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根据鲁家沟黄土剖面粒度、磁化率、有机质和碳酸盐含量等气候代用指标的变化和14C测年结果,分析和讨论了该区全新世以来的气候演化的过程。结果表明:11.2calk aB.P.以来的气候可划分为3个阶段:1)全新世早期(11200-7560cal aB.P.),气候开始转暖转湿,但整体上较为寒冷;2)全新世中期(7560-3600cal aB.P.),气候温暖湿润;3)全新世晚期(3600-1167cal aB.P.),气候变得干旱,夏季风强烈减退。该区全新世以来的气候变化是不稳定的,存在频繁的次级波动。大约从7800cal ka B.P.开始定西地区就有人类活动。在6000cal a B.P.左右温暖湿润的气候可能为古人类的生存和发展提供了优越的自然条件,人类活动范围扩大。由于当时生产力水平低下,人类也只是在居住地附近垦殖耕种。因此,人类活动并没有对环境产生明显影响。晚全新世以来,气候总体向干旱化发展的同时,叠加了人类活动的影响。尤其是唐宋以来,人类不合理的开垦土地、滥垦滥伐,使大面积的天然植被不复存在,致使生态环境不断遭到破坏,导致气候环境亦不断恶化。人类活动对气候环境变化的影响程度大大超过了气候环境自身由于自然原因而产生的变化。
According to the changes of climate proxy indexes such as grain size, magnetic susceptibility, organic matter and carbonate content and the results of 14C dating in Lojiagou loess section, the climate evolution process since Holocene was analyzed and discussed. The results show that the climate since 11.2calk aB.P. can be divided into three stages: 1) the early Holocene (11200-7560 cal aB.P.), the climate begins to turn warm and wet, but overall it is colder; 2) Mid-world period (7560-3600cal aB.P.), the climate is warm and humid; 3) Late Holocene (3600-1167cal aB.P.), the climate becomes arid, the summer monsoon decline strongly. Climate change in the area since the Holocene is unstable with frequent secondary fluctuations. About 70000 ka ka B.P. Dingxi area there is human activity. The warm and humid climate around 6000 cal a B.P. may provide superior natural conditions for the survival and development of the ancients, and their range of human activities has expanded. Due to the low level of productivity at the time, human beings cultivated only in the vicinity of their place of residence. Therefore, human activities have no significant impact on the environment. Since the Late Holocene, the climate has been superimposed with the influence of human activities at the same time as the overall development of the climate has progressed. Especially since the Tang and Song dynasties, human beings have unreasonably reclaimed land and indiscriminately deforested so that a large area of natural vegetation no longer exists. As a result, the ecological environment is continuously destroyed and the climate and environment are constantly deteriorating. The impact of human activities on the climate and environment changes greatly exceeds the climate and environment itself due to natural changes.