Astronomical calibration of the latest Aptian to middle Albian in the South Atlantic Ocean

Carbon cycle perturbations dramatically affected the ocean-climate system during the Aptian-Albian transition. However, the chronology of this interval is still intensively debated. Here we present a comprehensive astro-nomical calibration of planktonic foraminiferal and calcareous nannofossil bioevents along a complete marine sedimentary succession, comprising the latest Aptian to middle Albian interval at drilling Core SER-03, located in the Sergipe-Alagoas Basin. The SER-03 astrochronology is based on the tuning of a high-resolution gamma ray (GR) record to the long eccentricity (405 kyr) metronome, and is integrated with high-resolution paleomagnetic records. Our results span the interval between-114.7 and 109.5 Ma, within magnetochron C34n, and our age estimates for biostratigraphic markers agree within one long eccentricity cycle with previous estimates. We also present geochemical records, such as stable carbon isotopes (delta 13C), organic carbon and carbonate contents, as well as redox-sensitive elemental ratios, measured on bulk sediments at Core SER-03. Most of these proxy records depict marked changes across the Aptian-Albian boundary, likely characterizing the local expression of Oceanic Anoxic Event 1b (OAE 1b), filling the gap for low-latitude records of this event.

Automated summary

Perturbations in the carbon cycle have had a dramatic impact on the ocean-climate system during the Aptian-Albian transition. However, the exact timing of this period is still heavily debated. In this study, a comprehensive astronomical calibration is presented to estimate the age of planktonic foraminiferal and calcareous nannofossil bioevents in the Sergipe-Alagoas Basin. The results show that the biostratigraphic markers align with previous estimates within one long eccentricity cycle. Additionally, geochemical records such as stable carbon isotopes and organic carbon contents provide insights into the changes across the Aptian-Albian boundary, particularly related to Oceanic Anoxic Event 1b (OAE 1b) in low latitude records.