Late Permian ∼ 6 My cooling induced by basaltic weathering of the Emeishan large igneous province: Evidence from interbasaltic paleosols

Abstract

Land surface temperature variations during the Emeishan large igneous province volcanism helps to reveal the effect on the climate in the late phase of the late Paleozoic Ice Age. Paleosols preserved between the Emeishan basalts record hiatuses in basalt eruptions and provide detailed information on the Earth's surface environment. Forty-seven paleosol profiles in eleven locations were identified, described, and assigned to four pedotypes: I, II, III, and IV. The majority of pedotypes I, II, and III had a dominant mineral assemblage of kaolinites, hematite, and anatase, high chemical index of alteration values of 90–99 and Al2O3 and Fe2O3 enrichments, and were classified as Oxisols or Ultisols (alternatively, laterite). Pedotype IV contained large amounts of primary minerals from basalts, yielded low chemical index of alteration values of 35–65, and were classified as Entisols or Inceptisols. The eastern Emeishan large igneous province was dominated by highly weathered pedotypes I and II, with small amounts of pedotype III, while the western Emeishan large igneous province was dominated by pedotype III and weakly weathered pedotype IV. We interpreted this spatial distribution pattern of pedotypes as a result of the paleotopographic difference formed by the subaerial mafic lava accumulation, with steep highlands in the western Emeishan large igneous province and lowlands in the eastern areas. Based on the silica-alumina‑iron ratio climofunction, a land surface temperature cooling trend of ∼2–4 °C was recognized in the upper part of the Emeishan basalt succession (i.e., the waning phase) in three sections and was constrained to ∼260 to ∼253 Ma by new high-precision zircon UPb dates. This land surface temperature cooling trend was temporally coupled with the sea surface temperature cooling trend and the alpine P4 glaciation in eastern Australia. We propose that the intense weathering of extensive Emeishan basalts in the tropical humid belt, directly evidenced by the numerous thick laterites in the upper part of the basalt succession across the broad regions of the Emeishan large igneous province, elevated atmospheric CO2 consumption flux, leading to global cooling and further triggering the P4 glaciation.