Geological Society of America

T78 Advances in Reconstructing Paleotopography

Monday, 10 October 2022
8:00 AM - 12:00 PM
505

DEVELOPING TRIPLE OXYGEN ISOTOPE GEOCHEMISTRY AS A CENOZOIC PALEOALTIMETER USING CRYSTALLINE AND LACUSTRINE ROCKS

Paper number: T78-4
Program: Technical Sessions
Time: 8:40 AM – 9:00 AM

Authors

Daniel Ibarra Presenting Author
Brown University, Providence, RI
Katharina Methner
Stanford University, Stanford, CA
Tyler Kukla
Colorado State University, Fort Collins, CO
Max Lloyd
Penn State University, University Park, PA
Daniel A. Stolper
University of California Berkeley, Berkeley, CA
Yuan Gao
China University of Geoscience Beijing, Beijing
Jingen Dai
China University of Geoscience Beijing, Beijing
Andreas Mulch
Goethe University Frankfurt, Frankfurt
Andreas Mulch
Biodiversity and Climate Research Centre, Frankfurt Main
C. Page Chamberlain
Stanford University, Stanford, CA

Abstract

Triple oxygen isotopes of minerals preserved in lacustrine sediments and hydrothermally altered minerals from crystalline rocks can be used to determine past elevations of mountain ranges as they may preserve an isotopic record of ancient precipitation. Here we use the measurement of all three stable isotopes of oxygen (¹⁶O, ¹⁷O, and ¹⁸O) to create data trends in ¹⁷O/¹⁶O vs ¹⁸O/¹⁶O that are extrapolated back to the meteoric water line using water/rock mixing constraints and models for lake water evaporation. We summarize recent advances in this approach and focus on examples from Cenozoic western North America and Tibet.

Three key findings emerge from our analysis of hydrothermally-altered crystalline rocks and lacustrine systems. First, in combination with carbonate clumped isotope measurements we demonstrate that Eocene lacustrine chert forms during early burial diagenesis at temperatures <60 °C. Importantly, these Eocene lacustrine cherts still preserve signals of ancient evaporative lake systems demonstrating δ’¹⁷O-δ’¹⁸O mass laws shallower than Rayleigh-dominated meteoric processes. These relationships still allow for past paleoelevation to be reconstructed. Second, we compare this approach to prior work that jointly used oxygen and hydrogen isotopes to determine the isotopic composition of meteoric waters. Our analysis suggests that hydrogen isotopes may exchange with ambient fluids in some systems but not others and is dependent on mineralogy and cooling rate. Further, through a quantitative model, we show that chert oxygen isotopes are not as susceptible to this alteration. Third, hydrothermal system and core-complex based paleoaltimetry constraints agree well with carbonate and clay-based estimates from nearby age-equivalent sedimentary basins. This new tool is nascent but provides complementary information to be used in conjunction with more traditional isotope-based paleoaltimetry approaches.

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

doi: 10.1130/abs/2022AM-379707

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