Relationship between continental chemical weathering trends in the North China Basin and the high-latitude glacial cycles from the Late Carboniferous to the Early Permian

Abstract

Objective and Methods The Late Paleozoic Ice Age (LPIA; ca. 360‒254 Ma), the only period recording the transition from icehouse to greenhouse conditions throughout the geological history, can provide a deep-time perspective for glacier-environment-climate coevolution and future climate change. To gain a deep understanding of the potential relationship between the continental chemical weathering trends in low-latitude regions and the glacial cycles in the high-latitude Gondwana region from the Late Carboniferous to the Early Permian, this study investigated the mudstones of the Benxi-Taiyuan formations, Liujiang coalfield, North China Basin. Using multiple chemical weathering indices such as chemical index of alteration (CIA), chemical index of weathering (CIW), and plagioclase index of alteration (PIA) calculated from the elemental geochemical data of the mudstones, this study reconstructed the continental chemical weathering trends and paleoclimatic evolutionary characteristics of the Liujiang coalfield. Results The results indicate that the periodic changes of continental chemical weathering in the low-latitude Liujiang coalfield involved three weathering weakening stages (i.e., early-middle Bashkirian, Moscovian-Kasimovian, and early Asselian) and two weathering enhancement stages (i.e., late Bashkirian and Gzhelian). This cyclic alternation of weathering trends was closely associated with the glacial cycles of the high-latitude Gondwanaland. The weathering weakening stages represent shifts to relatively cool and dry climates, roughly synchronous with the glacial periods at high latitudes. In contrast, the weathering enhancement stages suggest changes to relatively warm and humid climates, coinciding with the interglacial periods at high latitudes. The comparative analysis reveals that frequent volcanic activity, increased atmospheric CO2 concentration, climate warming, enhanced hydrologic cycles, and sea-level rise during the interglacial periods jointly contributed to the reduced area of tropical rainforests and the enhanced continental chemical weathering, creating favorable conditions for the formation of bauxite. In contrast, the weakening volcanic activity, cooling climate, reduced atmospheric CO2 concentration, and increased rainforest area during the glacial periods led to weakened continental weathering, facilitating the formation of coals and organic-rich mudstones. ConclusionsThe results of this study reveal the relationship between the continental chemical weathering trends in the low-latitude North China Basin and the glacial cycles and the distributions of sedimentary minerals (e.g., coals and bauxite) in the high-latitude Gondwana region, providing a novel perspective for understanding the mechanisms underlying complex glacier-environment-climate interactions throughout the geological history.

Keywords

• late paleozoic era
• north china basin
• chemical weathering
• chemical index of alteration (cia)
• glacial period
• interglacial period