PALEOENVIRONMENTAL TRANSITION ACROSS THE PERMIAN-TRIASSIC BOUNDARY: INSIGHTS FROM PALEOSOLS OF THE JUNGGAR BASIN, NW CHINA

The terrestrial Permian-Triassic boundary (PTB) is known primarily from the southern high latitudes of Gondwana (South Africa, Antarctica, Australia). Here, we present new paleoenvironmental data from palesols from northeastern Tethyian localities exposed within the Junggar Basin of the Kazakhstan Plate, NW China. Paleosol morphological characteristics in the Upper Permian, Lower Wutonggou Fm include intense redoximorphy, accumulation of vascular plant organic matter, and subsurface enrichment of layer-lattice phyllosilicates and Fe-oxides, which suggests perennially wet soil moisture regimes. Upper Wutonggou Fm paleosols exhibit morphological features that include slickensides, clastic dikes, and redoximorphic accumulations of Fe-oxides, indicating a humid environment, but with distinct seasonal variations in soil moisture budget. Paleosol morphologies change significantly between the Upper Permian and Lower Triassic strata. Paleosol morphological characteristics of the Lower Triassic, Jiucaiyuan Fm include subsurface calcium carbonate accumulations, as well as pseudomorphs after gypsum, indicating a drier environment characterized by net soil moisture deficiency. Modern soil analogs suggest that lower Upper Permian paleosols formed in humid environments with >1000 mm of precipitation/yr, whereas Lower Triassic paleosols formed in environments with as little as 300 mm/yr. Clay mineralogical analysis indicates a transition across the PTB from smectite- and kaolinite-dominated to smectite- and illite-dominated paleosols. The presence of illite suggests less vigorous chemical weathering within the Early Triassic soil profiles, and is consistent with the observed changes in paleosol morphological characteristics. Preliminary carbon isotope analysis of vascular plant organic matter is limited to the Permian Wutonggou Formation. Nevertheless, the organic matter δ¹³C values range from -21.2 to -23.3‰, and an approximately -2‰ shift begins ~60 m below the perceived PTB.