Alan K. Chamberlain
A composite map of thermal measurements such as Conodont Alteration Indices and Vitrinite Reflectance of well cuttings and outcrops illustrates regions of thermal overmaturation in the eastern Great Basin. Thick (27,000 ft) sediment loading of the Pennsylvanian/Permian Oquirrh basin/Butte trough is probably responsible for overmaturation of Mississippian rocks of northwestern Utah and northeastern Nevada. Mesozoic/Tertiary heating associated with metamorphic core complexes in southwest Elko County and along the Utah/Nevada border is probably responsible for local regions of overmaturation. Overmature sediments occur along the east-west-trending Marysvale-Tonapah mineralized belt and the thermal hot spot in southern White Pine County, which are associated with regional Oli ocene mineralization and volcanism.
Except for areas involved in Mesozoic thrusting, thermal maturity measurements indicate a normal thermal gradient from regions with source rocks at the peak oil-generating window through the gas-generating window and to regions of overmaturity. A "maturation fairway" where Mississippian source rocks have been relatively thermally undisturbed since their deposition occurs just under and in front of the central Nevada Mesozoic thrust belt from Elko to north of Las Vegas. Along the west edge of the fairway, Mesozoic thrust sheets of older, overmature Paleozoic rocks cover immature, footwall rocks. Proximal Mississippian Antler basin and rocks in the Diamond and Eleana klippen probably underwent thermal deformation to the west before late Mesozoic thrusting juxtaposed them on immature, di tal Antler basin rocks.
AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990