ISWC OpenIR  > 水保所2018届毕业生论文
典型黄土-古土壤剖面有机碳和黏土矿物分布特征及古环境意义
张青青
Subtype硕士
Thesis Advisor赵世伟 ; 黄菁华
2018-05-25
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline土壤学
Keyword黄土-古土壤 黏土矿物 粒度 Caco3 有机碳组分 古气候
Abstract黄土-古土壤序列是记录第四纪气候环境变化的良好信息载体之一。本文以黄土高原南缘陕西省淳化黄土-古土壤序列为研究对象,通过调查剖面上土壤黏土矿物和有机碳含量、密度、组分以及结构的分布特征,并将黏土矿物与已有的古气候联系,有机碳与古气候替代指标土壤粒度、CaCO3含量进行相关分析,再结合已有第四纪气候的研究以及现代不同气候条件下土壤有机碳组分的变化规律的相关研究,探索土壤黏土矿物和有机碳特征对黄土高原第四纪古气候环境的指示意义,从而揭示黄土高原南部地区在更新世时期的气候环境演变规律。结果表明:
(1)淳化剖面不同黄土-古土壤层的黏土矿物类型基本相同,但其相对含量存在差异。在WL-3~S5阶段,即早更新世至中更新世中期,黏土矿物的组合类型为伊利石-蒙脱石-绿泥石-高岭石-蛭石,其中早更新世至中更新世早期(WL-3~L11阶段)伊利石相对含量相对偏低,以气候温凉为主,而中更新世中期(S10~S5阶段),伊利石相对含量上升,气候相对温湿;在中更新世晚期(L5~S1阶段),黏土矿物的组合类型改变为伊利石-绿泥石-蛭石-高岭石-蒙脱石,气候较为干冷。黏土矿物含量变化表明淳化地区从早更新世早期到中更新世晚期气候环境总体干冷化,并经历了温凉-温湿-干冷的变化过程。伊利石/绿泥石(I/C值)以及伊利石结晶度IC值在淳化剖面底部到顶部均经历了由小到大再到小的过程,它们与黏土矿物的含量所反映的气候变化规律一致。
(2)淳化剖面的黏粒、Md(f)和CaCO3含量在反演古气候方面具有较好的指示作用。淳化黄土-古土壤剖面黏粒含量和Md(f)垂直分异趋势一致,均表现为古土壤层相对黄土层的黏粒含量、Md(f)偏高,二者呈现正相关关系,CaCO3含量则表现出相反的趋势。黏粒和Md含量较高反映了气候温暖湿润,CaCO3含量越高反映了气候寒冷干燥,三者均反映了自早更新世以来,淳化地区气候总体干冷化,并经历暖湿-干冷的气候旋回。
(3)淳化黄土-古土壤剖面的有机碳含量、密度、矿物结合态有机碳含量以及矿物结合态有机碳分配比例(MOC/TOC)均表现为古土壤时期高于其下伏黄土时期,但在S8以下土层,有机碳含量、矿物结合态有机碳含量的波动幅度趋于稳定,而MOC/TOC在不同土层间的变化幅度较为明显。
(4)淳化剖面黄土-古土壤的有机碳官能团均含有烷基碳,大部分含有烷氧碳,芳香碳和羧基碳只在末次间冰期以来出现。
(5)将黄土-古土壤有机碳与古气候替代指标进行对比分析,我们发现有机碳含量、密度和组分指示古气候的变化效果不明显。但MOC/TOC与黏粒含量、Md(f)变化趋势一致,与CaCO3含量的变化趋势相反,且与它们具有很好的相关性,相关系数分别为0.54、0.59和-0.71,在S8及以下地层的MOC/TOC与三个古气候替代指标的相关程度更高,相关系数达到0.63、0.68和-0.75。结合现代关于MOC/TOC指示气候的研究,淳化黄土-古土壤剖面的MOC/TOC与第四纪冷干暖湿古气候旋回有关。黄土-古土壤剖面中MOC/TOC比值较高可能反映了温暖湿润的气候,而较低的比值则反映了相对寒冷和干燥的气候。相对有机碳而言,MOC/TOC排除了总有机碳的差异,在S8以下地层可以更好地指示古气候环境。
(6)本研究结果表明黄土-古土壤剖面中的黏土矿物的组合类型、I/C、IC值和MOC/TOC可以重建古环境变化,也为预测未来土壤有机碳库对植被和气候变化的响应提供了依据。其中,黏土矿物反演的古气候的阶段性变化比较明显,而MOC/TOC倾向于整体气候的反演。通过黏土矿物和有机碳共同反演古气候,我们发现自早更新世以来,淳化剖面气候整体上呈逐渐干冷的趋势,并经历了温凉-温湿-干冷的阶段性变化。
Other AbstractThe loess-paleosol sequence has been considered as an important information carrier recording changes in the global environment and climate of the Quaternary peroid. In this paper, a typical loess-paleosol sequence in the south of the Loess Plateau was selected as research object, and the distribution characteristics of clay minerals and organic carbon in the loess-paleosol profile have been investigated. Besides, the correlations between clay mineral chricteristics and magnetic susceptibility, and between organic carbon chricteristics and paleoclimate indexes, such as soil grain size and CaCO3, were also analyzed to explore the significance of clay mineral and organic carbon charicterisitcs in indicating the paleoclimate changes of the Loess Plateau in the Quaternary, based on previous studies investigating paleoclimatic and paleoenvironmental evolution in the Quaternary and changes of organic carbon charicteristics in modern soil under different climatic conditions. The results can provide new evidence to reconstructing the evolution of climate and environment in the southern part of the Loess Plateau since the Pleistocene. The main results were as follows:
(1) All the loess and paleosol layers of Chunhua profile had the same clay minerals, but relative contents of the clay minerals varied significantly from layer to layer. During the period from the early Pleistocene to the mid-middle Pleistocene (WL-3~S5), the clay minerals were composed mainly of illite-montmorillonite-chlorite-kaolinite-vermiculite, and this period could be divided into two stages according to the changes in relative contents of the clay minerals. From the early Pleistocene to the early middle Pleistocene (WL-3~L11), the relative content of illite was comparatively low while the relative content of chlorite was quite high, which indicates that a cool temperate climate prevailed in this period. However, in the mid-middle Pleistocene (S10~S5), the relative content of illite increased, while the relative content of montmorillonite and chlorite decreased, which indicates that the climate was relatively warmer and more humid in this period. In the late middle Pleistocene (L5~S1), the composition of clay minerals turned to be of illite-chlorite-vermiculite-kaolinite-montmorillonite, and the relative contents of illite and chlorite increased, implying a dry-cold climate dominated this period. Therefore, the changes in relative contents of the clay minerals in the Chunhua loess-paleosol profile indicate that from the early Pleistocene to the late middle Pleistocene, the climate generally became dry and cold, and experienced changes from cool temperate to warm wet and to cold dry. The ratio of illite to chlorite (I/C value) and illite crystallinity (IC value) also exhibited phased variations from the bottom to the top in the Chunhua profile, which increased first and then decreased. The distribution of I/C ratio and illite crystallinity indicates that the climate in the Pleistocene underwent an evolutionary process similar to that of the clay minerals in relative content. 
(2) In the Chunhua loess-paleosol profile, three paleoclimate proxies, grain size and CaCO3, show good indication of paleoclimate changes in the Quaternary. Soil clay content and median grain size (f) were higher in paleosol than in the underlying loess, and psotive correlation exsited bettwen the two proxies, while CaCO3 content showed an opposite tendency. The higher clay content and median grain size (f) in paleosol reflect warm and humid climate, but the higher CaCO3 content in loess reflects cold and dry climate. All of the three paleoclimate proxies reflect that in Chunhua area, the climate generally became dry and cold since the early Pleistocene, and experienced cold dry-warm wet paleoclimatic cycle.
(3) The total content and density of soil organic carbon, as well as the ratio of mineral-associated organic carbon in total organic carbon (MOC/TOC ratio), were generally higher in paleosol layers than in the underlying loess layers of the Chunhua loess-paleosol profile. But in the soil layers below S8, the contents of total organic carbon (TOC) and mineral-associated organic carbon (MOC) tended to be stable, while MOC/TOC ratios changed more obviously.
(4) Regarding to the distribution of organic carbon functional groups in Chunhua loess-paleosol profile, alkyl carbon was observed in all loess and paleosol layers, while alkoxy carbon exsited in most soil layers, and aromatic carbon and carboxyl carbon only appeared since the last interglacial period.
(5) Based on the comparative analysis of organic carbon charictersitics and paleoclimatic proxies, we find that compared to total content and density of organic carbon, MOC/TOC ratios showed more significant correlations with the changes of clay content, Md (f) and CaCO3 content in the Chunhua profile, which were positively correlated with the former two proxies and negatively correlated with the last one, and the correlation coefficients in the whole loess-paleosol profile were 0.54, 0.59 and -0.71, respectively, while in strata below S8, the correlation coefficients were 0.63, 0.68 and -0.75, respectively. Our results indicated that MOC/TOC ratios in the Chunhua loess-paleosol profile correlated with the cold dry-warm wet paleoclimatic cycle in the Quaternary. The higher MOC/TOC ratios in the loess-paleosol profile may reflect warm and humid climate, while lower ratios indicate relatively cold and dry climate. Compared to TOC, MOC/TOC ratios had greater significance in indicating paleoenvironmental evolution in the Quaternary on the Loess Plateau.
(6) The results of this study indicate that clay mineral charicteristics (relative content, I/C value and IC value) and MOC/TOC in loess-paleosol profile can offer new evidence to reconstructing paleoenvironmental changes in the Quaternary, and also provide a basis for predicting responses of soil organic carbon pools to vegetation and climate changes in the future. Among these indexes, clay mineral charicteristics can better reflect the phased paleoclimate changes, while MOC/TOC ratio can better reconstruct paleoclimate evolution at a long time scale. Therefore, through investigating the charicteristics of both clay minerals and organic carbon, we find that the paleoclimate changes in Chunhua area changed from cool temperate to warm wet and then to cold dry, and generally became dry and cold from the early Pleistocene.
Subject Area农学
Language中文
Document Type学位论文
Identifierhttp://ir.iswc.ac.cn/handle/361005/8113
Collection水保所2018届毕业生论文
Affiliation中国科学院教育部水土保持与生态环境研究中心
Recommended Citation
GB/T 7714
张青青. 典型黄土-古土壤剖面有机碳和黏土矿物分布特征及古环境意义[D]. 北京. 中国科学院研究生院,2018.
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