Aeronian–Telychian) of the East-Central Iowa Basin, Iowa, USA

Newsletters on Stratigraphy, Vol. 50/4 (2017), 391–416 Article Published online February 2017; published in print September 2017

Integrated carbon isotope and conodont biochemo- stratigraphy of the Silurian (Aeronian–Telychian) of the East-Central Iowa Basin, Iowa, USA

Neo E. B. McAdams1*, Alyssa M. Bancroft1,2, Bradley D. Cramer1, and Brian J. Witzke1

With 7 figures and 3 appendices

Abstract. Global integrated biochemostratigraphic studies of Silurian conodont biostratigraphy and carbon isotope chemostratigraphy typically focus on the biogeochemical events of the Wenlock through Pridoli epochs (Ireviken, Mulde, Lau, and Klonk events). The global change events that took place during the Llan- dovery Epoch (early Aeronian, late Aeronian, and Valgu events) are poorly understood in comparison. One major contributing factor is the fact that Llandovery strata are often shale-dominated or replete with uncon- formities in carbonate-dominated successions. As a result, only a handful of stratigraphically complete carbon isotopic and conodont biostratigraphic data sets are presently available from this interval worldwide. The Knapp Creek Core, Johnson County, east-central Iowa, preserves 228 feet (69.5 m) of dolomitic Silurian strata from the East-Central Iowa Basin and contains the Blanding, Hopkinton, Scotch Grove, and Gower for- mations. Integrated high-resolution carbon isotope chemostratigraphy and conodont biostratigraphy produced here demonstrate the presence of the late Aeronian, early Telychian ʻValguʼ, and early Sheinwoodian ʻIre- vikenʼ positive carbon isotope excursions in the core. Biostratigraphically significant conodonts recovered from the core include Pseudolonchodina (formerly Aspelundia) fluegeli, Distomodus staurognathoides, Aulacognathus kuehni, Aulacognathus bullatus, Wurmiella? polinclinata polinclinata, Pterospathodus eopennatus, Pterospathodus amorphognathoides angulatus, Pterospathodus amorphognathoides amorphognathoides, and Kockelella ranuliformis. Biochemostratigraphic data from the core indicate that the late Aeronian to early Sheinwoodian interval is well represented in the Iowa stratigraphic succession, help to val- idate recent and ongoing revisions to the Welsh Basin and base Telychian GSSP, and demonstrate that the East-Central Iowa Basin is an important region that provides the opportunity to study Llandovery biogeochemical events in an expanded carbonate setting.

Key words. Late Aeronian, Valgu, Ireviken, biostratigraphy, chemostratigraphy, conodonts

Authors’ addresses: 1 Department of Earth and Environmental Sciences, 115 Trowbridge Hall, University of Iowa, Iowa City, IA 52240; neo- [email protected]; City, IA 52240; [email protected], [email protected], brian-witzke@ uiowa.edu 2 Present address: Indiana Geological Survey, 611 North Walnut St., Bloomington, IN, USA 47405. [email protected] * Corresponding author: [email protected]