Permian corals of the Cordilleran-Arctic-Uralian Realm

Abstract

Permian rugose corals of the Cordilleran-Arctic-Uralian Realm are abundant in shallow-water carbonates along the northwestern and western margin of Pangaea, from the Ural Mountains, area in Russia, through the Svalbard Archipelago and arctic and western North America, to Bolivia and Peru. The colonial forms are of particular interest for the biostratigraphy and reconstruction of the paleogeography of this extensive region. A revision of the systematics of these corals has shown that, although important differences exist between the assemblages in the areas listed, the faunas are recognizable throughout the entire realm. Almost all of the faunas in the realm, on cratonal Pangaea, are Cisuralian (Asselian to Artinskian) in age although younger faunas occur in rocks of terranes subsequently accreted to North America. The cratonal faunas show a general trend from a predominance of relatively simple, fasciculate species with open axial areas or weakly developed axial structures in the lowest Permian, to younger, more complex fasciculate and massive species with a variety of morphological elements in their axial structures and dissepimentaria. Suppression of the walls occurs commonly in the youngest faunas. As a result of the northward movement of Pangaea into cooler waters, colonial rugose corals were exterminated from the more northerly areas by early to mid-Artinskian time, but persisted throughout the Artinskian and possibly into the Kungurian and early Guagalupian in the cratonic successions of the western U.S.A. Similarities between the coral faunas of cratonal North America and the western allochthonous terranes indicate that faunal interchange occurred between these various coral faunas during the Cisuralian. The only colonial corals recovered from Wordian to Lopingian rocks in this region are waagenophyllid corals of tethyan affinity from the Cache Creek and Quesnellia terranes of British Columbia and the Hayfork and Eastern Klamath terranes of California.