192 / 2025-04-14 15:44:18

The Middle-Late Pennsylvanian events: Timing and mechanisms

Kasimovian; LPIA; Conodont; bio-enviromental events; South China; Isotope

Theme 3: Earth-Life Co-evolution Through Time > Session 3d: Biotic and Environmental Changes during the Late Palaeozoic Ice Age

The Kasimovian (ca. 307-303.7 Ma) is the key climatic transition period during the Late Paleozoic Ice Age (LPIA), characterized by frequent climatic fluctuations that triggered a series of biotic and environmental events, including the Late Desmoinesian Extinction Event (LDE) and Idiognathodus Diversification Event (IDE) in the marine realm, and the “Carboniferous rainforest collapse event” (CRC) terrestrially. However, the timing and mechanism of these events remain poorly understood and controversial due to rare records of the Pennsylvanian rock successions, and difficult international correlations caused by frequent glacio-eustatic transgressions and regressions during the LPIA.

The Naqing section in southern Guizhou, South China, is a carbonate succession deposited in deep-water slope environments during the Carboniferous and is a candidate for the Global Boundary Stratotype Section and Point (GSSP) of Kasimovian. Abundant conodonts and continuous carbonate successions in this section provide a valuable opportunity to study the timing and mechanisms of bio- and environmental events. The nearby Narao and Shanglong sections, deposited in similar but shallower environments, serve as useful references.

Based on materials from these sections, we completed a comprehensive stratigraphic analysis for the Kasimovian, including conodont biostratigraphy, apatite strontium and oxygen isotope chemostratigraphy, and bulk rock carbon isotope chemostratigraphy. A total of 12 conodont biozones, 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. A three-stage model of co-evolution of biota and environment from the late Moscovian to the early Kasimovian are established. More precisely, the first to second phases during the Sw. sp. A and Sw. subexcelsa zones are correlated with the changes in dominance of rainforest biomes, i.e. CRC; while the second to the third phases during the Sw. subexcelsa and I. magnificus zones correlate with the LDE and IDE. A general warming trend of ~4–6 ℃ 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. Furthermore, isotopic chemostratigraphy may enhance the correlation potential for the global Moscovian-Kasimovian Boundary. Minor positive shifts in δ¹³C and ⁸⁷Sr/⁸⁶Sr support the FO of Idiognathodus heckeli, while a distinct negative shift in δ¹³C and a minor negative shift in δ¹⁸O align with the FO of Swdelina subexcelsa.