Assessing Eruptive Tempo of the Columbia River Basalt Group and Recalibrating Miocene Climate Records with Zircon Geochronology

Abstract:

Large igneous province volcanism in the Columbia River Basalt Group (CRBG) has been suggested to play a causal role in the elevated global temperatures and pCO₂ of the Miocene Climate Optimum (MCO). However, assessing the connection between volcanism and warming depends on developing an accurate and precise chronology for both events. Until recently, the eruptive chronology of the CRBG was hindered by large analytical uncertainties in the previously used K-Ar and ⁴⁰Ar/³⁹Ar methods. Proxy records of the MCO have age models dependent on biostratigraphy or magnetostratigraphic correlation to the Geomagnetic Polarity Timescale (GPTS), but lack radioisotopic ages.

Here, we use high-precision CA-ID-TIMS U-Pb geochronology on zircon-bearing volcanic ashes interbedded in the CRBG stratigraphy, to provide a detailed timeline of CRBG eruptions and to suggest revisions of the Miocene GPTS. Building on previous work (Kasbohm & Schoene, 2018), we present 6 new ages from the largest-volume formation of the CRBG and use Bayesian age modeling to better constrain eruption rates through the interval most likely to cause warming. Given the well-defined CRBG magnetostratigraphy, our data suggest a recalibration of the GPTS during an interval when several magnetic reversal ages are disputed. Applying this recalibration to MCO records with magnetostratigraphy, we show that the onset of CRBG volcanism falls in the same polarity chron as the onset of the MCO, with broad correlation between the warmest temperatures and the most voluminous eruptions. Given current MCO age models, initial warming still precedes the earliest eruptions. These new absolute age constraints help with recalibration of MCO climate records and improve comparison with our CRBG eruptive timeline, and may ultimately reveal the extent to which volcanism played a causal role in Miocene warming.