Correlations across a facies mosaic within the Lexington Limestone of central Kentucky, USA, using whole-rock stable isotope compositions

The chemostratigraphic (δ ¹³ C _carb ) record of the Lexington Limestone in central Kentucky is a high-resolution record in Chatfieldian and lower Edenian strata. Parts of the Lexington Limestone in this region reflect an anomalous structurally controlled carbonate buildup with complex facies relationships. Chemostratigraphic analysis of buildup and off-buildup composite sections, which exemplify the Lexington facies mosaic, reveals an overall decreasing trend in ¹³ C compositions throughout the formation and into the overlying Clays Ferry Formation. Superimposed on this trend are four locally correlative excursions. The most significant excursion is found within the Logana Member. The Guttenberg excursion is locally expressed as two prominent δ ¹³ C peaks (maxima +2.58‰). The excursion is important because of its stratigraphic position above the regional and globally correlated Millbrig K-bentonite, which allows for correlation with chronostratigraphically equivalent successions. The ubiquity of the Guttenberg excursion has been recognized throughout the eastern and central United States and the Baltic region. Additional excursions have been detected and are common in other sections, showing that the chemostratigraphic record of the Lexington Limestone is similar in buildup and off-buildup sections, even across complex lithofacies boundaries. The similarity of the record across complex facies, moreover, suggests that these localized excursions are "events," which can be used to constrain correlations and augment known facies relationships. Furthermore, the overall chemostratigraphic trend in the Lexington Limestone appears similar to published δ ¹³ C values from equivalent strata in Baltoscandia, emphasizing the global correlative value of chemostratigraphic trends in Upper Ordovician strata.