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为探讨更新世我国北方植被演化特征,对北京凹陷新5孔河湖相沉积进行孢粉植物群初步研究。结果显示,过去2.3Ma尤其1.7Ma以来北京地区总体上为疏林草原-草原植被所覆盖,西部和北部的山地上生长以松(Pinus)为主的针叶树。主要孢粉类型的含量变化显示,2.3~2.1Ma期间气候温和半干旱。1.70~1.45Ma期间,北京地区冬季气温下降,导致山地针叶树增加;同时,夏季风也得到了增强,导致落叶阔叶树和喜湿草本得到发展;这表明这一时期北京地区的季节性较早期(2.3~2.1Ma)明显增强。1.45~1.05Ma期间研究区气候延续了前期气候特征,并维持相对稳定。1.05~0.94Ma期间,针叶树松属花粉含量明显降低,随后自0.94Ma开始含量明显增加。这可能是对中更新世过渡期及随后全球冰量增加的响应。极地冰量增加,北半球径向温度梯度变陡,导致东亚冬季风加强。另一方面,1.05~0.94Ma期间,无论是落叶阔叶树花粉含量,还是喜湿草本和蕨类孢子的含量均有不同程度的增加,而且显示向上减少的变化趋势,暗示东亚夏季风在1.05~0.94Ma期间总体增强随后逐步减弱的变化趋势。据此我们推测,自中更新世气候过渡期开始,东亚冬季风和夏季风均明显增强。但伴随极地冰盖发展和全球气温下降,东亚冬季风持续增强而东亚夏季风则显示逐步减弱的变化趋势,使得我国中北部许多地区出现植被与环境短暂恢复后逐步衰退的演化趋势。自约0.5Ma开始,研究区以松为代表的针叶树花粉逐步减少,落叶阔叶树花粉含量也开始降低,反映研究区明显变干,相对喜湿的草本和木本逐步为喜干旱的蒿(Artemisia)和藜科(Chenopodiaceae)所代替。研究区这样的孢粉植物群演化模式与东亚、北太平洋乃至南半球具有较好的一致性。不过,中更新世全球气候过渡以及约0.5Ma显著转变的驱动因素还不清楚,值得深入研究。
In order to explore the characteristics of Pleistocene vegetation evolution in northern China, a preliminary study on the pollen flora in the new 5-hole lacustrine sediments in Beijing depression was conducted. The results show that in the past 2.3Ma, especially since 1.7Ma, Beijing is generally covered with grassland-grassland vegetation in Beijing, while Pinus dominated conifers grow in the mountainous areas in the west and north. Changes in the content of the main types of sporopollen showed that the climate was mild and semi-arid during 2.3 ~ 2.1Ma. During the period of 1.70 ~ 1.45Ma, the temperature in winter in Beijing decreased, leading to the increase of coniferous trees in mountainous areas. At the same time, the summer monsoon also increased, which led to the development of deciduous broad-leaved trees and hi-wet herbaceous plants. ~ 2.1Ma) significantly enhanced. During the period from 1.45 to 1.05 Ma, the climatic characteristics of the study area extended the previous climatic characteristics and remained relatively stable. During the period of 1.05 ~ 0.94Ma, the coniferous pine coniferous pollen content decreased obviously, then the content increased obviously from 0.94Ma. This may be a response to the mid-Pleistocene transition and the subsequent increase in global ice output. Increased polar ice volume, steep radial temperature gradient in the northern hemisphere, leading to the strengthening of East Asian winter monsoon. On the other hand, during the period of 1.05 ~ 0.94Ma, both the deciduous broadleaf tree pollen content and the hippophae rhamnoides and pteridophyte contents increased in varying degrees and showed a downward trend, indicating a trend of East Asian summer monsoon at 1.05 ~ 0.94 Ma generally enhances the subsequent trend of gradual decline. Based on this, we speculate that the East Asian winter monsoon and the summer monsoon have been significantly strengthened since the mid-Pleistocene climatic transition. However, with the development of polar ice sheets and the global temperature drop, the easterly monsoon in East Asia continued to increase while the easterly monsoon in East Asia showed a trend of gradual decline. This led to the gradual decline of vegetation and environment in many parts of central and northern China. From about 0.5Ma, the conifer pollen represented by Pinus sylvestris decreased gradually in the study area, the pollen content of deciduous broad-leaved tree also began to decrease, which reflected that the herbaceous and woody plants were obviously dry, And Chenopodiaceae (Chenopodiaceae) replaced. The evolution pattern of such pollen flora in the study area is in good agreement with East Asia, the North Pacific and even the southern hemisphere. However, the drivers of the mid-Pleistocene global climate transition and the significant shift of about 0.5 Ma are not yet clear and deserve further study.