Late Paleozoic and Triassic Conodont Biostratigraphy: Correlations Around the Expanding Atlantic Ocean

Abstract

The best Late Devonian configuration for the present Atlantic borderland area includes North America and northern Europe in contact or close proximity and a “proto-Atlantic Ocean” separating these continents from Africa and South America. During the Carboniferous, the Africa-South America block approached the North America-northern Europe block, destroying the “proto-Atlantic” and during the Permo-Triassic, there was no major separation of a tenuously fused South America, Africa, North America, Europe continent. By Late Triassic, the present North Atlantic began forming as the European and African continents began the shift to their present positions. The relationship of this continental movement to conodont biostratigraphy on either side of the present Atlantic Basin can be compared using the similarity index, 2w/ a + b, for conodont form-species. Conodont similarity between Europe and North America was greatest during the Late Devonian and Permian, with a gradual decrease in the Triassic that might be related to formation of the present Atlantic Basin. Similarity indices among other Atlantic borderland continents are somewhat ambiguous, as far as documenting continental proximity. This is because of limited taxonomic data. Also, such things as low Carboniferous Atlantic borderland conodont similarity may be explained by other factors such as the ecologic idiosyncrasies of the ancient Pacific and Tethyan water masses, or different continental elevations during the time interval. Regardless, some 100 conodont zones (43 Devonian, 23 Carboniferous, 12 Permian, 22 Triassic) provide an important biostratigraphic framework for the Atlantic borderlands. A calculated zonal similarity index mimics that of the form-species index. The greatest zonal similarity is during the Late Devonian, much less during the Carboniferous, but high again in the Triassic before dropping in the Late Triassic, perhaps, in part, reflecting Late Triassic separation of North America and Europe.