早中新世以来南海北部陆坡古生产力的碳酸盐和生物成因Ba元素记录

通过对南海北部ODP1148站岩芯454．8mcd以上（约23．2Ma以来）的175个沉积物样品中CaCO3以及生物成因Ba含量变化的研究,并结合初期对ODP1148站岩芯分析的一些相关地球化学组成结果,探讨了碳酸盐、生物成因Ba作为海洋古生产力指标的影响因素,以及早中新世以来南海北部陆坡古生产力的变化特征。结果显示,除中新世早期（23～21．4Ma）以外,生物成因Ba与CaCO3含量和沉积速率变化有很好的相关性,反映南海北部古生产力变化波动较大。对钻孔中生物成因Ba的研究表明,在沉积埋葬以及埋葬后的保存过程中（特别是在320mcd以下）。生物成因Ba会在少氧或缺氧环境下发生还原反应而迁移,影响了它在古环境研究当中的作用。另外,结合钻孔中CaCO3含量变化的数据,在南海北部陆坡,CaCO3的溶解作用并不是很强,其沉积后保存良好,可作为研究南海北部古生产力的基础性指标。     

南海东北部表层沉积中钙质超微化石的分布特征

对南海东北部188个表层沉积样品进行了钙质超微化石分析.结果表明,除2个样品外,其他样品均含有超微化石,但丰度相差悬殊,在(9～1 684)个/10视域范围内变化.钙质超微化石相对丰度在平面上的分布可划分为3个区.共鉴定出钙质超微化石17属27种,以Florishaera profunda,Gephyrocapsa oceanica,G.spp.(small)和Emiliania huxleyi为优势种.调查区钙质超微化石的分布受多种因素的综合影响.重点讨论了水深、陆源物质的输入、碳酸盐溶解作用等因素对超微化石丰度及优势种分布的影响.     

Assessing mine drainage pH from the color and spectral reflectance of chemical precipitates

The pH of mine impacted waters was estimated from the spectral reflectance of resident sediments composed mostly of chemical precipitates. Mine drainage sediments were collected from sites in the Anthracite Region of eastern Pennsylvania, representing acid to near neutral pH. Sediments occurring in acidic waters contained primarily schwertmannite and goethite while near neutral waters produced ferrihydrite. The minerals comprising the sediments occurring at each pH mode were spectrally separable. Spectral angle difference mapping was used to correlate sediment color with stream water pH (r²=0.76). Band-center and band-depth analysis of spectral absorption features were also used to discriminate ferrihydrite and goethite and/or schwertmannite by analyzing the ⁴T₁←⁶A₁ crystal field transition (900–1000 nm). The presence of these minerals accurately predicted stream water pH (r²=0.87) and provided a qualitative estimate of dissolved SO₄ concentrations. Spectral analysis results were used to analyze airborne digital multispectral video (DMSV) imagery for several sites in the region. The high spatial resolution of the DMSV sensor allowed for precise mapping of the mine drainage sediments. The results from this study indicate that airborne and space-borne imaging spectrometers may be used to accurately classify streams impacted by acid vs. neutral-to-alkaline mine drainage after appropriate spectral libraries are developed.     

Distributions and vertical variation patterns of sound speed of surface sediments in South China Sea

The distributions of sound speed show different characteristics in continental shelf, continental slope and Nansha Trough. The differences have closely related to the distributions of sediment physical properties in the southern South China Sea. According to the analysis of sound speeds and physical properties variation characteristics with buried depth, the vertical variations of sound speed are closely related to sediment texture, sedimentary environment, transport, erosion, compaction, consolidation, etc. The comparison results indicate 3 vertical variation patterns of sound speed: increasing model, invariant model and complicate variation model. The above 3 variation models represent the vertical distribution characteristics of sound speed in different depositional environments. Different variation patterns have different key factors which generally contain porosity or grain size. The calculated sound speeds with Buckingham’s theory of compressional waves in fluid-like marine sediments follows the trend of measured speeds accurately.     

南海北部湾全新世以来沉积物地球化学特征及物源分析

为探讨全新世以来南海北部湾沉积物的沉积环境变化,对北部湾海域的SO-31沉积物柱状样进行了元素地球化学分析。根据元素地球化学的垂向分布特征,将SO-31沉积柱划分为3个单元,反映了全新世不同时期的区域海平面波动以及沉积物物源的变化。SO-31沉积柱的稀土元素配分曲线和La/Co与La/Sc散点图分析表明:111 400~12 800 a BP(全新世前期),研究区海平面较低,红河、其他周边河流及海岸侵蚀物均为本区的主要物源;28 500~1 1400 a BP(全新世早期),随着海平面的逐渐上升,河口和岸线逐渐后退,各物源供给区对本区沉积物的贡献量也发生了相应变化,相对而言红河贡献率有所下降;30~8 500 a BP(中全新世至今),区域海平面持续上升导致了琼州海峡打开,北部湾水动力环境和物源供给发生了剧变,红河对本区的物源贡献逐渐变小,而来自北部湾东部的物质成为本区沉积物的主要物源。     

珠江口及南海沉积物碳黑的放射性碳年龄

放射性碳同位素(14C)是含碳物质年代测定的有效手段,它的半衰期是5730年.研究了珠江口及南海沉积物碳黑的放射性碳年龄,碳黑样品采取化学氧化方法提取,用加速器质谱仪(AMS)测定珠江三角洲沉积柱中碳黑的放射性碳同位素剂量.研究结果表明,位于珠江口的钻孔3的碳黑的14C年龄是倒置的,邻近香港的钻孔30的碳黑14C年龄旱现老.新.老的趋势,而钻孔E2的碳黑的14C年龄则儿乎是不变的.碳黑的这种14C年龄的变化趋势与碳黑的来源相关,化石燃料来源的碳黑的增加使得碳黑的14C年龄偏老.     

A preliminary study on the existing forms of elements in sediments from Northern South China Sea

Our studies show that major and trace elements in marine sediments can exist in four different forms: terrigenous detritus, clay mineral-adsorbed material, that occurring in carbonate and precipitated together with colloidal Fe-Mn oxides. The results of our investigations show that the existing form of an element depends mainly on its geochemical properties as well as on its sedimentary environment and mode of sedimentation. The sedimentary environment of the deep-sea area in northern South China Sea is obviously different from that of the inland-shelf area and of the relic sedimentary area. In the region studied the geochemical mobility of elements is similar to that in oceans elsewhere. Based on their mobilities, the elements can be arranged in the order of < Zr < Fe < Li < B < Rb < Cr< V < Ba < Cu < Co < Ni< Sr < Mn.     

南海表层沉积物中生物钡的分布特征及其与初级生产力的关系

分析了南海东部53个站位表层沉积物中生物钡、铝以及有机碳和生物硅等生源物质的分布特征。结果表明,南海东部表层沉积物中的有机碳含量在研究区的北部陆架区出现高值,而在吕宋岛以西的深海则最低;生物硅的平面分布则表现为在吕宋岛以西的深海低沉积速率区出现高值,而低值则出现在高沉积速率的北部海域;生物钡的平面分布与生物硅的分布特征相似,高值出现在吕宋岛以西的深海区,且表现出自北而南沉积物中生物钡的含量逐渐增加的趋势。研究区内初级生产力表现为从北向南增加的趋势,而沉积物中生物钡的含量也呈现相似的趋势,表明沉积物中生物钡的含量和上层水体的生产力有一定的相关性。但表层沉积物中生物钡与有机碳呈弱的负相关关系,而与生物硅显著相关,且生物钡和生物硅与水深的相关性均呈现显著的相关性。因此,在采用沉积物中生物钡含量研究南海上层水体初级生产力时应谨慎对待。     

Grain size and geochemistry of surface sediments in northwestern continental shelf of the South China Sea

Eighty-six surface sediments collected from the northwestern continental shelf of the South China Sea (SCS) were analyzed for grain size distribution, calcium carbonate, organic carbon, and major and trace element compositions to investigate sediment provenance and factors controlling their geochemical composition. Sediments from the eastern continental shelf of Hainan Island have higher sand and lower clay content, while the samples from the nearshore Hainan Island have higher contents of gravel and clay. Calcium carbonate contents in samples show a positive correlation with water depth in northwestern shelf of SCS, suggesting that it is related to biological factors. However, the nearshore sediments have higher contents of organic carbon compared to those of the outer shelf, possibly suggesting that the terrigenous organic matter usually deposited in nearshore environments such as bays and estuaries. Compared with the upper continental crust, the samples have relatively lower contents of SiO₂ and Al₂O₃, higher than those of the Pearl and Red river sediments. The low contents of K₂O and Na₂O in sediments from the northwestern continental shelf are consistent with intense chemical weathering in the river basin due to the seasonally hot and humid climate regime. The sediments mainly consist of three components, including the gravel fraction composed of calcareous debris, the sand fraction composed of quartz, and the silt and clay fractions mainly composed of clay minerals. The content of each component depends on grain size, sediment source, biogenesis, and hydrodynamic conditions, which finally controls the chemical composition of the sediments. The distributions of Co/Al₂O₃, Cr/Al₂O₃, and Zr/Sc ratios for sediments in the northwestern continental shelf suggest that source rocks are mainly composed of felsic rocks rather than mafic rocks. There is a distinct difference in sediment source between eastern and western shelf sediments; the eastern shelf sediments are characterized by high Zr/Sc ratios mainly derived from the Pearl River, while the western shelf sediments have relatively low values of Zr/Sc indicating a main contribution possibly sourced from the Red River Basin. Terrigenous materials from Hainan Island usually influence the geochemistry of sediments deposited in the nearshore area.     

Evaluating methods for quantifying cation exchange in mildly calcareous sediments in Northern Alberta

Cation exchange capacity (CEC) and exchangeable cation composition are important properties in defining water–sediment interactions in contaminant transport scenarios, such as the seepage of process-affected water from oil sands tailings impoundments. At present, detailed characterization of these properties has been overlooked in the surficial Pleistocene sediments of the Athabasca Oil Sands region in Canada. Although a great variety of methods for determining CEC exist and continue to be developed, there is a deficiency in detailed comparisons amongst these methods in the literature, and consequently uncertainty still remains as to which extractants/methods are most suitable for use with sediments containing partially soluble carbonate salts. The present study (1) conducts an up-to-date evaluation of several distinct methods for their suitability in characterizing cation exchange properties in mildly calcareous sediments; using them to (2) evaluate the sorptive capacity and easily displaceable cations of mildly calcareous, surficial sediments near Fort McMurray, Alberta. Four conceptually different CEC methods were chosen: (a) a summation method (Lithium Chloride extractant); (b) a method that displaces an index cation after intermediary washes (Sodium Acetate–Ammonium Acetate); (c) a method using a high affinity cation complex (Silver Thiourea); and (d) a titration method using an organic cationic dye (Methylene Blue). Exchangeable cations were characterized using the Lithium Chloride and Silver Thiourea methods. Analysis suggests that the Methylene Blue test is least impacted by the presence of carbonate mineral phases. Results from field sediments suggest that the exchangeable cations, in decreasing abundance, consist of Ca > Mg > K > NH₄ > Na; while the CEC was found to be 4.7 ± 2.7 meq 100 g⁻¹ in the clay-rich glacial till, 0.7 ± 0.0 meq 100 g⁻¹ in the underlying sand and 4.1 ± 2.3 meq 100 g⁻¹ in the till-sand transition zone.     

南海北部陆坡沉积物中硫酸盐浓度变化模型与硫酸盐甲烷界面(SMI)的计算

硫酸盐作为电子受体,在有机质早期成岩作用中扮演着十分重要的角色,且较浅的硫酸盐甲烷作用带往往预示着下部有较大的甲烷逸散,或下部暗含天然气水合物藏(或天然气藏)。南海北部作为天然气水合物赋存区,了解赋存区沉积物中硫酸盐浓度变化对我们研究沉积物早期成岩作用和水合物的赋存是有重要帮助的。本文在分析了南海北部陆坡多个站位的沉积物柱状剖面中硫酸盐浓度变化特征之后,提出了南海北部硫酸盐变化模型及SMI界面深度计算方法。根据南海北部硫酸盐变化特征由浅至深可依次划分为有机质氧化驱动硫酸盐还原带、中层过渡带及下部甲烷厌氧氧化还原硫酸盐带。其中部分站位下部甲烷厌氧氧化硫酸盐还原带可分为上、下两层,两者硫酸盐还原速率以及硫酸盐梯度具有明显差异。有机质氧化带与甲烷厌氧氧化还原硫酸盐带在区内各处广泛发育,中层过渡带的存在与否取决于下部甲烷通量,在通量较大的地区中层过渡带消失。表层硫酸盐浓度增大是由有机硫氧化产生硫酸盐引起的。还应该注意的是,在计算SMI界面深度时,应剔除上部有机质氧化消耗硫酸盐的相关数据后进行计算,若下部甲烷厌氧氧化层根据硫酸盐还原速率可以划分成不同的两层,则应该使用下层数据进行拟合,计算SMI界面深度。     

Sensitive grain-size records of Holocene East Asian summer monsoon in sediments of northern South China Sea slope

Changes in paleoenvironments over the last 17,500 yr have been documented by a high-resolution clay mineralogy and grain–size records of Core KNG5 from the northern slope of the South China Sea. Our results indicate that clay minerals are mainly from the Pearl River from 17,500 to12,500 cal yr BP, and the South China Sea modern current system began to form since 12,500 cal yr BP, as a result, Taiwan turns to be the major contributor of clay minerals after 12,500 cal yr BP. Two grain-size populations with high variability through time were identified in the 13–28 μm and 1–2.2 μm grain-size intervals. The 1–2.2 μm grain-size population are mainly controlled by provenance supply and current transport. The 13–28 μm grain-size fraction could be controlled mainly by the sea-level change. The 1–2.2 μm grain-size population record demonstrates that East Asian Summer Monsoon intensity generally follows changes in insolation and that the response is similar for a large area of China and other northern low-latitude records, implying the globality of the monsoon evolution since Holocene. The anomalous environmental conditions in the northern South China Sea may imply intensified ENSO activity during the late Holocene.     

The logratio approach to the classification of modern sediments and sedimentary environments in northern South China Sea

Grain-size measurements are a type of compositional data and thus subject to closure effects and nonnormality. The logratio transform of Aitchison successfully resolves these problems in compositional data analysis. An application to modern sediment data from the northern part of the South China Sea demonstrates that logratio principal components analysis provides a clear separation of data which cannot be obtained by ordinary principal components analysis, and that cluster analysis using logratio principal components gives a much better classification of sediments than does cluster analysis using raw data. The delineation of sedimentary environments on the basis of a logratio classification of sediment samples provides a better understanding of hydrodynamic conditions on the shelf.     

Velocity-porosity relationships in hydrate-bearing sediments measured from pressure cores,Shenhu Area,South China Sea

Evaluating velocity-porosity relationships of hydrate-bearing marine sediments is essential for characterizing natural gas hydrates below seafloor as either a potential energy resource or geohazards risks. Four sites had cored using pressure and non-pressure methods during the gas hydrates drilling project (GMGS4) expedition at Shenhu Area, north slope of the South China Sea. Sediments were cored above, below, and through the gas-hydrate-bearing zone guided with logging-while-drilling analysis results. Gamma density and P-wave velocity were measured in each pressure core before subsampling. Methane hydrates volumes in total 62 samples were calculated from the moles of excess methane collected during depressurization experiments. The concentration of methane hydrates ranged from 0.3% to 32.3%. The concentrations of pore fluid (25.44% to 68.82%) and sediments (23.63% to 54.28%) were calculated from the gamma density. The regression models of P-wave velocity were derived and compared with a global empirical equation derived from shallow, unconsolidated sediments data. The results were close to the global trend when the fluid concentration is larger than the critical porosity. It is concluded that the dominant factor of P-wave velocity in hydrate-bearing marine sediments is the presence of the hydrate. Methane hydrates can reduce the fluid concentration by discharging the pore fluid and occupying the original pore space of sediments after its formation.©2022 China Geology Editorial Office.     

南海北部西沙海槽沉积物管状黄铁矿特征及其形成机理*

南海北部西沙海槽S1站位的岩心柱沉积物中广泛发育自生矿物黄铁矿,其形态以管状为主,且具有内部中空的圈层结构。使用扫描电镜、电子探针、LA-ICP-MS、SIMS等测试方法研究了管状黄铁矿的形态及圈层结构,结果显示: (1)管状黄铁矿发育内部中空的圈层结构,其中内圈层(I_py)由莓球状黄铁矿呈五角十二面体紧密堆积组成,外圈层(O_py)由晶形较好晶粒较大的八面体黄铁矿组成,并混有沉积碎屑及钙质生物壳体;(2)内圈层和外圈层分别呈现出贫S富Fe和富S贫Fe的特征,其成因是甲烷渗漏造成的局部还原环境使得As进入黄铁矿中导致晶格空缺或被扭曲,从而促进Ni、Co、Cu、Zn、Pb等微量元素的掺入;(3)内圈层、外圈层发生了明显的硫同位素分馏现象,内圈层中 δ³⁴S 平均为-37.8‰,外圈层中 δ³⁴S 平均为-29.3‰。研究认为,管状黄铁矿作为曾经甲烷渗漏的通道,其生长机制可分为3个阶段: (1)气水通道形成阶段: 向上运移的甲烷流体在沉积物孔隙中逐渐形成气水通道;(2)外圈层形成阶段: 当向上运移的甲烷与硫酸盐发生甲烷厌氧氧化时,逐渐形成晶体较大、晶形较好的八面体黄铁矿外圈层;(3)内圈层形成阶段: 随着甲烷浓度逐渐降低,在气水通道中的微生物作用下,剩余甲烷与向下运移的硫酸盐继续反应形成莓球状黄铁矿内圈层。因此,南海北部的泥岩中大量发育的管状黄铁矿常常与地层中甲烷水合物的存在有关。     

Magnetic mineral variations of South Caspian Sea sediments at laminae scale

The 998-cm long sediment core was collected from the South basin of the Caspian Sea. Sediments from the lower, Late Pleistocene part of the core (998-90 cm) are marked by laminations, which rapidly disappear under oxidising conditions. TEM/EDS analyses of magnetic extracts, done at laminae scale, show the presence of iron monosulphide (greigite Fe₃S₄) in grey and black laminae. There are also small amounts of magnetite. Magnetic hysteresis parameters Mrs/Ms and Bcr/Bc, presented on a Day plot, cluster near SD/PSD boundary, with smaller particles for black laminae. This tendency is due to a higher content of greigite, relative to coarser grained detrital magnetite in black laminae, and to a lower relative content of greigite in grey laminae. Analyses of Ca/Mg carbonates, grain size of the bulk sediment, feldspars/quartz ratios and water content show that these parameters do not vary at laminae scale. These results suggest that the laminae are of early diagenetic rather than detrital origin, reflecting rhythmic, subtle variations in the geochemical environment during laminae formation.     

An assessment of selected heavy metal contamination in the surface sediments from the South China Sea before 1998

Rapid economic development in East Asian countries has inevitably resulted in environmental degradation in the surrounding seas, and concern for both the environment and protection against pollutants is increasing. Identification of sources of contaminants and evaluation of current environmental status are essential to environmental pollution management, but relatively little has been done in the South China Sea (SCS). In order to investigate the metal pollution status and source within the SCS, a total of 52 surface sediment samples were collected in 1998 from the SCS for the selected heavy metal measurements such as Pb, Zn, Cu, V, Cr, Cd and Sc. The total concentrations (in mg kg^− 1 dry weight) in sediments ranged and averaged (mean ± S.D.): Pb, 4.18 to 58.7 (23.6 ± 8.93); Zn, 10.7 to 346 (87.4 ± 47.7); Cu, 5.29 to 122 (38.1 ± 24.6); V, 0.03 to 148 (78.0 ± 37.0); Cr, 4.48 to 589 (105 ± 86); Cd, 0.08 to 2.14 (0.40 ± 0.40) and Sc, 0.33 to 20.6 (10.6 ± 4.4), respectively. Enrichment factor (EF) values and geoaccumulation indexes (I_geo) suggest that Cu, Pb, Zn and V contamination exists only in few localized areas, but Cr and Cd contamination can be found in large-scale area of the SCS before 1998. Further studies are needed to reconstruct deposition history and for trend analysis.     

南海沉积物中C30-C32烷基二醇的检出及可能的古环境信息

从南海17962钻孔沉积物中检出了C30－C32长链烷基二醇类化合物。C30长链烷基二醇的碳同位素值在－30．17‰－－38．98‰之间,反映出其先质母体为水生生物,认为是海洋微藻－黄绿藻Eustigmatophytes。这类化合含量能够反映以黄绿藻为代表的海洋古生产力的变化：冰期时C30二醇的高沉积通量显示出南海南部末次冰期黄绿藻Eustigmatophytes初级生产力增高。计算C30和C32二醇的相对比值获得二醇参数（diols indices）,发现本柱状样二醇参数的变化指示了南海3万余年来的古海洋及古气候变化：南海经历了从半封闭到开放的演化,其气候经历了三次Heinrich冷事件,在Heinrich事件之间出现了一系列百年到千年尺度的气候事件,即D／O循环;全新世的Younger Dryas事件也有明显反映,说明南海与高纬度地区3万余年来的气候变化存在遥相关。