INTERDUNE POND DEPOSITS EXAMINED AND DESCRIBED AS A SRATIGRAPHIC CONTROL ON FLUID MIGRATION THROUGH EOLIAN SANDSTONES

The Cedar Mesa sandstone was deposited in an ancient sand dune sea and is an exhumed stratum that has been a host for migration of and alteration by fluids. The Sandstone consists of interbedded and intertonguing eolian, fluvial, pedogenic and pond strata. The focus of the research conducted is the small scale pond and associated pedogenic lithologies that formed when the water table was high or when floods filled the interdune areas of the ancient desert. The geometric distribution of groups of ponds stacked within sandstones is predictable using outcrop observations and wind direction to reconstruct the dune topography. Pond deposits surveyed run parallel to the long axis of dunes in the interdune areas and are found in the transition areas between sandstone that has been altered by migration of fluids and sandstone that has not. Petrographic analysis was completed to aid in differentiation of pond lithologies and diagenetic events. Three end member types of pond deposits were recognized. Deposits containing dolomite, limestone, and dolomitized sandstone are interpreted as isolated deposits of ponds continuously flooded by fresh and saline water. Deposits occurring along prominent and widespread rooted horizons that contain numerous shale beds were repeatedly inundated from stream floodwaters. Deposits that are encased in and interbedded with sand dunes were small scale floods of rain and groundwater occurring during dune migration. The Cedar Mesa's interbedded pond lithologies, their thicknesses, and associated dune interaction zones are compared to aid in the interpretation of why migration did not occur vertically and was prohibited regionally along boundaries between sandstone beds.