Abstract:

In the Tarim Basin, the Taklimakan Desert is the second largest shifting dune globally. Holocene relic sites in the desert hinterland suggested ancient rivers flowing, oasis occupation, and human activities. The Keriya River is one of the rivers that originated from the glacier mountains of south Tarim Basin. The Yuansha Site is the earliest city in the Taklimakan Desert, located in the delta area of the Keriya River and provided an ideal case for illustrating the relationship between the natural environment and human activities. To better understand this area’s past environment, we selected the KYN22 section (22 km from north of the Yuansha Site) and 134 grain size samples in the section from each depth for particle size distribution measurement and grain size parameter calculation. We collected four OSL chronology samples from the depth of 230 cm, 490 cm, 590 cm, and 1070 cm, respectively. The measurement results showed the following. (1) The main components of sediment samples are silt and very fine sand. (2) The grain size median diameter, sorting coefficient, skewness, and kurtosis changed at approximately 3.27-6.86 Φ, 0.54-2.50 Φ, -0.30-1.48 Φ, and 0.71-1.71 Φ, respectively. (3) The OSL age measurement results are 6.4±0.4 ka, 9.8±0.6 ka, 10.1±0.5 ka, and 13.8±0.6 ka from the upper part to the bottom of the section, respectively. (4) The very fine sand content variation is consistent with that of fine sand and opposite with silt sand with depth increase, whereas the silty sand variation content is consistent with mild clay samples. (5) The sediment grains in the 0 to 550 cm depth composed mainly of silt, followed by very fine sand. In contrast, the sediment grains in the 550 to 1070 cm depth composed of very fine sand as the main content, and silt is the minor content. A reported OSL age (2.3 ka) at the upper layer of the section suggests that the KYN22 section recorded past environmental and landform changes of the Yuansha Delta in 13.8-2.3 ka. The section is mainly for fluvial activities, indicating that the Keriya River dominated this area most of the Holocene. The sediment sequence indicates the domination of aeolian activity at approximately 13.8 ka in earlier Holocene and the fluvial and aeolian activity in 9.8-10.1 ka; thus, fluvial activity controls from the middle to the late Holocene. The OSL age (13.8 ka) of the aeolian sand section bottom was followed with the formation of a paleochannel section at approximately 50 km east of the Yuansha and the high terrace formed in the upper reaches of the Keriya River, suggesting flooding events frequently occurred in the Tarim Basin’s south margin. The fluvial sediment deposited in 9.8-10.1 ka was coeval with the increase of northern hemisphere solar radiation and temperature rising, suggesting increasing melt water in the Kunlun Mountains. This study provides a relatively complete Holocene sediment sequence recorded with reliable chronology data at the Keriya River’s lower reaches. For oasis’ prosperity and inhabitants’ activities depending on the river, this section recorded the natural environment and the rise and fall of ancient civilization in the Keriya River delta.

Key words: Taklimakan Desert, Keriya River, Yuansha City, particle size, OSL dating, Holocene