George D. Fraser Ellis L. Yochelson 1973 <p>Field mapping in the southern part of the Pequop&nbsp;Mountains has shown the presence of a major structural high which has&nbsp;profoundly affected the stratigraphy of Pennsylvanian and Lower&nbsp;Permian beds; lesser effects of this high persisted into the later Permian. &nbsp;Within the Park City Group (Permian), the Plymton Formation,&nbsp;overlying the Kaibab Limestone, is divided informally into five parts. &nbsp;The uppermost Plympton has yielded silicified fossils. The faunule&nbsp;studied is characterized by the scaphopod Plagioglypta and by&nbsp;bellerophontacean and neritacean gastropods, suggestive of a middle&nbsp;Permian age. &nbsp;Specimens are worn, and several lines of evidence suggest&nbsp;that this is a high-energy beach deposit associated with a residual high. &nbsp;The interpretation supplements the field evidence of a hiatus between&nbsp;the Plympton and the overlying Gerster Formation. Other occurrences&nbsp;of elements of the faunule in the equivalent Phosphoria rock complex&nbsp;are noted, but only a few were probably deposited in a high-energy&nbsp;beach environment. A new species of Naticopsis that has the color&nbsp;pattern preserved is named and described.</p> application/pdf en U.S. Geological Survey Interpretation of depositional environment in the Plympton Formation (Permian), Southern Pequop Mountains, Nevada, from physical stratigraphy and a faunule article