2017, Vol.37
② 泰山学院旅游学院, 泰安 271000;
③ 中国科学院地质与地球物理研究所, 中国科学院新生代地质与环境重点实验室, 北京 100029;
④ 中国科学院大学, 北京 100049;
⑤ 中国科学院青藏高原地球科学卓越创新中心, 北京 100101)
在六盘山以东的黄土高原地区，晚中新世以来沉积的风尘堆积-古土壤序列是重要的陆相古环境记录，有效地揭示了7~8Ma以来东亚古气候、古环境演化的历史[1~12]。已有研究[1, 5, 13]显示这套风尘堆积物质以粉砂质粘土和粘土质粉砂物质为主，包含有大量的粘土矿物。近些年来，一些学者开展了较为系统的粘土矿物学研究，较好地揭示了粘土矿物的成因[13~19]、演化及其蕴含的古环境信息[20~27]，在黄土古气候学研究方面发挥了重要作用。
伊利石是这套风尘堆积中最主要的粘土矿物类型，其含量在50 %以上[13, 20~22]。关于伊利石的成因，早期对第四纪黄土研究的一些学者认为伊利石是源区或沉积区的成壤环境中形成的[19, 20]。近年来，利用X射线衍射(XRD)和透射电子显微镜技术对伊利石结晶度、多型和形貌等特征的研究发现，无论是黄土还是古土壤的伊利石主要是碎屑成因的[15, 16]，沉积后的成壤作用主要是结晶度的变化[16, 27]，伊利石结晶度可以作为夏季风代用指标[27]。但这些研究主要集中在末次间冰期以来的黄土沉积[15, 16, 27]，时代更老的黄土，特别是三趾马红土的研究相对较少[22, 25]，还需要进一步开展工作。另外，对于伊利石结晶度值的测定，由于样品制备和实验条件的差异，不同实验室之间很难进行比较。为此，IGCP 294 IC工作小组推荐了国际标样和测定条件[28]。这种方法不仅可以有效地解决实验室对比问题，而且确定出成岩带、近变质带和浅变质带的伊利石结晶度数值界限，对揭示伊利石的成因及其环境信息具有重要意义，因而在沉积学和岩石学上得到广泛应用[29~32]。目前，采用国际标样对黄土高原第四纪黄土伊利石结晶度的研究仅有洛川剖面[16]。因此，本文采用X射线衍射(XRD)技术，对西峰赵家川剖面第四纪黄土-古土壤和三趾马红土的粘粒组分(＜2μm)进行测试与分析，主要探讨风尘堆积中伊利石结晶度值(国际标样标定)变化特征及其环境意义。
2 材料与方法 2.1 研究剖面概况西峰赵家川剖面(35°53′N，107°58′E)位于甘肃省东部，地处黄土高原中部。该剖面由完整的第四纪黄土-古土壤序列和晚中新世-上新世三趾马红土两部分组成[2, 5]。西峰风尘堆积剖面总厚度为228.4m，其中，第四纪黄土-古土壤厚度为172.5m，三趾马红土厚度为55.9m。古地磁测年结果显示第四纪黄土与三趾马红土的界线约为2.6Ma B.P.，而三趾马红土的底界年龄约为7.6Ma B.P.[2]。在三趾马红土中，上部18.9m为典型的风成堆积(2.6~3.6Ma B.P.)，中部25.9m经历过地下水频繁作用(3.6~6.2Ma B.P.)，而下部11.1m的风尘物质经历过坡积作用(6.2~7.6Ma B.P.)[5]。西峰第四纪黄土-古土壤旋回层次较为清楚，特别是离石黄土以上部分黄土和古土壤颜色对比最为显著。而三趾马红土整套色调较深，以弱发育的浅红色黄土和发育较强的红棕色古土壤为主，在剖面上部(18.9m处时代对应于约3.6Ma B.P.)地层开始呈现类似第四纪黄土-古土壤序列的旋回特征[5]。
为揭示西峰风尘堆积中伊利石结晶度特征，我们分别在黄土层及相邻的古土壤层中挑选代表性样品进行测试分析(表 1)。其中，第四纪黄土-古土壤样品挑选18个；西峰三趾马红土(深度172.5~228.4) 主要选择在土壤层次较为清楚的上部挑选样品，共选择8个样品。
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表 1 西峰风尘堆积的伊利石结晶度(KI)与伊利石化学指数I(002)/I(001) 值 Table 1 The illite crystallinity (KI) and illite chemistry index I(002)/I(001) of the Xifeng eolian deposits |
粘粒的提取：1) 黄土和古土壤样品分别称取20g和10g，放入烧杯加10ml的10 %的双氧水去除有机质；2) 待静置过夜后根据Stokes静水沉降法提取 < 2μm的粘土悬浮液。将获得的粘粒溶液均匀分成两组，分别用于粘土矿物类型鉴别和伊利石结晶度测试。
第一组样品用于粘土矿物鉴别。每个样品溶液用1mol MgCl2溶液饱和处理，部分样品亦进行了1mol KCl溶液饱和处理。处理后的饱和溶液浓缩后制作成定向薄片，在自然条件下风干上机测量。测试采用的是PANalytical X′ Pert Pro MPD粉末X射线衍射仪，仪器参数设置为：电流和电压分别为40kV、40mA，Cu靶；扫描步长为0.0167°2θ，扫描速度为0.0711°/S，扫描范围为4°~32°2θ。测试是在6种条件下进行的，其中MgCl2饱和薄片分为原片、乙二醇和甘油饱和处理3种，KCl饱和薄片分为常温、400℃和500℃加热处理3种。伊利石的鉴别根据上述几种条件的衍射图谱综合分析获得[33]。伊利石化学指数采用乙二醇饱和处理条件下伊利石0.5nm(002) 与1.0nm(001) 衍射峰面积比[34]。数据处理是在Macintosh系统下，采用MacDiff(4.2.5版本)软件[35]。
第二组样品用于伊利石结晶度测试。将粘粒用1mol MgCl2溶液饱和处理，再制定成定向薄片。伊利石结晶度测试是在北京大学造山带与地壳演化教育部重点实验室的X′ Pert Pro MPD仪器进行。仪器参数设置为：电流和电压分别为40kV、40mA，Cu靶；扫描范围为4.2°~11°2θ，扫描步长为0.017°2θ，扫描时间为20 s。伊利石结晶度参数采用Kübler指数(KI)，即伊利石1.0nm衍射峰的半高宽[36]。较高的KI值指示伊利石结晶度较差，反之结晶度较高。测试结果经过Warr和Rice[29](1994) 建议的国际标样进行校正。
3 结果 3.1 粘土矿物类型图 1是西峰第四纪黄土和三趾马红土代表性粘粒样品的X射线衍射曲线。在各种测试条件下所有样品在1.41nm、1.0nm、0.71nm、0.5nm、0.47nm、0.354nm、0.334nm处均呈现出较强的衍射峰。1.0nm峰在Mg饱和的原样、乙二醇和甘油处理样品，以及在K饱和的原样和各种温度加热过程中位置基本保持不变，0.5nm和0.334nm峰亦显示类似的特征。这说明样品中含有伊利石，其中的1.0nm和0.5nm峰分别为伊利石(001) 和(002) 衍射峰，而0.334nm峰应为伊利石(003) 和石英(101) 的衍射叠加峰。
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图 1 西峰风尘堆积中代表性样品(＜2μm)的X射线衍射曲线 Fig. 1 The typical XRD patterns of < 2μm fraction from the Xifeng eolian deposits |
绿泥石(001) 系列衍射峰的位置依次分别为1.41nm、0.71nm、0.47nm和0.354nm[33]。由图 1可见，与Mg饱和样品衍射曲线对比，1.41nm峰在乙二醇处理后衍射峰位置基本不变，但强度显著降低，而0.71nm、0.47nm和0.354nm峰位置基本不变，这些特征说明样品中含有绿泥石。而0.71nm和0.354nm峰还可能意味着样品中含有高岭石，特别是K饱和样品的0.71nm衍射峰在加热到400℃峰强度减弱，而加热到550℃后衍射峰消失，呈显出高岭石的衍射特征。尽管加热方法不能准确地鉴别出高岭石[33]，但在0.354nm附近可以看到一个低矮的0.358nm衍射峰进一步表明样品中含有高岭石。因此，0.71nm峰为高岭石(001) 和绿泥石(002) 衍射峰，而0.354nm附近的峰则为高岭石(002) 和绿泥石(004) 衍射峰。
经过乙二醇处理后，Mg饱和样品的1.41nm峰除了位置不变、强度降低的绿泥石(001) 外，在1.75nm附近呈现一个新的宽缓的峰，甘油处理后向移到低角度的1.8nm附近则表明了蒙脱石(001) 和少量无序伊蒙混层矿物(I/S，R=0) 的存在[33]。蛭石1.41nm峰在甘油处理后亦可以向低角度移动，但是衍射峰呈现在1.45nm附近[33]。因此，样品中即使含有蛭石，其含量可能较低。
由此可见，西峰第四纪黄土-古土壤和三趾马红土的粘土矿物组合类型是一致的，主要包含有伊利石、高岭石、绿泥石和蒙脱石以及少量的伊蒙混层矿物。上述粘土矿物的鉴定结果与前人对黄土高原第四纪黄土和三趾马红土的研究[13~16, 20~22]相一致。
3.2 伊利石结晶度由表 1可见，在第四纪黄土-古土壤中，伊利石结晶度指数KI值在0.310°~0.638°Δ2θ(均值为0435°Δ2θ)之间，其中黄土在0.310°~0.412°Δ2θ(均值为0.356°Δ2θ)之间，古土壤在0.339°~0.638°Δ2θ(均值为0.514°Δ2θ)之间，古土壤的KI值均显著高于相邻黄土。
在三趾马红土沉积中，伊利石结晶度指数KI值在0.426°~0.794°Δ2θ(均值为0.627°Δ2θ)之间，其中的黄土层在0.426°~0.731°Δ2θ(均值为0.578°Δ2θ)之间，古土壤在0.522°~0.794°Δ2θ(均值为0.677°Δ2θ))之间。除XFRC100样品外，古土壤KI值亦高于相邻黄土样品，但这种差异不如第四纪黄土-古土壤差异显著。总体上来看，三趾马红土的KI值显著高于第四纪黄土和古土壤。
3.3 伊利石化学指数根据Esquevin[34](1969) 的标准，伊利石化学指数I(002)/I(001) 值小于0.15指示的是富Fe-Mg伊利石(黑云母)，为物理风化的结果，而比值大于0.5指示的是富Al伊利石(白云母)，代表了较为强烈的水解作用。由表 1可见，伊利石化学指数I(002)/I(001) 值在第四纪黄土-古土壤中变化范围在0.302~0.431之间，指示富Fe-Mg和富Al之间的伊利石。古土壤的I(002)/I(001) 值(0.327~0.431，均值为0.371) 显著高于相邻黄土(0.302~0.390，均值为0.340)。在上新世三趾马红土中，伊利石化学指数I(002)/I(001) 值变化范围在0.419~0.460之间，属于富Fe-Mg和富Al之间的伊利石，但三趾马红土的I(002)/I(001) 值显著高于与第四纪黄土-古土壤。三趾马红土古土壤的I(002)/I(001) 值(0.433~0.456，均值为0.446) 亦高于其黄土(0.419~0.460，均值为0.434)，但这种差异不如第四纪黄土和古土壤显著。
4 讨论在浅变质岩区，伊利石结晶度是描述成岩作用到变质作用变化的一个定量指标。已有的研究[31]表明伊利石结晶度的变化主要取决于沉积环境的温度、压力、时间和颗粒大小等，其中温度的作用最为重要。因此，伊利石结晶度可以有效地判断成岩带(diagenesis)、近变质带(anchizone)和浅变质带(epizone)环境信息的重要指标[28~32]。国际标样所测伊利石结晶度的近变质带上下界线为：0.25~0.42(°Δ2θ，Cu)[29]。在表生风化条件下，伊利石结晶度又与气候环境具有密切联系。在风化成壤过程中，伊利石的晶体结构发生变化、结晶度降低。随水解作用的增强，逐渐降解为伊利石/蛭石、伊利石/蒙脱石等混层矿物，伊利石结晶度的变化则主要反映了伊利石所含膨胀层的多少[37, 38]。基于上述规律，在海陆沉积记录中，伊利石结晶度的变化特征被广泛用来示踪沉积物物质来源、重建古气候演变特征[37~43]。
由表 1和图 2可见，西峰第四纪黄土样品伊利石结晶度KI值变化范围在0.310°~0.412°Δ2θ之间(均值为0.356°Δ2θ)，均落在近变质带内(0.25°~0.42°Δ2θ)[29]。这种特点表明第四纪黄土样品的伊利石结晶度在沉积后没有发生改变，主要继承了原始风尘特征，与洛川黄土研究结果[16]是相一致的。在海陆碎屑沉积记录研究中，伊利石结晶度指数被广泛用来示踪沉积物的物质来源[37, 39]。但伊利石结晶度指标能否用来示踪黄土的物源尚须考虑，因为落在浅变质带的伊利石结晶度指数只能记录原岩性质。大量研究[13, 44, 45]表明黄土高原风尘物质均来自广阔的物源区，是西北内陆山地的岩石经剥蚀、搬运，多次循环，并在搬运过程中各种矿物成分高度混合的产物。因此，只有对黄土高原黄土及其潜在源区开展细致的伊利石结晶度对比研究才有可能获得可靠的结论。
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图 2 西峰风尘堆积的伊利石结晶度(KI)与伊利石化学指数I(002)/I(001) 对比 Fig. 2 Correlations between the illite crystallinity(KI) and illite chemistry index I(002)/I(001) of the Xifeng eolian deposits |
在第四纪古土壤样品中，伊利石结晶度KI值显著高于相邻的黄土，古土壤平均值为0.514°Δ2θ，而黄土仅为0.356°Δ2θ(表 1)。以前伊利石结晶度的研究[16, 27]主要集中在末次间冰期以来的黄土沉积，本文的研究表明在时代更老的第四纪黄土沉积中，古土壤的伊利石结晶度KI值亦同样显著下覆黄土。而且，在土壤学研究[23, 47]显示的发育程度较高的古土壤S1、S5、S13、S26和S31中，KI指数也与成壤强度具有较好的对应关系，这些古土壤的KI值均高于其他土壤层。伊利石结晶度指标反映的成壤特征，与磁化率、古风化强度指标(FeD/FeT)和野外观察[23, 46]显示的成壤强度可以很好地吻合。伊利石化学风化指数I(002)/I(001) 值是指示沉积物风化作用的有效指标[34, 39]。在第四纪古土壤样品中，该指标亦显示古土壤的I(002)/I(001) 值显著高于黄土(表 1)。从KI值和I(002)/I(001) 值对比图上还可以清楚看出，除S7(XF744) 外古土壤整体上呈现出较高的KI值和I(002)/I(001) 值(表 1和图 2a)。上述特征表明古土壤较高的KI值是由于风化成壤作用所致。以前对黄土高原末次间冰期以来黄土沉积伊利石结晶度的时空变化研究[27]有效地排除了物源、沉积速率和粒度分选效应的影响，认为风化成壤作用是引起伊利石膨胀层增加而结晶度变化的主要原因，并可以有效指示东亚夏季风环流强度变化。因此，本文研究结果表明伊利石结晶度指数KI值亦能有效指示整个第四纪黄土沉积的风化成壤强度，而且对研究东亚夏季风的演化具有重要潜力。
在西峰上新世三趾马红土中，伊利石结晶度指数KI值和化学指数I(002)/I(001) 值整体上高于第四纪黄土-古土壤(表 1，图 2a和2b)。三趾马红土中并没有表现出古土壤KI值高于下伏黄土的特征，这可能与三趾马红土沉积-成壤旋回不如第四纪黄土-古土壤显著有关。但三趾马红土整体上表现出较强的风化成壤特征与野外观察以及土壤学、地球化学和古生物等研究[3, 5, 9, 47]结果是相吻合的。这表明上新世期间我国北方夏季风环流整体上较第四纪时期强盛，与第四纪时期表现显著的冰期和间冰期旋回显著不同[1, 3, 7, 9, 12, 48, 49]。
为了进一步揭示伊利石在化学风化过程中的行为特征，本文对西峰风尘堆积所有样品的伊利石KI值和与化学指数I(002)/I(001) 值进行了相关分析(图 3)。结果显示二者呈现较好的正相关(图 3)。由此可见，伴随着KI指数的增加，富Fe-Mg的伊利石逐渐向富Al伊利石转变，表明在风化成壤过程中，伊利石受风化作用的影响，Fe-Mg离子不断从晶体结构中淋失，引起伊利石发生退变，结晶度变差。该结果与现代土壤学对伊利石研究是相一致的[37]。因此，我们的研究结果也为暖温带气候条件下伊利石风化机理提供了新的证据。
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图 3 西峰风尘堆积样品的伊利石结晶度(KI)值和伊利石化学指数I(002)/I(001) 值的相关关系 Fig. 3 Linear correlation between the illite crystallinity(KI) and illite chemistry index I(002)/I(001) of the Xifeng eolian deposits |
本文对西峰第四纪黄土-古土壤和上新世三趾马红土粘粒样品(＜2μm)进行了X射线衍射测试，利用国际标样对伊利石结晶度指数KI值进行了标定，结合伊利石化学指数I(002)/I(001) 值以及野外观察和其他风化成壤强度指标，对伊利石结晶度指示的古环境意义进行分析。
(1) 西峰第四纪黄土伊利石结晶度指数KI值在0.310°~0.412°Δ2θ之间，落在近变质带，主要继承了原始风尘特征，而第四纪古土壤KI指数均显著高于相邻黄土，伊利石风化指标I(002)/I(001) 值，以及野外观察和成壤强度指标，如磁化率、Fed/Fet值等[23, 46]有较好的一致性，表明伊利石结晶度指数KI值可以有效地指示整个第四纪黄土沉积的风化成壤强度，对研究东亚夏季风演化具有重要的潜力。
(2) 上新世三趾马红土伊利石结晶度指数KI值和化学指数I(002)/I(001) 值整体上高于第四纪黄土沉积，其反映的风化成壤特征与野外观察以及土壤学、地球化学和古生物等研究[3, 5, 9, 47]结果是相吻合的。上述特征表明上新世期间我国北方夏季风环流整体上较第四纪时期强盛，与第四纪时期表现显著的冰期和间冰期旋回显著不同。
(3) 西峰风尘堆积的伊利石结晶度指数KI值和与化学指数I(002)/I(001) 值呈现较好的线性正相关关系，表明黄土在风化成壤过程中，伊利石结晶度的变化是伴随着Fe-Mg离子不断淋失，晶体结构发生改变而引起的。该结果也为暖温带气候条件下排水条件较好的土壤伊利石风化过程提供了新的证据。
致谢 感谢杨美芳老师和审稿专家在论文写作过程中给予的指导；感谢旺罗等老师在实验测试与结果分析给予的帮助。
| 1 |
Ding Z L, Sun J M, Yang S L et al. Preliminary magnetostratigraphy of a thick eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau. Geophysical Research Letters, 1998, 25(8): 1225-1228. DOI:10.1029/98GL00836 |
| 2 |
Sun D H, An Z S, Shaw J et al. Magnetostratigraphy and paleoclimatic significance of Late Tertiary aeolian sequence in the Chinese Loess Plateau. Geophysical Journal International, 1998, 134(1): 207-212. DOI:10.1046/j.1365-246x.1998.00553.x |
| 3 |
顾兆炎, 丁仲礼, 熊尚发等. 灵台红粘土和黄土-古土壤序列的地球化学演化. 第四纪研究, 1999(4): 357-365. Gu Zhaoyan, Ding Zhongli, Xiong Shangfa et al. Seven million geochemical record from Chinese red-clay and loess-paleosol sequence: Weathering and erosion in Northwestern China. Quaternary Sciences, 1999(4): 357-365. |
| 4 |
An Z S, Kutzbach J E, Prell W L et al. Evolution of Asian monsoons and phased uplift of the Himalaya-Tibtan Plateau since Late Miocene times. Nature, 2001, 411: 62-66. DOI:10.1038/35075035 |
| 5 |
Guo Z T, Peng S Z, Hao Q Z et al. Origin of the Miocene-Pliocene red-earth formation at Xifeng in Northern China and implications for paleoenvironments. Palaeogeography, Palaeoclimatology, Palaeoecology, 2001, 170(1-2): 11-26. DOI:10.1016/S0031-0182(01)00235-8 |
| 6 |
Ge Junyi, Dai Ying, Zhang Zhongshi et al. Major changes in East Asian climate in the Mid-Pliocene: Triggered by the uplift of the Tibetan Plateau or global cooling?. Journal of Asian Earth Sciences, 2013, 69(12): 48-59. |
| 7 |
Guo Z T, Peng S Z, Hao Q Z et al. Late Miocene-Pliocene development of Asian aridification as recorded in the red-earth formation in Northern China. Global and Planetary Change, 2004, 41(3-4): 135-145. DOI:10.1016/j.gloplacha.2004.01.002 |
| 8 |
Song Y G, Fang X M, Torii M et al. Late Neogene rock magnetic record of climatic variation from Chinese eolian sediments related to uplift of the Tibetan Plateau. Journal of Asian Earth Sciences, 2007, 30(2): 324-332. DOI:10.1016/j.jseaes.2006.10.004 |
| 9 |
Wang L, Lü H Y, Wu N Q et al. Palynological evidence for Late Miocene-Pliocene vegetation evolution recorded in the Red Clay sequence of the central Chinese Loess Plateau and implication for paleoenvironmental change. Palaeogeography, Palaeoclimatology, Palaeoecology, 2006, 241(1): 118-128. DOI:10.1016/j.palaeo.2006.06.012 |
| 10 |
Hao Q Z, Wang L, Oldfield F et al. Delayed build-up of Arctic ice sheets during 400000-year minima in insolation variability. Nature, 2012, 490: 393-396. DOI:10.1038/nature11493 |
| 11 |
Hao Q Z, Guo Z T. Spatial variations of magnetic susceptibility of Chinese loess for the last 600 kyr: Implications for monsoon evolution. Journal of Geophysical Research, 2005, 110: B12101. DOI:10.1029/2005JB003765 |
| 12 |
Nie J, Song Y, King J W et al. Six million years of magnetic grain-size records reveal that temperature and precipitation were decoupled on the Chinese Loess Plateau during 4.5-2.6Ma. Quaternary Research, 2013, 79(3): 465-470. DOI:10.1016/j.yqres.2013.01.002 |
| 13 |
刘东生等. 黄土与环境. 北京: 科学出版社, 1985, 1-481. Liu Tungsheng et al. Loess and the Environment. Beijing: Science Press, 1985, 1-481. |
| 14 |
郑洪汉, Theng B K G, Whitton J S. 黄土高原黄土-古土壤的矿物组成及其环境意义. 地球化学, 1994, 23(增): 113-123. Zheng Honghan, Theng B K G, Whitton J S. Mineral composition of loess-paleosol in the Loess Plateau of China and its environmental implications. Geochimica, 1994, 23(Suppl): 113-123. |
| 15 |
Ji Junfeng, Chen Jun, Lu Huayu. Origin of illite in the loess from the Luochuan area, Loess Plateau, Central China. Clay Minerals, 1999, 34(4): 525-532. DOI:10.1180/000985599546398 |
| 16 |
季峻峰, 陈骏, 王洪涛. 陕西洛川黄土-古土壤剖面中伊利石结晶度-黄土物质来源和古气候环境的指示. 地质论评, 1997, 43(2): 181-185. Ji Jufeng, Chen Jun, Wang Hongtao. Luochuan loess paleosol sequence, Shaanxi Province: Indicator origin and paleoclimate of loess. Geological Review, 1997, 43(2): 181-185. |
| 17 |
陈莉, 张立飞, 王河锦等. 陕北洛川黄土中两种不同类型的伊利石. 科学通报, 2005, 50(23): 2449-2454. Chen Li, Zhang Lifei, Wang Hejin et al. Two different illites in Luochuan loess, northern Shaanxi Province. Chinese Science Bulletin, 2005, 50(1): 82-87. |
| 18 |
Jeong G Y, Hillier S, Kemp R A. Changes in mineralogy of loess-paleosol sections across the Chinese Loess Plateau. Quaternary Research, 2011, 75(1): 245-255. DOI:10.1016/j.yqres.2010.09.001 |
| 19 |
Bronger A, Heinkele T. Mineralogical and clay mineralogical aspects of loess research. Quaternary International, 1990, 7/8: 37-51. DOI:10.1016/1040-6182(90)90037-5 |
| 20 |
Kalm V E, Rutter N E, Rokosh C D. Clay minerals and their paleoenvironmental interpretation in the Baoji loess section, southern Loess Plateau, China. Catena, 1996, 27(1): 49-61. DOI:10.1016/0341-8162(96)00008-2 |
| 21 |
Gylesjö S, Arnold E. Clay mineralogy of a red clay-loess sequence from Lingtai, the Chinese Loess Plateau. Global and Planetary Change, 2006, 51(3-4): 181-194. DOI:10.1016/j.gloplacha.2006.03.002 |
| 22 |
彭淑贞, 郭正堂. 风成三趾马红土与第四纪黄土的粘土矿物组成异同及其环境意义. 第四纪研究, 2007, 27(2): 277-285. Peng Shuzhen, Guo Zhengtang. Clay mineral composition of the Tertiary Red Clay and the Quaternary loess-paleosols as well as its environmental implication. Quaternary Sciences, 2007, 27(2): 277-285. |
| 23 |
Guo Z T. Succession de Paleosols et Des Lss du Center Ouest de La Chine: Approche Micro-morphologique. Paris-Grenoble: ANRT, 1990, 1-266. |
| 24 |
Zhao Liang, Ji Junfeng, Chen Jun et al. Variations of illite/chlorite ratio in Chinese loess sections during the last glacial and interglacial cycle: Implications for monsoon reconstruction. Geophysical Research Letters, 2005, 32: L20718. DOI:10.1029/2005GL024145 |
| 25 |
Han J, Fyfe W S, Gu Z. Assessment of the palaeoclimate during 3.0-2.6Ma registered by transition of Red Clay to loess-palaeosol sequence in central North China. Palaeogeography, Palaeoclimatology, Palaeoecology, 2002, 185(3-4): 355-368. DOI:10.1016/S0031-0182(02)00382-6 |
| 26 |
Peng Shuzhen, Hao Qingzhen, Frank Oldfield et al. Release of iron from chlorite weathering and links to magnetic enhancement in Chinese loess deposits. Catena, 2014, 117(2): 43-49. |
| 27 |
贾伟丽, 彭淑贞, 张伟等. 末次间冰期以来黄土中伊利石结晶度的变化与古环境. 第四纪研究, 2014, 34(3): 553-559. Jia Weili, Peng Shuzhen, Zhang Wei et al. Variations of illite crystallinity in the Chinese loess deposits since the last inerglacial periods and paleoclimatic significance. Quaternary Sciences, 2014, 34(3): 553-559. |
| 28 |
Kish H J. Illite crystallinity: Recommendation on sample preparation, X-ray diffraction settings and interlaboratory samples. Journal of Metamorphic Geology, 1991, 9: 141-152. DOI:10.1111/jmg.1991.9.issue-2 |
| 29 |
Warr L N, Rice A H N. Interlaboratory standardization and calibration of clay mineral crystallinity and crystallite size data. Journal of Metamorphic Geology, 1994, 12: 141-152. DOI:10.1111/jmg.1994.12.issue-2 |
| 30 |
Weaver C E ed. Shale Slate Metamorphism in the Southern Applachians. Elevier: Amsterdam, 1984. |
| 31 |
Frey M. Very low-grade metamorphism of clastic sedimentary rocks. In: Frey M ed. Low Temperature Metamorphism. Glasgow: Blackie & Son Ltd, 1987. 9~58
|
| 32 |
王河锦, 周健, 徐庆生等. 湘中北黄土店-仙溪中新元古界-下古生界的甚低级变质作用. 中国科学(D辑), 2003, 34(9): 742-750. Wang Hejin, Zhou Jian, Xu Qingsheng et al. Very low-grade metamorphism of the Meso-Neoproterozoic and the Lower Paleozoic along the profile from Huangtudian to Xianxi in the central-northern part of Hunan Province, China. Science in China(Series D), 2003, 34(3): 672-682. |
| 33 |
Moore D M, Reynolds R C. X-ray Diffraction and the Identification and Analysis of Clay Minerals. New York: Oxford University Press, 1989. |
| 34 |
Esquevin J. Influence de la composition chimique des illites surcristallinite. Bulletin de Centre Recherches, Rau-SNPA, 1969, 3(1): 147-153. |
| 35 |
Petschick R. MacDiff 4.2.5(Online). Available: [http://www.ccp14.ac.uk/ccp/web-mirrors/krumm/macsoftware/macdiff/MacDiff.htmlPetschick, 2000. Download 01-12-2009]
|
| 36 |
Kübler B. Les argiles, indicateurs de métamorphisme. Revue Institute Francais Pe'trole, 1964, 19(10): 1093-1112. |
| 37 |
Chamley H. Clay Sedimentology. Berlin: Springer, 1989, 487-558.
|
| 38 |
Meunier A. Clay. Berlin: Springer, 2005, 273-291.
|
| 39 |
Liu Z F, Colin C, Li X J et al. Clay mineral distribution in surface sediments of the northeastern South China Sea and surrounding fluvial drainage basins: Source and transport. Marine Geology, 2010, 277(1-4): 48-60. DOI:10.1016/j.margeo.2010.08.010 |
| 40 |
宋友桂. 沉积矿物学在古环境恢复中的应用进展. 东华理工大学学报(自然科学版), 2009, 32(4): 313-323. Song Yougui. Sedimentary mineralogy and its application for paleoenvironmental reconstruction. Journal of East China of Technology(Natural Science), 2009, 32(4): 313-323. |
| 41 |
胡彬, 张春霞, 郭正堂. 石膏岩中粘土矿物提取的一种新方法及在古气候重建中的应用. 第四纪研究, 2016, 36(4): 926-934. Hu Bin, Zhang Chunxia, Guo Zhengtang. A new method of clay mineral extraction from gypsum layer and its application in paleoclimate reconstruction. Quaternary Sciences, 2016, 36(4): 926-934. |
| 42 |
周世文, 刘志飞, 赵玉龙等. 北部湾东北部2000年以来高分辨率粘土矿物记录及古环境意义. 第四纪研究, 2014, 34(3): 600-610. Zhou Shiwen, Liu Zhifei, Zhao Yulong et al. A high-resolution clay mineralogical record and its paleoenvironmental significance in the northeastern Gulf of Tonkin over the past 2000 years. Quaternary Sciences, 2014, 34(3): 600-610. |
| 43 |
王春虹, 李明慧, 方小敏等. 柴达木盆地西部SG-1钻孔中伊蒙混层结构特征及环境意义. 第四纪研究, 2016, 36(4): 917-925. Wang Chunhong, Li Minghui, Fang Xiaomin et al. Structural characteristic of mixed layer illite/smectite clay minerals of the SG-1 core in the western Qaidam Basin and its environmental significance. Quaternary Sciences, 2016, 36(4): 917-925. |
| 44 |
Jahn B M, Gallet S, Han J M. Geochemistry of the Xining, Xifeng and Jixian sections, Loess Plateau of China: Eolian dust provenance and paleosol evolution during the last 140ka. Chemical Geology, 2001, 178(1): 71-94. |
| 45 |
Liang M Y, Guo Z T, Kahmann A et al. Geochemical characteristics of the Miocene eolian deposits in China: Their provenance and climate implications. Geochemistry, Geophysics, Geosystems, 2009, 10. |
| 46 |
Guo Z T, Biscaye P, Wei L Y et al. Summer monsoon variations over the last 1.2Ma from the weathering of loess-soil sequences in China. Geophysical Research Letters, 2000, 27(12): 1751-1754. DOI:10.1029/1999GL008419 |
| 47 |
Wu N Q, Pei Y P, Lu H Y et al. Marked ecological shifts during 6.2-2.4Ma revealed by a terrestrial molluscan record from the Chinese Red Clay formation and implication for palaeoclimatic evolution. Palaeogeography, Palaeoclimatology, Palaeoecology, 2002, 233(3-4): 287-299. |
| 48 |
葛俊逸, 郭正堂, 郝青振. 特征时期黄土高原风化成壤强度的空间特征与气候梯度. 第四纪研究, 2006, 26(6): 962-968. Ge Junyi, Guo Zhengtang, Hao Qingzhen. Spatial variations of weathering intensity of the Loess Plateau and the climate gradients within characteristic timeslices. Quaternary Sciences, 2006, 26(6): 962-968. |
| 49 |
Guo Z T, Zhou X, Wu H B. Glacial-interglacial water cycle, global monsoon and atmospheric methane changes. Climate Dynamics, 2012. DOI:10.1007/s00382-011-1147-5 |
, Zhu Lidong①
, Peng Shuzhen②,③, Lin Haiyi①, Zhang Wei②, Ding Min②, Hao Qingzhen③,④, Guo Zhengtang③,④,⑤
② School of Tourism, Taishan University, Tai'an 271000;
③ Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
④ University of Chinese Academy of Sciences, Beijing 100049;
⑤ Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101)
Abstract
Illite crystallinity of loess deposits is a useful proxy for the East Asian summer monsoon in the Chinese Loess Plateau. However, a few studies have only mainly centered on the record since the last interglacial periods. Examination of the paleoenvironmental information of illite crystallinity for the eolian dust deposits over a longer time span would significantly improve our understanding of the East Asian monsoon climate. In this paper, illite crystallinity and illite chemical index were investigated on the < 2μm of samples from Quaternary loess-palesol and Hipparion Red Clay sequences. The Xifeng section(35°53'N, 107°58'E), the typical eolian section in the eastern Loess Plateau and is about 228.4m in thickness is selected for this study. The section can be divided into two portions:the upper Quaternary loess-soil sequence(172.5m in thickness)and the lower Late Miocene-Pliocene red clay(55.9m in thickness). Magnetostratigraphic measurements have dated the boundary between the Quaternary loess-soil sequence and the red clay at around 2.6Ma B.P., and the bottom age of the red clay sequence was dated at around 7.6Ma, B.P. Previous studies show that the red clay sequence consists of three parts. The upper part(2.6~3.6Ma B.P.)is an eolian formation, similar to Quaternary loess-soil sequence; the middle part(6.2~3.6Ma B.P.)was significantly affected by groundwater oscillations; and the lower part(6.2~7.6Ma B.P.)is water-reworked deposits related to alluvial and slope process. 18 and 8 representative samples were selected from the Quaternary loess-soil sequence and the upper part of red clay (2.6~3.6Ma, B.P.), respectively. In this study, all samples for clay minerals analysis were disaggregated in deionized water and treated with 10% H2O2 and 1mol/L HAC to remove organic materials and carbonate, respectively. The particles less than 2μm were then subject to pipetting based on Stokes' law. Oriented specimens were prepared on glass slides by the pipette method at room temperature. Clay minerals were measured by X-ray diffraction(XRD)on oriented mounts of clay-sized particles( < 2μm). Illite crystallinity(Kübler index, KI)was obtained from the full width half maximum of the 1.0nm peak(Δ°2θ). Lower values indicate higher crystallinity, characteristic of weak hydrolysis under dry and cold climate conditions in continental environments. Illite chemistry index I (002)/I (001) was determined by the ratio of the Illite (002) and Illite (001) peak areas. Ratios lower than 0.5 are found in Fe-Mg-rich illites, which are characteristics for physical erosion; while ratios higher than 0.5 are found in Al-rich illites, which are formed by strong hydrolysis. Results indicate that in the samples from Quaternary loess layers the KI values range from 0.310°~0.412°Δ2θ(mean of 0.356°Δ2θ), mainly inherited from the characteristics of original dust. In contrast, the KI values(0.339°~0.638°Δ2θ, with a mean of 0.514°Δ2θ)for samples from the Quaternary palesol units are significantly higher than the Quaternary loess layers(0.310°~0.412°Δ2θ, with a mean of 0.356°Δ2θ). The changes in KI values in the Quaternary palesols are highly relevant to I (002)/I (001) values, which shows that KI can effectively recorded the strength of soil weathering in the whole Quaternary loess deposits and is a potential proxy for the changes in the intensity of East Asian Summer monsoon. The KI values(0.426°~0.794°Δ2θ, with a mean of 0.627°Δ2θ)in Pliocene Hipparion Red Clay is rather higher than in the Quaternary loess deposits(0.310°~0.638°Δ2θ, with a mean of 0.435°Δ2θ), indicating that summer monsoon in Pliocene is stronger than Quaternary in Northern China. Furthermore, the clear linear positive correlation between the KI and the I (002)/I (001) indicates that the changes of illite crystallinity may caused by the by Fe2+ and Mg2+ constantly leaching in soil weathering, which altered the illite crystal structure. The results also provide new evidence for the weathering sequence of illite in well-drained soils.