In this study we have assessed the relationship between cosmogenic nuclide content of individual clasts and the time since their deposition on three alluvium –diluvium fan surfaces. Cosmogenic nuclide accumulation represents the integrated total surface exposure of rocks in source regions during transport and since deposition. Post deposition processes (erosion

burial

bioturbation

and cryoturbation)

all of which decrease the quantity of cosmogenic nuclides produced in a rock in a given time and hence the apparent exposure age

also cause significant scatter among apparent ages of samples from the surface. Very low 10Be concentration in material from active streambeds and at depth below one of the fan surfaces indicates that exposure prior to deposition onto fan surfaces was minimal

Thirty two samples are collected on three alluvium –diluvium fan surfaces

southern Tianshan piedmont

Xinjiang

China. Using the cosmic ray exposure (based on in situ-produced 10Be) dating

the average ages for the three fans are (17±3)×103

(27±3)×103 and (25±3)×103 10Be years

respectively.