Preservation of autogenic processes and allogenic forcings within set-scale aeolian architecture II: the scour-and-fill dominated Jurassic Page Sandstone, Arizona, USA

Contributors:
  1. Gary Kocurek
  2. David Mohrig
  3. Cory M. Hughes
  4. Sarah C. Brothers

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Description: The stratigraphic architecture of aeolian sandstones is thought to record signals originating from both autogenic dune behavior and allogenic environmental boundary conditions within which the dune field evolves. Mapping of outcrop-scale surfaces and sets of cross-strata between these surfaces for the Jurassic Page Sandstone near Page, Arizona, USA, demonstrates that the stratigraphic signature of autogenic behavior is captured by variable scour depths and subsequent fillings, whereas the dominant signatures of allogenic boundary conditions are associated with antecedent surface topography and variable water-table elevations. At the study area, the Page Sandstone is ~ 60 m thick and is separated from the underlying Navajo Sandstone by the J-2 regional unconformity with meters of relief. Thin, climbing sets of cross-strata of the basal Page representing early dune-field accumulations fill J-2 depressions. In contrast, the overlying lower and middle Page consist of cross-strata that are one to a few meters thick, and packaged between outcrop-scale bounding surfaces. These bounding surfaces have been previously correlated to high stand deposits of the adjacent Carmel sea and at this site possess meters of erosional relief produced by dune scour. Notably absent within packages of cross-strata bounded by these outcrop-scale surfaces are strata of early dune-field accumulations, any interdune deposits, and climbing-dune strata. Instead, these packages preserve a scour-and-fill architecture created by large migrating dunes migrating within a dry, mature, dune field undergoing negligible bed aggradation. Any record of early phases of dune-field construction for the lower and middle Page are interpreted to have been cannibalized by the deepest scours of later, large dunes. Interpretations are independently supported by the relatively large coefficients of variation in lower and middle Page set thicknesses, which are consistent with set production by successive deepest trough scours, and the relatively low coefficient of variation for the depression-filling basal Page sets consistent with a significant component of bed aggradation. Numerical modeling presented here and more completely in the companion paper demonstrates how this cannibalization of early-phase stratigraphy is an expected outcome of autogenic dune-growth processes, and that early-phase strata can be preserved within antecedent depressions. Relative rise of the inland water table from basin subsidence and Carmel sea level forced preservation of multiple stacked packages composed of scour-and-fill architecture. Without these allogenic forcings, the Page would be little more than an erosional surface.

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