Timing and Coordination of Orogenic, Epeirogenic, and Eustatic Events

The Devonian-Mississippian Antler Orogeny is analyzed and reasons are advanced to show that its movements were felt all around western and Arctic North America. The Antler Orogeny began in the Franklinian Geosyncline during late Early Devonian time and became pervasive in all Arctic regions by the beginning of the Late Devonian. Antler erogenic events migrated southward during the Devonian and reached a climax along the whole span of continental margin, from Ellesmere Island to California, at about the beginning of the Mississippian. The Acadian Orogeny of eastern North America involved deformation of similar timing, suggesting that the two named orogenies are mirror-image events of a single master orogeny. The timing of the three other major North American orogenies of the Paleozoic and Mesozoic is analyzed more briefly.

During the Middle Ordovician to Cretaceous interval, the cratonic interior of North America underwent four major onlap-offlap cycles of sedimentation called sequences. Evidently orogeny, epeirogeny, and eustasy act in concert in response to the same driving mechanism, because the timing of orogeny in the geosynclines and of the spread of marine waters to their maximum extent on the cratonic interior is found to coincide with remarkable accuracy during three of the four orogenies, and to be permissively in accord with this correspondence of timing in the fourth. The name “Antler Effect” is suggested for this fundamental relation.

Because eustatic sea-level fluctuations are inadequate by themselves to explain the cyclic nature of Permo-Carboniferous sediments of the North American cratonic interior, consideration of the Antler Effect suggests pulsating orogenic movements at the continental margins during that time. In terms of plate tectonic theory, the North American and the European and African plates, juxtaposed during the Carboniferous-Permian, still must have been subject to the driving forces that brought them together, resulting in alternating compressional and relaxatory movements, offering an explanation of the diastrophic theory for the origin of cyclothems.

Interpretation of orogeny by investigation of the cratonic sedimentary sequences that are deposited in concert requires a view of orogeny as a long-lasting series of tectonic events separated by short anorogenic times in the geosynclines—a concept at odds with those offered up o t this time. If orogeny is the result of plate convergence, then transgression of epicontinental seas occurs when plates move. Short anorogenic interludes, corresponding to times of regression, appear to occur when the active vectors of the plate-driving force are reorienting. Eustatic sea-level fluctuations, resulting from the activity of oceanic rises, and epeirogenic warping of the continents, acting together, can explain the timing and paleogeographic patterns of the transgressive-regressive cycles on the continents. Because orogeny can occur simultaneously on opposite sides of a continental block, the driving mechanism for plates must involve processes which are independent of the plates themselves.