Title: Grain-size Characteristics of Sand Dunes in the Ejin Oasis since 2. 5 ka BP and Related Sedimentary Process
Abstract:The Ejin Oasis is located at an extremely arid area of China, where the Ejin section(41°46. 36'N,101°09. 26'E)named by us includes 1 layer of modern mobile sand dunes, 8 layers of paleo-mobile sand du...The Ejin Oasis is located at an extremely arid area of China, where the Ejin section(41°46. 36'N,101°09. 26'E)named by us includes 1 layer of modern mobile sand dunes, 8 layers of paleo-mobile sand dunes, 18 layers of paleo-semi-fixed sand dunes, 14 layers of paleo-fixed sand dunes, 2 layers of sandy immature soils and 2 layers of sandy loess to loess-like sand. Based on 11 samples for 14C dating and 263 samples for grain-size analysis, it has been confirmed in this paper that the sedimentary sequence composed mainly of dune deposition is a product of climate and geomorphological processes of wind-drifting sand. Grain-sizes of different sedimentary types and distribution regularities and geneses of Mz, σ and SC/D are discussed in detail. The study shows that (1) the Paleo-mobile, paleo-fixed and paleo-semi-fixed sand dunes in the Ejin section are quite similar respectively to modern mobile, fixed and semi-fixed sand dunes in either grain-size composition or Mz and σ distribution, thus it provides important evidence for the subdivision of dune types in the section. In comparison with the above three types of dunes, the content of sand substance of the sandy loess to loess-like sand and sandy immature soils markedly decreases, while the content of silt and clay obviously increases, indicating better pedogenesis and a certain soil-forming process. (2) The paleo-mobile sand dunes or paleo-semi-fixed sand dunes and the overlying paleo-fixed sand dunes and/or sandy loess to loess-like sand or sandy immature soils constitute 11. 5 sedimentary cycles, each showing changes from coarser to finer particles, from small to large Mz(Φ)and SC/D values, and from good to poor sorting degree indicated by σ, and representing a normal-reverse alternation process from to subsequent formation. (3) Since 2. 5 ka BP, the Ejin Oasis has undergone 11.5 cycles of ecological and environmental alteration between desertification and oasis formation, which are environmental changes with a time scale of several centuries. The driving force of such changes is chiefly related to the alternation between winter and summer monsoons in East Asia from that time on.Read More
Publication Year: 2005
Publication Date: 2005-01-01
Language: en
Type: article
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Cited By Count: 5
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