DETECTING THE TOPOGRAPHIC EXPRESSION OF THE YELLOWSTONE HOT SPOT: EVIDENCE FOR QUATERNARY DYNAMIC TOPOGRAPHY IN THE BIGHORN BASIN

This project will develop a Quaternary fluvial chronology based on ¹⁰Be dating of terraces from the Bighorn Basin of Wyoming and Montana, USA. Using this chronology, I propose to quantify the landscape response to dynamic topography forced by the Yellowstone hot spot over the past 2.5 Ma. The Yellowstone Crescent of High Terrain (YCHT)(Pierce and Morgan, 1992; 2009), a horseshoe-shaped area of high relief bordering Yellowstone Caldera, is thought to represent the topographic expression of a mantle hot spot. The caldera developed within compound topography resulting from these processes. In contrast, the Bighorn Basin remained a topographic low until the late Pliocene when it began its passage over the hot spot. Surface expressions of mantle anomalies occur as long wavelength and low amplitude topographic anomalies (Braun, 2010). Smith et al (2009) propose that the topographic swell measuring 500m high and 400 km wide, is centered on Yellowstone, and occurs in both the YCHT and the Bighorn Basin. The Shoshone River flows from the caldera rim eastward across the Bighorn Basin. The terraces in the basin are an ideal marker to detect dynamic topography because of the low relief in the basin, they should ‘feel’ hot spot-related uplift, and because the basin existed as a tectonically quiescent depocenter until 2.5 Ma. I propose to quantify the timing and magnitude of hot spot-related rock and surface uplift by dating the transition from deposition to incision in the neighboring Bighorn Basin.

Field reconnaissance and mapping of Quaternary deposits in the YCHT began in the summer of 2011. In the summer of 2012 I will map Quaternary fluvial deposits from the Western Bighorn Basin, near Cody, WY to the Central Bighorn Basin near Lovell, WY. I will present results of topographic analysis of the Yellowstone region and Bighorn Basin, in anticipation of collecting samples for age determination.