USING 3-DIMENSIONAL MAPPING TO DETERMINE THE POSSIBILITY OF STRUCTURAL CONTROL ON DEVELOPMENT OF THE UPPER ORDOVICIAN LEXINGTON LIMESTONE, CENTRAL KENTUCKY, U.S.A

The Upper Ordovician Lexington Limestone is a fossiliferous, largely bioclastic, limestone formation found across the Bluegrass region of central Kentucky. Extensive mapping of the Lexington Limestone during the U.S. Geological Survey (USGS)-Kentucky Geological Survey (KGS) Joint Mapping Program from the 1960’s through the 1990’s shows that the Lexington Limestone and its members do not exhibit the typical tabular, “layer-cake” form present throughout most of the east-central United States and is much thicker in central Kentucky than in nearby equivalent units. It has been suggested that the excess thickness and stratigraphic anomalies within the Lexington Limestone reflect a carbonate buildup on reactivated basement structures and is responsible for the roughly triangular distribution of the unit in central Kentucky. Structural reactivation in the study area was likely related to coeval, Taconian, far-field forces. Hence, as part of a USGS EDMAP-supported project in collaboration with the KGS to show the likely influence of structural reactivation, this study compiled field-measured data and data from preexisting USGS geologic maps from key member and formation bounding surfaces in Esri ArcGIS Pro to generate three-dimensional surface maps at the top of the Lexington and at key member bounding surfaces. Discontinuities from the horizontal that coincide with known basement faults very likely indicate structural control during formation. Conclusions will be made using isopach, three-dimensional maps, and cross sections to examine the location of abrupt facies (member) changes and stepwise changes in the upper formation boundary relative to known basement faults in the area.