CYCLIC ALTERNATION OF UPPER ORDOVICIAN LIMESTONE AND MUDSTONE STRATA FROM THE MADISON, INDIANA AREA

Stratigraphic layers can be separated into various "units," or "bundles," with each containing a succession of thin interbeds. The area in and around Madison, Indiana displays numerous outcrops (Ordovician age) where these bundles can be seen. Each unit contains a succession of interbedded shelly carbonates and mudrocks, occurring in cycles of various scales. In order to further understand the development of these interbeds, limestone samples were taken from three outcrops in and around Madison, Indiana. Using a multidisciplinary approach, increased resolution of small, meter-scale cycles is possible; this approach constrains correlations by using faunal abundance data, lithology, geochemistry, geomorphic features, and thin section analysis. Cluster analysis of fossil abundance data displays various faunal associations. Thin section analysis will be used to quantify phosphate levels and fragmentation in limestone samples; this will be based on several classification schemes. Variation in the nature of phosphate formation will be recorded, reflecting paleo-environmental conditions and helping correlate layers within the area. Samples will be analyzed with XRF. Carbonate analysis of samples provides geochemical data on the precise composition of strata, further constraining correlations between localities and showing how the strata may have formed. Geomorphic features indentified in the Madison, Indiana area, such as waterfalls, refine correlations across the area. An integrated correlative approach allows for increased resolution of meter-scale cycles and will provide further clarity regarding the mechanisms behind shell-bed generation, especially in terms of generation by episodic sediment starvation.