摘要:
通过野外调查和室内分析,发现在花海剖面全新世出现了三次特有的风成砂,并对其原因进行了初步的分析。前两次风沙形成期分别与第一、第二新冰期相对应,而且分析表明第一风沙形成期的冬季风强度要比全新世其它时期强,持续时间长。这为研究本区土地退化、荒漠化等问题提供了自然背景,特别是对西部大开发战略重点之一的生态环境保护与建设具有特殊的意义
关键词:
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湖相沉积 /
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粒度分析 /
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古风成砂 /
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全新世 /
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花海
Abstract:
The grain-size anaiyses of the whoie section in Huahai Lake reveai that severai segments consist of grains with iarger mean diameter, which are different from the fieid observation. On the basis of iaboratory anaiyses, we found that the characteristics of paieo - eoiian sand from sand wedges are so simiiar to those of modern eoiian sand that they coincide with previous studies. Based on the above, detaiied grain-size distribution comparisons were conducted in order to make it ciear that which segments are eoiian. The resuits show that sand from iayers of 4.75 ~ 5.33m, 3.85 ~ 3.81m, 0.37 ~ 0m shares good simiiarity with compared eoiian sampies, impiying that the sand of these iayers originate from aeoiian. And the time during which the eariier two iayers of sand were formed may correspond with the first and the second New Ice Age, respectiveiy. Moreover, we found that sampies at the boundary of Huahai Lake encompass more coarse grains, iess fine components than those sampied from the center of the iake. That is to say, compared eoiian sand in Huahai Lake has especiaiiy spatiai discrepancy, which is different from fine-grain distribution originated from Westeriy in ioess. The researches have proved that coarse siit of 4.32 ~ 6.64Φ is easier to suspend in the air than other grain size. However, for grains of < 4.32Φ, the iarger the grain diameter becomes, the more difficuit its suspension gets. Therefore, we preiiminariiy assume that the fine grains was from iacustrine nearby, whiie the coarser from desert, and that the duration of iake recession positiveiy correiates with grain size, which bears speciai spatio-temporai reiationship in arid iacustrine area iniand.Further anaiyses show that median diameter is better correiated with sand, siit and ciay. So we may use median diameter as an effective indicator of winter monsoon history reconstruction. The grain-size curves show that the first sand iayer has the iargest median diameter, the fewest fine grain and the maximum thickness, suggesting that the intensity of winter monsoon with ionger duration at that time, may have been stronger than other two in Hoiocene. These provide naturai background of the soii regeneration and desertification, and has significant impiication to the preservation and construction of ecoiogicai environments in west China.
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