Abstract: Far before us, many scholars have made their efforts on the deposition of loess in foot of northern Tianshan Mt. Two points are existed: one is that the loess was formed by wind, and the other is by water flow. Being absent of further study, the disputation over it has not been well settled.
Now, we have studied the loess on the fans along the northern foot of east Tianshan Mt. The section where we sampled is at 7 km depth in northeast of Liyu Hill, located at the center of Urumqi. Wefound lots of sedi-mental microstructures with microscope. The most importance is the stratification, including borizontal bedding, cross bedding and lenticlewave-hori-zontal bedding, vesicular structure, honey comb structure, clastic dyke, brush structure and mud contraction fissure. All about are the traces of water cur-rents with high viscosity. To test it, we compared the heavy minerals in the loess and the gravels of terrace at the headwater of Urumqi River. It is shown that the minerals are form the headwater rather than Zhunger Basin. So the loess at the area might be deposited under the mode of flood.