摘要
黄土高原完整的黄土-古土壤序列记录了2.6Ma以来的丰富的古气候信息，为研究第四纪古环境与古气候变化提供了很好的研究材料。黄土中含有大量的粘土矿物，粘土矿物是黄土物质组成中的重要组分，也是其中十分活跃，对气候非常敏感的部分，粘土矿物学在黄土研究中占据着不可忽视的作用，是黄土重要的研究方面之一。本文选取黄土高原地区自西北向东南的环县、西峰、长武、永寿和渭南五个黄土剖面，通过X射线衍射方法对五个剖面末次间冰期以来的粘土矿物做定性及半定量分析，并对其伊利石结晶度进行时空变化分析，在此基础之上，对邵寨剖面2.6 Ma以来黄土-古土壤序列的伊利石结晶度所记录的古环境信息进行初步探讨。本文的研究结果及认识主要有： （1）黄土高原末次间冰期以来黄土-古土壤粘土矿物主要类型为伊利石、绿泥石、高岭石和蒙脱石，在位于南部的永寿和渭南剖面古土壤层中还有少量的蛭石以及微量的层间羟基物矿物。黄土高原5个黄土剖面各地层粘土矿物的组成较为相似，其中主要以伊利石（69%~79.5%）为主，其次是绿泥石（7.3%~16.7%）和高岭石（6.3%~13.2%），蒙脱石（1.2%~7.2%）含量最少。
（2）在粘土矿物的剖面变化和空间变化中，伊利石在古土壤层中的相对含量高于黄土层，且古土壤层中的伊利石呈现从西北向东南增加的趋势，而黄土层中变化较小。绿泥石在黄土层中较多，古土壤中较少，
吉语
绿泥石变化在位置靠南的永寿和渭南剖面中更为显著，这种变化趋势与绿泥石在末次间冰期与全新世时期受湿热气候影响风化形成蛭石/绿泥石混层矿物有关。高岭石相对含量在五个研究剖面均较低，且变化波动小，这也可能与物质来源有一定的关系，可反映原始风尘的基本状况，受气候影响较少。蒙脱石的相对含量最少，但从地层对比来看，黄土层中相对较高而古土壤层较低，这可能与蒙脱石在末次间冰期和全新世时期受到丰沛的降水影响而进行风化有关。 （3）黄土高原末次间冰期以来的伊利石结晶度KI值基本都呈现古土壤层高于下覆黄土层，伊利石结晶度KI值在末次间冰期S1中最高，全新世S0中次之，在末次冰期L1中最低，这种变化趋势在位置靠南的长武、永寿和渭南剖面更为显著；在空间上，古土壤S0与S1中伊利石结晶度KI值呈自西北向东南逐渐增加的变化趋势，而黄土层L1中伊利石结晶度KI值的增加趋势较小，这与磁化率的变化趋势能够较好的对应起来。对比了伊利石结晶度KI值在黄土与古土壤中增加幅度在空间上的变化发现，自西北向东南伊利石结晶度KI值在黄土与古土壤中增加幅度逐渐变大。在排除粒度效应与沉积速率的影响之外，发现，黄土层中伊利石结晶度KI值的变化主要受源区物质的影响所控制，而古土壤中的伊利石结晶度KI值与风化成壤作用密切相关，伊利石结晶度KI值与磁化率良好的相关关系也能较好的说明这个问题。上述特征表明，伊利石结晶度KI值可以作为东亚夏季风变化的一个有效指标。
（4）从邵寨剖面2.6Ma以来的伊利石结晶度的变化记录中可以发现，整体上，伊利石结晶度KI值呈上升趋势，且在冰期-间冰期的旋回上，伊利石结晶度KI值与磁化率对比良好，尤其在0.8Ma以后，这表
明，伊利石结晶度可在短时间尺度冰期-间冰期旋回中很好的指示化学风化作用。对冰期黄土层与间冰期古土壤层伊利石结晶度KI值进行考察后发现，二者指示意义并不一致。冰期黄土层的KI值从0.65Ma以来逐渐上升，指示了黄土高原地区的物源的不断扩大，这主要与青藏高原的阶段性隆升和全球冰量影响下，源区物质经变质成岩作用，并且在各种“高山过程”后，表生物质的增多有关。间冰期古土壤中的伊利石结晶度KI值以0.8Ma为界限，在早更新世时期KI值相对较低，且呈逐渐下降趋势，但在中更新世以后KI值则相对较高，这指示了东亚夏季风在中更新世前后势力强弱的不同。早更新世东亚夏季风较弱，中晚更新世夏季风较强，我们的研究结果也支持海表温度梯度所导致的沃克环流对东亚夏季风的影响这一假说，但不排除受到青藏高原阶段性隆升所导致的间冰期夏季风增强的影响有关。
INBOS
关键词：黄土-古土壤；伊利石结晶度；化学风化；东亚夏季风；物源
V ARIATION OF ILLITE CRYSTALLIZATION AND ITS PALEOENVIRONMENTAL SIGNIFICANCE IN THE LOESS PLATEAU SINCE 2.6 MA
ABSTRACT
The Chinese Loess Plateau has very important scientific significance in the study of paleoclimate. The complete loess-paleosol sequence of the Loess Plateau records abundant paleoclimate information since 2.6Ma, and provides a good research material for the study of Quaternary paleoen
veavironment and paleoclimate change. Clay minerals are an important component of loess and the most active part of the loess material composition. The study of clay mineralogy of loess has been one of the important fields in loess research. In this paper, five loess profiles from Huanxian, Xifeng, Changwu, Yongshou, and Weinan from the northwest to the southeast of the Loess Plateau were selected, and the qualitative and semi-quantitative analysis of clay minerals in the five profiles since the last interglacial period was performed by X-ray diffraction. The illite crystallinity of these five sections was analyzed in space-time. Based on the above studies, this paper conducts a preliminary study of paleoenvironmental information recorded by the illite crystallinity of the loess-paleosol sequence since 2.6 Ma in the Shaozhai section. The main findings and findings of this article are:
(1) The qualitative and semi-quantitative analysis results of the Loess Plateau in China show that the main types of loess-paleosol clay minerals since the last interglacial period of the Loess Plateau are Illite, Chlorite, Kaolinite, and Smectite. There are also a small amount of Vermiculite, mixed layer minerals, and trace Hydroxy-interlayered Minerals (HIM) in the paleosol of the Yongshou and Weinan sections. The composition of clay
minerals in each layer of the five loess-paleosol sections of the Highland Plateau is similar. Among th
em, Illite (69%-79.5%) was the main content, followed by Chlorite (7.3%-16.7%) and Kaolinite (6.3%-13.2%), and Smectite (1.2%-7.2%) was the least.
(2) In the changes of the profile and space of clay minerals, the relative content of illite in the paleosol is higher than that of the loess, and the illite of the ancient soil shows an increasing trend from northwest to southeast, while the change in loess is small. Chlorite is more in the loess, but less in the paleosol. The change in chlorite is more pronounced in the Yongshou and Weinan sections, which are located south. This change trend is related to the chlorite in the last interglacial and Holocene Affected by the hot and humid climate, weathering has formed a vermiculite / chlorite mixed layer mineral. The relative content of Kaolinite is relatively low in the five study sections, and the fluctuations are small. This may also be related to the material source, which can reflect the basic conditions of the original wind and dust, and is less affected by the climate. The relative content of Smectite is the least, but it is high in the loess and the paleosol is low, which may be related to the weathering of Smectite under the influence of abundant precipitation during the last interglacial and Holocene periods.
(3) A study of the Illite Crystallinity KI values of the loess and paleosol in the Loess Plateau of China found that the illite KI values of the Huanxian, Xifeng, Changwu, Yongshou, and Weinan profiles sinc
e the last interglacial period basically show that the paleosol are even Higher than the underlying loess. The Illite Crystallinity KI is the highest in the last interglacial period S1, the second in the Holocene S0, and the lowest in the last glacial L1. This change trend is more pronounced in the Changwu, Yongshou, and Weinan sections that are located south; In terms of space, the Illite Crystallinity KI values in the paleosol S0 and S1 showed a gradual increase trend from northwest to southeast, while the increase trend in the
loess layer L1 was smaller, which can better correspond to the change trend of magnetic susceptibility. We compared the increase amplitude in the KI value of the loess and the paleosol on the profile, and analyzed the spatial changes of it, and found that it gradually increased from northwest to southeast. Excluding the effect of particle size and sedimentation rate, it is found that the change of Illite Crystallinity in the loess is mainly controlled by the influence of the source material, and the Illite Crystallinity in the paleosol is closely related to weathering. The good correlation between Illite Crystallinity KI value and magnetic susceptibility can also better explain this problem. The above characteristics indicate that the Illite Crystallinity can be used as an effective index of the change of the East Asian summer monsoon.
李承晚(4) From the change records of the illite crystallinity since 2.6 Ma in the Shaozhai section, it can be f易熔塞
ound that, overall, the KI value is increasing, and after comparing the KI value with the magnetic susceptibility, it is found that the glacial-interglacial cycle changes They have a good correspondence. This shows that the illite crystallinity can be a good indicator of chemical weathering in the short-time glacial-interglacial cycles. The KI values of illite crystallinity in the glacial loess layers and the interglacial paleosoil layers are not consistent. The KI value of the loess during the ice age gradually increased from 0.65 Ma, indicating the continuous expansion of the material source in the loess plateau, which may be mainly related to the periodic uplift of the qinghai-tibet plateau and global ice, and under its influence, it can lead to the addition of a large number of new surface biomass after various "alpine processes" in the material source area. The KI value of the Illite Crystallinity in the interglacial paleosol was 0.8 Ma as the limit of change. The value of KI was relatively low in the early Pleistocene and it gradually decreased, but the value of KI was relatively high after the Middle Pleistocene. It indicates the difference in the strength of the East Asian summer monsoon before and after the Middle Pleistocene. The East Asian summer monsoon is
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