LATE PALEOZOIC GLOBAL SEAWATER 87SR/86SR AND δ13C RECORDED IN SOUTH CHINA PROVIDE INSIGHTS INTO EARTH’S PENULTIMATE ICEHOUSE

Earth’s penultimate icehouse (~340–285 Ma) was a time of low atmospheric pCO₂, dynamic glaciation on Gondwana, formation of supercontinent Pangea, and radiation of the oldest paleo-tropical rainforests. Although it has been long appreciated that these major tectonic, climatic, and biotic events would have left their signature on seawater ⁸⁷Sr/⁸⁶Sr through their influence on Sr fluxes to the ocean, the temporal resolution and precision of the Carboniferous–Permian seawater Sr isotope record remains relatively low. Here we present a high temporal resolution and high-fidelity record of Carboniferous seawater ⁸⁷Sr/⁸⁶Sr based on conodont apatite from an open-water carbonate slope succession in south China. The new data refine the structure of the long-term rise in seawater ⁸⁷Sr/⁸⁶Sr from the Middle Mississippian through Early Pennsylvanian (~338–318 Ma) and document a rate of rise (from 0.7077 to 0.7082) comparable to that of Neogene seawater Sr. The onset of the previously documented decline in seawater ⁸⁷Sr/⁸⁶Sr is constrained to 301 Ma and follows a plateau through the Late Pennsylvanian (318–301 Ma). Coupling the ⁸⁷Sr/⁸⁶Sr and carbonate δ¹³C records provides insight into relative roles of continental weathering, expansion and retraction of the tropical wetland rainforests, widespread aridification and global-scale emplacement of basaltic provinces on atmosphere pCO₂ during Earth’s penultimate icehouse.