Published online by Cambridge University Press: 20 May 2016
Stratigraphic distribution of two key brachiopod species in the Ramp Creek Formation and Harrodsburg Limestone (middle Mississippian) in south-central Indiana suggests the boundary between the Osagean and Meramecian Series lies in the lower part of the Ramp Creek Formation. Marginirugus magnus (Meek and Worthen), an Osagean index fossil, ranges into the lower part of the Ramp Creek Formation. Warsawia lateralis (Hall), a Meramecian index fossil, also occurs in the lower part of the Ramp Creek Formation and in the lower part of the Harrodsburg Limestone. Thus, the upper part of the Edwardsville Formation and lower part of the Ramp Creek Formation in Indiana are temporally equivalent to the lower half of the Warsaw Formation in the Mississippi Valley. The upper part of the Ramp Creek Formation and the lower part of the Harrodsburg Limestone are temporally equivalent to the upper half of the Warsaw Formation.