The Wattis 7.5 Minute Quadrangle is located in central Utah, in the transition zone between the Basin and Range province and the Colorado plateau. Two small grabens, located in the quadrangle, are the easternmost evidence of Basin and Range faulting. Sedimentary units exposed are mainly Cretaceous in age and deposited in the Western Cretaceous Interior Seaway. This area is of economical importance due to its large coal deposits, coal bed methane, and groundwater. The Wattis Quadrangle provided an ideal opportunity to test, at a small scale, the applicability of a new groundwater model for stratified mountainous terranes. Water samples had 14C ages ranging from modern to 10,000 ± 500 years. Stable isotopes of oxygen and hydrogen showed that recharged precipitation fell when climate conditions were close to modern, or slightly colder. Three groundwater systems consist of one shallow groundwater system in the North Horn Formation, and two deeper aquifers located in the Blackhawk Formation and the Star Point Sandstone. Water in the North Horn Formation is modern, whereas the Blackhawk Formation and Star Point Sandstone waters are mixed systems, having tritium concentrations between 3 and 4 T.U., and 14C ages between 7,000 and 10,000 years. Geochemical modeling shows that there are no plausible reaction paths to evolve the North Horn Formation waters into waters contained in underlying units. Thus, water entering the top of the plateau does not flow through the stratified rocks to exit at its base. Instead, the waters represent discrete perched systems at various stratigraphic levels. The Star Point Sandstone has three parasequences with a single sequence boundary. The deposits show normal marine conditions containing lower shoreface biota of Skolithos and Ophiomorpha overlain by middle shoreface sedimentary structures. The Star Point Sandstone deltaic parasequences likely prograded into the basin during pulses of thrusting from the Sevier Orogeny. The Emery Sandstone Member of the Mancos Formation contains three parasequences all located in the lower shoreface, and also exhibits the normal marine biota of Skolithos and Ophiomorpha. The Emery Sandstone reflects density currents caused by major storm events, including Bauma C and D depositional structures. Thick sandstone bodies are restricted to paleochannels.



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Physical and Mathematical Sciences; Geological Sciences



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Sequence Stratigraphy, Wasatch Plataeu, Geological Map, Hydrogeology of Wattis Quadrangle, coal deposits central Utah

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