| Description |
The type section of the Round Valley Limestone, in Morgan County, Utah and an additional section in Wasatch County, Utah were systematically sampled for conodonts as a basis for study of Mississippian (Chesterian) - Pennsylvanian (Morrowan) conodont biostratigraphy in northeastern Utah. Five previously proposed conodont biostratigraphic zones are found in the Round Valley Limestone. In ascending order the zones are: the Gnathodus girtyi simplex Zone, the Rhachistognathus Zone, the Declinognathodus noduliferus Zone, the lower portion of the Neognathodus bassleri Zone, and the Idiognathodus humerus - I. sinuosis Zone. The Mississippian - Pennsylvanian boundary as defined by conodont assemblage zones lies within the Rhachistognathus Zone. It is suggested that the lower subzone of the Rhachistognathus Zone be named the Cavusgnathus - Gnathodus Subzone and the upper subzone the Adetognathus Subzone. The division between the subzones approximates the Mississippian - Pennsylvanian boundary. In both sections a sparse fauna of four species of Cavusgnathus Harris & Hollingsworth and three species of Gnathodus Pander clearly represents the Late Mississippian (Chesterian) fauna and is quite different from the Early Pennsylvanian (Morrowan) fauna, characterized by the occurrence of four species of Adetognathus Lane. Species characteristic of the middle and late Morrowan Streptgnathodus expansus - S. suberectus Zone are lacking in both Sections. Either a sedimentary hiatus exists or the fauna which elsewhere is used to define this zone is simply absent. Seventeen genera and 36 species are recognized. Important platform gerera are Adetognathus Lane, Cavusgnathus Harris & Hollingsworth, Declinegnathodus Dunn, Gnathodus Pander, Idiognathodus Gunnell, Idiognathoides Harris & Hollingsworth, Neognathods Dunn, Rhachistognathus Dunn, Spathognathodus Branson & Mehl, and Streptognathodus Stauffer & Plummer. One new species, Adetognathus stifeli, is proposed. |
