中国南方红土沉积与环境变化研究

南方第四纪红土沉积是揭示该地区古环境变迁的良好信息载体,红土发育与构造变动、季风演化存在耦合.就第四纪红粘土的研究进展作了回顾,认为红土形成时代、成因、网纹化机制等方面的争议制约了红土地层学的发展,系统研究红土的沉积学、年代学、土壤学、生物气候学、地球化学特征,可以推动红土地层学的发展,并丰富全球变化的内容.     

青藏高原不同地区沉积物的粒度特征与沉积环境判别公式适用性对比研究

以青藏高原地区从东北部到中部的9个典型沉积剖面为研究载体,通过研究本区域不同剖面沉积物粒度特征的差异性以及粒度判别公式的适用性,来探讨其对古环境研究的意义.研究结果表明,青藏高原中部与东北部沉积物粒度特征差异显著.根据粒度特征并结合判别公式,木格滩、英德尔、都兰、兴海、红土山、曲麻莱、可可西里7个剖面判别为风成沉积,而沱沱河、唐古拉沉积剖面判别为河湖相沉积.结果说明萨胡判别公式对青藏高原风成沉积,尤其是风成砂环境判别时,还存在局限性.综合分析得出,青藏高原不同区域沉积物的沉积特征与其所处高原位置具有一定的相关性.高原内部地区利用粒度特征研究古环境时会受到近源物质的干扰,往往不能真实反映气候变化信息.     

贵州红粘土塑性图分布特性及机理分析

通过对贵州红粘土 1399组实验数据的统计和分析,发现贵州红粘土散点在塑性图上的位置有自己的特点:散点的展布方向与一般土一致;随着液限值的增高,它的天然含水率增大,但稠度状态更坚硬;红粘土在天然状态下表现出粉土的特点.通过统计软件找到液限指标和塑性指数与天然含水率的相关关系;再通过粒度分析实验,证明红粘土天然状态下的"...     

对贵州红粘土成因的再探讨

贵州红粘土是覆盖于碳酸盐岩系地层之上,由碳酸盐岩系地层中的不溶杂质为物质来源而形成的特殊红土.岩溶作用决定了红粘土的成土早期和物质来源的特点不同于其它岩石形成的土类;岩溶残余堆积物后期又经历红土化作用,造就了红粘土的基本特征.从成土过程中的主要地质作用来讨论红粘土的成因,指出以上两个成土阶段及其相互间的联系是红粘土成因的最主要环节,并分析了成因对红粘土特性形成的控制作用.     

从陆架泥质沉积中寻找高分辨率的全新世东亚季风记录

当前对全新世东亚季风的研究,一是重造了不同地区的季风气候与环境特点,分析、划分了不同的阶段并总结了各阶段的特点;二是通过高分辨率的气候代用指标进一步开展定量古气候研究,揭示其变化与周期,探讨其驱动机制.已有的研究主要来自陆地,而利用海洋沉积物研究季风则集中在深海;且主要体现的是气候整体变化特征或侧重于夏季风,而专门论述全新世东亚冬季风的报道则较少;尚未在短时间尺度上有效地确定全新世东亚冬、夏季风的关系及其驱动机制.该文指出,可以利用中国边缘海陆架泥质沉积开展全新世高分辨率的东亚古季风研究,其粒度和Rb/Sr比值等元素地球化学指标可分别作为高分辨率的东亚冬、夏季风演化的替代性指标.     

近8 ka东亚冬季风记录在东海内陆架的建立

目的在于尝试从东海内陆架上建立全新世高分辨率的东亚冬季风替代性序列.通过对位于东海内陆架闽浙沿岸泥质中部的PC-6孔(740 cm)进行AMS14C年龄测试和粒度分析,综合沉积构造、沉积层序与海平面变化讨论该孔的沉积环境,其上(0~450 cm)、中(450~540 cm)、下(540~740 cm)段分别对应于前滨、近滨和与现今环境基本一致的浅海沉积环境,其中上段的沉积作用主要受控于东海冬季沿岸流.通过计算该孔的粒级-标准偏差,提取了环境敏感粒度组分,该孔沉积物粒度由以28μm为界的2个粒度子体构成,它们的峰值即约5~6μm与102~125μm分别为对应于冬季沿岸流和波浪的敏感粒级;细粒组分(<28μm)对应于沿岸流,为沿岸流所携带,表现为平行于海岸的横向迁移,粗粒组分对应于波浪,沉积物以垂直于海岸的纵向迁移为主.PC-6孔上段细粒组分的含量一般在85%以上,利用其平均粒径序列建立了研究东亚冬季风演化的替代性序列.     

龙永煤田坑柄井田南区沉积相研究

沉积相研究是揭示古泥炭沼泽形成的重要标志,而古泥炭沼泽是聚煤的主要场所.是恢复合煤地层沉积过程的重要环节.通过对龙永煤田坑柄井田南区地质资料的分析,从岩矿特征、粒度特征、层理特征、古生物特征等方面对沉积相及其古泥炭沼泽的发育演化过程进行研究.划分了三种沉积相类型并在此基础上分析其发展演化模式.     

黄河中游晚第三纪与第四纪古气候关系初探

通过对黄河中游红粘土所记录的古气候特征的研究,表明诸如古季风等第四纪古气候的许多重要特征在新第三纪晚期已见雏形,形成了上第三系红粘土和第四系黄土在粒度分布,对气候变化敏感的地球化学元素的波动形式及淋溶层一淀积层的多次叠置等方面的相似性。这些特征是古气候发展中共性的表现。从新第三纪末期,动物群组成开始明显变化,向着分异度降低和优势现象明显的方向发展,是古环境趋于极性的表现。     

济阳地区石炭-二叠系含煤地层砂岩粒度分布的分形特征研究

对砂岩进行粒度分布研究不仅有助于成因分析和环境解释，而且是评价砂岩储集性能和砂岩微观非均质性的重要指标。应用分形的思路和方法研究了石炭-二叠系含煤地层砂岩粒度分布的分形特征。研究表明，分维数大小能够反映砂岩形成背景的复杂性和环境，且分维越大，背景复杂性越高，自组织程度越低。因此，研究砂岩粒度分形特征，对分析沉积环境和沉积背景的复杂性具有指导意义。     

长江三角洲地区晚更新世晚期的孢粉特征及古环境

通过对长江三角洲地区晚第四纪沉积10多口钻井的孢粉、藻类资料分析研究，在以往较少见到化石的晚更新世晚期的硬粘土沉积中找到了能明确指示古环境的孢粉、藻类化石，发现了两种不同的孢粉组合，一种是以环纹藻Concentricystes占优势的孢粉组合，另一种是以陆生植物Pinus-Cupressaceae-Picea-Abies-Quercus（deciduous）-Grarnineae占优势的孢粉组合，证实了该层硬粘土形成期间曾经历滞水和水退的环境交替．也为探讨硬粘土成因、沉积环境提供了可靠的生物化石依据．     

Seven million-year iron geochemistry record from a thick eolian red clay-loess sequence in Chinese Loess Plateau and the implications for paleomonsoon evolution

Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe₂O₃ ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe₂O₃ ratio record from the red clay-loess sequence indicates that (ⅰ) variations of the free to total Fe₂O₃ ratios of the loess can correlate generally with the alternations of the loess and paleosol horizons; (ⅱ) the East Asia summer monsoon was stronger as a whole in Neogene than that in Quaternary; (ⅲ) the strongest East Asia summer monsoon may occur between 4.0 and 4.8 Ma. The relatively small ice volume and high global temperature may be responsible for the strong summer monsoon during the early Pliocene.     

中国风尘沉积环境磁学研究现状

中国黄土-古土壤-红黏土序列完整记录了7.5 Ma以来东亚季风演化历史。黄土-古土壤的低频磁化率已成为东亚夏季风演化的代用指标之一,并得到广泛的应用和全球对比。虽然古土壤磁化率增强的成土观点已得到广泛认可,但磁化率与成壤强度的相关性还不是十分清楚,磁化率应用方面仍存在问题。磁化率与成壤强度、生物化学作用和古气候关系尚在研究中。     

Terrestrial mollusk evidence for the origin and sedimentary environment of the Late Tertiary Red Clay Formation in the Loess Plateau, China

The origin and sedimentary environment of theLate Tertiary (Neogene) Red Clay Formation in northernChina had long been controversial. A new mollusk recordfrom the Xifeng red clay (red-earth) sequence in the centralLoess Plateau provides the biological evidence for addressingquestions of its origin and environmental implication. Thestudy of composition and preservation condition of seventymollusk fossil assemblages reveals the initial ecological con-dition of the red clay formation, avoiding the effect ofpost-deposited alteration. The result shows that all of identi-fiable mollusk species are composed of terrestrial taxa, mostof them are the common species found in the overlying Qua-ternary Ioess-paleosol sequence. Most of fossil individualspreserved in the red clay strata are in living conditions basedon the investigation of fieldwork, indicating the originalpopulation. Thus, the mollusk fossil assemblages can be usedas an indicator of primary environment of the red clay for-mation. The mollusk record from the Xifeng red clay se-quence supports the view that the red clay is an aeolian ori-gin, similar to the overlying Quaternary loess deposits. Ourdata also reveal the history of environmental changes atXifeng from 6.2--2.4 Ma, which is coupled in phase with theformation and development of the Arctic ice sheets and theprocess of the Tibetan Plateau uplift. Both may be the majorcause and forcing mechanisms of the late Tertiaryenvironmental changes in the Loess Plateau.     

中国北方新近系红土碳酸钙研究及其意义

天水、秦安新近系红土、湖相沉积物的碳酸钙含量均随岩性变化而变化,红色层的CaCO3平均含量维持在6%～7%之间,钙质层的CaCO3平均含量多在20%～40%之间,高值可达60%以上。对比分析表明,黄土的碳酸钙含量高值仅在20%左右,两者相差悬殊。因此,红土与黄土应是不同气候环境下的产物。在此基础上,作者结合周围地区红土的部分沉积学证据对中国北方新近系红土的风成成因提出质疑并明确今后可能的解决途径。     

Comparisons of grain size characteristics of red earth from southern China with that of loess and dune sand from Bering region

The comparisons of grain size distributions among eolian deposits along the monsoon wind trajectory are a fundamental task for the reconstruction of the past wind regimes. Here the authors sampled the dune sands in Hunsandak desert, loess deposits in Beijing region and red earth in southern China. Grain size analyses show that the distribution models of the loess and dune sand samples are unimodal whereas the red earth and paleosol are polymodal. The red earth, paleosol, loess and dune samples are distinguished and closely related to one another in grain size parameter diagrams. Moreover, the grain size distributions and parameters of the red earth and paleosol are similar, implying that the red earth in southern China and the paleosol in northern China had the same origin.     

Comparisons of grain size characteristics of red earth from southern China with that of loess and dune sand from Beijing region

The comparisons of grain size distributions among eolian deposits along the monsoon wind trajectory are a fundamental task for the reconstruction of the past wind regimes. Here the authors sampled the dune sands in Hunsandak desert, loess deposits in Beijing region and red earth in southern China. Grain size analyses show that the distribution models of the loess and dune sand samples are unimodal whereas the red earth and paleosol are polymodal. The red earth, paleosol, loess and dune samples are distinguished and closely related to one another in grain size parameter diagrams. Moreover, the grain size distributions and parameters of the red earth and paleosol are similar, implying that the red earth in southern China and the paleosol in northern China had the same origin.     

Relationship between magnetic fabric parameters and dynamic characteristics of deposits in different environments

Comparison of magnetic fabric parameters of deposits in different modern sedimentary environments indicates that values ofP, F andL of eolian deposits are lower obviously than those of hydrogenic ones respectively. On relationship diagrams of magnetic fabric parameters, data points of eolian samples concentrated in limited area near origin of coordinates indicate that dynamic intensity is lower with less variation; while those of hydrogenic ones depart from origin of coordinates suggest higher intensity of sedimentary dynamics. Analyses of dynamic characteristics of different sedimentary environments indicate that values of magnetic fabric parameters of deposits are determined by dynamic types and characteristics of depositional processes. Magnetic fabric analyses of deposits are effective in determination of sedimentary environments.     

Pollen evidence from Baode of the northern Loess Plateau of China and strong East Asian summer monsoons during the Early Pliocene

The red clay eolian sequence on the Chinese Loess Plateau (CLP) is an important archive for paleoclimate change from the late Miocene to Pliocene,and can provide significant information for the controversial problems of East Asian monsoon evolution and its forcing mechanism.In this study,we present a pollen record from Baode,northern CLP.The record shows four stages of paleoecological evolution.From 5.6-4.4 Ma,a forest steppe ecosystem developed under an extremely warm period with high seasonal precipitation.Since 4.4 Ma,a drier episode occurred,which prompted parkland landscapes to develop.During 3.5-3.05 Ma,the environment changed to a rather open steppe ecosystem with a much cooler and drier climate.After 3.05 Ma,the vegetation evolved to forest steppe.Using the percentages of arboreal plants to mirror precipitation,and comparing with other published pollen data from the CLP,we find the existence of S-N directionality of the precipitation change and high percentage of arboreal plants in the entire CLP during the Early Pliocene,which suggest the CLP was characterized by a strong East Asian summer monsoon.The strong summer monsoon corresponds well to the low global ice volume,which may illuminate global climate mechanism for the summer monsoon evolution in the early Pliocene.     

外掺剂对红黏土微观结构及脆性指数影响

为了研究外掺剂对红黏土的影响,对掺入氧化钙、氧化铝、氧化钙与氧化铝联合掺入的红黏土重塑样进行三轴不固结不排水试验;通过分析在不同外掺剂以及不同掺入率下改性红黏土的应力-应变曲线、抗剪强度峰值曲线,得出三种外掺剂对红黏土的力学性质的影响,并建立模型对红黏土脆性指数进行量化分析。采用场发射扫描电镜对改性红黏土的微观结构变化进行比对分析。试验结果表明:红黏土的强度随着氧化钙掺入率的增大而增大,氧化钙在显著提高红黏土强度的同时降低其脆性指数,导致其延展性变差;氧化铝的单独掺入对红黏土的力学性质影响甚微;氧化钙与氧化铝联合掺入能够提高红黏土的脆性指数,使红黏土的延展性能变好的同时提高了红黏土的强度。