CONJOINED USE OF STRATIGRAPHIC/PALEONTOLOGIC PARAMETERS IN ESTABLISHING A TEMPORAL FRAMEWORK FOR THE UPPER ORDOVICIAN (CARADOCIAN) LEXINGTON LIMESTONE, CENTRAL KENTUCKY, U.S.A

The Upper Ordovician Lexington Limestone of central Kentucky is a complex facies mosaic that largely reflects a carbonate platform and buildup, which formed during structural reactivation related to Taconian far-field forces. Since facies were controlled by faults reactivating at various times reflecting this facies mosaic, and the differences between buildup and off-buildup facies have never been completely reconciled because of similar facies and the absence of a temporal framework. Because no one technique has proved useful everywhere, we have relied on the conjoined use of several stratigraphic methods to establish a temporal framework, including 180 measured sections and cores to establish available lithostratigraphic correlations, over ten-thousand identified macrofossils, several with proven biostratigraphic value, correlatable event beds like bentonites and seismites, 754 stable-isotope data points, 118 trace-element data points, and recent radiometric dates from selected K-bentonites. Especially important are chemostratigraphic trends (i.e., Guttenburg Excursion and other minor regional and possibly global excursions) from stable-isotope (d¹³C) data selected from buildup, marginal-buildup, off-buildup areas. These data have contributed to correlation among some seemingly unrelated facies from the different areas in ways not previously expected. Superimposing these chemostratigraphic trends on established Caradocian conodont and graptolite biostratigraphy has served to make certain macrofossils more useful for detailed correlation in conjunction with regional stratigraphic cross sections. Impending U-Pb age dates on two key bentonites within the Lexington Limestone will hopefully provide an absolute framework in which to consider the various operating processes. At present we can clearly show correlations between buildup and off-buildup sections to the point that the Lexington Limestone in central Kentucky may serve as a model for a structurally controlled, carbonate-platform buildup. Furthermore, with added absolute control, we may also be able to relate structurally controlled stratigraphic changes to varying tectonic regimes in the adjacent Taconian orogen.