Telychian (Llandovery, Silurian) conodonts from the LaPorte city formation of eastern Iowa, USA (East-Central Iowa Basin) and their implications for global Telychian conodont biostratigraphic correlation

Abstract

Conodonts from the LaPorte City Formation of eastern Iowa (East-Central Iowa Basin) indicate an early to middle Telychian age for the formation. Conodonts diagnostic of the Pterospathodus eopennatus Superzone, Pterospathodus eopennatus ssp. n. 2 Zone, and Pterospathodus amorphognathoides angulatus Zone were recovered, allowing for the first direct comparison of the stratigraphic ranges of conodont species in the Illinois and Baltic Basins. A heretofore undescribed species of Pseudolonchodina similar to Pseudolonchodina fluegeli occurs in the LaPorte City Formation. It is distinguished from Pseudolonchodina fluegeli by the absence of fused denticles on Paelements and discrete to nearly-discrete denticles on the other elements. Due to the fragmented nature of the specimens, the species is left in open nomenclature. Wurmiella? polinclinata polinclinata ranges much lower in the East-Central Iowa Basin (Pt. eopennatus ssp. n. 2 Zone) than the Baltic Basin, and therefore cannot be used as an index fossil diagnostic of the Pt. am. amorphognathoides Zone in global correlations. This study documents the utility of the small limestone formations on the northwest flank of the East-Central Iowa Basin for refining global Silurian conodont biostratigraphic zonation.