The Middle–Late Pennsylvanian event: Timing and mechanisms

The Late Palaeozoic Ice Age (LPIA) was associated with climate fluctuations, significant biotic changes, the late Desmoinesian extinction, the conodont Idiognathodus diversification, and the “Carboniferous rainforest collapse”. These changes occurred in both marine and terrestrial realms during the Middle–Late Pennsylvanian, approximately 307–303.7 Ma. The timing, mechanisms, and magnitude of these events, especially the marine events, are poorly understood due to the scarcity of continuous Pennsylvanian successions and the challenges of international correlations caused by frequent glacio-eustatic transgressions and regressions during the LPIA. In southern Guizhou, South China, slope carbonate successions were deposited with abundant conodonts, providing opportunities to study these events. Based on materials from the Naqing, Shanglong, and Narao sections, conodont biostratigraphy, strontium and oxygen isotopes of conodont apatite, and carbon isotope of bulk rock across the Middle–Upper Pennsylvanian boundary interval are presented. Conodont zones, namely the late Moscovian Idiognathodus podolskensis, Neognathodus roundyi, and Swadelina sp. A zones, the Kasimovian Sw. subexcelsa, Sw. makhlinae, I. heckeli, I. turbatus, I. magnificus, “I.” guizhouensis, Heckelina eudoraensis, and “I.” naraoensis zones, and the Gzhelian H. simulator Zone are recognized. Focused on late Moscovian to early Kasimovian, three phases of environmental and biotic changes during the Sw. sp. A and I. magnificus zones are recognized. The first to second phases during the Sw. sp. A and Sw. subexcelsa zones are correlated with the dominance of rainforest biomes changing from cordaitaleans and lycopsids to marattialean trees. The second to the third phases during the Sw. subexcelsa and I. magnificus zones correlate with the late Desmoinesian extinction event, and radiation of Idiognathodus species. A general warming trend of ∼4–6 °C temperature rise calculated by δ¹⁸O could partly explain the aridification and collapse of rainforests. Changes in continental weathering were considered to partly drive the extinction and then radiation of conodonts during the middle–late Kasimovian supported by ⁸⁷Sr/⁸⁶Sr and δ¹⁸O of conodont apatite.