High-precision U-Pb geochronology recalibrates the Silurian Yangtze uplift and early gnathostome radiation in South China

The Silurian Period was a pivotal interval of biotic innovation and tectonic activity. In South China, Silurian strata host exceptional fossil assemblages, including some of the world’s earliest jawed vertebrates (gnathostomes), alongside a record of the regional Yangtze uplift. However, the timing and tempo of these key evolutionary and tectonic events remain poorly constrained due to a lack of precise radioisotopic ages and limitations of biostratigraphic correlation in shallow-marine clastic facies. This study provides a robust temporal framework for these events through high-precision U-Pb geochronology of zircons from three volcanic tuff beds within the Silurian Xiushan Formation of the Upper Yangtze region, analyzed using the chemical abrasion−isotope dilution−thermal ionization mass spectrometry method. Our new ages of 433.93 ± 0.52 Ma, 432.92 ± 0.54 Ma, and 430.68 ± 0.62 Ma (2σ total uncertainty), along with Bayesian age-stratigraphic modeling, anchor the deposition of the fossiliferous upper Xiushan Formation to the Telychian-Sheinwoodian boundary interval (latest Telychian). This absolute age framework refines the equivocal early Telychian age estimate for the formation based on previous biostratigraphic interpretations. The new geochronology recalibrates the timeline of early gnathostome evolution by placing the renowned Chongqing Lagerstätte and its diverse fauna within the Wenlock. This discovery helps to resolve the apparent “anachronism” of such complex faunas appearing in older strata, demonstrating that a major radiation of jawed vertebrates was well underway by the Wenlock—reshaping our understanding of one of the most critical Paleozoic evolutionary transitions. A major regional unconformity immediately overlying our 430.68 ± 0.62 Ma tuff indicates that the terminal marine sedimentation preceding large-scale regression in response to the Yangtze uplift extended into the latest Sheinwoodian in the Yangtze Platform interior. This recalibration shifts the onset of the Yangtze uplift by at least 4 m.y., refining models of intraplate orogenesis in East Asia.