CONICET | Buscador de Institutos y Recursos Humanos

New conodont results from the Sappington Formation in southwestern Montana revise its age from primarily Devonian to Mississippian, and question the utility of using global species like and and the palynomorph, for delineating the Devonian/Mississippian boundaryThis boundary has been placed at the top of the upper Sappington Formation (Unit 5) for over 40 years based on the latest Devonian conodont and the latest Devonian miospore found in the underlying Unit 4. An unconformable contact with the overlying Cottonwood Canyon/Lodgepole Formation is confirmed by conodonts of the Early Mississippian Zone with several missing zones at the contact. We present main results of a paleontologic and stratigraphic study of 33 localities studied using large sample sizes (especially for conodonts) and close sample spacing (Rice, 2021). Diverse miospore assemblages bearing were retrieved throughout the Sappington Formation in the lower Shale (U1), the middle shale (U4) and from rare shales occurring in the upper clastics (U5). In contrast, several localities yielded Early Mississippian conodonts and primary observations are: siphonodellids and were found coexisting in U3 from Beaver Creek East and in U5 at Snake Pit, Horseshoe Canyon West and Vermont, all barren of palynomorphs. Previous studies only found without in U3 and U5 at Lick Creek and other localities in the Basin; an Early Mississippian conodont with nodose ornamentation and rostral ridges, identified as cf. ,occurs with in a unique, fossiliferous lower U4 channel sandstone at Antelope Valley; an Early Mississippian conodont occurs in the middle of U5 at Horseshoe Canyon West and near the top of U5 at Devils Fence West; neither outcrop contains palynomorphs; an Early Mississippian conodont was found in oolitic grainstones within lower U5 at Moose Creek,above -bearing U4. Retispora lepidophyta