Greasy and Porous Mississippian Rocks, Antler Basin, Nevada

Alan K. Chamberlain

Maturation of Mississippian source rocks is an important parameter in exploring for new fields in the eastern Great Basin. Destructive thermal events have obliterated hydrocarbons in many areas. Significant hydrocarbon shows are ubiquitous in regions where thick, organic-rich Mississippian source rocks have been exposed to optimum thermal conditions. One of these regions is a maturation "fairway" extending from Pine Valley on the north to Railroad Valley on the south. The maturation fairway coincides with a region of the thickest, richest, and greasiest Mississippian source rocks.

Organic richness and quality patterns match paleogeography. Three lobes of higher organic richness match three Antler basin deltaic lobes. Organic richness increases westward in the lush Antler basin flood plain. Thousands of feet of rich source rocks were buried. Later they generated tremendous volumes of hydrocarbons that have migrated into Mississippian sandstone reservoir rocks.

The best Mississippian sandstone reservoirs formed as barrier bars and beach deposits that are up to 2,000 ft of highly porous, permeable, well-sorted sandstone. Thick, porous sandstones encased in rich source rocks provide one of the most intriguing exploration plays in the Great Basin.

Even more exciting is the region where source rocks and reservoir rocks are stacked together in thrust-related features. The chance of finding giant oil fields in Nevada may be greater than finding giant fields in the Utah/Wyoming Overthrust belt because the prospective area in Nevada is larger than the Utah/Wyoming Overthrust belt.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.