Lateral Heterogeneity in Exhumed Eolian Reservoirs Due to Preservation of Eolian Topography, Permian Cedar Mesa Sandstone, Southeast Utah

Richard P. Langford, Krystal Pearson, K. A. Duncan, and David Tatum
Unviersity of Texas at El Paso, El Paso, TX

Eolian reservoirs commonly exhibit 100-m to km-scale lateral heterogeneities that are difficult to explain with existing models of eolian bedform migration and aggradation. In current models some dunes or draas are assumed to climb during migration in the same manner as climbing ripples. When interdunes are stabilized at groundwater surfaces, eolian strata can be preserved by rises in the water table. In the Cedar Mesa Sandstone in southern Utah are 20-25 m high draas are preserved, oriented transverse to the paleo-transport direction. The draas are 300 m to 700 m wide and are separated by 700 m wide in intervening lows filled with small dunes and sand sheets. Within the dune complexes, high-angle second-order surface separate sets of downclimbing dunes barchanoid dunes from large transverse dunes that formed intermittently during draa migration. The upper surfaces of the draas are eroded before the intervening lows were filled with sand sheets and associated flood deposits. The dunes intertoungue with the sand sheets along the downwind margin of the draa, illustrating downwind migration of the dune masses over the inter-draa sand sheets. Tertiary migration of hydrocarbon-bearing fluids has bleached Cedar Mesa strata and illustrates potential for reservoir compartmentalization. Early cementation in ponds and bioturbated sand sheets along with deposition of shales during floods reduced infiltration and bleaching in the inter-draa lows. Topography was inherited in overlying strata which show similar changes in potential reservoir quality with non-reservoir quality eolian strata in intervening lows.