Episodic volcanic eruption and arid climate during the Triassic-Jurassic transition in the Qiangtang Basin, eastern Tethys: A possible linkage with the end-Triassic biotic crises

Abstract

During the Triassic-Jurassic (Tr-J) transition, a negative basin inversion, massive volcanic eruption and biological crises occurred in the Qiangtang Basin (eastern Tethys), while the volcanic eruption phases and the paleoenvironment characteristics during this transition were paid little attention. Here we present petrology, whole-rock geochemistry and zircon U-Pb isotopes data from the continuous Triassic-Jurassic sedimentary strata in the northern Qiangtang Basin, in order to reveal the volcanic eruption episodes, paleoenvironment characteristics during this transition, and to discuss the possible linkage with the biological extinction event. Our results show that the Late Triassic volcanic event displays episodic eruption process and contains about four phases. Zircon U-Pb ages of four tuff samples from the Quemo Co south section are, from bottom to top, 220.4 ± 1.1 Ma, 210.9 ± 0.9 Ma, 208.3 ± 0.8 Ma, and 202.9 ± 1.1 Ma, respectively. Statistical analysis of the zircon ages of the Late Triassic suggests that the age of the Late Triassic magmatic event ranges from 227 Ma to 201 Ma and shows about five age peaks. The Tr-J boundary is suggested to be located between the E’erlongba and Quemo Co formations in the eastern Qiangtang Basin. Geochemical indicators such as CIAcorr, C-value, Sr/Cu, and Rb/K ratios indicate that a moderate to high chemical weathering condition, semi-arid to semi-humid climate and normal marine water condition before the Tr-J transition, and suddenly changed to be low chemical weathering, arid to extreme arid climate, and freshwater water environment during the Tr-J transition, and then rebounded to be moderate to high chemical weathering and semi-humid to humid climate after the Tr-J transition. These evidences suggest that the basin inversion, significant paleoenvironment shift and regional regression occurred nearly coincidentally during the Tr-J transition. The extreme arid climate (probably cool) and ocean acidification may play an important role in the end-Triassic mass extinction in the eastern Tethys.