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河西走廊西端灌丛沙丘发育过程及其对沙漠化的指示意义

花匠小妙招
2024-12-17 18:04

摘要： 在风沙活动强烈的荒漠地区开展环境变化研究常缺乏符合要求的地质测年材料。灌丛沙丘是干旱区发育的一种特殊生物地貌类型，具有计年和储存环境信息的功能，可以用来重建沙丘的发育过程和过去的环境变化。以河西走廊西端花海盆地发育的灌丛沙丘沉积剖面为研究对象，基于AMS14C年代学及沉积物粒度、碳酸盐含量、地球化学元素等代用指标的分析，与文献记载、沙漠化监测数据和近几十年的器测气象资料对比分析，试图揭示区域灌丛沙丘的发育过程及其环境指示意义。结果表明：花海盆地灌丛沙丘的发育时间已超过800 年；20世纪60年代中后期至70年代早期人类活动的干扰曾使灌丛沙丘的堆积过程中断，但丰富的物源随后又促使灌丛沙丘再次快速发育。沙丘物源曾发生过剧烈的变化，使得灌丛沙丘沉积物中的粗颗粒组分和中值粒径并不适于作为环境代用指标重建区域的风沙环境变化，而细颗粒组分（<63 μm和<10 μm）和碳酸盐含量的变化，则揭示了研究区在20世纪70-80年代（沙丘高度300~420 cm）时获得了丰富的物质来源。灌丛沙丘沉积物中的Zr/Rb比值，能够作为良好的环境代用指标指示1970-1988年（沙丘高度300~420 cm）区域处在风沙活动较强烈的环境；近几十年花海盆地土地沙漠化明显，尤其是20世纪70年代和80年代。灌丛沙丘可以作为有较高可信度的地质记录载体，在河西走廊西端重建较长时间尺度的、高分辨率的区域气候环境演变历史。

关键词: 河西走廊, 灌丛沙丘, 物源丰富度, 风沙活动, 沙漠化

Abstract: Environments in arid and semiarid regions are extremely sensitive to climate changes.However,because of the absence of relatively high-resolved proxies,there still poorly understanding for the past environmental changes in these regions.In this paper,we investigate the environmental evolutions based on the evidence of multiple proxies (including the particle size distributions,carbonate contents,geochemical elements,and AMS14C dating results) from a nebkha that develops in the Huahai Basin,western Hexi Corridor,which has also been compared with meteorological observations,literature records,and desertification monitoring data.It indicates that the development of the nebkha is special in Huahai Basin.Although the continuously aeolian sedimentary sequence was disturbed by human activities between the mid-late 1960s and the early 1970s,it was then soon rebuilt and significantly enlarged due to the sufficient deposited material supply;and therefore,this nebkha sediments document high-resolution variations in regional environment condition.From the trends in contents of fine particles and carbonate as well as the values of Zr/Rb,there were sufficient sediment supply from the 1970s to the 1980s,and measured data indicated strong wind activities between 1970 and 1988,together with the rapid enlargement of the sampled nebkha.Afterwards,the ground surface was stable gradually and wind-energy regime changed to a large extent in this region.Above all,our results provide relatively high-resolution evidences on the variations in sediment availability and aeolian transport capability that occurred in this extremely arid area,which demonstrates the reliability of using nebkha sediments and proxies as indicators of past climatic and environmental changes.

Key words: Hexi Corridor, nebkha, sediment availability, wind regime, desertification

中图分类号:

P931.3