The transitional belt between Missourian rocks of Kansas and Oklahoma is characterized by complex facies and faunal relations and traditionally has been a subject of controversy. In contrast to the laterally persistent limestone beds of Kansas which terminate north of the state boundary as algal buildups, limestone beds of the transitional belt are local and consist of thin calcarenite and calcilutite, thick oolitic beds, and algal buildups. Where fossiliferous, intervening shale beds are dominated by crinoids and mollusks. Stratigraphic evidence indicates that the Hogshooter and Dewey Limestones of Oklahoma are not equivalent to the Dennis and Drum Limestones of Kansas. In Oklahoma the Iola Limestone disappears a few miles south of the state boundary. On the basis of cri oid evolution, the Iola interval farther south is considered to be above the Avant Limestone.

Lower Missourian Apographiocrinus typically has ornate surface markings which progressively disappear in evolution. Apographiocrinus arcuatus from the Avant Limestone retains some markings, whereas A. typicalis from slightly higher strata is essentially devoid of surface pustules. The latter species is from the Iola Limestone near the state line and the Wann Formation on the south. Two algal buildups are identified in the Avant. The Wann Formation consists of shale, sandstone, and several lenticular limestone beds. The limestone, previously referred to the Birch Creek Limestone, is known to occupy several stratigraphic positions. A Lansing unit, informally termed the "Tyro oolite," is present in southern Kansas and northern Oklahoma and bears Cibolocrinus conicus, Apographiocrinus typ calis, and other forms characteristic of Kansas Lansing limestones.

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