南海北部东沙海域巨型水下沙丘的分布及特征

本文基于多波束测深和高分辨率多道反射地震数据研究了东沙海域深水巨型水下沙丘的特征.巨型水下沙丘发育在230~830m水深的上陆坡范围内,呈斑块状分布.NW-SE向的近海底流体运动不仅冲蚀地层,形成了三条与水下沙丘间隔分布的冲蚀带,为水下沙丘提供了沉积物来源,同时也为水下沙丘的形成提供了动力源.研究区水下沙丘波长(L)范围55~510m,波高(h)范围1.5~20m,二者呈指数关系分布.沙丘的波长随水深增大而增大,波高则在500~700m水深范围内最大.水下沙丘NE—SW向展布的脊线和几何参数关系是与现今水动力条件相平衡的结果.     

南海北部末次冰期以来深水沉积物组成及其堆积速率的时空变化特征

通过对南海北部深水断面上MD12-3428(水深903m)、MD12-3433(水深2125m)和MD12-3434(水深2995m)三个岩芯的沉积物成分及其堆积速率分析,研究末次冰期以来南海深水沉积物组成和堆积速率的时空变化特征及其控制因素.研究结果显示,南海北部末次冰期以来的深水沉积物主要由陆源碎屑(59~89%)和碳酸盐(6~38%)组成,并含有少量蛋白石(1.6~9.4%)和有机质(0.7~1.9%).陆源碎屑和碳酸盐的堆积速率分别达到2.4~21.8和0.4~6.5g cm~(–2) ka~(–1)范围,比蛋白石和有机质堆积速率高出1~2个数量级.在末次冰期以来的时间序列变化上,沉积物各成分含量及其堆积速率都具有冰期-间冰期的旋回变化,陆源碎屑、蛋白石和有机质的含量及其堆积速率在氧同位素2期显著增加,而碳酸盐的含量及其堆积速率则呈反向变化或增幅不明显,表明南海深水碳酸盐含量在低海平面时期受到陆源碎屑稀释的影响.在从陆坡向深海盆的空间变化上,陆源碎屑的含量在同时期随水深的增加而增加,但其堆积速率锐减;碳酸盐含量及其堆积速率则随水深的增加而递减;而有机质和蛋白石的含量及其堆积速率随水深增加呈现复杂的变化特征.本文研究认为,南海北部末次冰期以来深水沉积物的组成及其堆积速率受到海平面变化的强烈控制,季风降雨引起的陆源物质供给、海洋初级生产力、以及陆源碎屑和海洋生源物质的相互稀释作用,共同影响了南海深水沉积物的堆积过程.     

南海北部深水底流沉积作用

南海北部深水陆坡区存在极为活跃的深水底流沉积作用. 通过浅地层地震剖面解释发现, 该地区由于深水底流的搬运作用, 在水深1000~2700 m左右的陆坡地带形成NE-SW向分布的迁移水道. 在水道东侧断续形成由东北向西南方向推进的高沉积速率堆积体, 堆积体内部叠加层呈NE-SW向前积堆积特征, 由牵引流沉积而成. 发育在东沙群岛东南侧的高沉积速率堆积体就是其中之一, 其12 ka以来沉积速率高达97 cm/ka, 是南海目前所知沉积速率最高的海区. 地震剖面显示, 该深水底流极有可能是由进入南海的西太平洋环流演变而成, 挟带南海北部来源的沉积物沿大陆坡由东北向西南方向搬运沉积, 最终消失在中央海盆中. 由于深水底流作用的存在, 造成南海北部深海区复杂的搬运沉积格局.     

南海北部深海潮汐的季节性变化特征

深海潮汐是深海混合过程的主要能量来源,对深海环流变异和沉积物搬运具有重要的调控作用.文章利用深水锚系观测系统在南海北部2100m水深处开展了近两年的高分辨率海流剖面观测,用于研究深海潮汐的季节性变化特征.通过谱分析显示,南海北部深海潮汐以全日潮为主,且在观测区域的深海中,全日潮和半日潮以垂向第一模态结构为主.斜压全日潮具有显著的季节性变化特征,夏季最强,深度平均的最大动能达86.7cm2s-2,分别是冬季的1.5倍、春秋季的2倍;而斜压半日潮没有明显的季节性变化.通过对比发现斜压全日潮的季节性变化受控于吕宋海峡附近的正压潮.另外,观测期间有三个强中尺度涡经过锚系站位,其中一个气旋式中尺度涡对深海海流影响较小,而另外两个反气旋式中尺度涡经过研究海域时可影响全水深海流,激发强亚惯性流,对深海潮汐产生边缘强化效应,并使深海斜压全日潮冬季的异相成分增强,占全日潮的85%.同时,中尺度涡对深海海水混合的增强弱化了海水层结,导致冬季的斜压全日潮流速减弱,低于夏季.南海北部深海潮汐季节性变化为研究深海盆沉积物在不同时间尺度上的分布及搬运过程提供了重要的动力机制.     

鄱阳湖典型湿地沉积物粒度分布及其动力解释

通过对沉积物粒度分析,揭示出翻阳湖典型湿地现代沉积物主要由含泥细粉砂至泥质极细粉砂组成,反映出三角洲前缘低能沉积环境,控制湿地粒度分布的动力,主要为重力型湖流,但波浪和风的作用也参与了沉积物的搬运与沉积,汛期,重力型湖流不仅控制了粒度分布的区域特征,而且决定了由草滩顶部－草滩下部－过滤带－泥滩沉积断面上粒度特征递变规律,枯水期,波浪作用的改造,使得沉积断面上的过滤带沉积物粗化,并使各粒度参数相应变化,特别是面积较大洼地的迎风岸,在过滤带地面坡度转折处,出现了粒度突变或跃变,风蚀“沙山”物质的搬运,使得“沙山”附近的湿地含砂量猛增,粒径变粗,这些动力作用,还控制着湿地的演化,即湿地范围增大,草滩扩张,过滤带以及泥滩下移,枯水期洼地水面缩小趋于消亡,严重影响湿地的生态环境,但可通过造造人工坝加以控制。     

风浪扰动下湖滨带悬浮物和营养盐响应特征

为研究风浪扰动下沉积物起悬过程中悬浮物浓度的分布特征和水体营养盐时空分布状况,以太湖西北湖滨带为例,选择代表4种不同生境的6个点位进行了连续12 d的野外观测.利用高精度分层同步采样装置,采用重量法计算悬浮量,并对悬浮过程中总磷(TP)、总氮(TN)、铵态氮(NH_4~+-N)和硝态氮(NO_3~--N)浓度进行分析.结果表明:风速是引起太湖西北湖滨带水体悬浮物增加的主要因素,沉积物悬浮的临界风速为3.6 m/s.各点位悬浮物浓度的均值差异明显,表现为:无植被区植被区河口区湖心区.太湖西北湖滨带水体氮、磷浓度日变化幅度较大,TN浓度为1.82~4.96 mg/L,TP浓度为0.10~1.47 mg/L.NH_4~+-N和NO_3~--N浓度分别在0.09~2.83和1.05~3.69 mg/L之间波动.近岸无植被区水柱的总悬浮量与风速的相关性最好,相关系数达到0.722;而远岸湖心区与风速的相关系数仅为0.039.悬浮物浓度除了受风情(风向和风速)的影响外,同样受水深、地形特征和水生植被的影响.     

2022年第5期封面

抚仙湖,位于云南省中部,为构造断陷湖. 面积214.7 km², 平均水深89m, 最大水深155m,蓄水量204×10⁸8 m³（水位1722.5m时）, 是我国第二深水湖泊和蓄水量最大的淡水湖.     

西藏班戈日阿铜多金属矿床地质特征及找矿前景

西藏班戈日阿铜多金属矿床位于班戈-腾冲多金属成矿带,是近年来新发现的矽卡岩型铜多金属矿床,已探明资源量达中型规模。最新研究和找矿成果显示矿带呈北西向展布,受燕山晚期白垩纪花岗岩类岩体侵入作用控制,矿体分布于岩体与下白垩统灰岩地层接触带及附近部位。在空间上,矿床主要分为三个矿段：主矿体分布在矿区中西部,目前在西矿段已圈定5个（条）铜矿体,矿体呈似层状、透镜状,其中最大的Cu13号矿体长221 m,平均厚9 m,沿倾向已控制延深100 m以上,铜品位：0.45%~2.01%,平均0.9%。主要金属矿物为黄铜矿、磁铁矿。中矿段已经圈定3条矿体,成矿元素除铜外,铅、锌、银含量也较高,为铜多金属矿体。矿体呈似层状、透镜状。其中以Cu-23号矿体最大,长达300 m,矿体最宽处达110 m。矿体平均品位Cu1.48%,Pb 1.25%,Zn 2.52%,A g 32.52×1-0 6。本文在矿区地质特征研究的基础上,通过对1：5万水系沉积物测量成果分析,对比中、西矿段成矿条件,对矿区东段进行了预测评价,指出该矿区具有较好的铜多金属找矿前景。同时建议对已圈定的1：5万水系沉积物异常开展1：1万土壤地球化学测量工作,进而圈定该区铜多金属矿带或矿（化）体,为矿区深入勘查工作提供依据。     

横断山区湖泊中溶解氧的分布特征

本文是对横断山地区17个湖泊水体中溶解氧含迸的测定。其平均含货在5.86~8.35mg/L之间,最大含里可达14.54mg/L。湖泊中溶解氧含量在地域分布上随箝海拔高度升高而下降。由于受湖泊中水体运动影响,湖泊表层水中溶解氧分布较一致,但在深水湖泊中表层和底层含量即有明显差异,且随着水深加大溶解氧下降,如马湖,在水深l00m以下为无氧区,致使生物大量死亡。在深水层的温跃层附近（10—50m）溶解氧出现跃变现象。此外,湖泊中水生生物分布,以及有机质污染,对水体中溶解氧含量和分布亦有直接影响。     

黄河三角洲不同气候条件下沉积物中胶黄铁矿的形成

胶黄铁矿的形成和保存可以指示沉积环境的理化特征.对黄河三角洲钓口叶瓣钻取的一根长30.4 m高取芯率岩芯ZK30孔进行了粒度和磁学性质测试,并对提取的磁性颗粒进行了扫描电镜(SEM)和X射线衍射(XRD)分析.研究结果表明,该岩芯在浅海相向河湖相转换处(29.4~29.7 m)以及河湖相向盐沼相转换处(26.1~27.1 m)的沉积物,具有显著高于其他层位沉积物的饱和等温剩磁(SIRM)及其与磁化率(x)的比值(SIRM/x),反映了这两层沉积物中存在胶黄铁矿的可能性,这一磁学性质的判断得到了SEM和XRD分析的支持.在河湖相底层处(29.4~29.7 m),沉积物较粗,胶黄铁矿与黄铁矿共存,但分布厚度较薄;而在河湖相顶层处(26.1~27.1 m),沉积物颗粒较细,黄铁矿少见,胶黄铁矿层分布厚度较厚.这一胶黄铁矿和黄铁矿存在方式的差异,反映了不同气候条件和沉积环境对胶黄铁矿赋存的控制.     

Geophysical survey on the tectonic and sediment distribution of Qinghai Lake basin

1 Introduction in China, with an area of 4400 km2 and a drainage area With the advancement of global change study, peo- of nearly 29,660 km2[2]. Occurring at a “climatic triple ple are paying more and more attention to the conti- junction” among the East Asian monsoon, Indian nental environment (in which we reside), its evolution Monsoon and the Westerly Jet Stream, it lies in the and its future tendency. As a component of the global transitional belt of the east monsoonal humid areas sys…     

A 12-kyr record of microbial branched and isoprenoid tetraether index in Lake Qinghai,northeastern Qinghai-Tibet Plateau: Implications for paleoclimate reconstruction

Branched and Isoprenoid Tetraether (BIT) index was considered as a proxy for terrestrial organic matter input in lake sediments, based on the assumption that branched glycerol dialkyl glycerol tetraethers (bGDGTs) are mainly derived from terrestrial soils. However, mounting evidences have showed that the in situ production of bGDGTs is widespread in lakes, challenging BIT as a reliable terrestrial input proxy. Recently, BIT has been proven to be a reliable proxy for paleohydrology in a small crater lake (Lake Challa) in accordance with a different mechanism. However, the response of BIT to paleohydrology variation may differ for different lakes. In this study, we investigate the variations in the BIT index and the concentrations of its related GDGTs in a 12-ka sediment core from Lake Qinghai, in combination with our previous results for surface sediments. We find that variations in BIT strongly depend on the concentration of crenarchaeol in both surface and ancient sediments of this lake, whereas bGDGT concentration varies much less remarkably. Considering that crenarchaeol production is positively correlated with water depth in Lake Qinghai, water depth may exert negative control on the BIT index in this lake. This case is inconsistent with the positive relationship between BIT and lake levels or rainfall intensity reported for Lake Challa, suggesting that the response of BIT to local paleohydrology is site specific in lacustrine systems. Hence, the application of sedimentary BIT as a paleohydrological proxy in a specific lake requires caution before confirming the environmental controls on BIT in that lake.     

柴达木盆地托素湖不同位置岩芯沉积物指标对比及其环境意义

湖泊不同位置岩芯沉积物相同代用指标的变化是否一致对于重建可靠的区域气候变化历史至关重要.目前多数研究仅利用深水区单一的沉积岩芯来反演区域的气候环境变化,对于不同位置岩芯重建结果的异同尚缺乏研究.本文选择托素湖不同位置、不同水深的4根短钻岩芯沉积物,在放射性核素(210 Pb和137 Cs)定年的基础上,对比分析各岩芯沉积物粒度、碳酸盐含量等代用指标的变化情况.结果显示,湖泊内相近的沉积岩芯沉积物粒度变化相似,但相距较远的岩芯之间粒度变化差异较大;浅水区的沉积物粒度(粒径或组分含量)在短时间尺度上变化很大,而深水区的沉积环境比较稳定,在百年尺度上的变化不明显;有机质与碳酸盐含量总体变化趋势一致且有较好的相关性,表明碳酸盐可能受到湖泊生产力的影响.碳酸盐含量、碳酸盐氧同位素(δ18 O)和TL06孔孢粉的A/C比值变化基本一致,反映的有效湿度变化与同期气象记录的相对湿度一致,但与降水量和蒸发量的变化不一致.因此,托素湖粒度指标仅指示不同位置钻孔沉积环境状况,与气候变化的关系并不明显,用碳酸盐及其同位素等地球化学指标恢复区域气候变化历史更可靠.     

The discovery of annually laminated sediments (varves) from shallow Sugan Lake in inland arid China and their paleoclimatic significance

Detailed examination of sedimentary cores retrieved from Sugan Lake in the northern Qaidam Basin of northwest China’s Tibetan Plateau reveal that fine laminated beddings form in the sediments where water depth exceeds 3 m. Seasonal surface sediments trapped at the bottom of the lake suggest that sediments deposited during summer and autumn are mainly light colored monohydrocalcites, while those deposited in winter are dark organic matter, indicating that varve layers form under modern limnological conditions. Continuous varve sediments comprising four types have accumulated in the upper 5.5 m of Core SG03I from the center of the lake. All types exhibit clear seasonality indicative of annual deposition. Varve counts correspondence with 210Pb dates on recent sediments in the upper core suggest the continuous varves of the upper 5.5 m of the core formed in the late Holocene (2670 a BP). The Sugan Lake varve sequence is the first demonstration of annually laminated sediments re-ported in arid western China.     

Salsvatn,a lake with old sea water

Salsvatn is a 464 m deep lake laying 16 m above sea level in North Trøndelag, Norway. The lake was isolated from the sea some 3,000 years ago. It is assumed that salt-water in the deepest 50 m of the lake is the remain of sea water being trapped in the lake at this time. The concentration of cloride in the salt-water layer corresponds to a salinity of 29‰ in ordinary sea water. Hydrography of the lake and changes in some components of the salt water compared with ordinary sea water are discussed. Comparison is made with changes in the stagnant layers of the Black Sea and Lake Rørholtjorden. The latest is another lake with old sea-water at its bottom. Surface sediment samples have been collected from the freshwater and salt-water layers in Lake Rørholtfjorden and from the salt-water layer of Lake Salsvatn. Some chemical components of the sediments and interstitial water have been analysed and discussed.     

Pedogenic zones in postglacial sediment of lake manitoba,Canada

The postglacial sediment record of Lake Manitoba is composed dominantly of silty clay to clayey silt with little variation in most physical, chemical, and mineralogical properties. Distinct in the sedimentary sequence of this large lake, however, are four zones that have a low moisture content, blocky to pelletal structure, and gleyed colour. All of these zones formed during the warmest and driest postglacial period in the region, 9500 to 4500 years ago. Although several possible hypotheses can be formulated regarding the origin of these zones including changes in sedimentation rate, clay mineralogy, lake chemistry, and depth of winter freezing, the most likely explanation is that they represent pedogenic horizons. Formation by pedogenesis during dry or extremely low water conditions is not mutually exclusive of the other hypotheses, and several are favoured by low water conditions.     

巢湖沉积物磁性特征及其对沉积动力的响应

对巢湖西部柱样以及杭埠河流域土壤的环境磁学研究表明,磁铁矿是决定磁性特征的主要磁性矿物,杭埠河流域是巢湖西部沉积物的主要来源．靠近巢湖西岸的柱样AC1砂含量较高,X、SIRM值较大而xARM／SIRM较低,说明磁铁矿含量较高、颗粒较粗．距岸稍远的柱样AC2砂含量较低,X、SIRM值也较低,其变化与XARM较相似,与粘土含量变化也有一定程度的相似,AC2沉积物X、SIRM值较ACI小,但XARM／SIRM较高,说明磁铁矿含量较低且颗粒较细．杭埠河流域土壤的磁性测量结果表明,砂、砾含量高的粗骨土磁性最强,富含粗颗粒磁铁矿．巢湖柱样沉积物砂的含量随踞岸远近而不同, 反映了沉积环境的水动力不同,由此产生明显的磁性特征差异,实质是对沉积动力的响应．研究表明磁性参数XARM／SIRM 可以间接反映沉积物中粘土含量的高低变化．     

Geochemical evidence of hydrothermal recharge in Lake Baringo,central Kenya Rift Valley

Lake Baringo, a freshwater lake in the central Kenya Rift Valley, is fed by perennial and ephemeral rivers, direct rainfall, and hot springs on Ol Kokwe Island near the centre of the lake. The lake has no surface outlet, but despite high evaporation rates it maintains dilute waters by subsurface seepage through permeable sediments and faulted lavas. New geochemical analyses (major ions, trace elements) of the river, lake, and hot spring waters and the suspended sediments have been made to determine the main controls of lake water quality. The results show that evaporative concentration and the binary mixing between two end members (rivers and thermal waters) can explain the hydrochemistry of the lake waters. Two zones are recognized from water composition. The southern part of the lake near sites of perennial river inflow is weakly influenced by evaporation, has low total dissolved species (TDS), and has a seasonally variable load of mainly detrital suspended sediments. In contrast, waters of the northern part of the lake show evidence for strong evaporation (TDS of up to eight times inflow). Authigenic clay minerals and calcite may be precipitating from those more concentrated fluids. The subaerial hot‐spring waters have a distinctive chemistry and are enriched in some elements that are also present in the lake water. Comparison of the chemical composition of the inflowing surface waters and lake water shows (1) an enrichment of some species (HCO₃^?, Cl, SO₄^2?, F, Na, B, V, Cr, As, Mo, Ba and U) in the lake, (2) a depletion in SiO₂ in the lake, and (3) a possible hydrothermal origin for most F. The rare earth element distribution and the F/Cl and Na/Cl ratios give valuable information on the rate of mixing of the river and hydrothermal fluids in the lake water. Calculations imply that thermal fluids may be seeping upward locally into the lake through grid‐faulted lavas, particularly south of Ol Kokwe Island. Copyright © 2006 John Wiley & Sons, Ltd.     

Variation characteristics of heavy metals and nutrients in the core sediments of Taihu Lake and their pollution history

The sedimentary environment change, trophic evolution and heavy metals pollution history of the northern Taihu Lake in the last 100 years are studied according to the sedimentary geo-chemical proxies of the core sediments, such as grain size, nutrients, heavy metals, diatom, etc. The nutrients in the sediments depended mainly on the lake internal circulation and the heavy metals were from natural geogenic sources before the 1920s, which were not influenced by human activities generally, and grain size was one of the key factors influencing heavy metals content in the sediments. The alternation of manner and strength of human activities in Taihu Lake catchment before and after the 1920s made the lake sediments coarser, and hence heavy metals and TP content decreased contrasted with that before the 1920s. TP content in sediments and water increased from the 1950s to late 1970s due to anthropogenic pollutants discharge, and the lake belonging to mesotrophic state. TN and TOC content and C/N ratio increased due to the increasing external pollutants into Taihu Lake by human activities, TP content also increased obviously in water and sediments, and the diatom association was dominated by eutrophic species since the late 1970s, indicating the eutrophication state of Taihu Lake in this period. Meanwhile the increasing in heavy metals content, such as Cu, Mn, Ni, Pb and Zn, and their proportion of valid fractions in the sediments indicates that they all result from human pollutants since the late 1970s. The heavy metals in the surface sediments have certain potential biological toxicity due to the higher SEM/AVS ratio.     

浙江东钱湖底泥污染物分布特征与评价

对东钱湖底泥做了全面调查,测定了底泥粒度组成、有机质、TN、TP及重金属含量,分析了底泥沉积特性及污染物分布特征,分别采用潜在生态危害指数(RI)法和相对背景值法对重金属污染风险和有机污染及营养盐污染进行了评价.研究结果表明:东钱湖底泥组成以细颗粒为主,重金属含量除镉污染达到中等生态危害程度外,其余均处于较低水平,湖区底泥中有机污染和氮污染问题非常突出.为有效治理东钱湖内源污染,有必要开展包括生态疏浚在内的内源污染治理措施.研究为进一步开展东钱湖水环境治理提供了理论依据.