains. Tennessee is also divided into three; East Tennessee, Middle Tennessee and West Tennessee. The East Tennessee includes the Unaka located in the Great Smoky mountains, the Valley and Ridge Province and all or part of the Cumberland Plateau and Mountains regions. Middle Tennessee is made up of low-lying area known as the Central or Nashville Basin which is surrounded by higher grounds of the Highland Rim. West Tennessee starts at the northward- flowing reach of Tennessee River and it include the Western Valley of Tennessee, the Tennessee parts of the Mississippi River Flood Plain at the western edge of the state, and the Plateau Slope of West Tennessee (Luther). The Paleozoic sediments found in the middle Tennessee were mainly deposited from the Ordovician to the Mississippian about 400 and 300 million years ago. The West Tennessee is made up of Mesozoic sediments and the Coon Creek formation is one of the formations. Most of Cenozoic deposits occurs in the west Tennessee near the Mississippi embayment as sands and silts. In 1979, sedimentary rock was declared the state rock in Tennessee because it is the predominant rock found out throughout Tennessee.

The Coon Creek formation has its location in Western Tennessee and in the extreme North west Mississippi. As noted by (Pryor and Glass, 38-51) Coon Creek formation is of cretaceous period of about 70 million years ago. Tennessee during this period was submerged by Mississippi Embayment. It was formed in shallow costal water of less than 100 feet deep, and the sea flow was initially populated with crab, and lobsters amongst other sea animals (Wade, 272). Geologists have employed biostratigraphy in the determination of the age of the Coon Creek formation. (Russell and Parks, 111), described biostratigraphy to being the use of index fossils in dating sedimentary rock units, and further define index fossils as species of plants or animals whose existence was to be over a vast area for a geological short period of time. In their record of Coon Creek formation, they were able to find the cephalopods Jeletzkytes nodosus found in rocks was younger than 70.6 million years old, while other fossils found were older than 70.6 million years old. This suggested that Coon Creek sediments deposits were probably deposited between 71 to 70 million years ago.

The shells of the cephalopods and reptilian bones were buried under the sandy mud of the sea floor. There is lack of distinct strata formation caused by burrowing organisms which mixed up the bottom sediments of Coon Creek formation. The fossil abundance in Coon Creek formation has made it to be amongst the top – twelve fossils sites in the United States; sometimes they can be even found on top of each other (Noble, 16-22). It is explained that the fossils of the Coon Creek formation have not been affected by groundwater or replaced by different minerals hence, the fossils tend to be found in their original state. Also, Coon Creek Formation got a very high concentration of minerals as compared to other sites that require concentration efforts to find a representative sample. Unconsolidated sediments in Coon Creek Formation also made it easy to collect and prepare samples.

The Appalachian Plateau of the Appalachian Mountains is made up of Cumberland Plateau and the Allegheny Plateau. The Cumberland Plateau is the Southeastern Plateau of the Appalachian Plateau and portion of the northern Alabama and northern Georgia are the region where the Cumberland Plateau comes. In Tennessee for instance, Cumberland Plateau western borders is the Highland Rim which is east of the Nashville Basin and Sequatchie Valley on the eastern plateau which extends to Alabama.

The sedimentary rocks that made up the Cumberland Plateau are of both the Mississippian (between 323 million year ago and 346 million years ago) and the Pennsylvanian (between 278 million years ago and 315 million years ago), and are mostly composed of near shore sediments washed toward the west progressively from the old Appalachian Mountains. Rocks layers laid down in shallow costal water were then interlaced with delta formation made up sandstones and sometimes conglomerates. About 285 Million years ago the beds were deposited horizontally were raised high enough to get eroded then lowered then there was deposition of more sediments on the eroded beds causing numerous discontinuities in the beds. Lateral erosion of the plateau has caused the bedrock of the formation to have age differences even by a move less than a tenth of an inch. There are dramatic cliffs, arches, rocks shelters, chimneys, and other interesting geologic features that are caved into the sandstone of the plateau.

The St. Louis Limestone Formation covers a wide area of the Midwest of the United States and is exposed in western Kentucky, and Middle Tennessee, including the city of Clarksville in Tennessee. The limestone deposits are said to come into existence or was formed about 330 – 340 million years ago, meaning it is a Mississippian limestone deposit. (Thompson, 252) in his exploration about the Stratigraphic sequences of St. Louis limestone, said that the formation nearly consists of sedimentary with scattered cherts beds, including river cherts bed on the Horse cave Member. The St. Louis limestone in Tennessee can be divided into two; the Upper St. Louis which consists about one – eighth to one – third of the total formation. It is made up of mainly thin beds of medium – to dark gray – brown micritic, pelleted, and skeletal limestone and very thin beds of medium – gray Shales (Carr, et al., 225). The lower St. Louis limestone is made up of mainly pelleted micritic limestone, Calcareous Shale, and silty dolostones. The common fossils found in St. Louis Limestone include the rugosan corals, and the bryozoan Fenestrellina.

The Chattanooga formation which covers five states including Tennessee, Arkansas, Alabama, Missouri and Kentucky. Fossils that date back to the Devonian periods have been found preserved in this formation, indicating the age of Chattanooga formation is approximately 419.2 to 358.9 million years old. Chattanooga Shale is surface geology with layers of Shale and it is located in Eastern Tennessee and it is reported to be an extension of and correlates with the Marcellus shale of the Appalachian region to the east. Chattanooga shale has been of interest to explorers as it has indicated the presence of significant amount of gas. The Chattanooga shale is an organic, hydrocarbon rich shale located throughout the Eastern Tennessee (Chattanooga Shale Natural Gas Field, oilshalegas.com).

There are other small formations like Lebanon limestones which is of Ordovician and is composed of thin – bedded gray limestone with calcareous shale partings. Nashville formation is the other which is also of Ordovician and is a brownish gray phosphatic calcarenite and light – gray to brownish gray, with fine to medium grains. This formation usually has a thickness of about 50 – 125 feet. The Hermitage formation is bedded in thin laminated beds of sandy and argillaceous limestone with shale; nodular snarly limestone and usually about 50 – 100 feet in thickness (Wilson, 407). Other formation is the Fort Payne formation which is Mississippian in age and is bedded chert, calcareous, and dolomitic silica-stone. It is also made up of minor limestone and shale that is scattered lenses of crinoidal limestone. It has thickness of about 250 feet but up to 475 feet in some areas like Wells Creek.

In summary the Geology of Tennessee is mainly mad up of sedimentary rocks which was even declared the state rock in 1979. Tennessee landscape is majorly made up of river valley plains, highlands and basins, and mountains. Tennessee is also divided into three; East Tennessee, Middle Tennessee and West Tennessee. The East Tennessee includes the Unaka located in the Great Smoky mountains, the Valley and Ridge Province and all or part of the Cumberland Plateau and Mountains regions. Middle Tennessee is made up of low-lying area known as the Central or Nashville Basin which is surrounded by higher grounds of the Highland Rim. West Tennessee starts at the northward- flowing reach of Tennessee River and it include the Western Valley of Tennessee, the Tennessee parts of the Mississippi River Flood Plain at the western edge of the state, and the Plateau Slope of West Tennessee. From the result we see that the main formations in Tennessee are; Coon Creek, Chattanooga formation, Cumberland Plateau formation, and St. Louis limestone. Despite the major formations there are other small formations like Lebanon limestone, Nashville formation, Hermitage formation and Fort Payne formations.