Evidence for microbiological manganese oxidation in the river Tamar Estuary, South West England

Water samples from the Tamar Estuary oxidized manganese when supplemented with Mn²⁺ (2 mgl⁻¹). The rates of oxidation were depressed in the presence of various metabolic inhibitors. The effect of Mn²⁺ and temperature on the rate of manganese oxidation suggested that a biological process was largely responsible for converting Mn²⁺ to Mn⁴⁺. Rates of manganese oxidation were much higher in freshwater (3·32 μgl⁻¹ h⁻¹ in water containing 30 mgl⁻¹ of suspended matter) than in saline water (0·7 μgl⁻¹ h⁻¹ in water of salinity 32‰) containing the same amount of particulate matter. The rate of manganese oxidation was proportional to the particulate load (up to 100 mgl⁻¹ particulates).     

The “slip law” of the free surface

A “slip law” connects the excess velocity or “slip” of a wind-blown water surface, relative to the motion in the middle of the mixed layer, to the wind stress, the wind-wave field, and buoyancy flux. An inner layer-outer layer model of the turbulent shear flow in the mixed layer is appropriate, as for a turbulent boundary layer or Ekman layer over a solid surface, allowing, however, for turbulent kinetic energy transfer from the air-side via breaking waves, and for Stokes drift. Asymptotic matching of the velocity distributions in inner and outer portions of the mixed layer yields a slip law of logarithmic form, akin to the drag law of a turbulent boundary layer. The dominant independent variable is the ratio of water-side roughness length to mixed layer depth or turbulent Ekman depth. Convection due to surface cooling is also an important influence, reducing surface slip. Water-side roughness length is a wind-wave property, varying with wind speed similarly to air-side roughness. Slip velocity is typically 20 times water-side friction velocity or 3% of wind speed, varying within a range of about 2 to 4.5%. A linearized model of turbulent kinetic energy distribution shows much higher values near the surface than in a wall layer. Nondimensional dissipation peaks at a value of about eight, a short distance below the surface.     

豆荚状铬铁矿豆状结构成因机制探讨--以遵化地区豆荚状铬铁矿为例

豆荚状铬铁矿是蛇绿岩套地幔构造岩中特征的矿产 ,其矿石发育丰富的岩浆 -变形结构构造类型 ,对认识大洋上地幔成因及其成矿过程具有重要意义。对遵化新太古代豆荚状铬铁矿的深入研究 ,发现它们发育了丰富的岩浆结构 (豆状结构、豆壳状结构等 ) ,还保留了大量凝缩标志和旋转特征。对比分析其各种特征结构发现豆状结构是由浸染状结构逐步演化形成的 ,并且旋转和凝缩是形成豆状结构的主要机理。豆荚状铬铁矿以其独特而稳定的物理化学特性 ,记录了大洋地幔深部岩浆活动(特别是扩张中心原始岩浆活动 )以及大洋岩石圈运动过程。因此 ,研究其成因机制能够为研究大洋上地幔动力学机制提供重要线索     

西昆仑穆呼锰矿晚石炭世含锰碳酸盐岩地质地球化学特征及其沉积环境

西昆仑玛尔坎苏地区晚石炭世发育一套碎屑岩—碳酸盐岩建造,近期研究成果揭示其具有巨大的菱锰矿找矿前景而备受关注。通过对穆呼锰矿含锰岩系剖面测量、薄片鉴定、电子探针、扫描电镜、地球化学分析和碳酸盐岩锶同位素测试,对其进行碎屑岩—碳酸盐岩岩相划分与沉积环境分析。研究结果表明,含锰岩系可以识别出八种碎屑岩—碳酸盐岩岩相:泥灰岩相、砂屑灰岩相、微晶碳酸锰相、微晶—粉晶灰岩相、砾屑灰岩相、含砾砂屑灰岩相、钙质砂岩相、钙质砾岩相和3种岩相组合。结合矿体及其顶底板岩石地球化学和锶同位素特征,指示古海水温度平均22.68 ℃,属于亚热带区。含锰岩系为海水较浅的碎屑滨岸相和浅海陆棚相沉积,矿体顶底板处于海水相对较浅的氧化—弱还原环境,菱锰矿则形成于海水相对较深的浅海陆棚沉积洼地,处于还原沉积环境,与海底火山热液有关。     

广西忻城县里苗-塘岭锰矿床控矿因素及成矿模式

广西宜州市龙头锰矿是我国石炭系锰矿的典型代表。2014~2016年,中国冶金地质总局广西地质勘查院在南丹-宜州地区开展矿产地质调查工作取得了新的突破,圈定了弄竹、塘岭找矿靶区。两个靶区经后续广西地勘资金勘查,在里苗-塘岭一带估算锰矿资源量达8000多万吨,成为我国石炭系最大的锰矿。为了揭示该矿床的成矿机制,本文从区域成矿地质背景、矿床地质特征、构造环境、岩相古地理、锰质来源、矿化富集规律等方面分析了其控矿因素,圈定了成锰盆地边界线,建立了成矿模式。认为里苗-塘岭锰矿床是受NE向同沉积断裂控制的海底热水沉积矿床,是走滑拉张断陷-含锰热水-台沟相沉积环境耦合作用的产物。     

贵州从江-黎平地区锰矿地质特征及找矿潜力分析

贵州从江-黎平地区锰矿产于南华系大塘坡组第一段黑色岩系中。通过对从江-黎平地区开展地质调查工作,查明该区含锰岩系分布于朝里向斜及寨柳向斜,区内两个已知矿床八当锰矿和高增锰矿即位于朝里向斜。文章系统阐述了从江-黎平地区锰矿成矿地质背景、含锰岩系特征、锰矿床地质特征,对该区南华纪大塘坡期锰矿成因进行了探讨研究,并总结了区内锰矿成矿规律,在此基础上,结合野外地质调查成果,对该区锰矿找矿潜力进行了分析,认为朝里向斜南部具一定找矿潜力。     

Deep‐water dunes on drowned isolated carbonate terraces (Mozambique Channel,south‐west Indian Ocean)

Subaqueous sand dunes are common bedforms on continental shelves dominated by tidal and geostrophic currents. However, much less is known about sand dunes in deep‐marine settings that are affected by strong bottom currents. In this study, dune fields were identified on drowned isolated carbonate platforms in the Mozambique Channel (south‐west Indian Ocean). The acquired data include multibeam bathymetry, multi‐channel high‐resolution seismic reflection data, sea floor imagery, a sediment sample and current measurements from a moored current meter and hull‐mounted acoustic Doppler current profiler. The dunes are located at water depths ranging from 200 to 600 m on the slope terraces of a modern atoll (Bassas da India Atoll) and within small depressions formed during tectonic deformation of drowned carbonate platforms (Sakalaves Seamount and Jaguar Bank). Dunes are composed of bioclastic medium size sand, and are large to very large, with wavelengths of 40 to 350 m and heights of 0·9 to 9·0 m. Dune migration seems to be unidirectional in each dune field, suggesting a continuous import and export of bioclastic sand, with little sand being recycled. Oceanic currents are very intense in the Mozambique Channel and may be able to erode submerged carbonates, generating carbonate sand at great depths. A mooring located at 463 m water depth on the Hall Bank (30 km west of the Jaguar Bank) showed vigorous bottom currents, with mean speeds of 14 cm sec^?1 and maximum speeds of 57 cm sec^?1, compatible with sand dune formation. The intensity of currents is highly variable and is related to tidal processes (high‐frequency variability) and to anticyclonic eddies near the seamounts (low‐frequency variability). This study contributes to a better understanding of the formation of dunes in deep‐marine settings and provides valuable information about carbonate preservation after drowning, and the impact of bottom currents on sediment distribution and sea floor morphology.     

海南岛新生代玄武质熔岩源区中再循环物质及其年龄的限定:来自Hf-Sr-Nd-Pb同位素的制约

再循环洋壳和沉积物在壳.幔循环过程中扮演着重要的角色。前人研究指出板片俯冲与海南地幔柱形成关系密切,然而地幔柱源区中是否存在再循环沉积物仍然不得而知。本文将首次报导海南岛新生代玄武质熔岩的Hf同位素,并将新的Sr-Nd-Pb同位素与前人数据相结合,限定再循环物质的组成及其年龄。与同位素地幔趋势相比,给定εNd时,海南岛玄武质熔岩的εHf值更低;而且Eu/Eu*>1、Sr/Sr*>1,与Al2O3、MgO都不存在相关性,说明Eu和Sr的正异常是继承了源区的特征,指示源区中存在再循环洋壳物质的参与。海南岛玄武质熔岩的Ce/Pb与εNd、εHf呈正相关关系,Nd/Pb与87Sr/86Sr呈负相关关系,它们都指向了沉积物端元。根据εHf-εNd模型和Pb同位素演化模型,推断源区中再循环洋壳和沉积物相对年轻,其年龄应小于1.0Ga。这些再循环洋壳和沉积物将进入深部地幔,并与地幔中的橄榄岩反应形成二阶段辉石岩,随着海南地幔柱不断上升而发生熔融,最终熔体喷发至地表形成海南岛玄武质熔岩。     

东北大兴安岭北段蛇绿岩的时空分布及与区域构造演化关系的研究

大兴安岭北段作为中亚造山带东段重要组成单元,该区域的构造背景一直悬而未决,它涉及兴安与松辽地块基底属性、额尔古纳地块亲缘性以及三者之间的拼贴位置、时限和方式等众多科学问题。蛇绿岩作为研究造山带的重要工具之一,不仅是古板块或微地块的重要边界,而且是认识地幔组成和壳幔演化的重要窗口。然而大兴安岭北段蛇绿岩却鲜有报道。根据近年来野外工作及结合前人研究成果,文章探讨了蛇绿岩形成时代及构造环境。研究表明：(1)大兴安岭北段蛇绿岩整体呈北东向展布,但时代跨越较大,主要包括新元古代、早奥陶世-志留纪、石炭纪-二叠纪;(2)大兴安岭北段蛇绿岩均有E-MORB地球化学特征,其中新元古代的蛇绿岩明显亏损高场强元素Nb、Ta,而晚古生代的蛇绿岩则相对富集高场强元素;(3)大兴安岭北段新元古代蛇绿岩可能形成于洋内岛弧环境,记录着前寒武纪陆弧碰撞信息,而早奥陶世-志留纪蛇绿岩可能与早古生代弧盆体系演化相关。尽管上述认识为大兴安岭北段古生代的地球动力学背景研究提供了新的依据,但大兴安岭北段蛇绿岩仍存在较多问题亟须解决。     

20世纪北大西洋温盐环流的年代际变化试评估

根据相对丰富的大气器测资料,综合前人对有限的海洋资料的诊断分析,从北大西洋涛动(NAO)变率、表层海温(SST)变率、格陵兰海和拉布拉多海的深对流活动长期变化等不同角度,对20世纪大洋温盐环流(Thermohaline Circulation,THC)变率进行了试评估.结果表明:(1)19世纪末以来,大西洋温盐环流的变化可分为4个时期:1900年以前的一段时期,THC较强;1904年到1930年,THC较弱;1931年到1972年,THC较强;1973年至1995年,THC较弱,目前则又有所增强.(2)与THC的变化相联系,大西洋主要气候要素的变化,相互间存在着某种协调关系,THC强,NAO弱,北大西洋北部SST升高,格陵兰海的对流活动增强,拉布拉多海的对流活动则减弱.