21-8 Foraminifer Stable Isotope Records of the Miocene Climatic Optimum and Monterey Carbon Isotope Excursion from the Haynesville (Virginia) Drill Site in the U.S. Atlantic Coastal Plain

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches

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The Miocene Climatic Optimum (MCO, 17–14.7 Ma) represents a temporary reversal in the long-term cooling of global climate that occurred over the past ~23 million years of Earth history. Warming associated with the MCO lead to partial melting of the Antarctic ice sheet and a concomitant rise in global eustasy, thus coastal records of the MCO provide a vista into the future effects of currently warming oceans and rising sea level. Here, we report results from benthic foraminifer stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope records constructed for a coastal MCO record recovered in a sediment core drilled at Haynesville, Virginia. The Haynesville site is located in a paleogeographic extension of the northeastern Atlantic Ocean called the Salisbury Embayment. Multiple lines of micropaleontologic evidence have constrained the MCO within the core. A sustained positive shift in our δ¹³C record indicates that the Plum Point member of the Calvert Formation was deposited during the globally-recognized Monterey carbon isotope excursion (MCIE, 16.7–13.5 Ma). As in deep-sea MCIE records, δ¹³C values oscillate between carbon minima and maxima in a quasi-rhythmic manner. Covariance between δ¹³C and δ¹⁸O values is observed with isotope maxima correlating to disconformities at the bases of shallowing upward sequences, linking sediment deposition to glacial-interglacial cycles and pulsed increases in organic carbon burial during the MCO. Ecological exclusion of benthic foraminifers in this overall shallowing-upwards sequence truncates the top of our isotope records, so the later stages of the MCIE and resumed cooling following the MCO are not recorded.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10890

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