4th International Conference of Palaeogeography

173 / 2019-06-06 16:15:46

Differences in the control of fault throw and fault slope on the sedimentation process of alluvial fans

Flume tank experiment; Alluvial fan; Sedimentary process; Fault throw；Fault slope

Alluvial fan is a type of debris deposit that commonly occurs at basin margin. It often represents as a cone that points to mountain pass and extends toward plain. During the sedimentary process of basins, fault activities are common and often affects the sedimentary process and sedimentary architecture of alluvial fans.In order to further understand the differences in the control of fault throw and fault slope on the sedimentation process of alluvial fans, the sedimentary process of alluvial fans under the differences fault throw and fault slope was simulated by flume tank experiment.
Experiment results reveal that at the early stage of sedimentation process, the larger the fault throw, the faster the vertical growth of the fans on fault plane and the weaker the longitudinal extension of fan body. At the late sedimentation process, the larger the fault throw, the faster the longitudinal extension rate and the larger the distribution range of alluvial fan. At the same time, the larger the fault throw, the more significant the shunting effect on fault plane, which leads to a larger dip angle of fan end. At the end of the experiment, the slope of alluvial fan plane and the proportion of the coarse particles near fault increase with the increase of fault throw.
The larger the dip angle of fault plane, the pattern of alluvial fans, “first regression and then transgression” is more obvious. The larger the dip angle, the more obvious the longitudinal development of fan body and the larger the distribution range, which leads to a smaller average thickness of fan body. At the same time, the larger the dip angle, the stronger the hydrodynamic condition of fan surface, the larger the water channel width, the lower the incised depth and the smaller the swing and channel variation frequency. At the end of the experiment, the slope of alluvial fan plane and the proportion of the coarse particles near faults increase with the increase of dip angle.
According to the experiment results, the difference of fault throw and dip angle mainly affects the accommodation space and hydrodynamic characteristics near faults and thereby affecting the overall sedimentation process. The larger the fault throw or dip angle, the more obvious the alluvial fan is affected by fault. The larger the fan distribution range and the slope of fan plane, the worse the particle differentiation. The smaller the fault throw or dip angle, the closer the alluvial fan to general alluvial fan and the more obvious the particle differentiation. This understanding in differences has guiding significance for the identification of outcropped alluvial fans and the restoration of paleo-geomorphology in future.