Date of this Version
Published in Transactions of the Nebraska Academy of Sciences, Volume 3 (1976).
The fauna of the Stull Shale Member (Upper Pennsylvanian, Virgil Series) in southeastern Nebraska and southwestern Iowa is dominated by brachiopods. The biofacies succession is largely represented by a double recurrence of the Crurithyris (Neochonetes) Assemblages, interrupted by the Crurithyris-(Productoidea Assemblages in the Middle Stull and by the Crurithyris-Low Diversity-Low Biomass Assemblage in the Upper Stull.
The Shannon-Wiener information function and some abiotic parameters (Rock color and lime content) have been used to interpret the paleoenvironment represented by each of these assemblages. Moderate diversity index values are present in the Crurithyris -(Neochonetes) Assemblages for the Lower Stull, a diversity consistent with the predominance of light-weight brachiopods and bivalves in relatively lime-poor sediment High index values are revealed by the Crurithyris-(Productoidea) Assemblages for the Middle Stull; such diversity is indicative of optimum biotic conditions as evidenced by the prominence of heavy shelled brachiopods, particularly the so-called "quasi-infaunal" productoids (Rudwick, 1970), and bivalves in relatively limy sediments. Moderate values are again present in the lowest part and highest part of the Upper Stull by the Crurithyris-(Neochonetes) Assemblages and are consistent with the predominance of light-weight forms; these assemblages are interrupted by the Crurithyris- Low Diversity Low Biomass Assemblage containing low index values characteristic of the black-colored rocks indicative of stagnant bottom conditions