Brachiopods of the Detroit River Group (Devonian) from southwestern Ontario and adjacent areas of Michigan and Ohio

The Detroit River Group is a widely distributed sequence of carbonate and evaporate deposits in the Michigan Basin and adjacent parts of the craton. In the type are a, these rocks can be lithologically subdivided as follows (in ascending order): Amherstburg Dolomite, Lucas Dolomite, and Anderdon Limes tone. Each of these formations is also characterized by its distinctive fossil assemblage. However, neither the formations nor the fossils maintain their identity much beyond the type area; in northwestern Ohio the section consists entirely of dolomite (the Lucas) whereas near Ingersoll, Ontario the rocks are all limes tone (Detroit River Group, undifferentiated) . The most diagnostic mega fossils in the Detroit River belong to the brachiopod genus Prosserella which originally included seven named species and subspecies; the genus is herein revised to two species, P. modestoides and P. lucasi. The total brachiopod fauna consists of sixty-seven species, of which forty-five are herein described (including three new species, Camarotoe chia (?) ehlersi, Meristella (?) livingstonensis , and Cranaena boucoti) . Fifty- one species are restricted to the Detroit River and five additional species are long- ranging forms present both in rocks older and younger than the Detroit River; these fifty-six species have only limited value in correlation. The geographic and stratigraphic distribution of the remaining eleven species (plus Cranaena boucoti possibly) indicate that the Amherstburg Dolomite is correlative with the Edgecliff Member of the Onondaga Limestone in New York, Zones A- F (after Stauffer , 1909) of the lower Columbus Limestone in Ohio, the upper five feet of the "Coral Zone" (after Campbell, 1942) of the Jeffersonville Limestone at the Falls of the Ohio River, and the upper Dutch Creek Sandstone and lower Grand Tower Limestone in southwestern Illinois. Similarly, the Anderdon Limestone is correlative with the upper Onondaga, Zone Hof the Columbus, the Par aspirifer acuminatus Zone of the Jeffers onville, and the upper Grand Tower below the occurrence of Brevispirifer lucasensis . These correlations are partially s upported by the stratigraphic distribution of the range-zones of the following important genera in the Detroit River and correlative rocks: Spinulicosta, Atribonium, Camarospira, Metaplasia, and Cranaena. All of the Detroit River species are confined to the Appalachian Faunal Province and so cannot be used for intercontinental correlation. Furthermore, the limits of the Detroit River generic range-zones overlap the Lower Devonian-Middle Devonian boundary or else the limits are so poorly known that they are of uncertain value in intercontinental correlation. However, conodonts and goniatites in the upper Onondaga and Columbus indicate that these rocks are of Eifelian (Middle Devonian) age; the Anderdon must therefore also be Eifelian. The age of the Lucas and Amherstburg is uncertain; these formations could be either lower Eifelian (Middle Devonian) or upper Emsian (Lower Devonian).