Surficial Geologic Map of the Upton 7.5-Minute Quadrangle, Kentucky

The Upton 7.5-minute quadrangle is located south of Elizabethtown along the boundaries between Hardin, Hart, and Larue Counties and within the Mississippian Plateau physiographic region (McDowell, 1986). Topography is characterized by the low relief Pennyroyal plain that sits at altitudes below about 750 ft above sea level, the ridges, spurs, and isolated knobs of the intensely dissected Dripping Springs escarpment; the low relief cap of the escarpment landforms is part of the Mammoth Cave plateau region. Moore (1972) mapped the bedrock geology of the quadrangle, which was later digitized by Toth (2006). Mississippian bedrock is exposed throughout most of the quadrangle and is cut by several northwest-southeast trending vertical faults. The Ste. Genevieve Limestone is the oldest lithology and underlies most of the Pennyroyal region. The Beaver Bend Limestone and Paoli Limestone, Sample Sandstone, and Reelsville Limestone stratigraphic sequence underlie the remaining areas of the Pennyroyal, as well as the lower slopes of the Dripping Spring escarpment. The Beech Creek Limestone, Big Clifty Sandstone, and Haney Limestone Members of the Golconda Formation are exposed along the upper slopes of the Dripping Springs escarpment the upper plains of the Mammoth Cave plateau. The Upper Mississippian Hardinsburg Limestone is exposed on the highest ridges of the Dripping Springs, and the Pennsylvanian Caseyville Formation is locally exposed around the highest peak in the southern part of the Upton quadrangle. Previously mapped surficial deposits include minor areas of alluvium in major tributaries, and “slumped” areas across the quadrangle (Moore, 1972)

Removal of the Northern Paleo-Teton Range along the Yellowstone Hotspot Track

Classically held mechanisms for removing mountain topography (e.g., erosion and gravitational collapse) require 10-100 Myr or more to completely remove tectonically generated relief. Here, we propose that mountain ranges can be completely and rapidly (\u3c 2 Myr) removed by a migrating hotspot. In western North America, multiple mountain ranges, including the Teton Range, terminate at the boundary with the relatively low relief track of the Yellowstone hotspot. This abrupt transition leads to a previously untested hypothesis that preexisting mountainous topography along the track has been erased. We integrate thermochronologic data collected from the footwall of the Teton fault with flexural-kinematic modeling and length-displacement scaling to show that the paleo-Teton fault and associated Teton Range was much longer (min. original length 190-210 km) than the present topographic expression of the range front (~65 km) and extended across the modern-day Yellowstone hotspot track. These analyses also indicate that the majority of fault displacement (min. 11.4-12.6 km) and the associated footwall mountain range growth had accumulated prior to Yellowstone encroachment at ~2 Ma, leading us to interpret that eastward migration of the Yellowstone hotspot relative to stable North America led to removal of the paleo-Teton mountain topography via posteruptive collapse of the range following multiple supercaldera (VEI 8) eruptions from 2.0 Ma to 600 ka and/or an isostatic collapse response, similar to ranges north of the Snake River plain. While this extremely rapid removal of mountain ranges and adjoining basins is probably relatively infrequent in the geologic record, it has important implications for continental physiography and topography over very short time spans