SHORELINE FEATURES OF PLEISTOCENCE PROGLACIAL LAKE TIGHT IN CARTER COUNTY, KENTUCKY

The karst system of Carter Caves State Resort Park (CCSRP; Carter County, northeastern Kentucky) is well-studied; however, the origins of other scenic geomorphic features in CCSRP have not been considered in the context of the Late Cenozoic history of the Upper Ohio Valley. Such is the case with a pair of sandstone arches, Fern Bridge and Cascade Bridge. Both arches are geomorphologically similar, being joint-controlled, alcove-type arches developed in the Upper Mississippian Carter Caves Sandstone (the caprock to the karst system). However, they are located in different areas of CCSRP, and on opposite sides of Tygarts Creek, the principal stream draining the area: Fern Bridge is located on a northeast-facing ridge above Cave Branch, a western tributary of Tygarts Creek, while Cascade Bridge is located over 2 km to the south in Box Canyon, a solution valley initiated as James Branch, an eastern tributary of Tygarts Creek. Recent GIS-based mapping by Erjavec (2018) of the extent of Pleistocene Proglacial Lake Tight (PPLT) indicates that the CCSRP area would have been flooded to the 275-meter contour during PPLT’s high stand, circa 0.77 Ma. This shoreline coincides with the elevations of both Fern Bridge and Cascade Bridge, and points to a previously overlooked erosional agent responsible for the development of these features. Incision of the northeastern-most Pennyroyal Plateau by tributaries of the preglacial Teays River during the Miocene-Pliocene left Carter Caves Sandstone exposed on the ridgetops. The impoundment of PPLT for some 10,000 years in the mid-Pleistocene allowed the development of wave-eroded shoreline features, including Fern Bridge and Cascade Bridge. Indications of large-scale collapses of undercut Carter Caves Sandstone elsewhere in CCSRP, especially in the Box Canyon area, suggest a larger number of shoreline features existed in the past.