Résumé
A small drainage basin system has been extensively studied in an active seismic area of Mongolia, in order to understand the seismic cycle over a long period of time (order of 130,000 years). This system is characterized by several generations of alluvial fans that have been dated by several techniques such as scarp degradation and cosmogenic nucleides. As a fundamental result, the successive alluvial fans appears with a period of 100,000 years and seems to trigger a period of tectonic uplift at a rate of 1 mm/year during the next 20,000 years. In order to check if such a cyclic behavior can progressively shape the overall structure of Gobi-Altay by successive increments of uplift and quiescence, a Surface Process Model (SPM) including weathering process, diffusion transport at small scale, fluvial incision and fluvial transport at larger scales has been developed. Calibration of each process parameters can be done on the recent history of the drainage basin system, and then included in the SPM model at larger time and space scales. However, each process involves a characteristic time scale and the interaction of all processes may lead to an internal cyclicity (autocyclicity) of sediment fluxes entering the alluvial plain in absence of any external cause. Because the time characteristics obtained could be related to the transport processes efficiencies, we present a set of numerical experiments to check how this signal and a 100 ky cycle can interact from a general standpoint, and test the limits of interpreting the sedimentary message in term of tectonic/erosion interaction.