Depositional Environments and Hydrocarbon Occurrence of Mississippian Antler Basin, Nevada and Utah: ABSTRACT

Abstract

New field and paleontological data suggest that much of the Utah/Nevada Mississippian Antler basin siliciclastic sediments shed eastward off the Antler Mountains were deposited in marginal marine to nonmarine environments. Tongues of siliciclastic sediments thicken and coarsen westward from central Utah to central Nevada. Terrestrial plants found in place throughout the basin offer the best evidence of nonmarine deposition. Other depositional indicators include fluvial sequences, coal beds, palynomorph assemblages, bars parallel to depositional strike, and regional depositional patterns. A correct understanding of depositional environments helps explain patterns of Mississippian source and reservoir rock in the basin. The main source rocks of the eastern Great Basin are Mississippian black shales. Three large lobes of higher organic richness in eastern Nevada coincide with three large delta lobes. Generally, source rocks become more coaly and herbaceous westward and more amorphous eastward. Locally, excellent reservoir rocks can be encased by these source rocks. The best reservoir rocks are clean, reworked sandstones associated with river mouth bars and shoreline sandstones. Upland facies are abruptly truncated to the west by a Mesozoic thrust belt. Subthrust Mississippian sediments are probably the main source for Tertiary, fault-trap, upper plate fields such as Grant Canyon, Trap Spring, and Blackburnmore » fields. All 16 million barrels of oil produced in Nevada are produced along the leading edge of the thrust belt. A great possibility exists for many more millions of barrels yet to be found in new, major pools associated with the thrust belt.« less