Paleoecology of selected Danian marine ostracods, geochemically pre-characterized by analysis of stable carbon (13C) and oxygen (18O) isotopes

The Cerro Azul Section provides a continuous record of the Cretaceous-Paleogene (K-Pg) transition in a shallow marine context of the South Atlantic Ocean in the Neuque ' n Basin. Ostracod assemblages were severely affected by environmental changes across the event. Excellent ostracod preservation at the Cerro Azul Section allows to infer paleoecological preferences of four Danian species based on carbon and oxygen stable isotopes. The studied species were Paracypris bertelsae Ceolin and Whatley, 2015, Cytherella spp., Togoina argentinensis and Henryhowella (Wichmannella) meridionalis (Bertels, 1974). To assess the reliability of ostracod 813C and 818O values as paleoenvironmental proxies, we pre-characterized valves with micro x-ray microdiffraction (mu XRD) and microRaman (mu Raman spectroscopy). Togoina argentinensis and Henryhowella (Wichmannella) meridionalis present in their major calcitic compositions, with small differences of crystallinity within intervals of environmental stress, but no authigenic phases formed during diagenesis. 813C and 818O values depict clear interspecific differences between smooth specimens and ornamented specimens. These differences in stable isotope values were likely controlled by microhabitat preferences, which would be comparable with patterns described for benthic foraminifera as well as paleonutrients variations, suing Ba/Ti and P/Ti ratios.