THE STRATIGRAPHIC SIGNIFICANCE OF A FOSSILIFEROUS SHALE IN THE LOWER PART OF THE RAYTOWN LIMESTONE MEMBER OF THE IOLA LIMESTONE (UPPER PENNSYLVANIAN) IN EASTERN KANSAS

There is a growing body of evidence that suggests that many of the Carboniferous cyclothems in the midcontinent region of the United States are not simply one transgressive-regressive cycle, but rather they are composed of two or more smaller cycles. These smaller cycles would presumably be of a shorter temporal duration, and hence are more compatible with recent interpretations concerning the waxing and waning of Gondwanan glaciation. The Iola Limestone is a major cycle or cyclothem that occurs along an outcrop belt that extends from Iowa to Oklahoma, and along the northern part of this belt it contains the typical repetition of lithofacies that characterizes a major cycle or cyclothem. The more marine part of the cycle is packaged between the nearshore to terrestrial facies of the thick outside-shales, and the offshore part of the cycle consists of a thin transgressive-limestone, a black core-shale (presumable representing maximum transgression), and a thicker regressive-limestone. In the central part of the Iola outcrop belt the core-shale thins dramatically (from over 1 m. to around 10 cm.), and the core-shale lithologies and part of the overlying regressive-limestone lithologies pinch out or lap out onto a surface that lies on top of the transgressive limestone.

An analysis of this surface and the overlying and underlying facies is critical to determining the nature of the cyclicity in the Iola. In the northern part of the study area the core shale is thick and organic and overlies the transgressive limestone by a sharp contact. In the south it is very thin fossiliferous shale that overlies an erosional contact with a phosphatic lag at the base. In the south the core shale is very similar to shale in the lower part of the regressive limestone in the north, and if it is the same stratigraphic layer, then it is very likely that the Iola is two cycles. This would imply that facies, rather than just changing laterally, are lapping out onto this surface making it disconformable and a cycle boundary. Bulk samples were collected at seven localities of the Iola, and the samples have been processed and examined to characterize the fossil assemblage in the shales.