ANALYSIS OF STREPTOGNATHODUS SPECIES SUCCESSION IN EUDORA SHALE MEMBER OF STANTON LIMESTONE (UPPER PENNSYLVANIAN) ON NORTHERN MIDCONTINENT SHELF
The Eudora Shale Member, which can be traced from southwest Iowa to northern Oklahoma, represents the offshore condensed interval of the Stanton cyclothem. This dark gray to black shale unit displays a change in Streptognathodus species from base to top. The lower gray facies contains several species that are common in older cyclothems, including S. elegantulus. Although Idiognathodus simulator dominates the deepest-water middle black facies, the upper gray shale is dominated by a similar, but distinct of species Streptognathodus, S. firmus.
My purpose is to determine whether or not forms intermediate between S. elegantulus in the lower gray shale and S. firmus in the upper gray shale exist in the middle black facies in several sections across the shelf. If intermediate forms are present, they would indicate that S. firmus is a descendant of S. elegantulus. Their absence would suggest extinction of the earlier Streptognathodus species and immigration of S. firmus from Eurasia, where it was first described. Results so far indicate a lack of intermediate forms, suggesting that S. firmus migrated from Eurasia. Studies of this type will aid in evaluating worldwide correlation of glacial-eustatic cyclothems.