ABSTRACT: Thermal History of Selected Areas in the Paradox Basin, Utah and Colorado

CRYSDALE, B. L., V. F. NUCCIO, and C. E. BARKER, U.S. Geological Survey, Denver, CO

The Paradox basin is a southeast-trending structural depression in southeastern Utah and southwestern Colorado that is dominated by a thick sequence of Pennsylvanian cyclic deposits of evaporites, carbonates, and black shales. Preliminary evidence from fluid inclusion, Rock-Eval pyrolysis, and burial history reconstruction data indicates that in different areas of the basin many of these Pennsylvanian strata are within the temperature range for generation of oil and/or gas. Fluid inclusions in calcite, halite, gypsum, and anhydrite in veins, layers, and nodules found in limestones and black shale samples indicate that temperatures have reached at least 100 degrees C in the basin. These inclusions suggest that cementation and vein formation occurred near maximum burial and/or temperatu e; oil inclusions in the veins imply that oil migrated through the rocks sometime after vein formation occurred. Burial history reconstruction shows lower Paleozoic rocks in the Paradox basin may have reached depths as great as 18,000 ft, with subsequent uplift and erosion of as much as 7000 ft of overburden.

Present-day geothermal gradients calculated from drill-stem tests range from 18 degrees F/1000 ft. (33 degrees C/km) in the southeast part of the basin to 8 degrees F/1000 ft (14.5 degrees C/km) in the western part of the basin. Paleogeothermal gradients calculated from fluid-inclusion homogenization temperatures and burial-history reconstruction are similar to or lower than the present-day gradients, suggesting that the basin is presently at or near maximum temperature.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)