“Impact and High-Magnitude Sedimentology: Nevada/Arizona”

Class taught by Dr. R. Douglas Elmore

Seated from left: Vanessa O’Brien, Shannon Dulin, John Warme (Colorado School of Mines). Standing from left: Devin Dennie, Alicia Branch, Louise Totten, Michelle McCarthy, Jennifer Eoff.

The Alamo Breccia is a carbonate megabreccia exposed in southern Nevada. It likely represents the detachment and resedimentation of 250+ km3 of carbonate rock following a moderate-sized bolide impact in the Late Devonian (Warme and Sandberg, 1996). The breccia contains chaotic debrites with stromotoporoid clasts, an upper graded zone and carbonate lapilli. Paleomagnetic samples collected by students on the trip will be used to test the origin of the breccia (hot or cold) and will also provide information on hydrothermal alteration. The fieldtrip also included a rim tour of the 550’-deep Meteor Crater, a recent (49 Kya) impact crater near Flagstaff, Arizona. Students examined non-impact, episodic sedimentation deposits as well, including debris flows, flood deposits and terrace sequences of the Colorado River at Lee’s Ferry and the Grand Canyon. The class also examined Mesozoic eolian deposits at Zion National Park. But the biggest lesson learned on the trip: a cheap motel in Vegas is not worth the money saved.

Large folded clast in the Alamo Breccia

Close up of Alamo Breccia

The Grand Canyon.

Balanced Rock, a “hoodoo” formed by differential erosion of softer material under boulders, near Lee’s Ferry, Arizona

Cross-bedded Navajo Sandstone, Zion National Park, Utah

Well-preserved impact structure, Meteor Crater, Arizona