【作者】 徐娟；

【导师】 魏明建；

【作者基本信息】 首都师范大学 ， 自然地理学， 2006， 硕士

【摘要】 全新世是地球发展演变历史的最新阶段，现代环境是全新世环境的延续和发展。研究全新世环境、特别是气候的演变过程，对认识现代环境的形成和预测未来的人类生存环境都有重要意义。古植被变化的记录不仅可以指示植被随气候变化的动态过程、间接检验气候模式，还可以认识地区环境要素的稳定性和敏感程度。因而它是识别全球的、区域的和局部的控制要素最好的方法之一。并可为预测未来环境在理论上和实践上做出贡献。 通过大量的野外考察，本次研究选取了黄土高原中部地区西峰董志塬的李家楼村剖面。该剖面地层稳定，发育连续、完整，保存良好，具有典型性。对该剖面进行不同地层不同尺度的采样，在全新世黑垆土发育阶段每隔2cm采样，其它层位分别有3cm和5cm的不等间距采样，整个剖面(2m)共采集了74个孢粉分析样品和3个释光测年样品。 通过本次课题的研究，对西峰地区全新世植被演化得出以下结论： (1) 西峰地区全新世环境演化可分为三个阶段：全新世早期温度上升，降水增加，是夏季风增强而冬季风减弱的气候波动改良时期。此阶段乔木花粉与草本花粉浓度相当，且乔木花粉浓度稍高于草本，此阶段的西峰地区发育着森林草原植被。在6.4～3.1 kaB．P(TL年龄)的全新世中期，气候温暖湿润，夏季风活动达到最大强度，降水增加，植被生长繁茂，植被类型以冷温性的松林和温凉性的落叶阔叶林为主。此阶段的西峰地区发育着森林植被。在全新世晚期，乔木花粉含量急剧下降，阔叶乔木基本没有出现(除表层人为影响较大，距地表20cm的范围外)。在此阶段草本植物花粉的平均浓度是乔木的7倍左右，草本植物发育良好，且主要以蒿和蓼科花粉为主。此阶段的西峰地区发育着疏林草原植被。 (2) 在全新世大暖期(6.4～3.1 kaB．P．)，有着稳定的森林植被生长，其过程为早期的针叶林(松属花粉的百分含量最高为97％)，到中期的针阔混交林，以及后期的落叶阔叶林。在此阶段，植物花粉浓度呈现出了一个“3峰2谷”的现象，记录了4.9～5.2 kaB．P．(近似5.3 ka B．P．降温事件)和5.6～5.8 kaB．P．两个气候波动事件。另外此阶段的草本植物花粉的平均浓度只有乔木的1/6，且蒿属花粉平均浓度在此阶段只有1粒/克，这与众多研究黄土高原植被的学者得出以蒿为主的草原植被是截然不同。 (3) 全新世晚期的早期(约3.1～2.5 ka B．P．)存在一个强的降温事件，在此期间松属、桦木科、臭椿、漆树科和禾本科这5种花粉同时出现含量低的现象。它们所占总花粉数量的百分比都不超过6.4％，花粉浓度均在1粒/克左右，只有松属在20号样出现过2粒/克和禾本科在21号样出现过6粒/克。更多还原

【Abstract】 From field investigation, we found the Xifeng profile in the middle part of the loess plateau, which developed in Holocene, appears the continuous sediment and consists of 1 paleosol layer, 2 loess bed and 2 transitional layers. Pollen-anaysis is ofen used in the research of pale-vegetaion and pale-environment. The high resolving-ratio pollen analysis in Xifeng profile reveals that the coniferous forest and deciduous broad-leaved forest grew in the region of Xifeng during the Holocene Megathermal. The coniferous forest was mainly composed of Pinus, and the deciduous forest was made up of Betulaceae Ailanthus and Anacardiaceae. According to pollen analysis, the vegetation succession during the Holocene was reconstructed:(1) In the forepart of the Holocen, the sequence shows the equation of the arboreal pollen concentration with the herb pollen concentration. The vegetation was a forest-steppe which contained some coniferous tree. During 6.4-3.1 kaB.P. (TL age), the period of Holocene Megathermal, pedological process was the strongest, and the precipitation increased remarkably, so was the temperature. The vegetation was a forest which comprised of coniferous trees and deciduous broad-leaved trees. In the terminal Holocen, the content of arboreal trees descended evidently and the concentration of the herb rose too much. In this period, the vegetation was a sparse forest-steppe which mainly contained Artemisia and Polygonaceae.(2) There are "3 wave crest and 2 trough" in the sequence of the Holocene Megathermal. These record the fluctuation of the climate’s descension, namely 5.2-4.9 kaB.P. (approximately 5.3kaB.P.) and 5.8- 5.6 kaB.P. degressive climate affair. It needs to point out that the concentration of the herb was greatly low in this period, and Artemisia merely appears about 1 grain/gram.(3) The Pinus Betulaceae Ailanthus Anacardiaceae and Gramineae descend so quickly that the concentration of them is around 1 grain/gram in the beginning of the terminal Holocen. It also record the degressive climate affair during about 3.1 -2.5 ka B.P..更多还原