Sediment Transport in the Western Interior Seaway of North America: Predictions from a Climate-Ocean Sediment Model

摘要

Whether from the foreshore, shoreface, shelf, or incised estuarine valleys, sedimentary deposits along the western edge of the Western Interior seaway quite uniformly record southerly directed paleoflows. Cardium Formation shoreface gravels at Willesden Green, Alberta, decrease in clast size to the southeast. Isoliths outlining clastic wedges, such as the Chalk Creek, are recurved to the south. Large-scale cross-strata in rocks considered to be either shelf sand ridges or detached shorefaces, such as the Kakwa and Musreau Members of the Cardium Formation and the Straight Cliffs Formation of southwestern Utah, indicate southerly directed paleocurrents. Estuarine incised valley-fills trend south or southeast, reflecting a high-stand shelf topography inherited by rivers as they cut across the inner shelf in response to a high-order sea-level drop. To explain this uniformity we conducted two numerical experiments that predict circulation and sediment transport paths in the seaway in response to (1) mean annual atmospheric forcing and (2) the passage of a mid-latitude winter storm. The mean annual forcing for the early Turonian is computed by GENESIS, an NCAR global climate model; the cyclone is computed using an idealized hurricane model. For the mean annual experiment, circulation of the seaway is computed using a three-dimensional, turbulent flow, coastal ocean model under the following initial and boundary conditions: (1) paleobathymetry according to a new interpretation of the litho-and bio-stratigraphy for the early Turonian; (2) fresh water runoff and precipitation-evaporation magnitudes as computed by GENESIS; (3) temperatures and salinities of the Boreal and Tethys Oceans based on GENESIS atmospheric temperatures; and (4) mean annual and daily wind stresses computed by GENESIS. For the storm experiment, circulation is forced solely by wind stresses.