252 Climate Transitions in the Paleozoic

This session will examine the major climate transitions in the Paleozoic Era, the paleoclimate evidence for their identification, their causes, and their consequence to the Earth System (e.g., ocean and atmospheric chemistry, sedimentology, biodiversity).

Wednesday, 22 October 2025
8:00 AM - 12:00 PM
HBGCC, 303C

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

Paper number: 252-6
Program: Technical Sessions
Time: 9:25 AM – 9:40 AM

Authors

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 δ18OVPDB 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 Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412887

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