How did erosion and rivers create sediment-filled basins between Tien Shan ranges?

The basins located between the ranges of the Tien Shan are filled with younger sediments primarily through the erosive action of the region’s rivers.1

This process is part of an erosional-depositional system where mountains are slowly worn away and adjacent basins are filled with sediment over geologic time. As rivers flow from the mountains into the basins, they transport sediment that accumulates at the mouths of canyons, often forming alluvial fans. These fans are depositional features where sediment is transferred from the upper parts of a watershed to lower reaches.23

In the Tien Shan, this process has been influenced by several factors:
* Sediment Transport: Rivers carry coarse material toward the apex of these fans, while finer sands and silts are deposited toward the base.2
* Tectonic and Climatic Drivers: The accumulation is driven by tectonic uplift, climatic changes, and the availability of water from seasonal rainfall or rapid snowmelt.2
* Accumulation: In some valleys, such as the Fergana Valley, these sedimentary accumulations have reached thicknesses of nearly 5 miles (8 km).1
* Additional Deposits: Beyond river-lain gravels, other materials like wind-deposited loess and glacial moraines have also contributed to the sediment filling these basins.1