ABSTRACT: Stigmaria: Indicator for Erosional Surfaces of Low Sea Level Stands in the Mississippian Antler Basin, Utah and Nevada
Alan K. Chamberlain
Stigmaria rootlets penetrating nonmarine and shallow-marine deposits in the Mississippian Antler basin suggest periods of erosion during low sea-level stands. Rootlets of Stigmaria penetrating bedding planes are found throughout the Antler basin in sediments that have been misinterpreted as deep-water turbidites and carbonates. In the Arrow Canyon Range, southern Nevada, rootlets penetrate marine carbonate rocks containing crinoids, corals, and brachiopods. In the Oquirrh Mountains, central Utah, rootlets penetrate marine shales that contain crinoids, ammonoids, brachiopods, and bivalves. Stigmaria and its rootlets are found associated with mudcracks in the Grant Range, east-central Nevada. Soil horizons and lag deposits mark the boundary between flora-bearing sediments t at sometimes contain coal beds and fluvial deposits and marine carbonate sediments containing shallow-water fauna such as fenestrate bryozoans, brachiopods, and corals in the Oquirrh Mountains.
The root zones and associated subaerial indicators mark significant lowering of relative sea level. Three tongues of nonmarine sediments protruding eastward into Utah from the Mississippian Antler Mountains in central Nevada suggest three periods of relative sea-level lowering. The last tongue, which is more regional than the others, may be related to eustatic sea-level lowering while the other tongues may be related to tectonic adjustments. The last tongue extends as far west as the Uinta Mountains and is composed of Chesterian delta plain sediments that fill a major east-west channel cut into Meramecian marine carbonates.
AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990