Abstract
Abstract The Topazan Stage is proposed for the interval between the Delamaran Stage and the originally proposed base of the Marjuman Stage. The proposed stratotype of the lower boundary of the Topazan Stage occurs 2.6 m above the base of the upper shale member of the Chisholm Formation, Drum Mountains, Utah. This boundary occurs within a shale sequence and is marked by the first appearance of Proehmaniella basilica, which also coincides with the disappearance of the common corynexochid Glossopleura. This faunal turnover can be recognized in stratigraphic sections in western North America and Tennessee, but cannot be recognized outside of Laurentia. The base of the overlying Marjuman Stage is restored to its originally proposed boundary, the FAD of Ptychagnostus atavus.
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