Conuláridos misisípicos de Nochixtlán, Oaxaca, México: consideraciones sistemáticas, estratigráficas y paleobiogeográficas

Abstract

MISSISSIPPIAN CONULARIIDS FROM NOCHIXTLAN, OAXACA, MEXICO: SYSTEMATICS, STRATIGRAPHIC AND PALEOBIOGEOGRAPHIC CONSIDERATIONS. This work represents the fi rst systematic study of conulariids of Mexico. Three species are described and illustrated: Conularia cf. C. subcarbonaria, Paraconularia chesterensis and P. cf. P. subulata, all of which come from four outcrops of the Santiago formation (informal unit), in the Santiago Ixtaltepec region, Nochixtlan municipality, Oaxaca. The stratigraphical distribution of these species corroborates the early Mississippian age (Osagean = late Tournaisian-early Visean) of the calcareous sandy lower member of the Santiago formation, and also supports the idea that at least part of the upper member belongs to the middle-late Mississippian (Meramecian-Chesterian = middle-late Visean). The studied conulariids reaffi rm the similarity between Carboniferous faunas of southwestern Mexico and those of the Mid-Continental United States, and hence the continuity of the epicontinental sea that covered both regions.