155 / 2022-02-27 16:06:14

Characteristics and Influence of coarse particle Sedimentation in terrestrial facies Source-Sink System：3D tank experiments

S2S,tank experiments

Coarse particles refer to particles that are not easily transported after being deposited under the action of external forces such as hydrodynamics due to their own conditions such as volume and gravity. In the simulation experiments, we found that in the study of a complete terrestrial facies source-sink system (including sedimentary facies such as alluvial fans, rivers, deltas, etc.), the distribution position and stacking style of coarse particles affected the sedimentary process and sand bodies of the sedimentary facies belt. form, which in turn affects the entire associated source-sink system.



In alluvial fans, the location of coarse particle is mainly affected by tectonic movements and topographic conditions. Affected by faults, particle transport is hindered. At this time, coarse particles often accumulate near faults to form water-dividing shoals, and reverse sand-gravel bars with coarse particles are developed near bulges or folds. Long strips of sand-gravel bars are often scattered in the middle of the fan and at the fan edge. Seasonal channels develop in the gaps of the sand-gravel bars. The location and scale of the sand-gravel bars are controlled by the slope of the fan body and hydrodynamic conditions, and directly affect the channel of the alluvial fan. The development location and the distribution of detrital matter further affect the shape of the fan body, the scale of the fan-edge channel and the flux of detrital matter.



In fluvial fan, the development location of coarse particle is mainly affected by factors such as river type, hydrodynamic conditions and migration frequency. During the development of a single channel, the coarse particles were mainly concentrated on the head of the tongue-shaped sand dunes and the edge of the channel, and a small amount appeared in natural dikes carried by floods. The coarse particle of braided river are mainly concentrated near the distributary shoal of the central bank. The reduction of the flow velocity caused by the division of the river promotes the unloading of the coarse particle here. The increment of coarse particles is positively correlated with the longitudinal extension of the shoal. Coarse particles in meandering rivers are mainly concentrated on the convex bank, while stable meandering rivers will unload a small amount of coarse particles at the edge of the channel. The arrangement shape of the coarse particles is similar to that of the channel, and the channel shape delineated by the coarse particles can be clearly identified in the depleted riverbed. The accumulation of coarse particles on the flanks of the channel will accelerate the erosion of the channel and the development of gully, and then affect the diversion and migration of the channel. The particle size and quantity of coarse particles in the channel are controlled by the upstream material source, and have an impact on the downstream river morphology, development location and migration frequency.



In the delta, the development location of coarse particles is mainly affected by factors such as channel hydrodynamics, topographical conditions, and wave action near the lake shoreline. During the flood period, a large number of coarse particles were transported by the surface of the sand body. At the estuary, they met the jacking action of the lake water, the flow rate decreased, and the coarse particles were unloaded on the front and side edges of the lobe in turn. During the dry season, the coarse particles are concentrated at the bottom and flanks of the underwater distributary channel, and the coarse particles undergo in-situ jumping and rolling friction due to hydrodynamic forces, which accelerates the erosion of the channel and provides assistance for the formation of the underwater distributary channel. When the sediment shale content is high, individual coarse particle are wrapped by shale components and push forward, and a small amount is carried to the vicinity of the fore-delta. The existence of coarse particle affects the delta channel and the distribution of detrital materials. The difference in the development location and stacking style of coarse particle is also a reflection of the differences in hydrodynamic conditions.