TOWARDS DEVELOPING A LOWER COLORADO RIVER CORRIDOR CORING (LOCORING) PROJECT: WHAT SUBSURFACE BOUSE FORMATION SEDIMENTS CAN TELL US ABOUT LATE MIOCENE (?) AND EARLY PLIOCENE TECTONICS AND PALEOCLIMATE IN THE SOUTHWESTERN US

The late Miocene (?) and early Pliocene Bouse Formation contains a contentious record of the evolution of the Colorado River as it integrated its course from the Grand Canyon to the Gulf of California roughly 5 Ma. Bouse sediments in northern basins are undisputedly lacustrine. In each basin, Bouse carbonate is overlain by exotic siliciclastic sediment that signals the arrival of Colorado River sediment and the final integration of the most iconic river in the American Southwest. Intense debate surrounds whether Bouse carbonate in Blythe basin represents (1) the last marine flooding event in a series of northward migrating marine flooding events associated with the ~ 8 to 6.5 Ma opening of the Gulf of California, (2) the last in a series of southward migrating < 5 Ma Colorado River-fed fill-and-spill lakes, or (3) a fascinating combination of marine- and lacustrine-influenced environments. At a recent workshop in Parker, AZ (Feb. 28 - March 3, 2019), a diverse panel of participants from 13 universities, 2 state agencies, the U.S. Geological Survey, and the Colorado River Indian Tribes expressed interest in coring pristine sub-surface Bouse sediments along the lower Colorado River corridor, particularly in Blythe and Yuma basins, to help resolve research questions. There was considerable interest in recovering Bouse sediments at two depocenter sites in Blythe basin. Cored sediment would provide an unparalleled opportunity to study unweathered material deposited during initial basin filling – material that is not exposed at the surface and that has not been accessible since a number of wells were drilled in the 1960s. Pristine Bouse sediments could address key questions concerning pre- and post-Bouse deformation, the onset and source of initial basin flooding, and could provide the first continuous record of late Miocene (?) and early Pliocene paleoclimate for southwestern North America. The Bouse Formation is not exposed at the surface in Yuma basin, thus, cored sediments there could address the timing of marine incursions and could provide critical isotopic and paleontologic context for assessing the competing marine-only, lacustrine-only, and marine-influenced models for the Bouse carbonate upstream in Blythe basin. Key observations, goals, and future directions for developing a LoCoRING project will be discussed.