bedrock is exposed and highly weathered, and gullies criss-cross amid steep hillsides. The terrain generally descends to the south, and there are no plants growing
on the hills and slopes.
– Depositional plains (II)
Depositional plains are mainly made up of the upper Pleistocene pluvial fans. The
terrain descends from the mountain front to the lake basin and gradually becomes
flat and open. According to genesis and lithology, depositional plains can be
divided into piedmont alluvial-pluvial plains and alluvial-lacustrine plains.
The piedmont alluvial-pluvial plains (II 1 ), with an altitude of 3170–3600 m, are
distributed in the south of Chaidamu Mountains. They are mainly composed of the
upper Pleistocene pluvial fan. The terrain descends from the mountain front to the
lake basin and gradually becomes flat and open. In terms of lithology, the strata are
mainly composed of coarse materials. Due to strong wind erosion and desertification of land surface, the vegetation is seriously degraded, and gravel and desert
landscapes are created. In the front edge of the alluvial fan (south of Dachaidan
Town), fine soil belts of different widths are formed and distributed in a strip shape
on the periphery of the alluvial-lacustrine plain. The slope of the terrain gradually
decreases from 4–9° in the piedmont pluvial plain to less than 4° in the middle and
lower parts. Modern gullies develop on the land surface and spread radially to the
downstream. The alluvial fan is cut deep (generally 1–5 m) on the top, creating
U-shaped gullies, but to a smaller extent (generally 0.5–1 m) in the downstream,
creating wide and shallow valleys. In the fine soil belts, due to thinner strata and
shallower depth to water table, springs and rivers emerge and vegetation grow on
the surface, which forms an oasis belt with sound lake basin ecosystem.
The alluvial-lacustrine plains (II 2 ), with an altitude of 3150–3170 m, are distributed in the fine soil plain area in the southwest part of the study area. The
extremely flat terrain slopes down to the lake area, making a gradient of 1–2°. The
strata are mainly composed of Holocene alluvial-lacustrine fine sand, silty sand,
sandy loam and silt. Springs and swamps emerge as the depth to water table is
limited. There are some salt flats and salt cursts and scarce vegetation due to strong
evaporation.
• Lithology
– Pre-quaternary strata
Upper Ordovician Tanjianshan Group (O 3 ).
It is mainly distributed in the North Chaidan Mountains, fails into medium- and
high-grade metamorphic volcanic rocks. It is main comprised of gray, grayish
white, gray-black phyllite, gray-white marble, gray-white and gray-green granulite,
schist, slate, phyllite, and crystalline limestone. It is in fault contact with the Upper
Carboniferous Zhongwu Nongshan Group (C 3 ).
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155
on the hills and slopes.
– Depositional plains (II)
Depositional plains are mainly made up of the upper Pleistocene pluvial fans. The
terrain descends from the mountain front to the lake basin and gradually becomes
flat and open. According to genesis and lithology, depositional plains can be
divided into piedmont alluvial-pluvial plains and alluvial-lacustrine plains.
The piedmont alluvial-pluvial plains (II 1 ), with an altitude of 3170–3600 m, are
distributed in the south of Chaidamu Mountains. They are mainly composed of the
upper Pleistocene pluvial fan. The terrain descends from the mountain front to the
lake basin and gradually becomes flat and open. In terms of lithology, the strata are
mainly composed of coarse materials. Due to strong wind erosion and desertification of land surface, the vegetation is seriously degraded, and gravel and desert
landscapes are created. In the front edge of the alluvial fan (south of Dachaidan
Town), fine soil belts of different widths are formed and distributed in a strip shape
on the periphery of the alluvial-lacustrine plain. The slope of the terrain gradually
decreases from 4–9° in the piedmont pluvial plain to less than 4° in the middle and
lower parts. Modern gullies develop on the land surface and spread radially to the
downstream. The alluvial fan is cut deep (generally 1–5 m) on the top, creating
U-shaped gullies, but to a smaller extent (generally 0.5–1 m) in the downstream,
creating wide and shallow valleys. In the fine soil belts, due to thinner strata and
shallower depth to water table, springs and rivers emerge and vegetation grow on
the surface, which forms an oasis belt with sound lake basin ecosystem.
The alluvial-lacustrine plains (II 2 ), with an altitude of 3150–3170 m, are distributed in the fine soil plain area in the southwest part of the study area. The
extremely flat terrain slopes down to the lake area, making a gradient of 1–2°. The
strata are mainly composed of Holocene alluvial-lacustrine fine sand, silty sand,
sandy loam and silt. Springs and swamps emerge as the depth to water table is
limited. There are some salt flats and salt cursts and scarce vegetation due to strong
evaporation.
• Lithology
– Pre-quaternary strata
Upper Ordovician Tanjianshan Group (O 3 ).
It is mainly distributed in the North Chaidan Mountains, fails into medium- and
high-grade metamorphic volcanic rocks. It is main comprised of gray, grayish
white, gray-black phyllite, gray-white marble, gray-white and gray-green granulite,
schist, slate, phyllite, and crystalline limestone. It is in fault contact with the Upper
Carboniferous Zhongwu Nongshan Group (C 3 ).
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