Analogue modelling of sedimentary breccias in a talus slope with or without extension—comparison with a natural case

Sedimentary breccias deposited on a talus slope during extension at the front of a normal fault or at the base of a slope are related to the creation of substantial topography. The architecture of talus slopes resulting from exhumation during extension is different from that of rock cliffs without deformation. In this work, we run several analogue models, with or without extension, in order to analyse the external geometry and internal organization of sedimentary breccias and their evolution in time and space. This temporal organization of the sand layers in the experiments shows that normal unroofing sequences are characteristic of progressive exhumation and continuous deformation during extension, whereas reverse unroofing is related to cliff destruction without vertical movement. In the experiment with wet layers of sand, the blocks that resulted from the aggregates of sand grains are generally deposited farther away than single sand grains and are located at the base of the slope; this is one of the main characteristics of rockfalls. The analogue results are compared to natural examples.