| Description |
Jurassic Navajo Sandstone outcrops across the San Rafael Swell, Utah, record the history of a transitional region between the thinner eastern erg margin and thicker southwestern erg center. Subregional stratigraphic correlations of three study locations are based on detailed observations of 11 distinct lithofacies. A lower stratigraphic zone contains thin, submeter scale planar sets of crossbedded sandstone and is typified by the presence of thin carbonate lenses. Interbedded carbonate lenses in the lower zone likely formed in shallow, evaporative interdune ponds during high water table conditions. Interdune carbonate matrix and cement in the lower zone show relatively enriched stable isotopic ratios of carbon (median of -3.4‰ δ13CVPDB) and oxygen (-2.8‰ δ18OVSMOW). An upper stratigraphic zone is comprised of large (5-10 m) trough crossbeds and intervals of strongly contorted and deformed strata. This upper zone represents dominant dune deposits. The spatial and stratigraphic distribution of these deposits suggest an intermediate depositional history with lithological and isotopic similarities with both the erg margin to the east and the erg center to the southwest. Vertical stratigraphic changes indicate an evolution of the ancient desert from a wetter eolian environment to a drier draa-dominated erg, reflecting the likely dynamic influence of changing climate, tectonics, and topography over the depositional history of the erg. Reservoir characterization of the ~150 m thick Navajo Sandstone in the San Rafael Swell provides criteria for evaluating storage of recaptured carbon near coaliv fueled power plants in Emery County, Utah. The lower zone, comprising the lower half of vertical section, contains low porosity (~15%), low permeability (~350 mD), and uncommon flow baffle/barrier interbedded lenses. The upper zone, which comprises the upper half of vertical section, has average porosity of ~20% and permeability of ~1500 mD. Horizontal anisotropies caused by lithologic variations may divert injected fluids horizontally and likely represent baffle/barriers to the vertical flow of buoyant carbon fluids. Gypsum and limestone beds in the overlying Carmel Formation provide a regional-scale seal. The presence of ~20 m net porosity footage indicate that the Navajo Sandstone is a suitable lithological reservoir for storage of ~11 million metric tons of supercritical carbon. |
