Public Debate! How did the Sevier Orogeny define the geology around Las Vegas, Nevada?

March 6, 2024
Students pose in front of a tightly folded Jurassic Aztec Formation in the footwall of the Keystone Thrust at Red Rocks Canyon.

This winter graduate and undergraduate students in the Advanced Field Methods course (EOSC 448 and EOSC 546) traveled to Las Vegas, Nevada, to study the outcrops around Frenchman Mountain, Red Rock Canyon, Buffington Pockets, and Valley of Fire State Park. 

At Frenchman Mountain the students observed the oldest sedimentary rocks in southern Nevada, which were initially deposited during the Cambrian, around 500 million years ago, following the breakup of the supercontinent of Rodinia. The deposited rocks were primarily limestones and dolomites that form on shallow seabeds due to the sedimentation of calcium carbonate sea shells. During the Mesozoic (~200 million years ago) the region transitioned from a marine to a terrestrial environment, and rock deposition was primarily clastic, i.e. rocks formed from fragments of other rocks. 

At Red Rocks Canyon, Buffington Pockets, and Valley of Fire State Park, the students observed the results of the Sevier Orogeny in which the deposited rocks were tectonically squeezed together during this Cretaceous (~100 million years ago) mountain building event. The area was stretched in the Miocene (~17 million years ago) as the plate tectonics of the area changed once again and the San Andreas Fault formed to the west. The result of this complex geological history is dramatic folded and deformed layers as well as deposition of new sedimentary rocks as the mountain building also created new sedimentary basins. 

Although the limited desert vegetation of the area means the outcrop and its features are easily visible, there are still unknowns in the story of the Sevier Orogeny. Using their field observations, literature references, and understanding of geological processes gained through EOSC 546, students will debate 1) whether the Sevier Orogeny formed during a distinct event in space and time, or it evolved over time alongside other deformation events, 2) if the geology of the basin surrounding the Sevier Orogeny is typical of a foreland basin. These questions are critical to our understanding of the processes involved in creating these formations and features like them.  

The public is welcome at the upcoming debate, taking place March 9 from 9:30 am to noon at Earth Science Building room 5108. There will be a chance for audience members to ask questions after several rounds of rebuttal. The audience will also get to vote for the arguments they find most compelling. 

Click here to read more about the EOSC 546 field experience.