Architecture and stratigraphy of the Lower Silurian Guelph Formation, Lockport Group, southern Ontario and Michigan

The Lower Silurian Lockport Group in Ontario and Michigan comprises, in ascending order: Gasport, Goat Island, Eramosa, and Guelph formations. Guelph facies architecture reveals deposition on an underlying carbonate ramp of Eramosa and/or Goat Island carbonates that dipped towards the Appalachian Basin. Temporally, Guelph facies reflect initial open marine transgressive phases that become increasingly restricted marine and karstic upward. Spatially, the facies display the most restricted marine and karstic fabrics in the central portion of the ‘Michigan Basin’ and are most open marine to the east. Newly acquired regional data supports the re-interpretation of the classic Guelph-pinnacle reef models as karst towers that formed in a paleokarst basin. This new regional perspective of the classic ‘Guelph-play’ will help to explain some of the challenges faced by oil/gas explorationists trying to both map/predict production zones and encourage re-evaluation of existing plays and enable successful exploration of new targets