Middle Ordovician faunal spatial differentiation in Baltoscandia and the Appalachians

The distributional differentiation of Baltoscandian Middle Ordovician shelly faunas in terms of confacies belts has a counterpart in the southern and central Appalachians, where three belts, parallel to the mountain chain, are distinguished: the Blount, Tazewell and Lee Confacies Belts. As in Baltoscandia, the boundaries between these belts are sharp. The Blount Belt high-diversity shelly macrofauna is closely similar to Scoto-Appalachian faunas of northeastern Ireland and southwestern Scotland (Girvan). The Lee Belt fauna is virtually the same as that of the North American Midcontinent, and that of the Tazewell Belt is transitional between those of the Blount and Lee Belts. The ecological factors causing the confacies differentiation are currently not clearly understood but the differentiation was evidently not due to a single factor such as water depth, although this factor was apparently important for second-order differentiation (biofacies) within a confacies belt. The spatial differentiation patterns of the shelly, graptolite, and conodont faunas do not always coincide, suggesting that the factors controlling the distribution were largely specific for each fauna.