Geochemistry of the Guadalupian—Lopingian carbonate rocks from the NE Sichuan Basin, China: implications for paleo-oceanic environment and provenance

Abstract

As the last part of the Hercynian cycle in the Yangtze region, the Dongwu Movement included the eruption of the Emeishan large igneous province (ELIP) and was an essential event between the Guadalupian and Lopingian, which had significant implications for the paleo-oceanic environment and paleoclimate of the area. To study the changes in the sedimentary environment in the Guadalupian and Lopingian, the Zhenba section was selected, and its trace elements and rare earth elements (REEs) were analyzed. From analysis of the trace elements and REEs in the Guadalupian, the limestone samples had prominent typical shallow-water seawater deposition characteristics and were less affected by terrigenous detritus, which was in an arid oxidation environment; Sr/Cu ranged from 4 to 1381, the Rb/Sr value was low, δCe < 1, Ce_anom < −0.1, Er/Nd ranged from 0.1 to 0.27, and Y/Ho ranged from 44 to 72. However, in the Lopingian, the limestone samples were more affected by terrigenous detritus, which was in a humid climate with a weak oxidation‒reduction environment; the Sr/Cu ranged from 1 to 656, the Rb/Sr value was high, δCe ≅ 1, Ce_anom ≥ −0.1, Er/Nd < 0.1, and Y/Ho ranged from 26 to 44. The geochemical diagrams of TiO₂‒Al₂O₃, Al₂O₃‒REE, La‒Th‒Sc, Th‒Co‒Zr/10, Th‒Sc‒Zr/10 and ⁸⁷Sr/⁸⁶Sr of a sample indicated that the terrigenous detritus of the sample mainly came from the South Qinling active continental margin, rather than the weathering of Emeishan basalt. Acid bentonite came from the Paleo-Tethys island arc or the island arc formed by the subduction of the South China Plate beneath the North China Plate, rather than the ELIP. This evidence supported the view that the North China Plate potentially collided with the South China Plate in middle to late Wujiaping.