3 Paleo-climate and -ecosystems of the Southwest and High Plains: From the Paleozoic to the Quaternary

Many Phanerozoic climates and ecosystems serve as potential analogues for the future; others highlight the Earth system response to tectonic and climatic forcings. We invite abstracts that probe the paleoclimate/ecosystems of the US Southwest

Monday, 18 May 2026
9:00 AM - 12:00 PM
Alvarado C

Tracing Aridity Across Equatorial Pangea Using Paleosol Carbonate δ¹³C

Paper number: 3-0
Program: Technical Sessions
Time: 9:00 AM – 9:20 AM

Authors

Abstract

The presence of an aridity gradient across equatorial Pangea in the late Paleozoic has been suggested by fossil flora and paleosol morphology of strata throughout North America, which straddled the equator in a slightly rotated paleogeographic configuration at this time. We use paleosol carbonate d13C measured from coeval deposits to assess the utility of this proxy as an archive of past plant productivity, which in turn reflects local moisture limitations. We employ a data compilation of over 100 upper Pennsylvanian through lowermost Permian paleosol carbonate stable isotope values from across North America. We also present 50 new paleosol carbonate stable isotope values collected from contemporaneous formations across Colorado. d13C measured from the samples in both datasets was used alongside estimates of atmospheric CO2 from this period to calculate soil respiration rates at each location. Combining this new data with our compilation, we infer spatial patterns in soil respiration rates recorded by these paleosols to compare with previously published estimates of aridity gradients across North America. Using a set of probable high (700 ppm) and low (200 ppm) values of atmospheric CO2 for the interval of study, we show that calculated soil respiration rates continue to follow a spatial pattern consistent with other proxies of aridity in this region. This agreement between d13C and other proxies indicates that soil CO2 production, rather than atmospheric CO2, was the predominant factor influencing the stable isotope record in this region. We utilize this data in tandem with other lines of proxy evidence to generate a narrative of terrestrial paleoclimate in terms of relative regional moisture states. In all, the data suggest drying across Pangea’s equatorial zone, with western North America experiencing at least seasonally drier conditions and lower levels of productivity than in the east. We suggest that this record of productivity is driven by regional moisture availability and can thus be utilized to evaluate gradients in terrestrial paleoclimatic conditions in the late Paleozoic. Our application of d13C to perform broader paleoenvironmental analyses beyond atmospheric CO2 reconstructions allows for more effective interpretations of land—atmosphere interactions across a range of climate states.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410668

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