Study on large-scale circular slump structures on Luokou Point Bar in Downstream of Yellow River
Li Hao Zhong Jianhua WU Kongyou
1.Key Laboratory of Marginal Sea Geology, Guangzhou Geochemical Research Institute of CAS, Guangzhou 510640
2 Earth Resource and Information College, Chian University of Petroleum, Dongying 257061,Shandong
Two large-scale circular slump structures are well developed on the middle-rear Luokou point bar of the downstream of Yellow River. The smaller one is 42.54 m long, 31.55 m wide and 0.63m high and the larger one is 58.30 m long, 46.24 m wide and 0.76 m high. These structures can be divided into three parts: the main body belt, the transitional belt and the vanishing belt according to the geometrical characters and the kinematical elements. Some larger collapsed blocks, which are 20～30 cm wide, 2～3 m long and 40～60 cm high and with the shape of arc-slice, dominate in the main body belt whose length is 8～15 m，what is more, the collapsed slots are open or filled with the silt in the main body of this structures.The 10～20 m long transitional belt, with the character of moderate collapsed blocks whose dimensions are 5～20cm wide, 0.5～2m long and 20～40cm high has the same shape of arc-slice as the main body belt, but the slots are somehow different because some are half-open and edothers are stuffed with the silt. It is important that the relative movement directions of the collapsed blocks have a change here, i.e. from the sere one-way movement to the relative movement. The relative glides with the circle center of a big radial cavum, which are formed by the associate erosive grooves’ gathering, contribute to this kind of ring-like collapsed and slippery structures. The 15～30 m long vanishing belt which is located beyond the area of the transitional belt, is characterized by the decreasing of the block’s dimension as well as the displacement space of the slide of blocks.The structures studied here are developed in a horizontal surface with the collapse gradient of 0.745 degree, and they are developed and accomplished in a “domino”manner. Some factors such as the liability to liquefaction of the fine sediments made up of silts and muddy-silts, the supersaturated pore water due to sudden and sharp rising or falling level of the Yellow River and the seepage water formed by the the special configurations of the Luokou point bar, all contributed to the development of the collapsed structures.
