大亚湾海域沉积物中放射性γ谱分析测定

本文报导了γ能谱相对比较法测量海洋沉积物中放射性核素238U、226Ra、232Th、40K和137Cs等方法,并进行了2005年和2006年夏季大亚湾海域三个站位沉积物γ谱测定,对结果进行分析,为今后大亚湾海域辐射环境监测提供基础。     

原地宇生核素^26Al和^10Be剖面定年及其在早期人类遗址年代研究中的应用前景

中、早更新世人类遗址年代的确定对于人类起源与演化的研究具有重要意义。原地宇生核素^26Al和^10Be浓度剖面定年法可用来测定百万年尺度河流阶地沉积物的同位素年龄,积极开展该法测年研究有望填补我国早期人类遗址如许家窑、郧县曲远河口等地点同位素地质年代研究的空白。本文简述该法的基本原理并展望其应用前景。     

原地宇生核素26Al和加10Be剖面定年及其在早期人类遗址年代研究中的应用前景

中、早更新世人类遗址年代的确定对于人类起源与演化的研究具有重要意义.原地宇生核素26Al和10Be浓度剖面定年法可用来测定百万年尺度河流阶地沉积物的同位素年龄,积极开展该法测年研究有望填补我国早期人类遗址如许家窑、郧县曲远河口等地点同位素地质年代研究的空白.本文简述该法的基本原理并展望其应用前景.     

海洋沉积物研究：数据聚焦分析

海洋沉积物是各种海洋沉积作用所形成海底沉积物的总称,其中包括海洋生物源和自生沉积物,如碳酸盐软泥、硅质软泥、铁锰结核等;陆地河流和大气输入海洋的物质以及人类活动中落入海底的东西,如软泥沙、灰尘、动植物的遗骸、宇宙尘埃等。1872—1876年,英国“挑战者”号的考察揭开了海洋沉积物研究的序幕。作为地球演化历史的良好记录,海洋沉积物是认识海洋形成和演变的主要依据,有着重要的研究价值。     

东沙海域沉积物有机碳、氮含量及其同位素分布特征对富甲烷环境指示意义

我国东沙海域是天然气水合物的潜在区,是目前世界上有机碳、氮同位素的环境效应研究的热点区域.通过对ODP184航次3个站位101件沉积物样品中的有机碳、氮含量,碳、氮同位素组成及碳/氮质量比分析测定,并结合沉积物中的顶空甲烷气体浓度和间隙水的盐度、SO42-、NH4+浓度分析,结果显示:1146站位430 m以下沉积层为富甲烷环境,该层段有机质1δ3C和1δ5N值变重,同时碳/氮质量比变小,表明沉积物母质主要来源于陆源高等植物,而1144和1148站位沉积物母质主要来源于海洋浮游动植物;沉积物中氮含量的增加和1δ5N值的亏损,推断可能与富甲烷环境中古细菌硝化作用和固氮作用有关;沉积物中碳、氮同位素的分布与有机碳、氮含量的规律相一致,也反映沉积物间隙水中相关离子的变化趋势.     

全球变化研究中的同位素地球化学

全球变化研究是90年代以来最为引人注目和关切的环境科学问题之一。全球环境变化的信息储存于树轮、湖泊、冰芯、黄土、地下水和海洋沉积物等载体中,随着稳定同位素技术的发展,同位素示踪剂指示环境变化的信息,成为了解古环境再造和现代环境信息变化的一个强有力的工具。     

两种测定海洋沉积物中总有机碳方法的比较

为了筛选出优越的测定海洋沉积物中有机碳的方法,分别用重铬酸钾氧化-还原容量法（简称重铬酸钾法）和高温催化燃烧-非色散红外测定法（简称高温催化燃烧法）测定海洋沉积物中总有机碳的含量.比较分析得出：高温催化燃烧法测定结果的相对偏差较小,测值较集中,回收率比重铬酸钾法的高.说明高温催化燃烧法用来测定海洋沉积物中总有机碳含量的准确性、稳定性和精密度都较重铬酸钾法好.     

女山单斜辉石巨晶的硼同位素组成:不均一性的发现及其意义

利用离子探针技术测定了一组安徽女山新生代玄武岩中单斜辉石巨晶的硼同位素组成. 硼同位素比值非常不均一:δ11B为+7.4‰～-28.6‰, 既表现在不同样品之间, 也表现在同一样品的内部. 巨晶的硼同位素组成既没有记录暴露地表后的后期蚀变影响,也没有记录被携带上升过程中与寄主玄武岩浆和/或围岩的相互反应. 不均一性继承自巨晶的地幔源区, 其源区曾经经历过流体的交代作用. 交代流体来自于初始硼同位素不均一并且经历不同程度脱水(脱硼)的海洋板块. 结合氧同位素和Sr-Nd同位素来看, 对交代流体的主要贡献可能来自于蚀变洋壳而不是海洋沉积物.     

深海沉积物中的钚

本文根据钚同位素的海洋地球化学行为,提出了钚从海水到沉积物的连续输入模式,讨论了层段输入因子与深海沉积物混合速率的关系,并计算了一个深海站位沉积物的混合速率.该站位沉积物与海水界面层混合速率147cm~2/kyr,近表层低混合区平均混合速率119cm~2/kyr,次表层高混合区平均混合速率343cm~2/kyr,反映了深海沉积物混合层中各层段混合状态的差异.     

大西洋洋中脊海底表层热液沉积物的铅同位素组成及其地质意义

新测得TAG热液区中6件海底表层热液沉积物样品的铅同位素组成,其变化不大,具有均一性的特征。在Pb-Pb图解上,热液沉积物的铅同位素数据大多落在MARB的铅同位素组成范围内,与大西洋沉积物和Fe-Mn结核相比明显具较少的放射成因铅,反映其上部洋壳岩石为该区热液沉积物的形成提供了铅。对比研究表明,因不同地质－构造环境中的海底热液区为热液沉积物形成提供物源的情况不同,是导致有沉积物覆盖洋中脊中热液沉积物的铅同位素组成与无沉积物覆盖洋中脊不同的主要原因。海底扩张中心的扩张速率与热液沉积物的铅同位素组成与无沉积物中脊不同的主要原因。海底扩张中心的扩张速率与热液沉积物的铅同位素组成有一定的对应关系,但其并不是热液沉积物铅同位素组成的唯一控制因素。     

Precise dating of Dansgaard-Oeschger climate oscillations in western Europe from stalagmite data

The signature of Dansgaard-Oeschger events--millennial-scale abrupt climate oscillations during the last glacial period--is well established in ice cores and marine records. But the effects of such events in continental settings are not as clear, and their absolute chronology is uncertain beyond the limit of (14)C dating and annual layer counting for marine records and ice cores, respectively. Here we present carbon and oxygen isotope records from a stalagmite collected in southwest France which have been precisely dated using 234U/230Th ratios. We find rapid climate oscillations coincident with the established Dansgaard-Oeschger events between 83,000 and 32,000 years ago in both isotope records. The oxygen isotope signature is similar to a record from Soreq cave, Israel, and deep-sea records, indicating the large spatial scale of the climate oscillations. The signal in the carbon isotopes gives evidence of drastic and rapid vegetation changes in western Europe, an important site in human cultural evolution. We also find evidence for a long phase of extremely cold climate in southwest France between 61.2 +/- 0.6 and 67.4 +/- 0.9 kyr ago.     

Reduced North Atlantic Deep Water flux to the glacial Southern Ocean inferred from neodymium isotope ratios

The global circulation of the oceans and the atmosphere transports heat around the Earth. Broecker and Denton suggested that changes in the global ocean circulation might have triggered or enhanced the glacial-interglacial cycles. But proxy data for past circulation taken from sediment cores in the South Atlantic Ocean have yielded conflicting interpretations of ocean circulation in glacial times--delta13C variations in benthic foraminifera support the idea of a glacial weakening or shutdown of North Atlantic Deep Water production, whereas other proxies, such as Cd/Ca, Ba/Ca and 231Pa/230Th ratios, show little change from the Last Glacial Maximum to the Holocene epoch. Here we report neodymium isotope ratios from the dispersed Fe-Mn oxide component of two southeast Atlantic sediment cores. Both cores show variations that tend towards North Atlantic signatures during the warm marine isotope stages 1 and 3, whereas for the full glacial stages 2 and 4 they are closer to Pacific Ocean signatures. We conclude that the export of North Atlantic Deep Water to the Southern Ocean has resembled present-day conditions during the warm climate intervals, but was reduced during the cold stages. An increase in biological productivity may explain the various proxy data during the times of reduced North Atlantic Deep Water export.     

U-series dating on late Quaternary sediments from Balikun Lake

The U-series component-dating method has been employed to date the sediment core B-194 from Balikun Lake. 230Th/ 232Th and 234U/ 232Th ratios in various components of the samples dissolved in different concentration acids were measured respectively. The results indicate that there is a good relationship of the isotopic ratios between the solutions and the residues, and that uranium and thorium isotopic fractionations did not occur during acid leaching. Based on the U-series ages obtained by using component-dating method, a 144-ka time sequence was established corresponding to the upper 25-m interval of the B-194 core, which is in agreement with palaeomagnetic dating results. The fact that the palaeoclimatic and palaeoenvironmental record labeled with U-series ages is correlative with the deep-sea δ 18O SPECMAP also demonstrates that the U-series component-dating method can be used to date lake sediments.     

A continuous 200-ka palaeoclimatic record from stalagmite in Tangshan Cave, Nanjing

An oxygen isotope temperature record from 381 to 166 kaB. P. (²³⁰Th/²³⁴U dating and tuned ages) has been obtained by combining data on the isotopic composition of calcites with that of fluid inclusions trapped in a stalagmite from a limestone cave in which a fossil cranium deposited. Several laminae in microsequence of the stalagmite represent climatic events or shifts. The Nanjing man fossil was older than 381 kaB. P.     

贵州荔波42.0kaB.P.~65.0kaB.P.气候变化的石笋记录

对贵州荔波董哥洞D42石笋进行TIMS-U测年和碳、氧同位素分析,建立末次冰期42．0ka B．P．～65．0ka B．P．的古气候变化时间序列。研究结果表明,荔波地区在65．0ka B．P．～42．0ka B．P．石笋记录的冷暖事件所反映出的季风气候变化,大致可分为3个气候阶段;65．0ka B．P．～60．6ka B．P．相当于海洋氧同位素MIS4晚期,反映本阶段东亚冬季风强盛,气温降低,表现为干旱寒冷的气候环境;60．6ka B．P．～48．4ka B．P．相当于海洋氧同位素MIS3早期,反映东亚夏季风相对增强,气温升高,有效降水相对较少,表现为温暖半干旱的气候环境;48．4ka B．P．～42．0ka B．P．相当于海洋氧同位素MIS3中期,显示东亚夏季风由强变弱,东亚冬季风相对增强,表现为干旱冷凉的气候环境。石笋记录揭示的2次寒冷事件在各类沉积物中均有记录,反映为全球变化的气候事件,相当于北大西洋沉积物中的Heinrich5和Heinrich 6冷事件,可以进行全球对比,显示荔波地区与北极地区存在着古气候的遥相关。     

Determination of specific activity of 230Th in uranium ore samples

A new method suitable for determining specific activity of 230Th in uranium ore samples is built. The method is characterized by adding the 230Th/ 232Th standard dilution agent with lower activity ratio (Its 230Th/ 232Th activity ratio and 230Th have been known) to the samples and using isotopic dilution analysis. The method can be applied to analyses of 230Th specific activity in various 230Th/ 232Th activity ratio samples. The precision can also be improved.     

Evidence from U-Th dating against Northern Hemisphere forcing of the penultimate deglaciation

Milankovitch proposed that summer insolation at mid-latitudes in the Northern Hemisphere directly causes the ice-age climate cycles. This would imply that times of ice-sheet collapse should correspond to peaks in Northern Hemisphere June insolation. But the penultimate deglaciation has proved controversial because June insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier. There is a clear signature of the penultimate deglaciation in marine oxygen-isotope records. But dating this event, which is significantly before the 14C age range, has not been possible. Here we date the penultimate deglaciation in a record from the Bahamas using a new U-Th isochron technique. After the necessary corrections for alpha-recoil mobility of 234U and 230Th and a small age correction for sediment mixing, the midpoint age for the penultimate deglaciation is determined to be 135 +/- 2.5 kyr ago. This age is consistent with some coral-based sea-level estimates, but it is difficult to reconcile with June Northern Hemisphere insolation as the trigger for the ice-age cycles. Potential alternative driving mechanisms for the ice-age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean-atmosphere system or changes in atmospheric CO2 concentration controlled by a process in the Southern Hemisphere.     

锶同位素地层学在海相地层定年中的潜在价值

锶同位素地层学在海相地层的对比和定年中具有十分重要的作用。随着锶同位素地层学的深入研究，人们清楚地认识到海水的锶同位素组成是全球变化的灵敏指示剂。显生宙以来全球海水的^87Sr／^86Sr比值是时间的函数，可以把锶同位素组成用于海相地层的定年和进行全球对比，估计沉积间断持续时间、生物带的时间范围和发展阶段，从而为重要地球化学周期的预测提供基础参数。当锶同位素地层学用于定年时，其地质年龄的精确度取决于几个因素，包括样品原始锶同位素组成的保存情况、分析精度、用于建立数据库样品年龄的可信度以及^87Sr／^86Sr比值—年龄曲线的最佳拟合方法等。     

钦州湾表层沉积物重金属分布特征

根据钦州湾表层沉积物中重金属元素Hg、Cd、Pb、Cu、As、Cr、Zn监测数据,利用数理统计和surfer软件对这7中重金属元素含量及其空间分布特征进行分析与评价.结果显示,表层沉积物中Zn和Cu的含量最大值分别是182×10-6和36.7×10-6,超过《海洋沉积物质量》（GB18668-2002）一类标准,其他元素含量的最大值均符合一类标准;钦州湾内湾沉积物质量较外湾差;重金属浓度较高的区域主要为龙门水道,其次是钦江口和犀牛脚镇沿岸海域.龙门水道大部分重金属含量较高可能是由于内湾携带大量污染物的较强径流与外湾海水在此交汇沉降所致,此外,还可能与龙门水道狭窄,地形复杂,岛屿众多等因素有关.     

Determination of specific activity of230Th in uranium ore samples

A new method suitable for determining specific activity of²³⁰Th in uranium ore samples is built. The method is characterized by adding the²³⁰Th/²³²Th standard dilution agent with lower activity ratio (Its²³⁰Th/²³²Th activity ratio and²³⁰Th have been known) to the samples and using isotopic dilution analysis. The method can be applied to analyses of²³⁰Th specific activity in various²³⁰Th/²³²Th activity ratio samples. The precision can also be improved.