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The Ediacaran-Cambrian transition was one of the most significant intervals in geological history, witnessing the origin of the metazoans and major environmental changes. Establishing a precise chronostratigraphic framework for the Ediacaran-Cambrian transition has great significance for understanding the geological and evolutionary processes during this transition. An integrated study on carbonate carbon isotopes and U-Pb zircon dating was conducted within the Liuchapo Formation in the Sifangjing section in northeastern Guizhou Province, South China to recognize the Ediacaran-Cambrian boundary in slope facies of the Yangtze Block. A substantial negative carbonate carbon isotope excursion was recognized within the lower part of the Liuchapo Formation. Moreover, a weighted-mean U-Pb zircon age of 540.7 ± 3.8 (±6.6) Ma was obtained from a tuffaceous interlayer approximately 2 m above the interval of the negative carbon isotope excursion. The carbon isotope and age-dating results indicate that the Ediacaran-Cambrian boundary within the Sifangjing section should be placed in the lower part of the Liuchapo Formation. Additionally, in the Sifangjing section, a distribution of Horodyskia minor extends up to the basal Cambrian, while the last appearance datum (LAD) of Palaeopascichnus jiumenensis correlates to the large negative carbon isotope excursion within the Liuchapo Formation. This relationship indicates that the LAD of the Palaeopascichnus jiumenensis is a potential tool for the stratigraphic correlation of the Ediacaran-Cambrian boundary successions in slope and deep-water basin settings of the Yangtze Block. • New carbonate δ13C dataset from slope facies of the Yangtze Block • The δ13C dataset shows a negative excursion within the Liuchapo Formation. • The absolute age of the negative δ13C excursion is about 540.7 ± 3.8(±6.6) Ma. • The Palaeopascichnus jiumenensis can be used to identify the E-C boundary. [ABSTRACT FROM AUTHOR]

Abstract The Permian-Triassic boundary (PTB) mass extinction, the most severe biocrisis in Earth's history, is thought to have been triggered by catastrophic volcanic activity. PTB sections in South China contain numerous volcanic ash beds, the source of which is inferred to have been either the Siberian Traps Large Igneous Province (STLIP) or intraregional subduction-zone arc volcanism. In this study, the provenance of these ash beds is determined through a comprehensive analysis based on the geochronological and geochemical signatures of zircons from four PTB sections (Dongpan, Xinmin, Ganxi and Shangsi). Inherited zircons yielded U–Pb ages of 250–3521 Ma with major age clusters in the Permian, Carboniferous to Silurian, early Cambrian to Neoproterozoic, early Neoproterozoic to late Mesoproterozoic, and early Paleoproterozoic. The age spectrum of these zircons is similar to those of detrital zircons from sedimentary and magmatic rocks of the South China and Indochina cratons but different from those of the Siberian Craton, providing evidence for an intraregional source of the volcanic material. The trace-element, εHf(t), and δ18O signatures of syn-depositional magmatic zircons are consistent with an arc-related/orogenic setting. PTB sections in South China can be assigned to sectors based on the number and cumulative thickness of ash beds and the length of zircon crystals. Sector I (South) includes the Dongpan and Xinmin sections, which have cumulative ash-bed thicknesses of 0.86–1.14 m and average zircon lengths of 151–217 μm. Sector II (North) includes the Ganxi, Shangsi and Daxiakou sections, which have cumulative ash-bed thicknesses of 0.17–0.33 m and average zircon lengths of 82–104 μm. Sector III (Northeast) includes the Niushan and Meishan sections, which have cumulative ash-bed thicknesses of 0.1–0.14 m and average zircon lengths of 71–73 μm. Systematic trends toward fewer and thinner ash beds and as well as smaller zircon sizes from Sector I to Sector III indicate a paleo-northward or -northeastward direction of ash transport. Collectively, our findings provide evidence that the source of volcanic ash in South China PTB sections was intraregional subduction-zone arc volcanism along the convergent margin between the South China and Indochina cratons. Highlights • Investigation of source(s) of volcanic ash in Permian-Triassic Boundary beds of 4 deepwater sections across South China • Geochemical signatures of syn-depositional magmatic zircons indicate an arc-related/orogenic setting. • Zircon U–Pb age distributions consistent with ash sourced from South China or Indochina cratons but not the Siberian Craton • Spatial variation in total ash bed number and thickness and in zircon crystal size indicates ash sourced from paleo-south. • Most likely ash source was subduction-zone volcanism along the South China-Indochina convergent plate margin. [ABSTRACT FROM AUTHOR]