The Late Devonian Michigan Basin was floored by the Middle and Upper Devonian Squaw Bay Limestone, which was deposited during the downwarping that produced the basin within a former Middle Devonian carbonate platform. The Squaw Bay comprises three beds, each having a different conodont fauna. The two upper beds, deposited during the transitans Zone, have different conodont biofacies that reflect this deepening. The basin was largely filled by the deep-water, anaerobic to dysaerobic, organic-rich, black Antrim Shale, which has a facies relationship with the prodeltaic, greenish gray Ellsworth Shale that prograded into the basin from the west. The Upper Devonian...