THE IOLA LIMESTONE – A CLASSIC KANSAS CYCLOTHEM, OR IS It? QUESTIONS FROM AN ANALYSIS OF VERTICAL AND LATERAL FACIES PATTERNS: UPPER PENNSYLVANIAN OF KANSAS AND IOWA

A cyclothem is a stratigraphic (transgressive –regressive) unit that is characterized by vertical repetition of specific lithofacies. Although the lithofacies that comprise a cyclothem seem to vary from region to region, a “Kansas Cyclothem” is characterized by a thin transgressive limestone, a thin offshore shale (“core shale”), a thicker regressive limestone, and a variable package of marginal marine and terrestrial facies. Is it possible that by looking for this specific repetition of lithofacies that one could miss important stratigraphic surfaces, such as unconformities or other discontinuities? This may have implications for the possible origin and duration of the cycle.

A detailed stratigraphic analysis of the Iola Limestone has been ongoing for several years. This has included measuring and sampling multiple sections in southern Iowa and eastern Kansas. Samples were examined petrographically for lithofacies assessment, and also processed for macrofossils and conodonts. Samples from a section in eastern Kansas yielded some interesting results. The samples from the upper part of the transgressive limestone had some unusually high yields for conodonts, and the taxa are those normally restricted to the overlying offshore (“core shale”) lithofacies (i.e. Gondollela). The upper part of the transgressive limestone of the Iola at this location has been interpreted as a hardground, and contains an open burrow network many of which with an oxide (pedogenic?) coating. Most of the offshore conodonts from this sample have this oxide coating and appear to be derived from these open burrows. This apparent stratigraphic leak has been the focus of a detailed lithofacies and paleontological study of the upper part of the transgressive limestone, the offshore shale, and the lower parts of regressive limestone in the Iola at a number of sections in eastern Kansas. The apparent stratigraphic leak occurs at sections where the actual offshore shale lithofacies appears to be either extremely thin or entirely missing. This suggests that this cyclothem may in fact be at least two high frequency sequences, and not a single classic cyclothem.