Late Early to Middle Devonian palynology of the Ramos x-1011 borehole from the Tarija Basin, northwestern Argentina

Abstract

Palynological analyses have been performed on a late Early to Middle Devonian clastic marine sedimentary succession of the Ramos x-1011 borehole, located in the southern area of the Tarija Basin, northwestern Argentina. Samples from the Icla, Huamampampa and Los Monos formations were processed. Palynomorphs from the Icla Formation were scarce and badly preserved, preventing their taxonomic classification. Samples from the Huamampampa and Los Monos formations yielded organic-walled phytoplankton and miospore assemblages of variable abundance, diversity, and preservation. Spores that suggest an Emsian age, such as Dibolisporites gaspiensis, Geminospora svalbardiae, and Grandispora protea were recovered from the Huamampampa Formation. Upwards in the borehole, the Los Monos Formation yielded spore species, such as Acinosporites acanthomammillatus, Acinosporites macrospinosus, Cymbosporites cyathus, Camarozonotriletes? concavus, Chelinospora ligurata, Cymbosporites variegatus, Geminospora lemurata, and Samarisporites cf. triangulatus, that point to an Eifelian to middle Givetian age. Among the organic-walled phytoplankton, Arkonites biluxus Cordobesia uruguayensis, Duvernaysphaera angelae, Duvernaysphaera tenuicingulata, Estiastra rhytidoa and Pterospermella pernambucensis support the age based on the terrestrial palynomorphs. The relative abundance of marine and terrestrial palynomorphs indicates a nearshore environment.