Succession of rugose coral faunas in the Lower and Middle Devonian of eastern North America

Abstract

Rocks of Early Devonian age are widely but sporadically distributed in the eastern half of North America and coral studies are based on a very incomplete record. Middle Devonian rocks are thicker and cover a greater area. Both Early and Middle Devonian corals are more similar to western European species than they are to presumably contemporary forms from western North America, although some of the eastern faunas contain a significant portion of endemic genera. The general outline of an eastern province was inherited from the Silurian, but disappeared by Late Devonian time when the worldwide Frasnian fauna invaded the area. A reef fauna of middle Helderberg age is known from the northeast part of the province and is composed of both endemic and widespread genera. Approximately contemporaneous off-reef deposits have few species, but these are common in argillaceous rocks of a somewhat larger area. Rocks of middle Onesquethaw (Schoharie) age, although thin and discintinuous, include the largest and most widespread Early-Devonian coral fauna. Endemic genera are numerous but other elements are widespread and some species are apparently ancestral to species in the succeeding Onondaga fauna. The late Onesquethaw (Onondaga) faunas are the largest and most widely distributed of all those under review. Succeeding faunas of the Cazenovia, Tioughnioga and Taghanic Stage (Hamilton-Tully sequence) are less widespread and are clearly derivatives of the late Onesquethaw fauna. The Taghanic fauna is the latest Middle Devonian rugose coral fauna in the area