An early Ordovician (Floian) conodont fauna from the Eastern Cordillera of Peru (central andean basin)

Abstract

Late Floian conodonts are recorded from a thin limestone lens intercalated in the lower part of the San Jose Formation at the Carcel Puncco section (Inambari River), Eastern Cordillera of Peru. The conodont association includes Gothodus costulatus LINDSTROM, Protopanderodus rectus (LINDSTROM), Drepanoistodus basiovalis (SERGEEVA), Drepanoistodus forceps (LINDSTROM), Drepanodus arcuatus PANDER, Trapezognathus diprion (LINDSTROM), Erraticodon patu COOPER, and Ansella cf. jemdandica (LOFGREN). This species association can be assigned to the upper part of the well-documented Oepikodus evae Zone. It is the northernmost conodont record of late Floian age in South America. This study updates the preliminary data presented in 2001 from this fossil locality, and it has important consequences for the paleogeographic reconstruction of the Peruvian part of the Central Andean Basin. In accordance with trilobites and brachiopods documented for the same strata, the conodont association represents a relatively cold-shallow-water platform environment. The record of late Floian conodonts towards the middle part of the San Jose Formation shows that the base of this unit in the studied section is considerably older than other sections of the distribution area, where its lowermost part is dated as early Darriwilian by the record of graptolites from the Undulograptus austrodentatus graptolite Zone. The diachronous initiation of the marine sedimentation makes the lower part of the Carcel Puncco shales penecontemporaneous with the volcanigenic rocks related with the Arequipa Massif, which transitionally underlie the San Jose Formation in other places of the Altiplano and the Eastern Cordillera of Peru.