Document Type

Poster Session

Document Subtype


Presentation Date


Conference Name

4th Annual Meeting of IGCP 591, Estonia, 2014

Conference Location

Tartu, Estonia

Source of Publication

4th Annual Meeting of IGCP 591 The Early to Middle Paleozoic Revolution Estonia, 10-19 June 2014, Abstracts and Field Guide


University of Tartu

Place of Publication

4th Annual Meeting of IGCP 591 The Early to Middle Paleozoic Revolution Estonia, 10-19 June 2014, Abstracts and Field Guide

Publication Date


Inclusive pages


Peer Review



The Upper Ordovician (Katian, Richmondian) strata of Ohio, Kentucky and Indiana, long noted for their abundant fossils and excellent exposures, have been subdivided into a series of three 3rd order depositional sequences by Holland and Patzkowsky (1996). Recent detailed field studies in southern Indiana and northern Kentucky suggests a major, regionally angular unconformity within their sequence C5. Evidence for this subtle disconformity includes the progressive southward loss of marker beds and intervals in the middle part of the Waynesville Formation in southern Indiana. This regional truncation has escaped notice despite a century of stratigraphic work, in part because of similarity of facies above and below the erosion surface. However, it appears to be equivalent to a Mid-Richmondian Unconformity recognized Ross and Ross (2002) in central Kentucky. Recent work confirms the significance of this surface. The Mid-Richmondian Unconformity in southern indiana is situated below a thin condensed interval containing a brachiopod epibole, the “lower Glyptorthis insculpta zone”, the base of which marks the traditional boundary between the Clarksville and Blanchester Members of the Waynesville Formation. In down-ramp locations, the surface is characterized by the presence of small crusts of pyrite. Further upramp (to the south), this surface is marked by a change from limestone and shale of the Bull Fork Formation to dolostone and dolomitic shales referred to by previous workers as the Rowland Member of the Drakes Formation. Approximately 15 – 16 meters of strata, present in northern distal section, are absent in the proximal sections on the west side of the Cincinnati Arch. This is explained by both erosional down-cutting beneath the unconformity, and depositional thinning of the shales in the proximal setting. Future correlation work will test the idea that this surface continues further south, eventually removing all of the lowest Waynesville and part of the Arnhem Formation below. This significant unconformity represents a third-order sequence boundary that splits Holland’s C5 sequence into two parts. Accordingly, we propose that the Blanchester, the uppermost member of the Waynesville, be elevated to a formation.


Earth Sciences | Paleontology | Sedimentology | Stratigraphy



Link to Original Published Item