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Van Tuyl Lecture: Theresa Schwartz, Research Square
February 15, 2018 @ 4:00 pm - 5:00 pm
Theresa Schwartz, Research Square
Van Tuyl Lecture, BE 241, 4 PM
“Landscape Evolution of the Rocky Mountain Cordillera: New Insights from Integrated Geologic Datasets”
Abstract: Spatio-temporal compilations of tectonic, sedimentary, topographic, and climatic data from across the North American Cordillera and Western Interior region provide a continental-scale view of landscape evolution and drainage reorganization during latest Cretaceous and early Cenozoic time. Late Cretaceous—Eocene Sevier/Laramide crustal thickening caused widespread, diachronous surface uplift in the Cordillera and Western Interior region, generating the “Nevadaplano” and partly inverting the Sevier foreland basin. Subsequent delamination of the Farallon slab caused diachronous gravitational collapse of the Cordillera, which modified prior contractional topography. These events were coeval with a climatic shift from warm/wet during Late Cretaceous—Paleocene time to cooler/drier during late Eocene—Oligocene time. In spite of our broad understanding of these Late Cretaceous—Paleogene events, the basin-scale relationships between tectonic activity, climatic change, and topographic evolution remains poorly understood in many areas.
Syntheses of different geologic data help to elucidate such relationships. This talk presents a synthesis of sedimentary, structural, igneous, and stable isotope paleoclimate data from the southwestern Montana sector of the Cordillera. Using detailed sedimentary interpretations as a foundation for interpretation, the disparate data types can be integrated to determine the timing, style, and causes of latest Cretaceous—Paleogene landscape evolution in southwestern Montana. Results show that Sevier-Laramide deformation generated a rugged topography that already had surface elevations > 2 km. As slab removal occurred, maximum elevations of ≥ 4 km were attained in the Sevier hinterland. Concurrent warm/wet climatic conditions prompted fluvial incision, generating a rugged topography (≥ 2 km relief). Late Eocene extension within the Cordillera further modified the landscape, amplifying topographic relief but lowering mean surface elevation, and also prompting drainage reorganization. Extension was accompanied by regional aridification, prompted by the formation of a rain shadow across the Cordillera.