EVALUATING LOWER ORDOVICIAN CHEMOSTRATIGRAPHY IN THE CORDILLERA ORIENTAL OF NORTHWESTERN ARGENTINA

Geochemical data of marine sedimentary rocks are commonly used to investigate palaeoceanographic conditions and perturbations in the carbon cycle in deep time. Notably, chemostratigraphic signatures provide a robust technique for correlating sections of rock on regional and global scales. The geochemical record of Lower Ordovician strata is widely studied in North America and Europe, but no chemostratigraphic work has yet been completed in the Central Andean Basin of South America. We use shale and mud-rich siltstone samples from outcrop exposures of the Lower Ordovician Pupusa, Saladillo, Parcha, and Acoite formations in the Cordillera Oriental of Northwest Argentina to evaluate regional geochemical trends. These sediments are exposed in the El Angosto de Lampazar-Pascha (~340 m), El Angosto del Moreno (~300 m), El Moreno (423 m), and the Aguas Blancas Creek (150 m) sections, located between Pascha and Altos de Lipán, Salta and Jujuy provinces, Argentina. These sections represent tidally dominated platform deposits to open water hummocky and trough cross-stratified fine- to very fine-grained sandstones. Here, we present major, minor, and trace element data along with organic carbon isotope values from ~80 samples gathered from various stratigraphic levels from the four sections within the western border of the Cordillera Oriental. The samples were analyzed using a Bruker 5G portable X-ray fluorescence (pXRF) spectrometer with the Bruker Mudrock Calibration, which provides elemental data from 30 distinct elements. Samples were homogenized and acidified to remove carbonate content for organic carbon isotope analysis. The geochemical data was plotted stratigraphically and integrated into the existing biostratigraphic framework to evaluate regional geochemical change recorded between the study sections. The new chemostratigraphic data from these formations along with recent conodont-graptolite biostratigraphy provides key age constraints, allowing for better regional correlation between these localities and for expanding regional correlations in the Central Andean Basin to time-equivalent sections globally.