Early-Middle Permian carbon-isotope stratigraphy of marine carbonates in the northern edge of the South China: implications for global correlation

The Early-Middle Permian delta C-13(carb) variations are recorded by the marine carbonates of the Luduba section in the northern margin of the South China Block. The investigated interval (similar to 300 m) spans the Chihsia and Maokou formations. Preservation of the investigated micritic carbonates was evaluated by multiple petrographic and geochemical screening tools. The delta C-13(carb) and delta O-18 values of near-primary micrites range from 2.3 to 5.0 parts per thousand (VPDB) and from - 6.4 to - 3.4 parts per thousand (VPDB), respectively, showing insignificant correlation (R-2 = 0.13). Similarly, the Mn/Sr ratios show insignificant correlation with delta C-13(carb) or delta O-18 ratios. In addition, the Al and Sr concentrations exhibit insignificant correlation, which suggests preservation of at least near-primary delta C-13(carb) signatures that can be utilized to construct a reliable C-isotope profile of the equatorial eastern Paleo-Tethys for global correlations. The C-isotope profile exhibits distinct short-time negative shifts superimposed on the general long-term trend of increase in delta C-13(carb) values. The long-term trend likely reflects a consistent global sea-level rise during the Early Guadalupian, which was associated with one of the largest Permian transgressions. The general sea-level rise was disrupted by few minor short-term sea-level low-stands associated with negative delta C-13(carb) shifts (similar to 1-2 parts per thousand) on the C-isotope profile, which are associated with similar minor positive Sr-87/Sr-86 shifts (similar to 0.0005 each) on the Sr isotope profile and with Al enrichment, possibly caused by the combination of global eustasy and regional tectonics in South China. Two negative delta C-13(carb) shifts have been recorded in the lower and upper Chihsia Formation that can be correlated with the Early Kungurian and the Kungurian/Roadian boundary, respectively. Also, the Maokou Formation records a middle negative shift that inferred correlates with the Early Wordian. These three negative delta C-13(carb) shifts are globally comparable with those documented by both the eastern Paleo-Tethys and western Panthalassa Early-Middle Permian sedimentary records and can be utilized as chemostratigraphic markers. The general increase in the delta C-13(carb) values peaks at similar to 5 parts per thousand near the top of the Maokou Formation that resembles the Kamura event recorded in Tethy but there are issues with the origin and timing of this positive delta C-13(carb) excursion. The petrological characteristics of the Luduba section carbonates support the suggested scenario of the general long-term trend of sea-level rise.

Automated summary

The Early-Middle Permian delta C-13(carb) variations are recorded in the marine carbonates of the Luduba section. The study reveals important characteristics of the C-isotope profile and different negative C-13(carb) excursions, which can serve as important chemostratigraphic markers for comparative studies.