NSF Award
2420431
River networks form and evolve in response to topographic gradients across continents, and they are sensitive indicators of the direction and magnitude of such gradients. In the geologic past, ancient river deposits are often used to reconstruct the position, height, and uplift timing of mountain belts. Frequently, the composition and/or age of mineral grains within ancient river deposits are used to “fingerprint” river sediment and interpret where it originated. This approach can determine the direction of topographic gradient at the time a particular ancient river was active. However, these “detrital” methods have many limitations including that they cannot determine the specific sediment transport pathway or whether transport occurred exclusively in a river (as opposed to by wind or longshore drift). This research uses a relatively new set of techniques to estimate the paleohydrology (ancient river flow depth, slope, and water discharge) of deposits from which existing interpretations have been made using detrital methods. This will test whether these two independent approaches yield consistent results. This work uses Cretaceous (ca. 80 million years old) to Eocene (ca. 50 million years old) strata exposed across the western United States as a natural laboratory for this experiment. This research will provide important societal outcomes by: 1) supporting the training of graduate and undergraduate students in STEM fields including minority and underrepresented students at a Hispanic Serving Institution; 2) serving as the focal point for a pilot field research training program for undergraduate students; and 3) testing and refining scientific approaches to understanding the geologic past.<br/><br/>The proliferation of detrital zircon U-Pb provenance analysis over the last two decades has led to substantial increases in our understanding of sediment transport globally in both modern and ancient systems. However, detrital zircon provenance tools have substantial limitations including that they do not account for zircon-poor sediment sources, zircon is often recycled, and they do not explicitly discriminate between different transport processes (e.g. fluvial, longshore, eolian). Although much work has focused on addressing these limitations, most detrital provenance studies do not explicitly test whether interpreted drainage patterns are paleohydrologically consistent with the physical features of sampled strata. This research will address this issue using a relatively new suite of quantitative stratigraphic tools to investigate changes in fluvial hydrology in Laramide (western US) basins between Late Cretaceous and early Eocene time. Based on detrital provenance methods such as detrital zircon U-Pb dating, Laramide deformation is interpreted to have driven substantial partitioning and reorganization of drainage networks across the western United States as surface gradients shifted and basement-cored uplifts blocked river pathways. This project combines new quantitative paleohydrologic reconstruction approaches with existing detrital provenance data and interpretations to test whether these two independent datasets are paleohydrologically consistent. The researchers will use fluvial strata in the Green River, San Juan, and Uinta basins to test their central hypothesis, that paleohydrology—particularly paleo flow depth—reflects drainage length and area changes from Late Cretaceous to early Eocene time interpreted from existing detrital provenance analyses. This work will focus on three study areas that represent a range of expected results: the length and area of fluvial systems is interpreted to have increased in the Green River basin, decreased in the San Juan basin, and remained largely unchanged in the Uinta basin from Late Cretaceous to early Eocene time. These locations enable the bracketing of potential changes and control for changes in paleohydrology driven by regional climate.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
