Lunchtime Expedition: Mystery Cobbles in the Bighorn Basin

November 5 | Noon
Coe Auditorium

Join Jacob Thacker, assistant professor of geology at Rocky Mountain College in Billings, for a fascinating look at one of the Bighorn Basin’s geological mysteries.

The Bighorn Basin has preserved a detailed record of millions of years of erosion and mountain building. But some rocks found within that record seem to tell a different story. Fist-sized igneous cobbles in the Frontier Formation were deposited in a river delta about 95 million years ago, yet they closely resemble rocks found today in the Beartooth Mountains, which many researchers believe did not form until 20 to 30 million years later.

So where did the cobbles come from?

Thacker will explore how detailed geological analysis, chemical “fingerprinting,” and radiometric dating have helped unravel the mystery. The findings offer new clues about the history of the Beartooth Mountains and add another intriguing chapter to the geological story of the Greater Yellowstone region.

Thacker’s interest in geoscience began during his early years living up the South Fork near Cody. He earned a bachelor’s degree from Cleveland State University, a master’s degree from Montana State University, and a PhD from the University of New Mexico. His field experience includes work with the National Park Service in Yellowstone, the U.S. Geological Survey in Flagstaff, Stillwater Mine, and the New Mexico Bureau of Geology.