REVISED STRATIGRAPHY OF THE LOWER SIMCOE GROUP OF SOUTHERN ONTARIO AND CORRELATION WITH THE CINCINNATI ARCH
The Bobcaygeon Formation (Upper Ordovician, Black Riveran-Trentonian) of southern Ontario represents a composite unit on the basis of sequence stratigraphy, lithostratigraphy, chemostratigraphy, and paleontological evidence; it contains one or more major erosional unconformities, disparate facies, and markedly distinct faunas. Most of the present Coboconk, previously considered to be the lower member of the Bobcaygeon, should be elevated to the status of formation as it represents the uppermost portion of the Sandbian M4 sequence and is bounded at the top by a regional erosional disconformity. The middle and upper members of the Bobcaygeon should be reverted to their original definition as the Kirkfield Formation. The upper Bobcaygeon can be further divided into two members (middle and upper Kirkfield), placing a 1–2 m thick sharply-based grainstone at the base of each member, which thus correspond to small scale depositional sequences. Based upon carbon isotope chemostratigraphy as well as biostratigraphy and allostratigraphy, these units are correlated with equivalent strata and sequences (Katian M5A [upper cycle] and M5B) of the Cincinnati Arch region.