Geomagnetic Polarity Events in China since 2.48 Ma

This paper presents the results of palaeomagnetic studies of Cenozoic volcanic rocks and Quaternary strata in China, which have confirmed the occurence of some short-period polarity events, After a correlation with the worldwide palaeomagnetic data, a geomagnetic polarity time scale for the time since 2.48 M has been compiled.     

Paleosalinity evolution of the Paleogene perennial Qaidam lake on the Tibetan Plateau: climatic vs. tectonic control

International Journal of Earth Sciences - As the largest Cenozoic terrestrial intermountain basin in the Tibetan Plateau, the Qaidam Basin is an ideal basin to understand the coupling controls of...     

Late Quaternary Calcareous Nannofossils from the Offshore Sediments in southern Hongkong

Based upon the features of nannofossil composition, distribution, abundance and diversity, the fossil-bearing sediments exposed by five drill holes in the offshore area of southern Hongkong can be divided into the upper Middle Pleistocene, the Upper Pleistocene and Holocene. There were two palaeoclimatic stages in the Holocene in this area according to fossil palaeoecologic and sedimentation analyses: the temperature-rising stage and the warm stage. The latter involves two temperature-falling periods, which could be the major factor causing sea-level fall during that time.     

珠江河口的能量传播和能量耗散

建立了包括河网区、河口湾区和近海水域的ECOMSED-3D数学模型,计算了珠江河口的能量传播和能量耗散特征。研究表明:1)珠江河口能量来源受潮汐和径流共同作用,季节性变化明显;2)珠江河口存在若干高能耗区,其单位面积能耗率比上下游河段平均能耗率高1—2个量级,它们和一定的动力结构与地貌单元相联系。根据地貌特征和消能特点,可以划分为以下3种类型:门的高能耗区、曲折河段高能耗区和分汊汇流高能耗区。     

同化海温观测数据研究波浪破碎对海洋上层结构的影响

首先利用考虑波浪破碎效应的Mellor-Yamada 2.5阶湍流闭合方案,探讨了海表温度(SST)对波能因子α和Charnock数β的敏感性问题。然后采用变分数据同化途径,基于Papa海洋天气站(OWS Papa Station)的上层温度观测数据,对该参数化方案中的波能因子α和Charnock数β两个参数进行了最优估计。最优估计的结果表明,当α约为167、β约为4.1×105时,价值函数达到最小值。利用上述参数的最优估计进行海温的数值模拟,可以较好地反映出海表温度的日变化和月变化过程,模拟的上混合层的温度和深度也与观测较为一致。最后利用以上参数的最优估计结果对湍动能方程进行诊断计算,研究了波浪破碎对海洋上层湍能量收支的影响。     

南海北部陆架区底层渔业资源的空间分布特征

根据2006年10月至2007年9月南海北部大陆架海域4个航次底拖网调查资料,分析了该海域渔业资源的种类组成、种类丰富度和渔获率的空间分布。结果表明,渔获种类数以湛江断面最多(405种),汕头断面最少(337种)。种类数随水深变化呈非对称正态分布,以40—80m水深组种类数最多。物种丰富度指数D的空间分布与种类数基本一致。在总渔获物中,鱼类、头足类和甲壳类3大类群重量组成比例为80:12:8,在断面分布上,组成比例鱼类以珠江口断面最高,头足类以湛江断面最高,甲壳类以阳江断面最高。在水深分布上,鱼类占比随水深的增加而增加,头足类占比在40—100m水深较高,甲壳类在10—20m浅水区最高。鱼类最主要的优势种有6种,其中,深水金线鱼主要在90—120m水深占优势,黄鳍马面鲀在60—90m水深占优势,条尾绯鲤在60—120m水深占优势,单棘豹鲂鮄在120—200m水深占优势,六指马鲅在30—60m水深占优势,龙头鱼在10—30m水深占优势。鱼类渔获率断面分布以珠江口和粤西海域较高,汕头海域最低;水深分布渔获率随水深的增加而增加。头足类渔获率以粤西和珠江口海域较高,粤东海域较低;在100m水深范围内,渔获率随水深的增...     

集合滤波和三维变分混合数据同化方法研究

发展了一种新的混合数据同化方法——基于集合滤波和三维变分的混合数据同化方法。该方法将集合调整卡尔曼滤波(ensemble adjustment Kalman filter,EAKF)得到的集合样本扰动通过一个转换矩阵的形式直接作用到背景场上,利用顺序滤波的思想得到分析场的一个扰动;然后在三维变分(three dimensional variational analysis,3D-Var)的框架下与观测数据进行拟合,从而给出分析场的最优估计。文中以Lorenz63模型为例,开展了理想数据同化试验,结果表明,相比于集合调整卡尔曼滤波,这种新的混合同化方法可以给出更好的同化结果。     

南海盆地新近纪浮游有孔虫带、气候、生物生产力爆炸事件和沉降速度的转换时限

依据浮游有孔虫带的研究,南海北部浅海区LH-19-4-1井和南海北部陆坡区ODP1148站更新世的N22带,晚上新世的N21带和N20带,早上新世的N19—N18带,中新世的N17带至N4带,和晚渐新世的N3带(N3带=P22带)的地层相当,可以对比。如生物多样性在时间上的变化所示,南海北部浅海区,从晚渐新世的N3带末期至更新世N22带经历了五次降温事件(C1—C5)。C1,晚渐新世N3带末期(23.20~23.40Ma),可能相当于Mi-1事件;C2,早中新世早期N4带中晚期(22.50~21.80Ma),它与Mi-1a事件相当,C2降温事件在陆坡区也有反应;C3,早中新世晚期N7带早中期(17.15~17.10Ma),可能相当Mi-1b事件;C4,中中新世中期N10带晚期(14.65~14.60Ma),可能与Mi-3事件相当;C5发生于早更新世N22带早期。14.60Ma是C4事件结束的时限、是本区古环境长时间尺度变化的时限,也是南海盆地在新近纪期间的沉降速度由慢速转入快速的时限。它还可能是青藏高原在中中新世中期开始由慢速隆升转入中速隆升变化的时限。本区从晚渐新世末期至更新世早期的环境为中-外浅海环境,在此期间,共有五次生物生产力爆炸事件(BEE1—BEE5)。BEE1和BEE2发生在早中新世早期N4带,23.2~21.5Ma期间;BEE3发生在早上新世N18—N19交界处,4.80Ma;BEE4发生在晚上新世晚期N21带,3.10~1.80Ma期间;BEE5发生在早更新世初期,1.60Ma。爆炸事件期间的生物生产力高出非爆炸事件期间平均生产力5~11倍,为原生油气藏提供了丰富的物源,给探寻原生油气田提供了重要的信息。     

Metallogeny of the Lannigou Sedimentary Rock-hosted Disseminated Gold Deposit in Southwestern Guizhou Province, China

The Lannigou deposit is a large-sized sedimentary rock-hosted disseminated gold （SRHDG） deposit located in the Youjiang Basin. It is hosted by the Middle Triassic turbidite. Wall rock alterations, including silicification, pyritization, arsenopyritization, carbonatization and argillization, commonly occur along fractures. PGE study demonstrates that either Permian basalts or Triassic ultrabasic intrnsives are unlikely to be the main source of gold mineralization. Coupled with the lack of other nmgmatic activity in the vicinity of the mining area, an amagmatic origin is proposed. Organic matter compositions and GC-MS analysis of the ores and host rocks show that the organics in the ores and the host rocks have a common source; the organic matter in the ores was mainly indigenous. The positive correlation between S2 and Au contents, along with the common occurrence of organic inclusions, suggest involvement of organic matter in the ore-forming process in terms of promoting Au leaching from the source rocks, making colloidal Au migration possible, as well as hydrocarbon reduction of sulphate. Geological and geochemical characteristics of the Lannigou deposit suggest that it was formed through circulation of meteoric water and probably less importantly organic bearing formation water driven by high geothermal gradient caused by late Yanshanian extension, which leached Au from the source bed, and then migrated as Au-bisnlfides and colloidal Au, culminating in deposition by reduction-adsorption and surface complexation of gold onto the growth surface of arsenlan pyrite.     

Occurrences of Excess ^40Ar in Hydrothermal Tourmaline： Interpretations from ^40 Ar-^39Ar Dating Results by Stepwise Heating

The occurrences of excess ^40Ar within a hydrothermal tourmaline is discussed in term of the analysis data of syngenetic muscovite and tourmaline from the Lushui hydrothermal tin-tungsten deposit in western Yunnan, China, using the ^40Ar-^39Ar stepwise heating technique. About 80% excess ^40 Ar was released in the last step when the tourmaline was fused, corresponding to a release of only -3% ^39 Ar （K）, which indicates that most excess ^40 Ar was held in the mineral lattice rather than in the channels parallel to the Z-axis. This suggests that the excess ^40 Ar was incorporated during crystallization and not diffused into the tourmaline during the post-crystallization history.