HIGH-PRECISION U-Pb GEOCHRONOLOGY FOR THE MIOCENE CLIMATE OPTIMUM AND A NOVEL APPROACH FOR CALIBRATING AGE MODELS IN DEEP-SEA SEDIMENT CORES

Scientific ocean drilling cores recovered years ago (legacy cores), especially as recovered by rotary drilling, commonly show incomplete recovery and core disturbance. We present a novel method to date such cores, by presenting the first high-precision U-Pb zircon ages obtained by chemical abrasion - isotope dilution - thermal ionization mass spectrometry to target the duration of the Miocene Climate Optimum (MCO; ~17-14 Ma) from volcanic ashes at Ocean Drilling Program Site 1000 (Nicaragua Rise). We place these ages within a newly developed framework to address incomplete core recovery and use them to calibrate a high-resolution bulk carbonate δ¹³C and δ¹⁸O record. Our Site 1000 ages show that volcanism of the Columbia River Basalt Group (CRBG) large igneous province was coincident with the interval of greatest sustained MCO warmth at this site. However, if the CRBG were the primary driver of the MCO, our chronology may allow for outgassing preceding volcanism as a major source of CO₂. We thus document a promising new way to obtain highly-resolved, accurate and precise numerical age models for legacy deep-sea sediment cores that does not depend on correlation to other records.