Distribution pattern of Lower Triassic (Scythian) conodonts in the Western United States; documentation of the Pakistan connection

Sweet's prototype 1970 Lower Triassic conodont zonation based on collections from West Pakistan stimulated worldwide studies of equivalent faunas. In the western United States, however, recognition of many of the Tethyan zonal forms was delayed by an early research emphasis on Lower Triassic nearshore paleoenvironments in the Great Basin. An ongoing regional study of the entire Lower Triassic depositional basin in western United States establishes a commonality of North American conodonts with those of Eurasia, and clarifies the distribution pattern of mid-Scythian conodonts in the Rocky Mountains and Great Basin. Seldom-reported Neospathodus kummeli and Neospathodus pakistanensis are present in a crescent-shaped "basinal" region along the depocenter trend centered in southeast Idaho. Recent modification of the Lower Triassic conodont zonation by Sweet and Bergstroem utilizing graphic correlation has created an evolving but workable worldwide tool, and all nine Scythian zones are now recognized in the western United States. Many conodont species, as well as other marine biota, were effectively dispersed across a 20,000 km equatorial span of the Early Triassic seaway, and inhabited both the eastern and western shores of Pangaea.