秦岭南侧郧县弥陀寺剖面黄土地层序列及其风化成壤特征研究
发布时间：2018-09-03 06:23
【摘要】：黄土作为记录过去环境变化的重要信息载体,一直被用于全球变化中古气候的演变研究,尤其是对末次盛冰期以来的气候记录更为关注。汉江上游地区地处秦岭南侧,为北亚热带北缘,是气候环境变化的敏感区域。区内普遍分布着厚层风成黄土覆盖物,但对于该黄土沉积的研究很有限。本文选取郧县段汉江左岸弥陀寺黄土剖面(MTS)为研究对象,对沉积物样品的理化性质(粒度、化学元素组成等)、微结构形态(石英颗粒形态、集粒形态、孔隙、粗颗粒、土壤生成物)等进行了测试,用OSL方法获得地层年龄,以这些实验数据为基础,对秦岭南侧汉江上游黄土的地层、组成结构、风化成壤特征以及对气候变化的响应等问题进行分析研究,获得了以下主要结论：(1)汉江上游一级河流阶地上黄土的地层序列自上而下依次为：表土层(TS)→全新世黄土(L0)→古土壤(S0)→过渡层黄土(Lt)→马兰黄土(L1)→黄土和砂交互层(JH)→河流相沉积(AL-1),结合OSL测年数据,建立起汉江上游一级阶地上黄土序列的年代框架,黄土和砂交互层底部年龄大约为55000 aB.P.,顶界年龄约为25000 aB.P.,马兰黄土L1的顶界年龄为11500aB.P.,古土壤S0底界年龄则为8500 aB.P.,顶界年龄为3100 aB.P.(2)MTS剖面黄土粒度组成、化学元素、微结构形态等特征显示汉江上游一级阶地交互层以上稳定沉积物质为风尘沉积,交互黄土层与上部马兰黄土组成相近,为风尘堆积,而砂层与下部河流相组成类似,为水成成因。各地层的沉积特征又存在差异,具体体现在：①各层粒度组成以粉砂为主,古土壤S0层相对于黄土层(L1/Lt/L0)粒级更细,各层平均粒径大小排序为S0TSLtL0L1JH。②化学元素的变异系数均很小(除JH层外),体现同一区域黄土中成分一致且混合性强,易迁移元素(Ca、Sr等)与稳定元素(Al.Cu等)在剖面垂直方向上呈相反镜像变化,易迁移元素在古土壤S0层中含量呈现低值,在黄土层(L1/L0)中含量则高,稳定性元素则反之。③微结构形态中石英颗粒以次棱-次圆为主,石英颗粒表面多为碟形坑、麻坑等风成机械标志,而交互砂中出现贝状断口、三角痕等水成标志；从S0→Lt→L0→L1次棱状-棱状石英颗粒增多,磨圆度逐渐变差,古土壤S0中石英颗粒的机械标志上叠加的硅质沉淀、SiO2溶蚀刻蚀等化学成因特征明显增多；剖面骨架颗粒之间的微结构连接方式从TS→L0→S0→Lt→L1→JH-t→JH-s依次为絮凝胶结→微镶嵌半胶结→凝块胶结→镶嵌半胶结→支架微胶结→支架微胶结→单颗粒接触结构；孔隙形态则多以复合堆叠状态为主,多囊状、气泡状孔隙,孔隙率排序为S0LtL0L1；从S0→Lt→L0→L1粗颗粒依次增多,圆度变小,C/F10μm依次变大；弥陀寺剖面中土壤生成物在So层出现居多,以次生黏土铁锰侵染和铁锰凝团为主,未见次生方解石。④MTS剖面在古土壤层150～190cm处色度、黏粒、100μm的中粗砂、化学元素等数据均显示有异常变化值,与上下层古土壤层理化性质有一定差异,微结构形态也显示其石英颗粒磨圆度变差,集粒间孔隙增多,之间的胶结状态也变差,粗颗粒明显增多,暗示该时段气候发生变异,导致沉积物质性状有较大变化。(3)秦岭南侧汉江上游地区黄土处于由低等向中等化学风化过渡阶段,Ca、Na淋失严重,钾长石变化不大,风化程度古土壤So过渡性黄土Lt全新世黄土L0马兰黄土L1,具体表现为：①磁化率与全铁、游离铁、晶质铁等铁形态指标变化均有良好的对应关系,其值均在S0LtL0L1,反映古土壤S。风化最强。②化学蚀变指数CIA和CPA均指示MTS黄土剖面整体处于由低等向中等化学风化过渡阶段,A-CN-K三角图显示弥陀寺黄土经历了以斜长石风化为主的风化过程,次生风化黏土矿物以蒙脱石、伊利石为主,尚未达到以高岭石、水铝石为主产物的强风化阶段。③K/Na、Fe/Mg、Rb、Sr三个化学风化参数的值均呈TSS0 LtL0L1,而硅铝系数Sa变化与上面四个指数相反,四者共同指示古土壤层风化要强于黄土层。此外,磁化率、铁形态、CIA、K、Na、Fe、MgRb、Sr及硅铝系数等风化指标在剖面150～190cm处有变异值,指示该段古土壤发育出现弱风化,反映出该时期古气候有异常。(4)郧县汉江段MTS黄土的风化成壤特征有效地反演了汉江上游一级阶地在大约25000 aB.P.稳定抬升以后古气候演变的4个阶段：末次冰期冰盛期(25000～11500aB.P.),全新世早期(11500～8500aB.P.),全新世中期(8500～3100aB.P.),全新世晚期(3100aB.P～至今),气候状况依次为冷干→凉干→暖湿→冷干,此外全新世大暖期期间存在多次气候波动,MTS剖面古土壤中150-190cm的弱风化层就是对全新世中期5.5ka冷事件的一次直接记录。(5)对比秦岭南北黄土的地层序列、粒度特征、化学元素以及风化程度,得出秦岭南北两侧黄土的几点异同：①两地区的剖面地层序列一致,自上向下都为TS→L0→S0→Lt→L1,区别在于汉江上游马兰黄土L1下部为黄土和砂的交互层以及河流相沉积,而关中地区马兰黄土L1下部仍为黄土,两剖面的年代框架也一致,L1顶界和S0发育年龄相同。②两地粒度均以粉砂尤其是粗粉砂为主,且二者土壤质地均属粉质黏土亚黏土；汉江上游古土壤S0层颗粒要比关中地区黄土古土壤都要细,而马兰黄土中颗粒要粗些,这与汉江上游黄土混入近源物质有关。③两地黄土中的化学元素变异系数都比较小,组成一致且均一,秦岭南侧汉江上游黄土中活动性元素(Ca、Mg、Sr等)要比北侧关中地区黄土的有所减少,稳定元素(Ca、Mg、Sr等)相对增多,反映出秦岭南侧黄土中不稳定成分淋失较多,经历风化淋溶作用更强。④两地区黄土中磁化率、化学蚀变指数(CIA)、元素比值(K/Na、 Ca/Mg、Rb/Sr)、淋溶系数以及残积指数等相关风化指标均显示在古土壤层风化要强于黄土层,说明秦岭南北两侧黄土经历了相似的沉积发育过程,但汉江上游地区黄土中风化指数更高,风化程度更强,说明秦岭南侧古气候更为暖湿。
[Abstract]:Loess, as an important information carrier for recording past environmental changes, has been used to study the evolution of paleoclimate in global change, especially since the last glacial maximum. In this paper, the physicochemical properties (grain size, chemical element composition, etc.) and microstructure (quartz grain shape, aggregate shape, pore, coarse grain, soil product) of the sediment samples from the Mituosi loess section (MTS) on the left bank of the Hanjiang River in Yunxian were studied. Based on these experimental data, the stratigraphic age of the Loess in the upper reaches of the Hanjiang River on the southern side of the Qinling Mountains is obtained by OSL. The main conclusions are as follows: (1) The stratigraphic sequence of the Loess in the upper reaches of the Hanjiang River is from top to bottom. The following sequence is: surface soil (TS) Holocene loess (L0) paleosol (S0) transitional loess (Lt) Malan loess (L1) loess and sand interaction layer (JH) fluvial facies deposition (AL-1). Combined with OSL dating data, the chronological framework of loess sequence on the first terrace of the upper Hanjiang River is established. The age of loess and sand interaction layer is about 55 000 aB.P. The top age is about 25 000 aB.P., the top age of Malan Loess L1 is 11500 aB.P., the bottom age of Paleosol S0 is 8500 aB.P., and the top age is 3100 aB.P. (2) The characteristics of loess grain size, chemical elements, microstructure and morphology in MTS section show that the stable sediments above the first terrace in the upper reaches of Hanjiang River are aeolian-dusty sediments and interactive loess. The sedimentary characteristics of each layer are different. The grain size composition of each layer is mainly silt, and the grain size of Paleosol S0 layer is finer than that of loess layer (L1/Lt/L0). The average grain size of each layer is in the order of S0TSLtL. The variation coefficients of chemical elements (except JH layer) are very small, indicating that the composition of loess in the same region is consistent and strong mixing, and the content of migrable elements (Ca, Sr, etc.) and stable elements (Al. Cu, etc.) in the vertical direction of the section is opposite mirror change. The content of migrable elements in the S0 layer of Paleosol is low, but in the L1/L0 layer is high. In the microstructure, the quartz grains are mainly sub-edge-sub-circle, and the surface of quartz grains is mostly dish-shaped pits, pits and other wind-forming mechanical indicators, while in the interactive sand, shellfish-like fracture and triangular marks appear; from S0 Lt L0 L1 prismatic-prismatic quartz grains increase, the roundness gradually deteriorates, and the stones in the paleosol S0 appear hydrological indicators. The chemical origin of the siliceous precipitation and SiO2 etching on the mechanical markers of the British particles increased obviously, and the microstructure of the cross-section skeleton particles was in turn from TS L0 S0 Lt L1 JH-t JH-s to flocculation micro-mosaic semi-cementation mosaic semi-cementation scaffold micro-cementation scaffold micro-cementation scaffold micro-cementation scaffold micro-cementation The pore morphology is mainly composed of composite stacking, multi-cystic, bubble-like pores, and the porosity ranks as S0LtL0L1; coarse particles from S0 Lt L0 L1 increase in turn, roundness decreases, and C/F10 micron increases in turn; soil products in the Mituosi section appear mostly in the SO layer, with secondary clay Fe-Mn infection and Fe-Mn coagulation. Fourthly, MTS profiles showed abnormal variations in chroma, clay, 100-micron medium-coarse sand, chemical elements and other data at 150-190 cm of paleosols, which were different from the physical and chemical properties of upper and lower layers of paleosols. Microstructure and morphology also showed that the roundness of quartz particles became worse, the porosity between aggregates increased, and the cementation between them. (3) Loess in the upper reaches of the Hanjiang River in the south of Qinling Mountains is in the transitional stage from low to moderate chemical weathering, Ca and Na leaching is serious, K feldspar has little change, weathering degree of Paleosol so transitional loess Lt Holocene L0. Malan Loess L1, the specific performance is: 1) magnetic susceptibility and total iron, free iron, crystalline iron and other iron morphological indicators have a good corresponding relationship, the values are in S 0LtL0L1, reflecting the strongest S. weathering paleosol. 2 Chemical alteration index CI A and CPA indicate that the overall MTS loess profile is in the transition from low to moderate chemical weathering stage, A-CN-K triangle. The map shows that the main weathering process of Miduosi loess is plagioclase weathering. The secondary weathering clay minerals are mainly montmorillonite and illite, but have not reached the stage of strong weathering with kaolinite and diaspore as the main products. In addition, magnetic susceptibility, iron morphology, CIA, K, Na, Fe, MgRb, Sr and Si-Al coefficients have variation values at 150-190cm of the section, indicating that Paleosols in this section developed weakly weathered, reflecting the abnormal paleoclimate during this period. The paleoclimatic evolution of the first-order terrace in the upper reaches of the Hanjiang River has been effectively inverted in four stages: the last glacial glacial maximum (25 000-11 500 aB.P.), the early Holocene (11500-8500 aB.P.), the middle Holocene (8500-3100 aB.P.), and the late Holocene (3100 aB.P-present). The weak weathering layer of 150-190 cm in the MTS section is a direct record of 5.5 Ka cold event in the middle Holocene. (5) By comparing the stratigraphic sequence, grain size characteristics, chemical elements and weathering degree of the Loess in the north and south of Qinling Mountains, the Loess in the north and south of Qinling Mountains can be obtained. Some similarities and differences are as follows: 1) The stratigraphic sequence of the two sections is the same, and the upper and lower parts of the Malan Loess L1 in the upper reaches of the Hanjiang River are the interbeds of loess and sand and fluvial deposits, while the lower part of Malan Loess L1 in the Guanzhong area is still the loess, and the chronological framework of the two sections is the same, the top boundary of L1 and the development age facies of S0 are the same. Similarly, the grain sizes of the two places are mainly silt, especially coarse silt, and both of them belong to silty clay subclay. The grain size of S_0 layer of Paleosol in the upper reaches of Hanjiang River is finer than that in the Loess of Guanzhong area, while the grain size in Malan loess is thicker, which is related to the mixing of loess in the upper reaches of Hanjiang River with near-source materials. The variation coefficients are relatively small and the compositions are uniform. The active elements (Ca, Mg, Sr, etc.) in the Loess of the upper reaches of the Hanjiang River in the south of Qinling Mountains are less than those in the north of Guanzhong Mountains, and the stable elements (Ca, Mg, Sr, etc.) are relatively increased, reflecting that the Loess in the south of Qinling Mountains leached more unstable elements and experienced stronger weathering and leaching. The weathering indexes such as medium susceptibility, chemical alteration index (CIA), element ratio (K/Na, Ca/Mg, Rb/Sr), leaching coefficient and residual index showed that the weathering of Paleosol layer was stronger than that of Loess layer, indicating that the Loess in the north and south sides of Qinling Mountains experienced similar sedimentary development process, but the weathering index in the upper reaches of Han River was higher and the weathering degree was higher. Stronger, indicating that the southern side of Qinling Mountains is more warm and humid.
【学位授予单位】：陕西师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S151;P539
[Abstract]:Loess, as an important information carrier for recording past environmental changes, has been used to study the evolution of paleoclimate in global change, especially since the last glacial maximum. In this paper, the physicochemical properties (grain size, chemical element composition, etc.) and microstructure (quartz grain shape, aggregate shape, pore, coarse grain, soil product) of the sediment samples from the Mituosi loess section (MTS) on the left bank of the Hanjiang River in Yunxian were studied. Based on these experimental data, the stratigraphic age of the Loess in the upper reaches of the Hanjiang River on the southern side of the Qinling Mountains is obtained by OSL. The main conclusions are as follows: (1) The stratigraphic sequence of the Loess in the upper reaches of the Hanjiang River is from top to bottom. The following sequence is: surface soil (TS) Holocene loess (L0) paleosol (S0) transitional loess (Lt) Malan loess (L1) loess and sand interaction layer (JH) fluvial facies deposition (AL-1). Combined with OSL dating data, the chronological framework of loess sequence on the first terrace of the upper Hanjiang River is established. The age of loess and sand interaction layer is about 55 000 aB.P. The top age is about 25 000 aB.P., the top age of Malan Loess L1 is 11500 aB.P., the bottom age of Paleosol S0 is 8500 aB.P., and the top age is 3100 aB.P. (2) The characteristics of loess grain size, chemical elements, microstructure and morphology in MTS section show that the stable sediments above the first terrace in the upper reaches of Hanjiang River are aeolian-dusty sediments and interactive loess. The sedimentary characteristics of each layer are different. The grain size composition of each layer is mainly silt, and the grain size of Paleosol S0 layer is finer than that of loess layer (L1/Lt/L0). The average grain size of each layer is in the order of S0TSLtL. The variation coefficients of chemical elements (except JH layer) are very small, indicating that the composition of loess in the same region is consistent and strong mixing, and the content of migrable elements (Ca, Sr, etc.) and stable elements (Al. Cu, etc.) in the vertical direction of the section is opposite mirror change. The content of migrable elements in the S0 layer of Paleosol is low, but in the L1/L0 layer is high. In the microstructure, the quartz grains are mainly sub-edge-sub-circle, and the surface of quartz grains is mostly dish-shaped pits, pits and other wind-forming mechanical indicators, while in the interactive sand, shellfish-like fracture and triangular marks appear; from S0 Lt L0 L1 prismatic-prismatic quartz grains increase, the roundness gradually deteriorates, and the stones in the paleosol S0 appear hydrological indicators. The chemical origin of the siliceous precipitation and SiO2 etching on the mechanical markers of the British particles increased obviously, and the microstructure of the cross-section skeleton particles was in turn from TS L0 S0 Lt L1 JH-t JH-s to flocculation micro-mosaic semi-cementation mosaic semi-cementation scaffold micro-cementation scaffold micro-cementation scaffold micro-cementation scaffold micro-cementation The pore morphology is mainly composed of composite stacking, multi-cystic, bubble-like pores, and the porosity ranks as S0LtL0L1; coarse particles from S0 Lt L0 L1 increase in turn, roundness decreases, and C/F10 micron increases in turn; soil products in the Mituosi section appear mostly in the SO layer, with secondary clay Fe-Mn infection and Fe-Mn coagulation. Fourthly, MTS profiles showed abnormal variations in chroma, clay, 100-micron medium-coarse sand, chemical elements and other data at 150-190 cm of paleosols, which were different from the physical and chemical properties of upper and lower layers of paleosols. Microstructure and morphology also showed that the roundness of quartz particles became worse, the porosity between aggregates increased, and the cementation between them. (3) Loess in the upper reaches of the Hanjiang River in the south of Qinling Mountains is in the transitional stage from low to moderate chemical weathering, Ca and Na leaching is serious, K feldspar has little change, weathering degree of Paleosol so transitional loess Lt Holocene L0. Malan Loess L1, the specific performance is: 1) magnetic susceptibility and total iron, free iron, crystalline iron and other iron morphological indicators have a good corresponding relationship, the values are in S 0LtL0L1, reflecting the strongest S. weathering paleosol. 2 Chemical alteration index CI A and CPA indicate that the overall MTS loess profile is in the transition from low to moderate chemical weathering stage, A-CN-K triangle. The map shows that the main weathering process of Miduosi loess is plagioclase weathering. The secondary weathering clay minerals are mainly montmorillonite and illite, but have not reached the stage of strong weathering with kaolinite and diaspore as the main products. In addition, magnetic susceptibility, iron morphology, CIA, K, Na, Fe, MgRb, Sr and Si-Al coefficients have variation values at 150-190cm of the section, indicating that Paleosols in this section developed weakly weathered, reflecting the abnormal paleoclimate during this period. The paleoclimatic evolution of the first-order terrace in the upper reaches of the Hanjiang River has been effectively inverted in four stages: the last glacial glacial maximum (25 000-11 500 aB.P.), the early Holocene (11500-8500 aB.P.), the middle Holocene (8500-3100 aB.P.), and the late Holocene (3100 aB.P-present). The weak weathering layer of 150-190 cm in the MTS section is a direct record of 5.5 Ka cold event in the middle Holocene. (5) By comparing the stratigraphic sequence, grain size characteristics, chemical elements and weathering degree of the Loess in the north and south of Qinling Mountains, the Loess in the north and south of Qinling Mountains can be obtained. Some similarities and differences are as follows: 1) The stratigraphic sequence of the two sections is the same, and the upper and lower parts of the Malan Loess L1 in the upper reaches of the Hanjiang River are the interbeds of loess and sand and fluvial deposits, while the lower part of Malan Loess L1 in the Guanzhong area is still the loess, and the chronological framework of the two sections is the same, the top boundary of L1 and the development age facies of S0 are the same. Similarly, the grain sizes of the two places are mainly silt, especially coarse silt, and both of them belong to silty clay subclay. The grain size of S_0 layer of Paleosol in the upper reaches of Hanjiang River is finer than that in the Loess of Guanzhong area, while the grain size in Malan loess is thicker, which is related to the mixing of loess in the upper reaches of Hanjiang River with near-source materials. The variation coefficients are relatively small and the compositions are uniform. The active elements (Ca, Mg, Sr, etc.) in the Loess of the upper reaches of the Hanjiang River in the south of Qinling Mountains are less than those in the north of Guanzhong Mountains, and the stable elements (Ca, Mg, Sr, etc.) are relatively increased, reflecting that the Loess in the south of Qinling Mountains leached more unstable elements and experienced stronger weathering and leaching. The weathering indexes such as medium susceptibility, chemical alteration index (CIA), element ratio (K/Na, Ca/Mg, Rb/Sr), leaching coefficient and residual index showed that the weathering of Paleosol layer was stronger than that of Loess layer, indicating that the Loess in the north and south sides of Qinling Mountains experienced similar sedimentary development process, but the weathering index in the upper reaches of Han River was higher and the weathering degree was higher. Stronger, indicating that the southern side of Qinling Mountains is more warm and humid.
【学位授予单位】：陕西师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S151;P539
【参考文献】
相关期刊论文 前7条
1 雷祥义;秦岭黄土的粒度分析及其成因初步探讨[J];地质学报;1998年02期
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