Onset timing and palaeoenvironmental records of Carnian Pluvial Episode (Late Triassic) in southwestern Guizhou, China

Abstract

The Carnian Pluvial Episode (CPE) in the Early Mesozoic was an extreme climate event that globally perturbed the Carbon cycle, significantly enhanced the hydrological cycle, and intensified ocean anoxia due to global warming, thereby exerting a significant influence on sedimentary environments. This study investigates the CPE in South China through integrated biostratigraphic, petrological, and geochemical analyses. Our findings of δ¹³C records reveal a progressive increase from 1.71‰ to 3.54‰ and 1.53‰ to 2.88‰ in the lower to middle Julian 1 substage, followed by a major negative excursion from 2.91‰ to 1.47‰ and 2.88‰ to 1.09‰ in the late Julian 1 at the Yongning and the Wusha sections respectively. The δ¹³C records from the two study sections generally correlate well with each other and are earlier than published records. Moreover, fluctuations observed in various redox proxies (U/Th, V/Cr, V/(V+Ni), Mo/Al) strongly coincide with δ¹³C excursions during the late Julian 1 substage, pointing the marine environment shift from oxic to dysoxic/anoxic condition. While the carbonate platforms are overlain by deep-water anoxic facies at the Yongning section. Sr and Ba levels revealed a significant freshwater influx during the CPE, leading to oscillating decreases in palaeosalinity within the study area. In addition, recorded data for Al, Zr, Hf, Ti and Th suggest that the intensified continental weathering, resulted from a humid climate during the CPE, increased the terrigenous clastic input.