Formation mechanism and global implications of the early Guadalupian phosphorite deposition along the eastern Palaeo-Tethys upwelling region (South China)

Abstract

The Guadalupian (Middle Permian) marks a critical interval of climatic–oceanographic transition during the waning of the Late Palaeozoic Ice Age (LPIA), accompanied by widespread phosphorite deposits in South China and North America. However, the linkage between palaeoenvironmental change and phosphorite formation remains poorly understood. Here we investigate the Kuhfeng Formation phosphorite deposition of the Lower Yangtze region in South China through integrated petrographic, mineralogical, geochronologic, and geochemical analyses. Our results suggest that phosphorite accumulated mainly in continental margin slope settings during the early Guadalupian (∼272.95 – 270.6 Ma), with phosphorus (P) hosted primarily in apatite. Left-sloping REE patterns, high Y/Ho values, and strong Al–P₂O₅ anti-correlation point to a dominantly marine source of phosphorus with limited volcanic input. Palaeoenvironmental proxies reveal warm-humid climates, strong upwelling, high productivity, suboxic-anoxic conditions, and elevated salinity during deposition. Based on an integrated tectonic–climatic–oceanic analysis, we propose an upwelling-driven high productivity mechanism under deglacial warming and intensified tectonism, controlling phosphorite formation. Following the deglaciation of the LPIA, enhanced upwelling and volcanic activity supplied abundant P, stimulating high primary productivity and abundant organic matter formation. This process promoted the deposition and decomposition of P–rich organic matter near the sediment–water interface, releasing large amounts of P into pore waters and finally facilitating phosphate precipitation. Comparison with contemporaneous phosphorite deposits in North America further suggests a global upwelling-driven mechanism for Guadalupian phosphorite formation.