The Taconic Orogeny

The Taconic orogeny of eastern North America was not, as traditionally defined, a single orogenic event that occurred at the end of the Ordovician period, but rather a complex series of orogenic episodes or climaxes spread over the larger part of that period. In most sectors of the northern Appalachians it included at least three of the following: disconformity in an external belt where carbonate was accumulating; severe early deformation in an internal volcanic belt; gravity slides from internal uplifts into the external belt; and widespread deformation, especially in the more external belts. In general, these events did not occur at the same time in the various sectors; each took a considerable time, and they overlapped to some extent. The Taconic orogeny also affected the southern Appalachians and may have been the most important one there, but evidence for this assertion is meager and inconclusive. Detailed analysis of the "fine structure" of the Taconic orogeny combats the dogma that orogenies are sharp, discrete events punctuating the geologic record (separating periods and abruptly terminating geosynclinal sedimentation) and suggests instead that they reflect "random-walk" processes within the Earth, in all likelihood the same as those responsible for sea-floor spreading and the present tectonic state of the Earth.