Shoreline evolution in the Late Cretaceous North American Cordilleran foreland basin: An exemplar of the combined influence of tectonics, sea level, and sediment supply through time

The stratigraphic record from the North American Cordilleran foreland basin (CFB) serves as a critical archive of how tectonics, sea level, and sediment supply interacted throughout the geologic past, providing valuable insights into the formation and filling of foreland basins. By integrating a range of stratigraphic, sedimentologic, and geochronological datasets, the roles of various geological processes within the CFB are better constrained, especially more enigmatic subcrustal processes probably related to large-scale mantle flows. This study summarizes the complex shoreline evolution of the central part of the CFB (Wyoming, Utah, Colorado, and New Mexico) in 25 temporally constrained paleogeographic maps illustrating high-resolution shoreline history (location and migration trend) and distribution of gross depositional environments through the Late Cretaceous. Detailed stratigraphic synthesis indicates that sediment fill of the CFB was subject to complex interactions of tectonics (both local and regional scale and both crustal and subcrustal processes), eustasy, and sediment supply because stratigraphic stacking patterns and shoreline migration trends varied along the coeval shoreline during most of the Late Cretaceous. The spatial variability in the shoreline migration trend, as well as changes in the sediment dispersal pattern help to disentangle the effects of subsidence caused by crustal and/or subcrustal processes, and provide constraints on the spatial and temporal scales these processes operate on. Subcrustal processes such as mantle flow, possibly associated with enhanced coupling by subduction of an oceanic plateau (i.e., the conjugate Shatsky rise) attached to the Farallon plate, were documented as an important mechanism influencing the subsidence/uplift and sediment dispersal patterns in the CFB since at least ~85 Ma. The along-strike variation in shoreline migration trend along the coeval shoreline is likely the norm, rather than the exception, due to the spatial variation in topographic load, lithospheric strength, mantle-induced dynamic topography, and sediment supply across the CFB. Although quantifying the relative roles of different allogenic factors on the architecture of the CFB strata remains a challenging task, the chronostratigraphic framework, shoreline trends, and paleogeographic maps compiled herein could provide critical boundary conditions for forward modeling, such as geodynamic and landscape models, to better understand th