Geology Research
Image: Bare Mountain, Nevada.
PhD work on continental deformation
The slow deformation of continents is a subtle process that demands a broad spectrum of analytical methods to measure and observe. My work measures deformation in areas of continental deformation and links that deformation to geodynamic mechanisms that may control its distribution, rate, and style. The majority of my work has been in the Basin and Range extensional province in the western United States, but I have also studied the Lesser Caucasus Mountains in Armenia and Azerbaijan.
Basin and Range Extension
Image: The Ruby Range near Elko, NV. The Ruby Range is a metamorphic core complex, a geologic feature created when stretching of the crust allows 20 km deep metamorphic rocks to rise to the surface.
The Niemi-Clark lab field truck in the mountains of northern Nevada near the Idaho border in 2018.
When a mountain belt reaches the end of its life, how does it collapse?
Basin and Range geologists are faced with a challenging inverse-problem: when all you have to look at are the deformed and dissected remains of a once great mountain range, can you reverse engineer the process of its collapse and maybe even glimpse the grandeur of that original topography?
The Basin and Range province of western North America is a vast area of active tectonic extension, where multiple phases of crustal stretching have resulted in structurally complex continental crust. To understand the timeline and spatial distribution of extension during the past 40 million years in the Basin and Range, we can use geologic tools like thermochronology, detrital zircon U-Pb geochronology, geologic mapping, and cross-section restoration.
Geologic mapping of the Eocene-Oligocene Titus Canyon Formation in Death Valley, California
One approach to investigate when and where continental extension has occurred in the past is to study the remnants of ancient sedimentary basins that opened up during extension. Death Valley National Park is one of the best examples of large magnitude continental extension in the world, but during the Eocene, 35 million years ago, the extension that created the modern topography of Death Valley hadn't happened yet, instead the region was just starting to experience an earlier phase of extension in response to changes in the Pacific-North American tectonic plate boundary.
The record of this early phase of extension in Death Valley is the Titus Canyon Formation, a colorful sequence of sandstones, conglomerates, and limestones that were deposited in a rift valley by ancient rivers and lakes during the Eocene and Oligocene epochs (approximately 40-30 million years ago). In the picture below, the Titus Canyon Formation is labeled as OgEotv and OgEotr (abbreviations of Oligocene-Eocene-Titus, plus a letter specifying the specific part of the formation). Above the Titus Canyon Formation, you can see a number of younger rocks labeled with symbols that contain Mi for Miocene (an epoch spanning 23 to 5 million years ago). These Miocene rocks are mostly volcanic, together showing a trend of increasing volcanism in response to the crust thinning during progressive extension.
We are in the process of publishing the results of our study in the journal Geosphere. I also made an ArcGIS story map that has a cool interactive version of the geologic map we created, check it out here:
The public presentation of my dissertation defense:
"But Geology carries the day; it is like the pleasure of gambling, speculating on first arriving what the rocks may be; I often mentally cry out 'three to one Tertiary against primitive'; but the latter have hitherto won all the bets."
Charles Darwin, correspondence with W.D. Fox, May 1832
Image: Sand dunes in Death Valley National Park.