Long-Term Record of Sediment Transport and Deposition at the Crossroads of North America's Orogenic Systems, West Texas, U.S.A.: A Detrital Zircon View
The Appalachian and Cordilleran orogenic belts of North America and their related sedimentary basins intersect in the Trans-Pecos region of west Texas. The strata representing these major orogenic belts are exposed within a long-lived continental margin that records several cycles of tectonism, basin development, volcanism, and climate change. The main objectives of this thesis are: (1) to understand the various stages of geologic development of the southern continental margin of North America by using detrital zircon geochronology to interpret spatial and temporal changes in sediment sources over time, and (2) to correlate stratigraphic and sedimentologic changes in fluvial strata with specific paleoclimatic events. The first objective expands upon recent studies utilizing detrital zircons that suggest continental-scale sediment dispersal systems represent a complex interplay between Appalachian and Cordilleran sources of sediment. Exploring this concept, samples collected from Precambrian to Cenozoic strata exposed in the Trans-Pecos region of west Texas were analyzed using U-Pb detrital zircon geochronology. This study generated 3,981 new U-Pb ages from individual detrital zircons and is the focus of Chapter 2. Based on U-Pb detrital zircon probability curves and peak age populations, changes in detrital zircon age populations represent a “seesaw” effect on long-term sediment transport between dominantly Grenville and Appalachian-Ouachita orogenic sources of eastern North America to Cordilleran magmatic arc and Basin and Range sources of western North America. The second objective investigates the correlation of stratigraphic and sedimentologic changes in Paleogene fluvial strata with specific paleoclimatic events. The climate of the early Paleogene records both long-term trends and rapid climate events superimposed upon a hot greenhouse state. Evidence of this dynamic climate is archived in the Paleogene fluvial strata of the Big Bend region, where sedimentologic data suggest that a meandering fluvial systems developed during the Paleocene (63 Ma–55.5 Ma) before transitioning to a braided fluvial system at the Paleocene-Eocene Thermal Maximum (55.5 Ma). This shift in fluvial dynamic is interpreted to reflect both a change in discharge/sediment supply associated with the more arid, monsoonal, and less vegetated environment and, after 54 Ma, enhanced regional Laramide tectonism during the early Eocene greenhouse climate. The Paleogene fluvial strata of the Big Bend region provide a nearly continuous, subtropical terrestrial paleoclimate record useful for characterizing the response of terrestrial landscapes to climate variations.
Ridgway, Purdue University.
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