ABSTRACT

Ground-penetrating radar was used on a large, complex, eolian dune along the margin of Great Sand Dunes National Monument, Colorado, to delineate the two-dimensional length scales of internal sediment packages for input to eolian hydrocarbon reservoir models. The ground-penetrating radar illustrated internal structures in the dune to a depth of 16 m, in a transect approximately 280 m long. Radar reflectors defined a main dune set 5 to 8 m thick, with foresets as long as 23 m. Thickness of other wedge- and tabular-planar sets ranged from 0.75 to 1.5 m, averaging 1 m; set lengths ranged from 6 to 12 m, averaging 8.5 m. Trough-shaped sets ranged in thickness from 0.5 to 3 m, averaging 1.1 m, and ranged in width from 5 to 22 m, averaging 10 m. Trough structures are the result of migration of superimposed dunes, or scour fills from reversing winds. Reversing winds resulted in the formation of numerous, subtle bounding surfaces along the lee slope of the dune as it migrated, defining sets ranging in thickness from 0.5 to 2 m, averaging 1 m, and with foreset lengths ranging from 15 to 23 m, averaging 20 m. This study demonstrates the potential of ground-penetrating radar in resolving the length scales of internal sedimentary units in modern sands. Work is in progress on delineating the three-dimensional length scales of these complex eolian dune sands.

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