Utah Geological Survey Open File Report

By: Craig D. Morgan

This open-file report is a series of maps and cross sections to aid in evaluating the oil and
gas exploration potential of the Pennsylvanian Paradox Formation, with special emphasis on the
"Cane Creek" shale zone. The mapped area covers T. 24 - 26 S., R. 17 - 21 E., Emery and
Grand Counties, and T. 26 - 30 S., R. 19 - 24 E., San Juan County. The scale of the maps is
1:500,000. The cross sections have a vertical scale of 1 inch equals 400 feet, and a horizontal
scale of 1 inch equals approximately 7,000 feet. Table 1 lists the wells that are used as data
points for the mapping.
During Pennsylvanian time the Paradox Formation was deposited in a large, continually
subsiding basin. The basin subsided along a series of northwest-trending faults. The nearly equal rates of subsidence and sedimentation produced a thick sequence (greater than 6,000 feet) of cyclic carbonate, black organic-rich shale, and evaporite units deposited in a marginal marine to sabkha environment. The Paradox Formation consists of a maximum of 29 recognized cycles of evaporation and precipitation. These cycles were assigned numerical values by Rite (1960), starting with cycle 1 at, or near, the top of the formation and cycle 29 at, or near, the base. A typical cycle consists of a lower clastic zone, overlain by a generally thick (100+ feet) upper evaporite zone of anhydrite, halite, and occasionally potassium and magnesium salts. The clastic zone consists of organic-rich black shale and carbonate rocks (mostly dolomite) with thin interbedded anhydrite. The top of each cycle is an irregular surface thought to represent dissolution of salt . by less saline normal seawater. The shale zones are often fractured and contain hydrocarbons. The "Cane Creek" is the thickest shale zone, and oil and gas have been
produced from it for many years.

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