6 - Classification and correlation of nonmarine Permo-Triassic boundary in China

Summary

Introduction

In China, nonmarine Permian and Triassic strata are distributed mainly in the vast area north of a line formed by the Kunlun, Qinling, and Dabie mountains. They are particularly well developed in the Junggar, Turpan, and Shaanxi-Gansu-Ningxia basins. South of the line, nonmarine Permo-Triassic sediments occur mostly in eastern Yunnan and western Guizhou. In addition, alternating marine and continental Permian and Triassic rocks are also developed in a few areas in both South and North China. In the past decade or so great progress has been made in studies of both the biological and nonbiological features of the nonmarine Permo-Triassic boundary. Existing data reveal distinct changes across the boundary in biologic groups such as vertebrates, bivalves, ostracodes, spores, pollen, and other flora, and in nonbiologic features such as grain size and color of sediments, sedimentary environments and climate. These changes suggest an event between the Permian and Triassic and can be applied to correlation of the nonmarine Permo-Triassic boundary.

Biotic changes

Determination of the Permo-Triassic boundary in nonmarine sequences is made at present mainly on the basis of vertebrates and spore-pollen assemblages, and to a lesser extent, on the basis of ostracodes, bivalves, and other elements of the flora.

Vertebrate fauna

The vertebrate fauna changes markedly from Permian to Triassic. Dicynodonts such as Kunpania scopulusa, Striodon magnus, Jimusaria sinkiangensis, Dicynodon tienshanensis, Jimusaria taoshuyanensis, Turfandon bogdaensis and Kansuodon sp. are represented in Upper Permian strata in the Junggar and Turpan basins of Xinjiang and Gansu provinces, northwest China (Zhao, 1980; Yang et al., 1986). A Pareiasaurus fauna, represented by Tapinocephalidae and Shihtienfenia permica, and Shansisaurus xuecunensis, has been reported from equivalent strata in Shanxi and Shaanxi provinces, North China.