兰州地区最老黄土的发现及其特征

通过1：5万通远乡幅等2幅区调工作对兰州北部永登县地沟村山城湾岭剖面的磁性地层研究，发现剖面底部黄土为兰州地区迄今为止最老的黄土沉积，形成于1．84Ma.BP以前。磁性地层中出现布容正极性期（B）、松山反极性期（M）。松山反极性期内自上而下出现后贾拉米析、贾拉米格、奥杜威等亚极性期。对CaCO3含量、黄土剖面所反映出的古气候进行了研究。     

秦岭黄土及其记录的古环境变迁

在秦岭的一些山间盆地、河谷阶地等弱剥蚀的地段发育着黄土—古土壤系列。凤州杨家山剖面(34°00′N,106°39′E)可以作为秦岭的代表黄土剖面。该剖面黄土厚约82m,由33层黄土和33层古土壤构成。黄土层中夹有两层粉砂质黄土(L_9和L_(15)),古土壤层中S_5是由3层古土壤组成的。黄土下伏晚第三纪红粘土。该剖面磁性地层测量结果表明,剖面包括了布容正极性带和松山负极性带,二者的界线(B/M)位于第8层黄土(L_8)中部。松山反极性时黄土中记录了贾拉米洛正极性亚时     

南方红土中的磁极倒转以及磁化率变动记录

江西省修水县杨梅山剖面244个定向样品的岩石磁学研究表明,杨梅山剖面的磁极倒转自上而下分别为布莱克(Blake)K向极性偏移、安比拉(Emperor)反向极性偏移、布客—松山(Brunhes—Matuyama)极性带界线以及上部贾拉米洛(Upper Jaramillo)正向亚带;杨梅山剖面样品的磁性矿物为磁赤铁矿;杨梅山剖面浓度(数量)归一化的磁化率变动和深海氧同位素变化具备较好的一致性,该剖面的磁化率变动对应着深海氧同位素自第5阶至第23阶的变化;杨梅山剖面跨越了布容—松山极性带界线以及深海氧同位素的第19阶,中国南方红土的底界年龄可能大于78Ma,即早于中国北方黄土的L8黄土层。     

川西甘孜地区黄土的磁性地层学研究

川西高原位于青藏高原的东南边缘, 气候主要受印度洋季风、高原季风的影响。广泛分布于川西高原的黄土-古土壤序列是高原周缘地区连续的古气候记录类型之一, 记录了上述环流系统的演化过程及其与青藏高原阶段性演化的关系, 对探讨高原隆升的环境响应具有重要意义。对川西甘孜地区甘孜-A剖面进行了系统的磁性地层学研究。结果表明, B/M界线出现在L₇的底部, 并且在剖面下部出现了松山负向期的贾拉米洛正向极性亚带。以古地磁界限点作为时间控制点外推该剖面典型风尘沉积的底界年龄约为1.16 Ma BP。      

长江三角洲地区第四纪磁性地层学研究

根据长江三角洲地区18个新老钻孔的古地磁、磁化率、天然剩余磁化强度等磁性特征的综合研究，证明布容正向极性带、松山反向极性带与高斯正向极性带，以及哥德堡、布莱克、贾拉米洛、奥尔杜维极性亚带在本区都存在；结合岩石地层、生物地层和测年数据等资料，与微古、孢粉等分析结果都有一定的吻合性；这对第四纪地层的划分具有重要的参考价值。同时认为，第四纪时长江三角洲地区继接受碎屑沉积物以来，基本表现为一连续沉积区，并无长时间的大规模沉积间断。     

昆明滇池湖盆晚新生代磁性地层研究

通过对昆明滇池湖盆三个钻孔较密集的古地磁采样和系统的测量,获得了该区沉积500余米厚新生代地层的较为完整的磁极性剖面。自上至下测定出了三个极性带(布容、松山、高斯)。在松山反极性带内判别出了4个极性亚带(贾拉米洛、滇池、奥杜威、留泥汪);高斯正极性带内判别出了2个极性亚带(凯纳、猛犸);布容正极性带内分辨出了6~9个短暂的地磁极性变化。根据本文研究结果,参考孢粉、介形虫,腹足类化石及碳14测年资料,对照国际地磁极性年表,确定出滇池湖盆晚新生代地层包括了整个第四系和上新统晚期部分,并对该套地层进行了具体的划分和粗略的对比。     

九江地区网纹红土的时代

长江中下游地区广泛发育网纹红土。本文对九江长虹大道剖面进行了初步研究。该剖面地层自下而上可分为河流相冲积砂砾石、以发育水平状网纹为特征的铁质网纹红土、以垂向网纹为特征的网纹红土、红色粘土和风成下蜀黄土,分别厚3.3、4.5、5.9、3.6和4.1m。磁性地层研究结果,布容正向极性带/松山反向极性带的界限出现于网纹红土层中部,距顶深部12.9m处;贾拉米洛正向极性亚带出现在铁质网纹红土层中,距顶深度15.1-16.1m处。根据CandeandKent古地磁极性年表的模式年龄和热释光年龄,计算出沉积速率,进而计算出各层的界限年龄。结果表明,铁质网纹红土沉积于1232-869kaBP;网纹红土大约沉积于869-392kaBP;红色粘土沉积于392-101kaBP。九江长虹大道剖面代表了该地区从河流沉积、铁质网纹红土、网纹红土、红色粘土到风成黄土沉积的演变过程,并显示出准0.4 Ma的周期变化。这与黄土高原、青藏高原构造层和地球公转轨道偏心率变化所反映的准0.4 Ma构造气候旋回基本一致。      

五大连池磁性地层初步研究

五大连池玄武岩磁性地层以市容正向斯磁性地层为主，分布较广；也存在有松山反向期磁性地层，还发现了拉尚及贾拉米洛磁性事件的地层。     

川西甘孜黄土磁性地层学研究及其古气候意义*

文章对川西甘孜地区甘孜寺剖面进行了系统的磁性地层学研究及石英颗粒表面形态特征分析。磁性地层学研究结果显示,B/M界线出现在S₈的顶部,并且在剖面下部12.7~14.0m处出现了松山负向期的贾拉米洛正向极性亚带。本次测试以及结合以前的研究结果表明,甘孜地区典型的风尘堆积形成于约1.15MaB.P.以前。石英颗粒表面形态特征的分析结果说明风尘物质可能经历了风、流水、冰川等多种外动力作用,进一步证明该区的风尘物质主要来源于青藏高原及其周缘地区的冰水沉积。另外,研究结果指示青藏高原及其周缘地区的环境状况大约在1.15MaB.P.发生了很大变化,主要表现为干旱化程度以及高原冬季风的明显增强,而这些变化又与青藏高原在该时期的快速隆升密切相关。磁性地层的研究结果将为在该区进一步开展古环境演化过程的对比分析及阶地地貌发育历史的研究奠定基础。     

长江三角洲SZ04孔磁性地层研究及其意义

文章对位于长江三角洲南翼平原区西部的SZ04孔进行了详细的磁性地层学研究。结合绝对测年,并与标准极性柱对比认为269.2 m岩芯清楚的记录了布容(Brunhes)、松山(Matuyama)、高斯(Gauss)极性带,及贾拉米洛(Jaramillo)、奥尔都维(Olduvai)等亚极性带和布莱克(Black)地磁漂移,其中B/M、M/G界限深度分别为100 m和155 m;SZ04孔底部碎屑沉积物形成的年龄大于5.23 Ma。研究发现,钻孔沉积物磁化率、岩石地层特征在特殊的时代界限附近有明显变化可进行区域对比。分析表明,第四纪以来长江三角洲地区一直存在持续的构造沉降,且沉降中心持续往南东方向移动,构造沉降运动的发生和发展存在三个重要的期次分别为2.58 Ma,0.78 Ma和0.125 Ma。     

黄土地区挤密桩桩周土体挤密模型的确定

研究分析了邓肯-张模型在挤密桩周土体应用中的不足。通过室内试验及对黄土地区挤土桩成孔对桩周土挤密原理的分析,认为桩周挤密黄土变形模量在破坏前符合邓肯-张模型,破坏后可用重塑土室内压缩试验的压缩模量与建议的转换系数? 确定,并进一步给出了相应的计算模式,提出了黄土成孔挤密模型并通过一个实例验证了模型的合理性。此模型为以后对桩周土体的应力分析打下了良好的基础,对进一步完善挤密桩设计理论具有参考价值。     

Stability of loess

Lutenegger, A.J. and Hallberg, G.R., 1988. Stability of loess. Eng. Geol., 25: 247–261.

The natural stability of loess soils can be related to fundamental geotechnical properties such as Atterberg limits, water content and void ratio. Field observations of unstable conditions in loess deposits in the upper midwest, U.S.A. show relationships between instability and the in situ moisture content and the liquidity index of the loess. Unstable loess can attain natural moisture contents equal to, or greater than, its liquid limit. Implications of these observations for applied engineering works are described.     

“In-situ” theories of loess formation and the significance of the calcium-carbonate content of loess

It is generally accepted that loess deposits form by action and yet the concept of “loessification” is still encountered, particularly in some European literature. Loessification often seems to be invoked when the deposit being investigated is rich in calcium carbonate because the use of the concept depends upon an eclectic definition of loess. Loessification is irrelevant if loess is defined in terms of the fine quartz material, but may be meaninful if the loess is defined in terms of calcium carbonate. The Russell theory of in-situ formation can possibly be reconciled with deposition by eolian action and production of quartz material by glacial grinding but the Berg theory cannot, and appears to be based on false premises. The “soil science” approach to the problem of loess formation may be responsible for the overvaluing of the significance of the carbonate content; the “geological” approach, with some emphasis on transportation problems, leads logically to the concept of eolian deposition but has, so far, failed to focus attention on the problem of the formation of the actual loess material. The fine quartz material is mostly formed by glacial grinding; there appear to be no other natural forces powerful enough to produce appreciable quantities of loess-sized quartz particles. Deposition of the secondary carbonate is usually the last of the significant stages in the formation of the deposit; scanning-electron-microscope studies suggest that it exists as discrete encrustations (gnarls) rather than as continuous coatings on the quartz grains.     

Problems of loess chronology

Loess as a typically subaerial, loess deposit has long been regarded a Pleistocene sediment and its date of formation has been put to ca 600 ka BP. Recently, the beginning of the Pleistocene is identified in the official concord reached — at 1.6 Ma BP, while not infrequently others propose 2.4 Ma BP. Until the fifties the whole loess (loess-paleosol-sand) sequence could be referred into the shorter Pleistocene period, which —according to the climatic claendar by Milankovitch — consisted of nine cold and eight warm intervals. Some supporters of the longer Pleistocene chronology hold that the beginning of loess formation can be put as far back as 1.6 – 2.4 Ma BP. Loess formation intervals are usually correlated with the cold stages (nos 2, 4, 6 etc.) of the Emiliani oxygen isotope timescale, while soil formation is believed to correspond to the warm stages (nos 1, 3, 5, 7 etc.). The typical loess, i. e. loess proper, are not older than stage no 23 (Jaramillo event — 0.96 Ma BP). Previous to this date climatic conditions had not generally favoured loess formation and paleosols formed one above the other with clay, loam or carbonate intercalations.     

饱和黄土的性质与非饱和黄土流变模型

对西安地区相关数据统计分析，把西安市饱和黄土、软黄土的工程性质与一般黄土进行详细对比，指出它们之间的工程性质差异。同时重点介绍推导非饱和黄土加载体积流变模型过程以及模型的适用条件，对该模型的应用作了分析。     

Methodology of loess palynology

Basic climatic indexes for loess deposits may be determined by the floristic method of palaeoclimatic reconstruction. Spectra of loess pollen are selective, thus may or may not reflect adequately the original composition of the vegetation. Presence of a steppe may be unambiguously stated based on pollen of taxa characteristic for a steppe cenose or of taxa zonally restricted to steppes. Family ranked taxa may often not be regarded as indicating a steppe, because inferior taxa included may be of different cenotic requirements. In order to determine the vegetation and other conditions during the deposition of loess it is important to take into consideration the palaeofloristic data as well.     

Non-classical types of loess

The purpose of this contribution is to describe the sequence of physical and chemical processes resulting in the sediment-type named loess, a fine-grained sediment deposit of universal occurrence. Owing to historical causes, loess has been (and still is) implicitly linked to glacial/periglacial environments among most naturalists. However it is known today that most eolian dust is deflated from tropical deserts. Hence, that sequence of processes is more comprehensive than the former narrow cold scenario. Six examples of different “non-classical” cases (from South America and Europe) that fit well to the loess definition are developed: 1) volcanic loess in Ecuador: pyroclastic eruptions/valley wind/mountain praire/silica structuring; 2) tropical loess in northeastern Argentina, Brazil and Uruguay: deflation of river and fan splays/savanna/iron sesquioxide structuring; 3) gypsum loess in northern Spain: destruction of anhydrite/gypsiferous layers in a dry climate/valley wind/Saharian shrub peridesert/gypsum structuring; 4) trade-wind deposits in Venezuela and Brazil: deflation in tidal flats/trade wind into the continent/savanna/iron hydroxide structuring; 5) anticyclonic gray loess in Argentina: continental anticyclone on plains/anti-clockwise winds and whirls/steppe/carbonate structuring. All these non-classical types conform to the accepted loess definitions and they also share the most important field characteristics of loess such as grain size, friability, vertical or sub-vertical slopes in outcrops, subfusion and others. Other cases can probably be recognized when systematically scrutinized.     

Cation exchange capacity of loess and overlying soil in the non-carbonate loess sections, North-Western Croatia

The adsorption properties in terms of cation exchange capacity and their relation to the soil and sediment constituents (clay minerals, Fe-, Mn-, and Al-oxyhydroxides, organic matter) were investigated in loess, soil-loess transition zone, and soil at four loess-soil sections in North-Western Croatia. Cation exchange capacity of the bulk samples, the samples after oxalate extraction of Fe, Mn and Al, and after removal of organic matter, as well as of the separated clay fraction, was determined using copper ethylenediamine. Cation exchange capacity (pH～7) of the bulk samples ranges from 5 to 12 cmol _c /kg in soil, from 7 to 15 cmol _c /kg in the soil-loess transition zone, and from 12 to 20 cmol _c /kg in loess. Generally, CEC values increase with depth. Oxalate extraction of Fe, Mn, and Al, and removal of organic matter cause a CEC decrease of 3–38% and 8–55%, respectively, proving a considerable influence of these constituents to the bulk CEC values. In the separated clay fraction (<2 μm) CEC values are up to several times higher relative to those in the bulk samples. The measured CEC values of the bulk samples generally correspond to the clay mineral content identified. Also, a slight increase in muscovite/illite content with depth and the vermiculite occurrence in the loess horizon are concomitant with the CEC increase in deeper horizons, irrespective of the sample pretreatment.     

黑方台黄土崩解性试验研究

为研究黄土的崩解特性,探讨黄土崩解机理,以黑方台马兰黄土为研究对象,通过自制的黄土崩解装置,对该地区原状黄土进行了一系列的室内崩解试验。选择影响黄土崩解的土样尺寸、初始含水率、水温、酸碱度、盐度5种因素,采用控制变量法逐一进行崩解测试,记录崩解的整个过程,绘制崩解曲线,求出对应的崩解速率,进行拟合,得到崩解速率与各变量间的关系。试验发现,该黄土的崩解过程可以划分为浸湿、软化和塌落3个阶段,前两个阶段持续的时间较短且崩解很弱,崩解主要集中在第3个阶段。由各组崩解曲线得出黄土的崩解速率与水温呈正相关,与土样尺寸、初始含水率呈负相关;pH值介于5.5~6.5以及9.5~10.5时,黄土的崩解速率较高;而盐度对黄土的崩解速率影响不大。此外,黄土的崩解特征与自身的结构、颗粒成分、胶结物等密切相关。