Delamaran trilobites from the La Laja Formation, San Juan, Argentina

Abstract

La Laja Formation crops out almost continuously along the western margin of the Chica de Zonda and Villicum hills. This limestone unit bears a remarkable fauna of Cambrian trilobites. In this work, the Delamaran trilobite fauna of the La Laja Formation, between the upper part of the El Estero Member and the lower third of the Soldano Member, is analysed. Glossopleura walcotti Poulsen, Glossopleura lodensis (Clark), Fieldaspis sp., and Prozacanthoides marianae n. sp. are described. Poliella denticulata, Mexicella mexicana?, and Glossopleura walcotti Zones are documented; these had been previously included in a hiatus. On the basis of the studied fauna, correlations are established between the La Laja Formation and olistoliths of the Western Precordillera. Additional correlations are also suggested between the Precordillera and different localities from Laurentia. Finally, the biogeographic implications of the described material are discussed. Delamarian taxa reported for the La Laja Formation are characteristic and so far restricted to Laurentia. The analysis of the trilobite fauna from this unit largely supports the allochtonous origin of the Precordillera.