【作者】 熊平生；

【导师】 袁道先；

【作者基本信息】 西南大学 ， 自然地理学， 2012， 博士

【摘要】 我国南方红土分布范围大致北起长江南岸,南到南海诸岛,东至台湾列岛,西抵川贵高原,集中分布在江西、湖南、浙江、福建、安徽、湖北、广东、海南等省,总面积约为200多万km2。随着全球变化研究的深入,有关红土的风化速率、发育年龄、成土过程、环境指示意义、磁化率意义、构造意义、区域对比等等一系列重要问题取得了重要进展。长期以来,红土科技工作者对南方网纹红土作了大量的研究,也取得了丰硕的成果,但是,因为南方气候湿热、雨水多,土壤侵蚀严重,加上红土相关研究技术不够成熟。迄今对网纹红土的沉积方式、发育年龄、发生层、是否能记录古气候变化等关键性科学问题还未统一认识。本文通过综合运用粒度分析、矿物成分分析、化学成分分析、磁化率分析、孢粉分析等手段,揭示赣南地区第四纪红土的沉积方式以及红土的成土过程。对比3个第四纪红土剖面ESR测年结果,推测赣南地区第四纪红土发育时期,结合硅迁移强度和时间关系数学模型,推测花岗岩红色风化壳的发育年龄。综合对比红土剖面孢粉环境指示、粒度环境指示、磁化率环境指示,揭示赣南地区第四纪红土沉积时期的环境变化。在野外调查过程中,我们发现,赣南地区第四纪红土为非连续成片的堆积体,厚度多为4米左右,少数厚度为5米以上,不具备北方黄土成片堆积的分布特征。对比了2个红土剖面的化学成分分析结果,北方黄土和赣南地区第四纪红土在关键性的化学成分含量(CaO和Si02)相差很远。通过对三个第四纪红土剖面样品的粒度分析,结果表明,粗粉砂(10-50μm)平均含量分别为29.14%,30.80%,38.15%,风尘粒级组含量不突出(黄土一般大于50%)。综上三个方面,我们认为,赣南第四纪红土非风尘堆积。运用粒度分析技术,对比分析了赣南地区第四纪红土和花岗岩红土,发现他们在粒度组合、粒度参数、频率曲线等方面有一定的差距。此外,运用X衍射技术对黄金(HJ)剖面第四纪红土和下覆砂页岩样品分别进行测试,发现第四纪红土样品与下覆砂页岩样品的图谱相差较远,矿物成分含量也不相同。我们认为,赣南第四纪红土非下覆母岩风化残积而成。通过对赣南地区三个红士剖面的粒度分析显示,黄金(HJ)、沙河(SH)和当塘(DT)第四纪红土剖面砂粒(>63gm)的平均含量分别为：19.78%,21.84%,12.16%；细粉砂(2-10μm)平均含量分别为29.43%,32.23%,30.59%。红土剖面粗颗粒含量较多,全剖面皆含大于2mmm的砾石颗粒,表现出冲积、洪积相特征。粒度参数判别式计算结果显示,三个剖面为流水沉积环境而成。三个第四纪红土剖面样品在粒度参数特征上表现出较好的一致性,推测他们具有相对一致的沉积环境和动力条件。此外,对黄金(HJ)第四纪红土剖面的孢粉分析发现,该红土剖面样品中发现了一些水生草本花粉和喜湿润环境的蕨类孢子。基于野外调研的基础上,我们发现,赣州市第四纪红土集中分布在章江、贡江和赣江河流两侧第二或第三级阶地上。综上分析,我们推测,赣南第四纪网纹红土系高处古土壤和古风化壳被流水冲刷而下在地势低洼处沉积而成,后来由于地壳抬升、河流下切,至今沿着河流分布在100-200m左右的红土坡岗丘陵上。综合运用化学成分分析、磁化率分析等技术手段,对黄金(HJ)剖面、沙河(SH)剖面和田村(TC)剖面间隔20cm取样分析,研究表明,田村红土剖面常量常量元素Si、K、Ca、 Mg和Na在整个剖面基本上表现为淋溶迁移的特征,由下部往上表现出迁移程度逐渐增强的趋势。微量元素V、Cr和Mn的累积率多数处于0.2-0.5之间,属于中度累积,并且由下往上呈现逐渐增强的趋势。这些都说明了赣南地区红土在当前气候条件下仍进行着明显的脱硅和富铝化作用。研究发现,三个剖面红土层位的低频质量磁化率大小关系：红壤层<均质红土层<网纹红土层,第四纪红土低频质量磁化率平均值低于花岗岩红土。接近地表的样品同时出现了低频质量磁化率值反而较低,可能与赣南地区长期高温多雨的气候环境有关。研究还发现,三个剖面硅铝系数值、铝铁系数值由底部往上呈现逐渐递减的趋势,而铝铁硅系数曲线值由底部往上呈现递增的趋势,此外,(<1μm)的粘粒百分含量曲线也有这样的变化趋势,综合反映了三个剖面风化程度由下往上逐渐增强的趋势,剖面曲线变化曲线锯齿状波动,说明风化程度也不是完全按照由底部往上正向递增的变化。基于ESR测年技术,分别在黄金(HJ)、沙河(SH)和当塘(DT)红土剖面底部和顶部各取土样1个,测试结果显示,三个红土剖面测年数据相近似,大致处于80～120Ka.B.P.之间,属于晚更新世早期沉积物。基于赵其国院士硅迁移强度与时间关系数学模型,结合对赣南田村(TC)花岗岩红色风化壳剖面硅质迁移强度的计算,我们得出了红土发育年龄范围为80-360Ka.B.P.。剖面下部样品T45-T23发育年龄界于270～370Ka.B.P.之间,属于中更新世晚期(Q22)-中更新世早期(Q21)发育的红色风化壳,剖面上部样品T22-T1发育年龄处于80～220Ka.B.P.范围,除了样品TC-16属于中更新世晚期(Q22)发育外,其余样品年龄皆为晚更新世早期(Q31)。运用孢粉分析技术,分析赣南地区花岗岩上覆红土表土样品3个、第四纪红土表土样3个和砂页岩上覆红土表土2个样。共鉴定出孢粉131种,统计有效孢粉2694粒。研究发现,研究区孢粉组合为乔木、灌木植物、草本植物、蕨类孢子,植被结构表现为乔木植物和蕨类植物的组合特点。孢粉组合中马尾松、罗汉松、青冈栎、里白蕨、圆羊齿和凤尾蕨等喜酸性、耐瘠薄性植物的孢粉含量较多,尤其是松科马尾松和蕨类植物的里白蕨对红土环境具有独特的适应能力。此外,研究区表土孢粉组合显示,现生植物中的绝大多数植物在孢粉组合中均有发现,其不同类型孢粉的比例关系与该区域内的现生植物情况大致相同,基本能反映出该区现生植物群落的特征。我们对黄金(HJ)红土剖面网纹层每间隔20cm采样,经过孢粉测试分析,结合对比了该剖面的低频磁化率和Kd值曲线变化特征,我们发现,黄金剖面(HJ)网纹红土沉积时期经历了四个阶段的古气候变化：温暖偏湿—温暖湿润—温暖偏干—暖热偏湿,与全球变化大气候事件上的研究较为一致。对比了赣南地区网纹红土剖面孢粉和表土孢粉的组合情况,研究发现,黄金剖面木本花粉和草本花粉平均含量比表土孢粉略高,而蕨类孢子略低,此外,黄金剖面孢粉组合中含量较多喜湿润环境的蕨类花粉,而表土中相对较少。我们推断,网纹红土层沉积时期的气候比现代气候要略暖略热。更多还原

【Abstract】 The red clay in the south occurs from the southern bank of the Yangtze River in the North to South Sea Islands in the South, and from the islands of Taiwan archipelago in the east to Yunnan-Guizhou plateau in the west. It distributed mainly in Jiangxi Province, Hunan Province, Zhejiang Province, Fujian Province, Anhui Province, Hubei Province, Guangdong Province, Hainan Province and so on. The entire area covers about2000000km2. Along with the deeper research of global change, the red clay research have reached a great success, especially in weathering rate, soil forming process, formation date, environmental significance, geomagnetism significance, tectonic significance, regional correlation and so on. A large number of scientific and technical workers have made a lot of carefully and thoroughly study works and obtained many important results for southern patterned red soil for a long time. There are many problems that have not reached consistent recognition on red clay, such as the deposition fonnation, the question whether it can record geologic climate change or not, formation ages and so on. The research focused on the three scientific problems:red clay sedimentary characteristics, formation date and the quaternary red clay sedimentary environment change. In this paper, the Quaternary red clay sedimentary characteristics were analyzed, making comprehensive use of particle size analyse, mineral composition, chemical composition, magnetic susceptibility, sporo-pollen analyse and so on. The forming ages of the Quaternary Red Earth were infered in contrast with three section ESR dating. Combining mathematical model between time with silicon transport intensity, we can concluded that the forming ages of granite red weathering crusts. The environmental change about the Quaternary Red clay depositional dates could be infered in contrast with the red clay profile sporo-pollen Environmental Indication, susceptibility environment significance, by making comprehensive use of palynology, soil science, geology, geochemistry in studying the above scientific problems. It can help us to study the Quaternary climate change, and fill in geographical space on red clay research in Gannan region.On the basis of field investigations, it was found that the Quaternary red clay is distributed in non-continuous accumulations. The thickness of them are mainly about4m, some are above5m, which do not possess the same feature of eolian deposition in northern China. By comparing the chemical compositions of2red clay sections, it was indicating that there are big differences in important chemical composition contents between the north loess and the Southern Quaternary red clay in Gannan region. Through particle size analytical technique, the results showed that the average contents of coarse silt (10-50μm) were respectively29.14%,30.80%,38.15%in the three red clay sections. While the average contents of loess usually is greater than50%. Through the analysis above, we may conclude that the Quaternary red clay was not aeolian origin.By way of contrastive analysis Grain-size characteristics between the Quaternary red clay and granite red clay, the results showed there are some differences among Grain-size combination, Grain-size parameters and Grain-size curve. By using X diffraction analysis technology, it was found that there were difference of map and mineral composition between red clay and its beneath arenaceous shale. We may conclude that the Quaternary red clay did not derive from weathering of arenaceous shale.Through particle size analysis of huangjin (HJ), shahe (SH) and dangtang (DT) red clay sections, the results showed that the average contents of coarse sand grain (>63μm) were19.78%,21.84%,12.16%respectively. There were more coarse particles in red clay sections, and contained gravel (>2mm) in the whole red clay sections; suggesting be characteristic of alluvial deposition, by way of particle parameters criterion, and showed that the three red clay section were formed in alluvial sedimentary environment,By way of Pollen Analysis, it was founded that there are some aquatic herbs in huangjing(HJ) red clay section. Based on field investigations, we found that the Quaternary red clay distributed maily in the terrace II or III in Zhangjiang rive, Gongjiang rive and Ganjiang rive. So We may infer that the Quaternary red clay in Gannan region derive from pinnacled soil and weathering shell, which was washed down the mountain by the river and collected in low-lying depressions; and later the earth crust were elevated and stream were trenched. Nowadays the Quaternary red clay distributed in the red hill about100～200m along rives in Gannan region.The chemical compositions and magnetic susceptibility were tested and analyzed in Huangjin (HJ) section, Shahe (SH) section and Dangtang (DT) section. It was found that the major elements (SL、K、Ca、Mg、Na) show the characteristic of leaching and movement in Tiancun section, and increasing tendency from the bottom to the top. The accumulation of trace element (V、Cr、Mn) located between0.2～0.5, and belong to moderate accumulation, and the increasing tendency from the bottom to the top. All this points support the same conclusion: the desilica-allitization of red clay is in the pipeline on modern climate environment. The low frequency magnetic susceptibility of red clay horizon:the vermiculated red clay horizon is better than red soil horizon is better than soil horizon in magnetic susceptibility. The average magnetic susceptibility of the quaternary red clay is less than that of granite red, the magnetic susceptibility surface soil get lower than underneath red clay. This may have some connection with warm and wet climate environment in gannan region. The coefficient of SiO2/Al2O3and Al2O3/Fe2O3has a decreasing tendency from the bottom to the top, while the coefficient of R2O3/SiO2has an increasing tendency from the bottom to the top, reflecting that the degree of weathering were getting stronger and stronger from the bottom to the top. By the way of ESR dating for the bottom and top samples in Huangjin (HJ) section, Shahe (SH) section and Dangtang (DT) section, the results show a good approximation, age datas in three red clay section fluctuates between80～120Ka.B.P., belonging to the deposition of early late Pleistocene. Based on a mathematical model of relation between silicon migration intensity and time from Zhao qiguo academician, Ages of red clay of these samples in Huangjin (HJ) section range from80～360Ka.B.P.. Age datas for the superior part samples of section fluctuates between80～220Ka.B.P.,Belonging to early middle Pleistocene or later middle Pleistocene. Age datas for the underpart samples of section fluctuates between270～370Ka.B.P., belonging to early middle Pleistocene.Based on the sporo-pollen data of eight surface samples which include three red soil samples on granite type, three samples on the Quaternary red clay and two samples on sand shale in Gannan region, Luo-Pacias spore-pollen appraisal system identification of spore-pollen were used, sum up to131species, and Statistics valid pollen2694, it was found that the production of spores-pollen are rich in species and genus in red soil in Gannan region, surface sporo-pollen assemblages are composed of trees, shrubs herbs, pteridophytes; the vegetation structure of spores-pollen assemblage include arbors and shrubs. There were more acidity and barren palynoflora, such as Pinus massoniana, Podocarpus macrophyllla, Hicriopteris glauca, Nepholepis cordifolia and so on, especially Pinus massoniana and Hicriopteris glauca are strongly adaptable to the laterite environment. Spore-pollen assemblages showed that its proportions can reflects basic characteristics of botanical community in modern times.We took20cm intervals samples in Huangjin(HJ) red clay section. Through spores-pollen experiment, magnetic susceptibility value and Kd value have been studied by comparison of sporo-pollen assemblages change in Huangjin(HJ) section. It was concluded that the red sedimental date had experienced four stages climate change:warm and moisture stage, warm and wet stage, warm and dry stage, heat and moisture, there are consistent in big climate incident with Change of Global Climate, By comparison of surface and section sporo-pollen assemblages, we concluded that the geological climate of red sedimental were warmer and more moist than modern climate environment.更多还原