T179 Quaternary Climate from the Great Plains to the Great Basin: Geomorphic and Sediment Records across “Great” Landscapes

Tuesday, 11 October 2022
1:30 PM - 5:30 PM
505

MIOCENE CLIMATE DYNAMICS OF THE RIO GRANDE RIFT REGION

Paper number: T179-2
Program: Technical Sessions
Time: 1:35 PM – 1:50 PM

Authors

Abstract

Climate is thought to provide a first-order control on landscape evolution; yet, there are few quantitative constraints regarding the climatic history of the Rio Grande Rift and how changes in climate might have affected rift evolution. During most of the extension of the Rift, global climate was substantially warmer than the Quaternary, suggesting that there may have been changes in the overall climate of the Rio Grande Rift region. We present new stable isotope records of mid-Miocene terrestrial carbonates from the Española basin in northern NM, along with new 40Ar/39Ar ages that establish an updated, high resolution age model. Our δ18O and δ13C records span 17-12 Ma and cover a period of extraordinary warmth during the Neogene—the Miocene Climate Optimum (MCO)—and the onset of late Neogene cooling. Stable isotopes of meteoric waters in this region reflect the influence of the two main circulation systems that deliver moisture to the Rift region: high δ18O moisture reflects the influence of the North American Monsoon, whereas low δ18O is delivered by mid-latitude westerly moisture sourced from Pacific extratropical cyclones. In turn, δ13C reflects changes in plant productivity and vegetative cover in the region. Overall, δ18O decreases over the course of the MCO, with local δ18O minima that correlate with cool episodes observed in the benthic marine δ18O record. Values of δ13C and δ18O are positively correlated, such that minima in δ18O are accompanied by minima in δ13C. Compared to modern precipitation δ18O, carbonate δ18O suggests that the region received more low δ18O—presumably wintertime—precipitation than it does today. The covariation in δ13C suggests that these increases in wintertime precipitation produced increases in soil productivity, likely driven by increasing plant productivity. These hypothesized changes in hydroclimate and soil productivity are supported by the paleontological record at the site, which show a diverse and dynamic faunal assemblage during the MCO, but that becomes increasingly reflective of arid conditions during cooling following the MCO. Collectively, our new data suggest that during periods of active extension, much of the Rift experienced more winter wet conditions and greater vegetative cover than today.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-380827

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