The Mississippian Section for the North Alabama and Tennessee Valley area, compared with the Illinois Standard Section of southwest Illinois. The North Alabama Section is based on Drahovzal, 1967 and Thomas, 1972, and the Kentucky section is based on Ettensohn and others, 1984.

Carboniferous Period 354 to 290 Million Years

The Carboniferous Period is the international term used for the coal bearing sedimentary rocks. The Carboniferous in North America is divided into the mostly marine limestone Mississippian Period, Lower Carboniferous, and the mostly terrestrial sandstone, muds, and coal beds of the Pennsylvanian Period, Upper Carboniferous. They are easily distinguished from one another and have become internationally recognized sub-periods of the Carboniferous. This was a time of active mountain building to the east and the many changes in sea level causing the many sedimentary changes across the North American continental region. This was a period of active plate movement and causing the mountain building in and around the North America plate. The Carboniferous Period is one of the most economically valuable Geological Ages with the massive high quality limestones of the Mississippian Period, Lower Carboniferous and coal, natural gas, and oil of Pennsylvanian Period the Upper Carboniferous.

Mississippian Period 354 to 325 Million Years

A warm shallow sea covered the North American mid-continent area during the Mississippian Period. Extensive Mississippian marine outcrops are exposed across the Tennessee Valley and are primary divided into the lower and upper parts. The lower part of the Mississippian is primarily composed of the Fort Payne Chert and Tuscumbia Limestone throughout the Tennessee Valley Region. Most of the exposed Mississippian rocks around the Tennessee Valley are from these intervals and are composed of thick limestones, see Figure 5. The lower interval represents deep basin deposits grading to a shallow marine carbonate platform. The Fort Payne Chert is a chert-limestone unit that overlies the black Chattanooga Shale at the base of the Mississippian Period and under the Tuscumbia Limestone. Along the Tennessee River at Florence, Alabama the Fort Payne appears to be an even mix of dark gray, blue gray, brown cherts and gray limestones. Some fine silicified fossils can be found in the Fort Payne Chert interval all across the area. Many nice arrowheads are made from these cherts. You can identify the Fort Payne Chert when you see a lot of reddish to yellowish colored weathered chert with the characteristic large crinoid stem segments or casts of these crinoid stem segments in the cherts. The large crinoid stem segments are common in this interval and were called Indian money when I was very young.

The Tuscumbia Limestone is a thick light gray cross bedded limestone with layers of light gray/white chert nodule lenses that overlies the Fort Payne Chert and under the Monteagle Limestone/Pride Mountain Formation. Colony corals (tabulate) are generally found in the Tuscumbia Limestone interval and many times echinoid plates and spines are seen on the bedding plains. Many Paleozoic Shark Teeth of all types have been found in this interval. Fish, especially boney fish and the Chondrichthyes, the sharks, rays and their relatives, became common and diversified in the oceans of the world. Chondrichthyes, Shark and Ray, teeth can be found scattered throughout the Mississippian limestone outcrops of the area.

The upper Mississippian Section, Chester Series is composed of two primary lithofacies across the Tennessee Valley. The Chester Series begins with clay shale, shale, and sandstone units present in the western area, Pride Mountain Formation, and gradually grades northeasterly into a limestone with some shale intervals present in the eastern area, the Monteagle Limestone. The Pride Mountain Formation is the northeastward extension of the Floyd Shale from west Alabama that lies under the Hartselle interval (Thomas, 1972) in North Alabama. The Pride Mountain Formation is primarily a dark gray–grey clay shale unit with some barrier sandstones units in west Alabama with occasional thin fossiliferous limestones. Marine fossils like the brachiopod Chonetes, the coral Favosites, and cephalopods are commonly found in association with the thin limestones and rarely a crinoid or Ammonite (Goniatites) can be found.

The Monteagle Limestone was named for Monteagle, Tennessee, the type section for this unit. Huntsville, Alabama in the Heart of the Tennessee Valley is well known for its Monteagle Limestone fossils. Monteagle Limestone fossils have been collected here for over 150 years by many famous Paleontologists and many fossil collectors. The Blastoid, Pentremites, is easy to recognize and is one of the most common fossils from the Ste. Genevieve interval and Chester series in the Huntsville area. When I was young these blastoids were referred to as “rose buds” and you could ask people who lived in the area if they knew where some rose buds were and they would direct you to a spot for you to go look. No one will know the area you want to collect better than the people that live there. You will be able to find new areas to collect fossils with a little help, your knowledge, interests, and effort. Remember fossils are common and easy to find, you may not find what you are looking for today but with a little persistence and experience you gain each time you go collecting you’ll likely find what you are looking for in time.

The lowermost Monteagle Limestone, St. Genevieve interval - Platycrinites huntsvillae Zone, is well developed in Huntsville and is famous for the crinoids collected within. Platycrinites huntsvillae a Camerate crinoid is the most common crinoid found in this interval, and is also used as an index fossil of the St. Genevieve interval because its unique stem is easy to recognize in the sedimentary units. The southern edge of the Tennessee Valley is the southern most occurrence of Platycrinites huntsvillae Troost, 1850. Residential subdivisions have been built upon most of the St. Genevieve Glades of Huntsville so very few St. Genevieve age fossils can be found today. Due to the changes that took place in the marine environmental conditions throughout the central basin a vast change in the crinoid population took place at the close of the St. Genevieve though brachiopods and other invertebrates were virtually unaffected. Camerate crinoids became a minor element in most of the crinoid communities and Cladid crinoids such as Zeacrinites, Agassizocrinus, and Phanocrinus dominated most crinoid communities throughout the Chester. The Chester Series is marked by the appearance of Pentremites godoni and the crinoids Zeacrinites Phanocrinus and abundant Agassizocrinus. Pentremites godoni, Agassizocrinus IBB cones, horn coral, and brachiopods are the most common fossils found in the Monteagle Limestone above the Platycrinites Zone, St. Genevieve age.

The Hartselle Formation is predominantly a light colored fine grain sandstone interval across the region referred to as the Hartselle Sandstone, and was named for Hartselle, Alabama. The Hartselle Formation is a thick sandstone unit in the western area and a sandstone, clay shale, and limestone unit in the eastern area around Huntsville, thins eastward, with the sandstone disappearing in this interval just east of Madison County. A great assortment of marine fossils can be found in the limestones and shales of the Hartselle interval around Huntsville. Eastward of Huntsville the Hartselle interval grades into the Monteagle limestone below and the Bangor Limestone above. You can not differentiate the Monteagle from the Bangor Limestone where the Hartselle interval is missing in the eastern area. Most of the plant fossils found in the Chester section have been associated with the sandstones of the Hartselle Interval. Very thin coal/lignite seams have been observed in some Hartselle interval shale units. Lepidodendron, Sigillaria, and their roots Stigmaria, Calamites, and a few other plant fossils have been observed from the Hartselle interval. A 10-12 foot section, by about 16-18 inches wide, Lepidodendron was present in a 2 foot thick block of Hartselle Sandstone on Mathus Mountain before a subdivision road was built over it. This is the largest plant fossil cast I have seen in the Hartselle interval. Plant fossils can be found in the Pride Mountain Formation, Hartselle Interval, Pennington and Parkwood Formations. Not much is know about the terrestrial ecosystem of the Mississippian, and amphibian and tetrapods continued to diversify and insects were apparently common.

The Bangor Limestone is the thick bedded crinoidial limestones having thin shaly partings above the Hartselle interval and below the clastic Parkwood and Pennington Formations. Marine fossils like brachiopods, bryozoans, corals, and echinoderms are common in the limestone shale intervals of the Bangor Limestone. There are some large coral reefs present above some of the oolitic limestones of the area. The Bangor Limestone grades into the Parkwood Formation and Floyd Shale in the west and south parts of the region. The Upper Bangor grades into the Pennington in the central and northeast parts of the Region. The Parkwood represents coastal and lagoonal muds with barrier sand bars and is similar to the Floyd/Pride Mountain Formation in having dark grey/grey clay shales. It is differentiated in having interbeds of grey/light grey very to fine grained micaceous argillaceous calcareous sandstones.