Devonian–Permian sedimentation in the Central Yunnan basin, SW Yangtze block (South China): Insights into provenance and paleogeography of Li-rich bauxitic claystone

Late Paleozoic sedimentary environments and the associated paleogeography of the SW Yangtze block of South China are critical for understanding the formation of bauxite and clay-type Li deposits, which in turn provide insights into the tectonic evolution of East Asia. However, there is a lack of consensus on the sedimentary environments and provenance of these deposits. Analysis of rock assemblages and sedimentary structures shows that Devonian to Permian sediments in the Central Yunnan basin are dominated by siliciclastic and carbonate rocks that are indicative of deposition in coastal tidal environments. Permian bauxite and bauxitic claystone exhibit variable but elevated Li₂O contents ranging from 0.35% to 1.62%, with an average Al₂O₃ content of 60.46%. The lithium (Li) content in these bauxitic claystones is strongly influenced by sedimentary environments, texture, and postdepositional weathering and leaching. Geochemical data suggest that the sediments are highly mature in composition, with sources primarily from felsic igneous rocks and minor contributions from mafic rocks of an uplifted basement within a passive margin setting that underwent significant recycling and intense weathering. Detrital zircon U-Pb age determinations indicate that Devonian and Carboniferous sediments share a primary source, with ages of ca. 832−808 Ma, and minor input from Paleoproterozoic rocks. In contrast, Lower Permian sediments exhibit age distributions similar to those of Ordovician sediments, with key age peaks at ca. 964 Ma, 812 Ma, 624 Ma, and 546 Ma. Regionally, Middle to Upper Devonian coastal−tidal deposits unconformably interfinger with pre-Devonian and Carboniferous shallow-marine sediments. Additionally, Lower Permian tidal lagoon sediments of the Daoshitou Formation unconformably overlie the Carboniferous deposits. These findings suggest that both lithium and aluminum oxides in the Daoshitou Formation originated primarily from the weathering and recycling of ancient sedimentary and felsic primary rocks, and subsequently accumulated in a tidal lagoon environment within an extensional basin. This basin, located in the southwestern Yangtze block, was associated with the late Paleozoic opening of the Paleo-Tethyan Ocean.