252-6 The Devonian-Mississippian Climate Transition (DMCT): A clumped isotope study of a greenhouse-to-icehouse transition

Session: Climate Transitions in the Paleozoic

Presenting Author:

Bryce Barney

Authors:

Barney, Bryce B¹, Sharma, Ayush², Nana Yobo, Lucien³, Li, Shihan⁴, Zhang, Shuang⁵, Day, James E.⁶, Joachimski, Michael M.⁷, Zaton, Michal⁸, Grossman, Ethan L.⁹

(1) Department of Geology & Geophysics, Texas A&M University, College Station, TX, USA, (2) Department of Geology & Geophysics, Texas A&M University, College Station, TX, USA, (3) Department of Geology & Geophysics, Texas A&M University, College Station, TX, USA, (4) Department of Oceanography, Texas A&M University, College Station, TX, USA, (5) Department of Oceanographcy, Texas A &M University, College Station, TX, USA, (6) Department of Geography, Geology & the Environment, Illinois State University, Normal, IL, USA, (7) GeoZentrum Nordbayern, Friedrich-Alexander Universität of Erlangen-Nürnberg (FAU), Erlangen, Germany, (8) Institute of Earth Sciences, University of Silesia in Katowice, Katowice, Poland, (9) Department of Geology & Geophysics, Texas A&M University, College Station, TX, USA,

Abstract:

Understanding the relationship between biodiversity and climate requires accurate quantitation of temperature through time.  Here, we present new oxygen and clumped isotope (Δ₄₇) microanalyses of well-preserved Devonian and Mississippian brachiopod shells from low paleolatitude (<35°) sites across the US Midcontinent (USM), Canada, and the Central Devonian Field (Russia). Sample preservation was evaluated using microtextural and cathodoluminescence analysis.  Because clumped isotopic temperature (T(Δ₄₇)) can be reset at burial temperatures above 90 to 100°C, we evaluated the burial histories of all localities with available literature.  Localities in Indiana, central and western Iowa, Manitoba, and Russia experienced shallow burial, with maximum burial temperatures < 90°C. Samples from these sites yielded T(Δ₄₇) values of 24 to 41°C.  In contrast, samples from southeastern Iowa and Illinois (USA) and Northwest Territories (Canada) experienced burial temperatures of 120 to 140°C, hot enough to partially reorder (reset) Δ₄₇ temperatures. Low burial temperature (LBT) samples reveal ~5°C warming from the Givetian through the early Famennian, followed by ~8°C cooling in the Mississippian. Using burial thermal histories and Δ₄₇ reordering kinetics, we can reconstruct the original T(Δ₄₇) of samples with high burial temperatures. These corrected T(Δ₄₇) range from 27 to 42°C, similar to the range for LBT samples. The combined dataset reveals distinct temperature trends across discrete time intervals. Givetian trends in USM average 32 ± 3°C (±1SE), increasing to 37 ± 4°C throughout the Frasnian and Famennian in the USM, Canada, and Russia. Cooling is observed in the Tournaisian of USM, where temperatures decrease to 29 ± 3°C, followed by potential warming in the early Visean.

Combining T(Δ₄₇) and δ¹⁸O_VPDB and the δ¹⁸O paleotemperature equation yields an average seawater δ¹⁸O for the Devonian through earliest Mississippian samples (383-358 Ma) of -1.2 ± 0.7‰ (±1SE, VSMOW), consistent with estimates for a deglaciated world. In contrast, Mississippian samples from USM yield an average seawater δ¹⁸O of 2.3 ± 0.6‰, higher than expected but consistent with documented aridity.

The Devonian to earliest Mississippian results align with previous studies suggesting warm temperatures and an ice-free world in the late Devonian. The Devonian-to-Mississippian climate transition is marked by ~8°C cooling. While limited in spatial and temporal coverage, these Δ₄₇ data provide critical constraints on temperature shifts and serve as independent validation of other evidence for a Devonian-to-Mississippian greenhouse-to-icehouse transition.

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

doi: 10.1130/abs/2025AM-7826

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