The chemical index of alteration in Permo-Carboniferous strata in North China as an indicator of environmental and climate change throughout the late Paleozoic Ice Age

Comparison of chemical index of alteration (CIA) values and estimated land surface temperatures (LSTs) from upper Carboniferous-Permian successions in low paleolatitude North China and middle- to high-paleolatitude successions of Gondwana facilitates reconstruction of global climate changes during the late Paleozoic Ice Age. Four synchronous excursions between the North China and Gondwana Basins toward lower CIA and LSTs are recognized and interpreted as four cooling events, respectively. Two severe cooling events occurred around 300 Ma and 287 Ma, respectively, with large decreases in global temperatures (mostly >5 degrees C), while another two less-pronounced cooling events at 297.5 Ma and 295 Ma with global temperature drops of <5 C are defined as discrete pulses superimposed on the earlier, more severe cooling interval. Overlap in the timing of decreased chemical weathering intensity in different parts of North China and glaciations in some Gondwanan Basins that coincide with stepwise decreases in pCO2 suggest that CO2-forced climate change was likely one of the most important driving factors for the continental weathering changes and the onset and demise of glaciations. Local tectonism, atmospheric and ocean circulation, and orbital parameters also played the roles in driving the glaciations and deglaciations. The continued effects from weathering of worldwide mafic rocks along with expansion of paleotropical forests are considered to be contributors to the cooling intervals along with glacial events and evolution of ecosystems during the late Pennsylvanian-Cisuralian.