Geochemical evidence for non-marine depositional environment of foraminiferal fossils from the Nihewan Basin, China

From the first finding in 1970s, the findings of foraminiferal fossil assemblages in inland basins have been reported from time to time, especially in recent years. The debates on the depositional environment of foraminiferal fossils have become the hot spot of researches again in China. Based on the researches of trace element geochemistry and electron scanning microscope of shells of Quaternary foraminiferal fossils from the Xiaodukou section in the inland Nihewan basin, the original ⁸⁷Sr/⁸⁶Sr and other geochemical information of shells were believed to be preserved well and could be used to rebuild the geochemistry of contemporary waters where foraminifera deposited, although there existed some effects of burial diagenesis on the geochemistry of shells to a certain extent. The ⁸⁷Sr/⁸⁶Sr ratios of well-preserved Xiaodukou foraminiferal shells were measured, giving a range of 0.711190±25–0.712018±14, apparently higher than the value of contemporary seawater (0.709087–0.709147) and similar to that of the Sanggan River, proving that it represented the value of the ancient lacustrine water. The hyperbolic mixing models of ⁸⁷Sr/⁸⁶Sr-palaeosalinity and ⁸⁷Sr/⁸⁶Sr-Sr/Ca indicated that the contemporary waters where Xiaodukou foraminifera inhabited was an inland lake and there was no seawater input to the depositional environment.     

Comparative study on CO2 sources in soil developed on carbonate rock and non-carbonate rock in Central Guizhou

In this paper, by using concentration and carbon stable isotope the CO2 sources of soil profiles developed on limestone, dolostone and claystone basements in Central Guizhou, China are comparatively studied. The results show that CO2 concentration of soil profiles developed on different basements is different, having the following sequence: limestone>dolostone>claystone. Below the soil depth of 20 cm from the surface the ? 13C value of CO2 in soil profile developed on limestone ranges from -12.811‰ - -13.492‰(PDB), that in soil profile developed on dolostone varys from -13.212‰ - -14.271‰(PDB) and that in soil profile developed on claystone is about -20.234‰ - -21.485‰(PDB). Taking the carbon isotope of soil organic matter and carbonate rock as two isotopic endmembers, the proportion of soil CO2 generated by dissolution of carbonate rock is calculated, about 21%-25% for soil profile developed on limestone basement, 19%-21% for soil profile developed on dolostone basement. There is almost no influx of CO2 generated by the dissolution of carbonate rock in soil profile developed on claystone basement.     

碳酸盐岩风化成土过程中REE超常富集及Ce强烈亏损的地球化学机理

碳酸盐岩的REE含量极低，但最近在贵州一些碳酸盐岩风化表土层底部首次发现了REE的超常富集层，REE总量最高可达近31000μg/g;Ce强烈亏损，δCe值最低达0.007。这种低背景、高富集、强分异的REE富集现象在贵州碳酸盐岩风化壳中具有一定的普遍性。选取发育在下三叠统花溪灰岩和平坝白云岩之上的两个较具代表性的碳酸盐岩风化壳进行研究，结果表明，这种富集现象与碳酸盐岩风化成土的两阶段性密切相关。（1）在残积土形成阶段（风化早期），碳酸盐的快速溶解导致风化前缘形成一个垂直方向相对狭窄、突变的碱性障(pH值为8左右）。此障既能有效地将碳酸盐岩分解释放的REE以及下渗水携带的REE分解沉淀和以吸附于粘土矿物上的方式富集，也容易使Ce^3 氧化成Ce^4 ，与HCO3^-形成稳定的可溶性络合物随下渗雨水流走，从而使Ce进一步亏损。（2）残积土演化阶段，轻、重稀土发生明显分异，Ce^3 氧化成Ce^4 并发生水解沉淀，致使下渗水富重稀土而贫Ce，最终使REE在剖面上显示出一般风化壳共有的分异特征。另外，根据对碳酸盐岩中的酸不溶物、可溶性稀土的提取以及质量平衡计算，碳酸盐岩能够提供足够的REE物源；以可溶态为主的赋存状态有利于REE的淋滤（活化）。     

碳酸盐岩酸不溶物作为贵州岩溶区红色风化壳主要物质来源的证据

贵州岩溶区红色风化壳是中国南方红色负化壳的重要组成部分，本文根据部分红色风化壳剖面野外特征、矿物学、地球化学及土壤物理学等的研究结果，对其物源及成因进行了探讨。各剖面，尤其邻近剖面显著的矿物学、地球化学差异排除了远程风成沉积物、火山灰、上覆或者高处碎屑岩层作为统一且重要物源的可能。极低的石英含量表明贵州常见的长石石英砂岩不是其主要物源，具有中稀土（MREE）富集的特征也排除了粘土岩、页岩作为主要物源的可能。风化壳剖面间的差异性均可从基岩酸不溶物的差异性得到很好解释，表明它们是下伏碳酸盐岩风化、酸不溶物（准）原地堆积的结果。部分剖面甚至显示了典型风化壳剖面的一些特征，具有正常风化序列的剖面结构特征。     

早震旦世大塘坡期锰矿成因新认识

中国南方早震旦世大塘坡期锰矿的形成一直存在热水成因、生物成因或化学成因的争议。通过对贵州松桃早震旦世大塘坡期锰矿的碳、硫同位素和藻类化石的研究，认为早震旦世大塘坡期锰矿是在700－695Ma全球性Sturtian冰期后形成，由于大气中含有很高的CO2与海洋中的Ca^2 、Mn^2 反应，造成大量CaCO3和MnCO3快速沉淀，形成“碳酸盐岩帽”（碳酸锰）所致。对大塘坡组藻类化石研究还表明，在含锰矿的层次，藻类化石很少，而锰矿层上下，微体藻类化石都很丰富，这说明锰矿成矿与藻类关系并不那么密切。     

引起红土表层硅铝比值增大原因的可能性探讨

Si/Al或SiO2/R2O3常常作为表生化学风化作用强度的重要指标。随着化学风化作用的进行。硅铝比或硅铝铁率表现出逐渐降低的演化趋势，中国南方的红土风化壳，是强烈化学风化作用的产物，被认为处于或经历了脱硅富铝化阶段，但是在红土剖面上部常常出现该比值不降反升的现象。给运用这一指标指示化学风化强度带来了困难，通过对贵州平坝，新蒲及花溪碳酸盐岩红色风化壳化学风化程度的研究，以及对中国南方几种不同结晶母岩上发育的红土的化学风化强度指标的对比讨论。探讨了产生这种现象的可能性原因。指出Fe,Al氧化物的下渗和淋失作用及其硅质的相对富集是引起中国南方红土表层出现Si/Al和SiO2/R2O3升高的主要原因。     

贵州平坝县白云岩风化壳中稀土元素分布特征之初步研究

本文报道了平坝白云岩风化剖面风化前缘稀土元素超常规富集(总量达3%以上)现象及其特征,并通过主元素、稀土元素的测定,结合白云岩中“酸不溶物”的提取和代表性样品的化学淋溶实验研究,讨论了白云岩风化壳剖面稀土元素的分异特征,认为风化前缘稀土元素的富集是由3方面的因素共同作用造成的:1)对白云岩风化残积的继承;2)剖面上部一部分轻稀土淋滤聚积;3)碳酸盐岩中非均匀分布的原生含磷矿物风化产生的稀土磷酸盐矿物的聚集,后者是最重要的原因。     

The Variation of Soil Organic Matter in a Forest-Cultivation Sequence Traced by Stable Carbon Isotopes

On the basis of different photosynthetic pathways.there is an obvious difference in δ^13C values between C3 and C4 plants,In terms of this characteristic,we analyzed the organic carbon content (forestlands:1.81%-16.00%;farmland:0.45%-2.22%) and δ^13C values(forestlands:-23.86‰--27.12‰;farmland:-19.66‰--23.26‰)of three profile-soil samples either in farmland or in forestland near the Maolan Karst virgin forest,where there were developed plant C3 plants previously and now are C4 plants.Results showed that the deforestation has accelerated the decomposition rate of soil organic matter and reduced the proportion of active components in soil organic matter and thus soil fertility.     

土地利用/土地覆被变化对长江流域水环境的影响研究

不合理的土地利用方式／土地覆被变化已成为长江流域水环境不断恶化的重要原因之一，长江上游植被破坏和陡坡开垦造成严重的水土流失，直接威胁到三峡库区的生态安全，中流的围湖造田等损害了湖泊的生态功能，导致严重的洪涝灾害，化肥，农药的过量使用，农田污水灌溉等成为长江流域农业非点源污染的重要来源。文章提出了进一步研究构想，以山－河－湖－海互动系统为研究对象，以系统内各子系统之间的能量流和物质流的联系为纽带，揭示系统自组织、自反馈机制，利用遥感技术和地理信息系统结合数学模型，动态模拟土地利用／土地覆被变化的水文及水环境效应。     

撞击事件对古环境的影响——来自ODP1144站A孔样品的证据

本文通过对ODP1144站A孔BM界线附近样品中微玻璃陨石的挑选和研究,确定在中更新世曾发生过地外物体撞击地球的灾变事件。样品中浮游有孔虫壳体碳氧同位素的对比研究表明,在微玻璃陨石事件发生的后期,曾发生了浮游有孔虫壳体碳氧同位素组成的变化,表现为^δ13 C值的降低和^δ18 O值的增加。文中还探讨了其形成的原因。