THE MISSISSIPPIAN STRATIGRAPHIC SEQUENCE AND INDEX MACROFOSSILS IN NORTH ALABAMA

Mississippian marine sediments (359 to 323 Ma) are uniformly exposed across north Alabama and are generally very fossiliferous. There are seven main intervals in the Mississippian stratigraphic sequence in the Tennessee Valley: the Maury Shale, Fort Payne Chert, Tuscumbia Limestone, Pride Mountain Formation-Monteagle Limestone interval, Hartselle interval, lower Bangor Limestone, and upper Chester interval (upper Bangor, Pennington, Parkwood). Mississippian strata are dominated by marine carbonates and marine invertebrate, vertebrate fossils, and locally plants, are common in Mississippian sediments in the Tennessee Valley of north Alabama. Marine macrofossils (biostratigraphy) and stratigraphic succession are used to correlate strata in north Alabama with other areas of the Eastern Interior. Crinoids evolved more rapidly than other readily preserved marine fauna and are particularly useful in Mississippian biostratigraphy. Blastoids, brachiopods, bryozoans, and corals are also useful. Crinoid communities of the Fort Payne Chert are dominated by a diverse set of monobathrid camerates. The two diagnostic St. Louis corals species of Acrocyathus are common in the upper Tuscumbia Limestone. Cladid crinoids became more diverse than camerates that dominate all crinoid populations in the lower Monteagle Limestone (St. Genevieve). A major reorganization of the echinoderm community occurred in the transition to the middle Monteagle (Gasper), cladid crinoids dominated nearly all the crinoid communities in numbers and species present. Archimedes became very common in the middle Chester (Hombergian) as another reorganization of the echinoderm community occurs. Generally smaller in size and represented by far fewer species camerate crinoids occasionally dominated a crinoid community in the middle and upper Chester.