ON THE LIUFENGGUAN FLYSCH
Jiang Chunfa, Zhu Zhizhi (Institute of Geology of the Chinese Academy of Geological Sciences) Kong Fanzong (Party of Regional Geological Survey of Shanxi Bureau of Geology)
The Liufengguang flysch here refers to the early Triassic flysch formation of the Liufengguang group in the East Qinling miogeosyncline. It is characterized not only by typical flysch features such as rhythmic sedimentation of turbidites and cast molds, but particularly by cyclic sedimentation forming a cyclic sequence. A cyclic sequence is composed from below upwards of the following strata: arenaceous flysch, argillaceous flysch and thin-bedded non-rhythmic limestone. The first two are turbidites, while the latter is not turbidite. The alternation of turbidites and nonturbidites gives rise to a cyclic sequence. The period during which no turbidites are deposited is called a break of turbidite sedimentation. The cyclic sedimentation differs from the rhythmic sedimentation in that the former is not restricted to the sedimentation of turbidites, whereas the latter is characteristic of turbid currents. From the genetic point of view, such a cyclic flysch sedimentation reflects the duration of turbid currents. It may show the following features: (1) the intensity of turbid currents is characterized by the repeated change from strong to weak; (2) the turbid currents are intermittent; and (3) the break of turbidite sedimentation indicates a period during which the earth's crust is relatively stable. The study of cyclic sequences and their cyclicity is of great significance in deciphering the origin of turbid currents and their dynamic processes.