CONICET | Buscador de Institutos y Recursos Humanos

Graptolites from northwestern Argentina have been studied for more than a century to establish regional and global biostratigraphic correlations. Meanwhile, the scarce studies focused on the thermal maturity of the Early Paleozoic strata have been restricted to the Conodont Color Alteration index (CAi), clay mineralogy, chlorite geothermometry, and Kübler analyses. in the framework of the Ph.D. thesis of the first author (N.C.H.S), 14 graptolite samples were used to evaluate, for the first time, the graptolite reflectance and thermal maturity of the Early Paleozoic strata in northwestern Argentina. The studied graptolites come from the Los Colorados section, in the Cordillera oriental, mainly comprising the Acoite and Lipeón formations. Additional samples were also collected from the Huaytiquina and Muñayoc sections, in the Puna highland, corresponding to the ?Coquena? Formation and the Cochinoca-Escaya Magmatic-Sedimentary Complex, respectively. The lower reflectance and absence of anisotropy of graptolites from the Cordillera oriental region are indicative of their low maturity. Conversely, the graptolite fragments from the Muñayoc and Huaytiquina sections in Puna are high reflecting, pointing to considerably higher maturity. Furthermore, the vitrinite reflectance equivalent values obtained for the Puna region (4.23%?4.99%) are higher than those attained for the Cordillera oriental (0.62%?0.97%). This could be the result ofthe combination of hydrothermal fluids, associated volcanism, and deformation related to tectonics events, which produced a higher geothermal gradient in the Puna. We expect that work in progress will expand our current knowledge and help us draw additional interpretations of the evolution of the Central Andean Basin.