Abstract

During Devonian time the shoreline of the Cordilleran geosyncline lay approximately north-south in central Utah. Sediment is thicker to the west where two kinds of lithology, a bioclastic limestone and a black shale, comprise part of the Middle Devonian and all of the Upper Devonian sediments. Several thousand feet thick at their maximum, these beds were deposited in successive westerly migrating sedimentary wedges during several million years. Conodont faunas in the upper beds of the limestone in western Utah are the same composition as those present 700 feet below the top of the limestone 200 miles west in central Nevada. Deposition of the overlying Pilot Shale progressed in the same manner from east to west and conodonts present 300-400 feet above the base of the shale in western Utah are the same species as those in upper beds of the limestone in central Nevada. These conodont assemblages, seemingly fades independent, indicate diachronism and demonstrate that the top bed of the limestone in central Nevada was deposited at the same time as the middle part of the shale in western Utah.

Sedimentation changed during Mississippian time and the lowest beds from central Utah to central Nevada contain the Kinder-hookian guide Siphonodella at a uniform stratigraphic level.