Atokan Conodonts from the Pennsylvanian Outlier of the Michigan Basin

TitleAtokan Conodonts from the Pennsylvanian Outlier of the Michigan Basin
Publication TypeJournal Article
Year of Publication1981
AuthorsLanding, E, Wardlaw, BR
JournalJournal of Paleontology
Keywordsgeology paleontology
Conodonts occur in thin marine lenses in the upper part of the Saginaw Formation (commonly referred to as the Verne Limestone Member), Eaton and Clinton counties, Michigan. Associated fusulinids, macrofaunas, and floras establish equivalency with both the upper part of the Pottsville Formation and the upper Atokan Series. The conodont fauna by itself is open to interpretation as lower through upper Atokan. The rarity of Neognathodus (P) elements in the marine lenses precludes a precise correlation with the Neognathodus acme-zone sequence established for the Lower and Middle Pennsylvanian in Ohio and northwestern Illinois. Associated conodonts are stratigraphically long ranging in the Lower and Middle Pennsylvanian and Idiognathoides sinuatus is interpreted to range as high as the upper Atokan. Idiognathoides sinuatus is abundant and may fill the niche of Neognathodus in the Idiognathodus-Idiognathoides-Idioprioniodus-Hindeodus-Diplognathodus-Neognathodus-Aethotaxis assemblage from the marine lenses. Whether this assemblage represents a new eastern Midcontinent conodont biofacies or indicates a faunal connection with the western Midcontinent is unknown. Idiognathodus is dominant to the near exclusion of Idiognathoides in black shales with sparse benthic faunas at the base (transgressive) and top (regressive) of the thin marine lenses. Multielement "Idioprioniodus conjuctus" and Hindeodus minutus and the platform elements of Diplognathodus coloradoensis, Idiognathodus delicatus, Idiognathoides sinuatus, and Neognathodus medexultimus are systematically described. Idiognathoides sinuatus and I. corrugatus are asymmetrically paired platforms ("parasymmetry pairs") representing morphologically distinct sinistral and dextral elements of a probable Type 1 apparatus.