Multidisciplinary Chronostratigraphic Calibration of the Aptian-Albian Tran-Sition in the Araripe Basin, Brazil: Results from the Cronos Project

The CRONOS Project aims to establish a high-resolution temporal calibration for the Alagoas local stage (Lower Cretaceous), a critical interval for hydrocarbon exploration in Brazilian basins. Given the complexities of the Aptian–Albian transition, this project integrates multidisciplinary proxies to build a robust predictive model, facilitating correlations between Brazilian interior basins and the South Atlantic continental margin. This study focuses on the primary reference sections from wells 2-AB-1-CE and 2-AP-2-CE (Araripe Basin, Northeastern Brazil). A refined biostratigraphic zonation was established based on ostracods, redefining the Pattersoncypris spp. Biozone – wich is now divided into three subzones –, and the Damonella? grandiensisBiozone. The integration with calcareous nannofossils (Hayesites albiensis) and planktonic foraminifera (Microhedbergella renilaevis) permitted the precise placement of the Aptian-Albian boundary within the Romualdo Formation. Furthermore, geochronological control was anchored by Re-Os absolute dating (111.9 ± 2.9 Ma) and the probably identification of the global Oceanic Anoxic Event 1b (Kilian sub-event) through geochemistry data (negative δ13Corg excursion and Molybdenum enrichment). As the project evolves, high-resolution physical proxies will be fully integrated to refine this framework. Forthcoming research includes the completion of magnetostratigraphic analysis to identify global magnetic events (such as the ISEA reversal) and the application of cyclostratigraphy to estimate biozone durations based on orbital cycles (eccentricity and precession). These data will subsequently be coupled with ongoing research in the neighboring Parnaíba Basin to test the regional synchronicity of these events. By anchoring biological, geochemical and geophysical events within a global timescale, the project provides a unified model for the stratigraphic evolution of the Lower Cretaceous of the Western Gondwana. The authors gratefully acknowledge the support and funding from TotalEnergies.