Glaciation, aridification, and carbon sequestration in the Permo-Carboniferous: The isotopic record from low latitudes
To evaluate the isotopic record of climate change and carbon sequestration in the Late Paleozoic, we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from Carboniferous through Middle Permian (359–260 Ma) strata. We focus on the isotopic records from the U.S. Midcontinent and the Russian Platform because these two regions provide well-preserved marine fossils spanning a broad time interval. Both regions show a δ18O increase at the Mid-Carboniferous boundary (ca. 318 Ma) that roughly correlates with geologic evidence for an expansion of Gondwanan glaciers. Only the Russian Platform record shows a δ18O maximum during the glacial maximum in the Asselian. In contrast to a previous study [Korte, C., Jasper, T., Kozur, H.W., and Veizer, J., 2005. δ18O and δ13C of Permian brachiopods: a record of seawater evolution and continental glaciation. Palaeogeogr. Palaeoclimatol. Palaeoecol. 224, 333–351.], our data show no oxygen isotope evidence for glacial retreat in the early Permian, but instead show increasing δ18O values related to aridification. Dissimilarity in the δ18O trends for the epicontinental seas of North American and the Russian Platform suggests that at least one region experienced periodic restriction that altered regional salinities and seawater δ18O values. These results highlight the need for complementary proxies to identify restricted circulation in epicontinental seas. 
 
Carbon isotopic compositions of carbonates exhibit substantial regional variation with low values in western North America, intermediate values in the midcontinent, and high values in the Sverdrup Basin, Russian Platform, and northern Spain. Nevertheless, both U.S. Midcontinent and Russian Platform records show a late Serpukhovian minimum, a sharp increase across the Mid-Carboniferous boundary, and a minimum centered on the Kasimovian. The correlative increase in brachiopod δ13C and δ18O values at the Mid-Carboniferous boundary is our best isotopic evidence for a link between the carbon burial and glaciation in the Permo-Carboniferous.