REVISITING THE DEVONIAN-CARBONIFEROUS BOUNDARY INTERVAL IN THE U.S. MIDCONTINENT: TYPE KINDERHOOKIAN AREA OF ILLINOIS, MISSOURI, AND IOWA

In light of the revision of the Devonian-Carboniferous Boundary Global Stratotype Section and Point (GSSP) and the Iowa Geological Survey’s (IGS) recent bedrock mapping efforts in SE Iowa (as part of USGS STATEMAP), a detailed restudy of the Late Devonian and the type Kinderhookian strata of the tristate area appears warranted. Faculty and students at the University of Iowa’s Department of Earth and Environmental Sciences and the IGS initiated an investigation of Famennian-Osagean rocks of the tristate area that includes litho-, bio-, chemostratigraphy, and sequence stratigraphy of these strata. Chemostratigraphy will play a central role in this investigation because this short interval of Earth history is characterized by records of two of the largest carbon isotope excursions of the Phanerozoic (Hangenberg and Kinderhook-Osage Boundary excursions). This work began in the summer of 2017 and is beginning to yield results. The goal of this investigation is to provide a revised stratigraphic framework for the Devonian-Carboniferous boundary interval in the U.S. Midcontinent.

The McCraney Formation of the classic Kinderhookian succession was established by Moore for the limestone bluffs on McCraney Creek near Kinderhook, Illinois. In southeast Iowa, the McCraney consists of alternating beds of lithographic limestone and fine crystalline dolomite. The Iowa McCraney outcrops are very similar in appearance to the Louisiana Formation, whose type area is near the town of Louisiana in northeastern Missouri. The McCraney and the Louisiana underlie parts of SE Iowa, NE Missouri, and NW Illinois. Both typically underlie a siltstone unit or are unconformably overlain by the Burlington Formation. Both overlie siltstone or shale units of the Upper Devonian Series. Although both units share some of the same brachiopod fauna, the Protognathodus kockeli Zone fauna of the Louisiana is older than the conodont fauna with distinctive Siphonodella in the Iowa McCraney. Stratigraphic distinction of these two units has been confounded by the fact that there are no outcrops where both units are present in direct sequence. Furthermore, Witzke suggested that the ‘McCraney’ in SE Iowa may not be the same as the type McCraney of Illinois and could be a lithologically similar unit of a different age that is yet to be formally recognized.