An expanded stratigraphic record of the Devonian-Carboniferous boundary Hangenberg biogeochemical Event from Southeast Iowa (U.S.A.)

coincides with a mass extinction on the scale of the ‘Big Five’ (Sepkoski 1996, Kaiser et al. 2016) and a major perturbation to the global carbon cycle (Cramer et al. 2008, Saltzman & Thomas 2012). The DCB strata of the tri-state area of Missouri, Illinois, and Iowa have been studied for over a century and contain historically important strata for the type Mississippian area including the type area of the lowest Carboniferous North American Kinderhookian Stage (global lower Tournaisian Stage) of the Mississippian Subsystem. The majority of this work occurred more than 50 years ago (e.g., Scott & Collinson 1961) with more recent work limited to the late 1990’s (Chauffe & Nichols 1995, Witzke & Bunker 1996, Chauffe & Guzman 1997). However, significant problems with unit correlation remain due to long standing nomenclature divides across state boundaries, lack of study, or lowresolution sampling. Two units of strikingly similar lithologies, the McCraney Formation and the Louisiana Formation, are critical to the placement of the DCB in the tri-state area. These units often occur within a few miles of one another; however, they have never been identified in the same succession, either in outcrop or in the subsurface. Historically, a nearly equal number of publications have considered these units to be equivalent (e.g., Weller 1900, Weller & Sutton 1940, Harris 1947, Stainbrook 1950) as have considered them to be temporally distinct (Keyes 1895, Weller 1906,