PROBLEMS WITH A STRICT LITHOSTRATIGRAPHIC CLASSIFICATION SYSTEM IN THE PENNSYLVANIAN CHEROKEE GROUP OF THE MIDCONTINENT

A strict lithostratigraphic classification system for the Midcontinent Cherokee Group has led to a proliferation of names, mainly due to the fact that most states within the outcrop belt have a different classification system and “local” names for units abound. Most early (19^th and early 20^th centuries) mapped and named units were the economically important coals. Because of lateral variation in the character and thickness of the coal beds, use of laterally discontinuous sandstone bodies between the coals, and the fact there are more units to the south, there have been numerous problems of correlation of units within and between states. In Oklahoma and Missouri the Cherokee Group is divided into the Krebs and Cabaniss subgroups, while Iowa and Kansas do not use subgroups. Oklahoma has five formations, Missouri has at least seventeen formations, Iowa has five formations, while Kansas has two in the Cherokee. In Missouri, coals were considered to be the most persistent units, so the coals were placed at the top of the formations and the coal names were also used as formational names. This classification system, suggested by Searight and others in 1953, is the closest to an allostratigraphic (cyclothemic) classification system, used by any of the states, but is very confusing when looking at genesis of sediments. A cyclothem is defined as a package of rocks deposited during a single transgressive-regressive cycle, bounded by discontinuities which are often traceable laterally over wide areas. In the northern Midcontinent these unconformities are usually paleosols (top of underclays) below the coals. Most marine units within Cherokee cyclothems are only locally expressed (change facies), except for the high stand deposits which often contain abundant conodont faunas, which allow cyclothems to be correlated. Once the cyclothems have been defined and correlated by their conodont faunas, the discontinuities can be used to delineate the cyclothem boundaries. By placing the coal at the base of the cyclothem, rather than the top of the underlying formation as in lithostratigraphy, genesis of the units can be better understood. Thus a formal cyclothem classification system for the middle and lower Cherokee can be more useful than a strict lithostratigraphic classification system.