Abstract:

According to their density，turbidity currents can be classified into low density，sandy high density and gravelly high density currents. Their rheology mechanisms especially that of the highˉdensity currents，are still highly controversial. This article explored the distribution，triggering mechanism，suspension process and depositional velocity of the turbidity current，and identified five dynamicˉdeformation zones，including erosion，frontal adjusting，depositional offloading，rear adjusting and balanced zones. From the view of flow mechanism，the erosion zone keeps a steady state because of its perfect mobility. It swathes coarser grains and daggles finer grains，forming a nebulousˉlike trail behind. The depositional off loading zone presents only a slow and subtle change in flowing time and space under a mixing force. When the turbulence force by flow differentiation is less than the viscous dampening effect，the deposits start to offload and accumulate in sequence. Both the adjusting and balanced zones perform the functions of dynamic conversion，structural connection，and deposition and erosion balancing in currents. It is highly possible that turbidity current with high flowing speed become more structurally unstable and complicated in supporting mechanisms. And this may explain the phenomenon of transition，alteration and transformation between turbidity currents and other types of gravity currents.

Key words: flowing mechanism, depositional response, turbidity current, depositional dynamics, Dongying Sag