Late Famennian conodonts from the Cerro la Cueva, Sonora, NW Mexico

Abstract

This paper reports for the first time the presence of Famennian conodonts from a shallow marine succession exposed in the Cerro La Cueva, central Sonora, northwestern Mexico. The conodont fauna includes Bispathodus aculeatus aculeatus (Branson and Mehl), Bispathodus stabilis (Branson and Mehl), ‘Icriodus’ darbyensis Klapper, Polygnathus extralobatus Schäfer, Polygnathus semicostatus Branson and Mehl, Polygnathus cf. inornatus E.R. Branson, and Polygnathus aff. purus Voges, which are typical species from the late Famennian. The most biostratigraphically important species of this assemblage are “Icriodus” darbyensis and Polygnathus extralobatus, which indicate an expansa Zones age interval. This finding allows identification of Devonian rocks in the area of San Pedro de la Cueva located north of the El Novillo dam, where only Ordovician and Mississippian fossils have been previously documented. The identified conodont genera preliminarily indicate an outer marine shelf paleoenvironment. Studied strata are correlated with Devonian lithostratigraphic units previously defined in other areas of Sonora, especially in the Sierra Agua Verde, located approximately 15 km west of the Cerro La Cueva section.