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Timing and Spatial Distribution of Loess in Xinjiang, NW China.

Li Y, Song Y, Yan L, Chen T, An Z - PLoS ONE (2015)

Bottom Line: Central Asia is one of the most significant loess regions on Earth, with an important role in understanding Quaternary climate and environmental change.The well-outcropped loess sections have mainly developed since the middle Pleistocene in Xinjiang, reflecting the appearance of the persistent drying and the present air circulation system.However, the oldest loess deposits are as old as the beginning of the Pliocene in the Tarim Basin, which suggests that earlier aridification occurred in the Tarim Basin rather than in the Ili Basin and the Junggar Basin.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710061, China.

ABSTRACT
Central Asia is one of the most significant loess regions on Earth, with an important role in understanding Quaternary climate and environmental change. However, in contrast to the widely investigated loess deposits in the Chinese Loess Plateau, the Central Asian loess-paleosol sequences are still insufficiently known and poorly understood. Through field investigation and review of the previous literature, the authors have investigated the distribution, thickness and age of the Xinjiang loess, and analyzed factors that control these parameters in the Xinjiang in northwest China, Central Asia. The loess sediments cover river terraces, low uplands, the margins of deserts and the slopes of the Tianshan Mountains and Kunlun Mountains and are also present in the Ili Basin. The thickness of the Xinjiang loess deposits varies from several meters to 670 m. The variation trend of the sand fraction (>63 μm) grain-size contour can indicate the local major wind directions, so we conclude that the NW and NE winds are the main wind directions in the North and South Xinjiang, and the westerly wind mainly transport dust into the Ili basin. We consider persistent drying, adequate regional wind energy and well-developed river terraces to be the main factors controlling the distribution, thickness and formation age of the Xinjiang loess. The well-outcropped loess sections have mainly developed since the middle Pleistocene in Xinjiang, reflecting the appearance of the persistent drying and the present air circulation system. However, the oldest loess deposits are as old as the beginning of the Pliocene in the Tarim Basin, which suggests that earlier aridification occurred in the Tarim Basin rather than in the Ili Basin and the Junggar Basin.

No MeSH data available.


Related in: MedlinePlus

Map showing the contours of the >63 μm particle component of topsoil in Xinjiang: (A) the Junggar Basin; (B) the Tarim Basin; and (C) the Ili Basin.Cross symbols represent our sampling sites, dots represent the city/county, and arrows represent the possible wind direction.
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pone.0125492.g008: Map showing the contours of the >63 μm particle component of topsoil in Xinjiang: (A) the Junggar Basin; (B) the Tarim Basin; and (C) the Ili Basin.Cross symbols represent our sampling sites, dots represent the city/county, and arrows represent the possible wind direction.

Mentions: Grain-size contour maps of the >63 μm sand fraction of the Xinjiang topsoil are shown in Fig 8. Due to various distances to source regions, the grain size of the Xinjiang surface soils differ from each other. Latitudinally, from desert to loess, the >63 μm (Fig 8A and 8B) particle content of topsoil ranges from 90% to 20% between Shihezi and Qitai in the Junggar Basin and 85% to 40% between Hotian and Yutian in the Tarim Basin. The grain-size contours become increasingly dense (i.e., >63 μm grain-size component changes more rapidly) and are concentrated on the northern slope of the Tianshan Mountains and Kunlun Mountains because the wind speed decreases when the wind is forced to pass over high mountains. This phenomenon further suggests that the Gurbantunggut Desert and the Taklimakan Desert are the main sources of loess for the northern Tianshan and Kunlun Mountains, respectively [19]. For the north of the Gurbantunggut Desert, the contours of the >63 μm particle content (Fig 8A) present a negative trend with increasing distance away from the Gurbantunggut Desert, with the content ranging from 90% to 30%. This pattern is in accord with the different regional landscape zones, including desert, shrub, and grassland, along with increasing altitude [54]. The >63 μm grain-size contours of surface sand of the Junggar Basin are more dense than those of the Tarim Basin (Fig 8A and 8B), especially around the loess-desert interaction region on the piedmont of high mountains (Fig 1). The topsoil particles >63 μm in diameter in the loess zone only account for 20% in the Tianshan Mountains, whereas the proportion reaches up to 50% in the Kunlun Mountains. Scarce precipitation and strong evaporation lead to the extreme aridity of the Tarim Basin, and stronger wind can transport coarser dust to deposits in the downwind zones on the northern slopes of the Kunlun Mountains. Meteorological observation data have also demonstrated that sandstorms occur more frequently in South Xinjiang than in North Xinjiang due to their different climates [65]. Fig 8A depicts the spatial variations of the >63 μm particle content around Tacheng in the western Junggar Basin. In general, it displays an evident closed-curve (Fig 8B) and mainly ranges between 30% and 50%, which decreases from the outer zones to the interior. This pattern indicates that decreasing wind speed leads to the increased settling of fine grains and an apparent intermontane basin defined by the local topography (Fig 1). The contours of >63 μm particle content component (Fig 8C), from west to east in the Ili Basin, change from dense to sparse with values shifting from 70% to 10%, especially on the western part of the Ili Basin. However, Fig 8C illustrates that in the east and southwest Ili basin around Zhaosu, the >63 μm grain-size content only accounts for 10% or less. This phenomenon is correlated with the varying distance from the source region, reduced wind speed caused by increasing elevation, and the blocking effect of the Tianshan Mountains.


Timing and Spatial Distribution of Loess in Xinjiang, NW China.

Li Y, Song Y, Yan L, Chen T, An Z - PLoS ONE (2015)

Map showing the contours of the >63 μm particle component of topsoil in Xinjiang: (A) the Junggar Basin; (B) the Tarim Basin; and (C) the Ili Basin.Cross symbols represent our sampling sites, dots represent the city/county, and arrows represent the possible wind direction.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4430276&req=5

pone.0125492.g008: Map showing the contours of the >63 μm particle component of topsoil in Xinjiang: (A) the Junggar Basin; (B) the Tarim Basin; and (C) the Ili Basin.Cross symbols represent our sampling sites, dots represent the city/county, and arrows represent the possible wind direction.
Mentions: Grain-size contour maps of the >63 μm sand fraction of the Xinjiang topsoil are shown in Fig 8. Due to various distances to source regions, the grain size of the Xinjiang surface soils differ from each other. Latitudinally, from desert to loess, the >63 μm (Fig 8A and 8B) particle content of topsoil ranges from 90% to 20% between Shihezi and Qitai in the Junggar Basin and 85% to 40% between Hotian and Yutian in the Tarim Basin. The grain-size contours become increasingly dense (i.e., >63 μm grain-size component changes more rapidly) and are concentrated on the northern slope of the Tianshan Mountains and Kunlun Mountains because the wind speed decreases when the wind is forced to pass over high mountains. This phenomenon further suggests that the Gurbantunggut Desert and the Taklimakan Desert are the main sources of loess for the northern Tianshan and Kunlun Mountains, respectively [19]. For the north of the Gurbantunggut Desert, the contours of the >63 μm particle content (Fig 8A) present a negative trend with increasing distance away from the Gurbantunggut Desert, with the content ranging from 90% to 30%. This pattern is in accord with the different regional landscape zones, including desert, shrub, and grassland, along with increasing altitude [54]. The >63 μm grain-size contours of surface sand of the Junggar Basin are more dense than those of the Tarim Basin (Fig 8A and 8B), especially around the loess-desert interaction region on the piedmont of high mountains (Fig 1). The topsoil particles >63 μm in diameter in the loess zone only account for 20% in the Tianshan Mountains, whereas the proportion reaches up to 50% in the Kunlun Mountains. Scarce precipitation and strong evaporation lead to the extreme aridity of the Tarim Basin, and stronger wind can transport coarser dust to deposits in the downwind zones on the northern slopes of the Kunlun Mountains. Meteorological observation data have also demonstrated that sandstorms occur more frequently in South Xinjiang than in North Xinjiang due to their different climates [65]. Fig 8A depicts the spatial variations of the >63 μm particle content around Tacheng in the western Junggar Basin. In general, it displays an evident closed-curve (Fig 8B) and mainly ranges between 30% and 50%, which decreases from the outer zones to the interior. This pattern indicates that decreasing wind speed leads to the increased settling of fine grains and an apparent intermontane basin defined by the local topography (Fig 1). The contours of >63 μm particle content component (Fig 8C), from west to east in the Ili Basin, change from dense to sparse with values shifting from 70% to 10%, especially on the western part of the Ili Basin. However, Fig 8C illustrates that in the east and southwest Ili basin around Zhaosu, the >63 μm grain-size content only accounts for 10% or less. This phenomenon is correlated with the varying distance from the source region, reduced wind speed caused by increasing elevation, and the blocking effect of the Tianshan Mountains.

Bottom Line: Central Asia is one of the most significant loess regions on Earth, with an important role in understanding Quaternary climate and environmental change.The well-outcropped loess sections have mainly developed since the middle Pleistocene in Xinjiang, reflecting the appearance of the persistent drying and the present air circulation system.However, the oldest loess deposits are as old as the beginning of the Pliocene in the Tarim Basin, which suggests that earlier aridification occurred in the Tarim Basin rather than in the Ili Basin and the Junggar Basin.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, 710061, China.

ABSTRACT
Central Asia is one of the most significant loess regions on Earth, with an important role in understanding Quaternary climate and environmental change. However, in contrast to the widely investigated loess deposits in the Chinese Loess Plateau, the Central Asian loess-paleosol sequences are still insufficiently known and poorly understood. Through field investigation and review of the previous literature, the authors have investigated the distribution, thickness and age of the Xinjiang loess, and analyzed factors that control these parameters in the Xinjiang in northwest China, Central Asia. The loess sediments cover river terraces, low uplands, the margins of deserts and the slopes of the Tianshan Mountains and Kunlun Mountains and are also present in the Ili Basin. The thickness of the Xinjiang loess deposits varies from several meters to 670 m. The variation trend of the sand fraction (>63 μm) grain-size contour can indicate the local major wind directions, so we conclude that the NW and NE winds are the main wind directions in the North and South Xinjiang, and the westerly wind mainly transport dust into the Ili basin. We consider persistent drying, adequate regional wind energy and well-developed river terraces to be the main factors controlling the distribution, thickness and formation age of the Xinjiang loess. The well-outcropped loess sections have mainly developed since the middle Pleistocene in Xinjiang, reflecting the appearance of the persistent drying and the present air circulation system. However, the oldest loess deposits are as old as the beginning of the Pliocene in the Tarim Basin, which suggests that earlier aridification occurred in the Tarim Basin rather than in the Ili Basin and the Junggar Basin.

No MeSH data available.


Related in: MedlinePlus