Dimorphinites (Ammonoidea, Jurassic, Upper Bajocian) in the Precordillera of Northern Chile

Abstract

A new upper Bajocian ammonite assemblage containing the morphoceratids Dimorphinites dimorphus
(d’Orbigny) and Vigoriceras defrancei (d’Orbigny) is reported from the circum-Pacific area. These ammonites were
found at the top of the Torcazas Formation, in the Quebrada San Pedro area, Precordillera of northern Chile.
Taphonomic, systematic, and paleobiogeographic data confirm these dimorphs were part of indigenous populations
within the Tarapaca Basin, belonging to the same demic biospecies: Dimorphinites defrancei (d’Orbigny). The West
Tethyan and East-Pacific distribution of D. defrancei corroborates the availability of the migratory seaway, the socalled
Hispanic Corridor, between the western Tethys and the eastern Pacific Ocean during the upper Bajocian
Parkinsoni Zone. The discovery of this upper Bajocian Dimorphinites assemblage provides a new biochronostratigraphic
horizon in the Tarapaca Basin and an interoceanic correlation point for the latest Bajocian.