UPPER MIOCENE CALCAREOUS MICROFOSSILS (FORAMINIFERA AND OSTRACODA) FROM NORThWESTERN ARGENTINA

Abstract

Although the Neogene deposits of the Calchaquíes Valleys, northwestern Argentina, have been intensively studied, there are only a few works dealing with the calcareous microfauna. Thus, this study aims to provide detailed systematic descriptions of the calcareous microfauna recorded at the Playa del Zorro Alloformation and Chiquimil Formation, units exposed at the El Cajón Valley and Pampa hill respectively, Catamarca Province. Also, an assessment of the paleoenvironment, based on the calcareous microfossil association was carried out for both units. As a result, a new species of the ostracod genus Cyprideis Jones was recognized, namely Cyprideis calchaquiensis nov. sp., which was found associated with Perissocytheridea carrenoae Nicolaidis & Coimbra, Limnocythere spp. and the foraminifera Ammonia tepida Cushman. The low diversity assemblage, the predominance of rounded sieve pores on the valve surface of C. calchaquiensis nov. sp., and the presence of abnormal tests of A. tepida point to a shallow stressed water body that suffered evaporation episodes, resulting in fluctuating salinity. Interestingly, close similarities were observed between the Playa del Zorro Alloformation and Chiquimil Formation with the upper section of the Yecua Formation, Bolivia. This affinity could be explained by the passive dispersal capacities of the ostracods and foraminifers, the ecological preferences of the recognized taxa and the proximity of the outcrops, assisted by the development of mega wetlands.

Keywords

• Miocene
• Non-marine ostracods
• Foraminifera
• Paleoenvironments
• Playa del Zorro Alloformation
• Chiquimil Formation