| 阿拉善沙漠全新世钙质根管形成机制及其古环境指示意义:来自微观形态学证据 |
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| 引用本文： | 李卓仑,高有红,李若兰,王乃昂,朱瑞霞.阿拉善沙漠全新世钙质根管形成机制及其古环境指示意义:来自微观形态学证据[J].沉积学报,2018,36(6):1131-1138. |
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| 作者姓名： | 李卓仑 高有红 李若兰 王乃昂 朱瑞霞 |
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| 作者单位： | 兰州大学资源环境学院 兰州大学冰川与沙漠研究中心, 兰州 730000 |
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| 基金项目： | 国家自然科学基金项目（41771211，41301217） |
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| 摘 要： | 阿拉善沙漠腹地广泛分布着全新世时期的钙质根管。虽然已有研究将其应用于古环境重建工作，但对其形成机制尚缺乏明确认识并且存在较大的分歧，这些分歧限制了其在古环境重建中的应用，同时对钙质根管是否具有明确的古环境指示意义提出了需要进一步深入探讨的问题。对阿拉善沙漠32组全新世钙质根管进行了扫描电镜分析，观察了钙质根管中是否具有方解石结晶垫和钙化细丝等明确生物成因的微观结构。研究结果显示:全部32组样品中均发现了方解石结晶垫结构或钙化细丝结构，其中20组样品发现了方解石结晶垫结构；19组样品发现了钙化细丝结构。证实了植物根系和根围微生物活动参与了该地区钙质根管的形成。阿拉善沙漠钙质根管的形成主要是由于土壤水分的季节性亏损，在蒸发作用的影响下，土壤中的次生碳酸盐在植物根系周围形成了管状的沉积，而非由地下水重结晶作用形成的。由于阿拉善沙漠钙质根管在形成过程中，不仅受到了土壤含水量以及蒸发量的影响，还受到植物根系和微生物作用的影响。因此，钙质根管中记录了区域古环境和古植被信息，是沙漠腹地古环境重建良好的信息载体。可从钙质根管中提取古环境信息，重建沙漠腹地古气候以及古植被的变化。但是对沙漠腹地湖泊周围的丘间洼地和局地滞水环境下形成的钙质根管，更多的指示了一种局地土壤水分环境而非区域古气候环境。本研究为沙漠地区古气候变化提供了新的重建材料和证据，并拓展了干旱区古气候和古环境变化的研究领域。
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| 关 键 词： | 阿拉善沙漠 钙质根管 次生碳酸盐 全新世 气候变化 |
| 收稿时间： | 2018-01-12 |
Formation Mechanism and Environmental Significance of Holocene Calcareous Root Tubes in the Alashan Desert,as Revealed by Micromorphology |
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| Institution: | College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China |
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| Abstract: | Holocene calcareous root tubes occur widely across the hinterland of the Alashan Desert and have been used for paleoenvironmental reconstructions. However, a clear and common understanding of their formation mechanism is still lacking, which limits their application to paleoenvironmental reconstructions. In addition, whether calcareous root tubes have any specific environmental significance needs to be investigated further. In this study, 32 calcareous root tube samples from the Alashan Desert were analyzed by scanning electron microscope to observe the calcite crystal mats or calcified filaments that characterize their absolute biogenic origin. Results showed that these structural features existed within all 32 calcareous root tube samples, which indicated that plant roots and rhizosphere microorganisms participated in the formation of the calcareous root tubes. Under a pronounced seasonal soil moisture regime, dissolved bicarbonates precipitate around the roots because of water evaporation in the rhizosphere and then cement loose sediments or sands, resulting in formation of calcareous root tubes. Recrystallization of groundwater could not explain the formation of such tubes. Calcareous root tube formation was found to be affected by soil moisture content and evaporation, which demonstrated that these tubes have explicit environmental significance. Furthermore, paleoenvironmental signals can be obtained from them to reconstruct changes in paleovegetation and paleo-effective moisture. This study could provide new valuable archives of paleoclimatic changes in desert hinterlands and develop research into paleoenvironmental evolution in arid regions. |
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