ABSTRACT

This multidisciplinary collaborative project evaluates the role of subsidence of the lithosphere and deposition of sediments in Cordilleran foreland in response to Cretaceous subsidence caused by subduction of an oceanic tectonic plate beneath the western margin of North America. The research has the potential to transform understanding of lithosphere-scale processes by clarifying the effect of flat subduction on the upper crust and basins using a combination of sedimentary and basin analyses, thermochronology and geodynamic modelling to enable discrimination of the relative contributions of crustal loading mechanisms. In addition to the scientific goals of the project, the collaboration is advancing important societal outcomes by contributing to STEM (science, technology, engineering and mathematics) educator development, the broadening of participation of underrepresented groups in science, the training of a postdoctoral researcher and graduate and undergraduate students. Public outreach efforts by the University of Alaska and education of middle school students through newly established relationships between the University of Houston and local middle schools and middle-school aged homeschooled students contributes to increased public scientific literacy and public engagement with STEM. The project also supports the development of a new partnership between the participating universities and industry, thereby contributing to the increased economic competitiveness of the United States.

Although migrating dynamic subsidence has long been invoked to explain the broadening and migration of the Late Cretaceous depocenter, no research has taken a high resolution, large-scale approach to characterizing the timing or direction of migration or to discriminate flexural from dynamic subsidence. However, flexural loading and subcrustal loading leave distinct foreland-basin deposits that record sediment source area and source area exhumation rate and have a characteristic fill geometry that records the locus and rate of subsidence. Detailed investigation of stratigraphic architecture, sediment volumes, sediment sources, and depositional products allows the research team to explore the potential influence of flat subduction of an oceanic plateau versus continued or enhanced thrust belt exhumation or incipient basement-cored uplifts. The Cordilleran system presents an unparalleled opportunity to establish the effect of flat subduction of an oceanic plateau in the best dated retroarc foreland basin system on the planet; thus, the results of this investigation are applicable to other ocean-continent convergent systems. The research team is evaluating mechanisms for observed changes in basin architecture by integrating sandstone compositional data, detrital thermo- and geochronology, high-resolution sequence stratigraphy, high-resolution isopach maps, geohistory analysis, and forward stratigraphic, flexural, and geodynamic modelling. New detrital geochronology and sandstone compositional data are supplementing published geochronology and sedimentology to more accurately identify changes in sediment provenance and routing during this time. Detrital thermochronology is delineating up-section changes in lag time, corresponding to changes in source exhumation rates, or introduction of a new sediment source. Sequence stratigraphy, decompacted isopach maps, and forward stratigraphic modelling allow calculation and comparison of the average sediment supply to discriminate changes in basin architecture due to sediment supply from accommodation-driven changes. Reconstruction of basin subsidence is being accomplished using detailed isopach maps and geohistory analysis, which facilitates discrimination of crustal loads from a subcrustal load. Finally, flexural and geodynamic modelling enables discrimination of the relative contributions of loading mechanisms. This project will combine, for the first time, the strengths of detrital geo- and thermochronological double-dating, high-resolution sequence stratigraphy, and multiple modeling efforts at a scale and resolution capable of discriminating the mechanisms for subsidence. As a result of this collaboration, this project has potential to transform the understanding of lithosphere-scale processes by clarifying the effect of flat subduction on the upper crust and basins.

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.

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