长江口现代潮滩表层沉积物磁性特征和自生铁硫化物的分布*

以长江口崇明岛北支潮滩的3个潮滩为对象,在粒度测量和磁性分析的基础上,揭示了现代潮滩表层沉积物的磁性变化,探讨了磁性矿物、尤其是自生亚铁磁性矿物—硫复铁矿（Fe₃S₄）在潮滩沉积微相的分布规律及机制。研究结果表明：长江口潮滩表层沉积物的磁性特征由亚铁磁性矿物及超顺磁颗粒(SP)主导。淤积型中高潮滩磁铁矿以单畴(SD)和SP为主,侵蚀型潮滩的中低潮滩则更多假单畴/多畴(PSD/MD)晶粒,反映了水动力的分选及以细颗粒矿物溶解为主的早期成岩作用。此外,最东侧的北四滧港剖面潮上带—高潮滩芦苇带普遍存在自生亚铁磁性硫复铁矿,北堡港和新卫剖面的高潮滩也局部存在硫复铁矿,反映了本区高潮滩—潮上带丰富的有机质及细颗粒沉积物、加上有限的海水淹没时间,是早期成岩作用过程中生成硫复铁矿的主要机制。     

南通近海潮滩表层沉积物重金属含量特征与生态风险评价

基于南通近海(洋口港—吕四)潮滩特点布设潮滩断面并采集表层沉积物,根据样品汞、镉、铅、砷、铬等7种重金属元素含量测试结果,分析研究区沿海潮滩表层沉积物主要重金属元素含量特征,并与江苏其他滨岸地区潮滩沉积物的重金属含量进行对比,初步探讨2009—2012年南通沿海滩涂表层沉积物重金属含量变化与元素的相关性。采用潜在生态危害指数法评价南通近海潮滩表层沉积物中7种重金属元素的潜在生态危害系数及潜在生态风险。南通潮滩表层沉积物重金属含量分布均匀,且低于江苏省苏北其他地区沿海潮滩的沉积物含量。7种重金属元素的相关分析表明,Cu与Pb、Zn具有较好的相关性,Pb与Cd、Hg的相关性最差。潜在生态危害指数法评价表明,南通近岸潮滩表层沉积物7种重金属潜在生态危害系数均属低生态危害范畴,近岸海域(洋口港—吕四段)潮滩表层沉积物环境质量总体较好。     

中全新世福建沿海地区海平面波动：基于NDQK5岩芯介形类化石记录

福建沿海地区第四系较为发育,是研究晚更新世以来相对海平面变化的理想区域。本文以福建宁德NDQK5岩芯中产出的高分辨率介形类化石为研究对象,结合加速器质谱法(accelerator mass spectrometry, AMS)14C和光释光测年技术建立岩芯年代框架,重建了中全新世期间福建沿海地区的相对海平面变化。结果显示,NDQK5岩芯中的介形类化石记录主要分布于4~17. 1 m段,对应年代约为8. 2~6. 9 ka BP。岩芯内共计识别出海相介形类23属26种,根据优势种以及特征种的相对丰度变化特征可将岩芯内的介形类动物群划分为3个组合：① 介形类组合A以Bicornucythere bisanensis和Sinocytheridea impressa为主,代表潮下带环境;② 介形类组合B以Sinocytheridea impressa和Neomonoceratina delicata为优势种,指示近岸内陆架的沉积环境;③ 介形类组合C以Sinocytheridea impressa和Loxoconcha ocellifera为主,代表潮间带的沉积环境。基于介形类组合的分布特征,本文推断福建沿海地区海平面约在8. 2~7. 4 ka BP期间持续上升,并在约7. 9~7. 4 ka BP区间达到最高;7. 4~7. 0 ka BP期间海平面下降,随后再次上升。因此,介形类化石记录指示福建沿海地区在全新世高海平面背景下依然存在相对海平面的次一级波动。同时,结合已有福建沿海地区海平面变化驱动机制的研究结果,本研究推断8. 2~7 ka BP期间福建沿海地区的海平面变化可能主要受控于冰盖融水;7 ka BP后该地区的海平面波动可能受控于“冰川- 水均衡调整”作用。     

长江口北支潮滩不同沉积微相有机地球化学元素分布*

利用在长江口崇明岛北支北四滧港（SY）、北堡港（BBG）以及新卫村（XW）潮滩获取的表层沉积物,测试总有机碳（TOC）、总氮（TN）及总硫（TS）含量,分析有机地球化学元素在潮滩微相的分布规律及影响因素,试图建立TOC/TN、TS/TOC等潮滩微相识别指标。研究结果显示,影响长江口潮滩TN、TS微相分布的重要因素为有机质含量及类型。在淤涨型潮滩,TOC/TN在高潮滩一般大于10,在中潮滩明显降至10以下;中潮滩植被带TS/TOC最高,平均值达0.063,其次为高潮滩互花米草带和中潮滩光滩（分别为0.055和0.054）,高潮滩芦苇带最低;TS-TOC一元线性回归斜率在高潮滩芦苇带呈现为显著低值,自高潮滩米草带向光滩,逐渐增大。在侵蚀型潮滩,TOC/TN从高潮滩到低潮滩均大于10,而且中、低潮滩的比值大于高潮滩,潮下带骤降至小于10;TS/TOC自陆向海逐渐增大,TS-TOC一元回归斜率高潮滩最低,中潮滩最高。另外,侵蚀型潮滩各微相的TS-TOC一元线性回归斜率均明显低于淤涨型潮滩。上述研究结果表明,长江口沉积物的TOC/TN和TS/TOC及TS-TOC一元线性回归斜率与潮滩沉积微相之间存在一定的关系,具有应用于全新世钻孔识别潮滩沉积物微相的潜力。     

长江三角洲全新世海平面重建研究综述

通过综述国内外全新世海平面重建研究进展,总结了全新世海平面重建的各种指标和海平面重建存在的科学问题,认为冰川—水均衡作用、区域差异性构造沉降、沉积物压实和侵蚀再沉积作用是各地区全新世海平面差异性存在的主要原因;对长江三角洲各海平面重建指标进行了有效性分析,得出基底泥炭、硅藻、有孔虫转换函数,海相地层、古人类遗址、TOC/TN和δ13C、TOC/TS和自生铁硫化物是重建海平面的有效指标,并对每个指标的优缺点及重建时需要考虑的问题进行了阐述。     

巴丹吉林沙漠湖泊表层硅藻分布的初步研究

硅藻广泛生长于河流、湖泊和海洋中.硅藻对环境的变化极为敏感,可建立硅藻与环境参数之间的转换函数,并应用于古环境的定量重建[1～5].大量的研究表明一些硅藻种类具有很强的耐盐耐碱特征,广泛生长在干旱、半干旱地区的咸水湖中,不过目前尚无极端干旱地区现代湖泊硅藻分布状况的研究.     

云龙天池湖泊水深与硅藻生物多样性的关系

以云龙天池湖泊为研究对象,通过分析不同深度表层硅藻样品的生物多样性以及100年来硅藻生物多样性的变化特征,探讨硅藻生物多样性与水深变化之间的关系.虽然硅藻组合随水深发生了明显的变化,浅水区底栖硅藻占优势,深水区浮游硅藻占优势,但是不同深度表层样品中硅藻的属种数(简单分异度)基本相同,硅藻种群的生物多样性也没有发生显著的趋势性变化.这主要是由于硅藻各属种在不同深度的权重互补,导致云龙天池硅藻的多样性在湖泊的不同深度变化不大.近百年来的湖泊沉积速率显示,自1960年前后,湖泊水位在波动中逐步升高,但是硅藻种群的生物多样性并没有发生相应的变化.以上研究结果说明,云龙天池硅藻种群的生物多样性,不管是在时间上,还是空间上,与水深变化均无明显相关性.     

河北省海岸带地面沉降现状及形成机理研究

河北省沿海地区位于华北平原与渤海的交会地带,是一个人口聚集、生态环境脆弱、开发程度较高的地区,存在着较为严重的地面沉降灾害,对沿海地区人民生活、城市建设和社会发展造成了不利影响。本文通过In SAR监测及二等水准测量相结合的方式来研究河北省沿海地区地面沉降状况,分析影响海岸带In SAR提取形变精度的误差源及其校正方法,获取大比例尺高精度海岸带形变监测结果,并在此基础上分析研究河北省海岸带地面沉降的原因,为工程建设、区域规划、防灾减灾监测提供技术参考。     

潮滩脆弱性评估方法研究综述

由于潮滩组成要素不稳定、地理区位特殊以及人为因素的制约,导致潮滩极易受外在和内在因素的影响,发生自然系统脆弱性(包括固有脆弱性和特殊脆弱性)。在总结国内外关于潮滩脆弱性评估方法(诸如综合指数法、层次分析法等综合评估方法以及主成分分析法、高程面积法等单一影响评价法)基础上,根据潮滩脆弱性评估的选择原则,构建了潮滩脆弱性评估指标体系,以期为沿海地区的可持续发展提供理论和技术支撑。     

渤海湾中北部表层沉积硅藻分布及环境指示意义

发现渤海湾中北部表层沉积硅藻21属37种,确定了Cyclotella striata/stylorum,Paralia sulcata和Coscinodiscusperforatus等9个优势种的地理分布;进而根据聚类分析,将研究区表层沉积硅藻划分为6个组合区。讨论了控制它们分布的环境因素,发现盐度与深度是重要控制因素,沉积物底质类型亦对硅藻的分布有一定的影响。     

利用盐沼泥炭重建长江三角洲北部全新世中期海平面

根据对长江三角洲北部海安地区4个钻孔标志性沉积物(潮上带盐沼泥炭、高潮滩沉积)的年龄测定和高程测量,以及沉积物压实沉降量的分析研究,重建了本研究区全新世中期8.1～7.3 cal kyr BP和5.6～5.4 cal kyr BP的相对海平面位置。结果显示,8.1～7.3 cal kyr BP海平面缓慢上升1.46m,上升速率仅为0.2cm/yr, 与三角洲南部全新世早期海平面的快速上升(2cm/yr)形成鲜明对比,验证了冰盖控制下的全球海平面阶段性波动上升模式。对比长江三角洲地区海平面曲线发现,三角洲北部海平面曲线较南部低5～6m,长江三角洲海平面曲线与世界各地海平面曲线也存在明显差异,分析认为主要是由长江口地区的差异性沉降和中国东部边缘海的水均衡作用两个因素引起的。     

安徽宿松上石炭统碳酸盐岩台地沉积物定量分析与海平面变化

安徽宿松地区上石炭统碳酸盐岩发育,厚约100m,化石丰富,属于比较典型的浅海碳酸盐岩台地沉积。定量分析显示,研究区岩石类型主要为颗粒灰岩和泥粒灰岩,颗粒平均含量分别为81.2％和69.6％,以浅海生物碎屑为主;其次为粒泥灰岩和泥晶灰岩,颗粒平均含量分别为26.4％和4.1％。依据岩石学特征,研究区主要发育开阔台地相和潮坪相,并可进一步划分出5种沉积亚相,分别是台内滩、台内盆、台内坪、潮间坪和潮上坪。在研究区上石炭统中共识别出3个长期的海进—海退旋回,其表现出在海平面变化总体呈下降趋势的背景之上叠加了短期的高频海平面波动的特征。这3个旋回与扬子板块其他地区及欧美板块同时代地层中的长期海进—海退旋回相当,表明海平面的变化可能受到晚古生代冈瓦纳大陆冰川的冰期和间冰期交替活动的影响。     

Diatom‐based tidal‐level transfer functions as an aid in reconstructing Quaternary history of sea‐level movements in the UK

This research analyses the diatom asssemblages recorded from six UK coastal sites and relates these diatom assemblages to tidal levels. The relationship between diatom assemblages and tidal levels is examined statistically in order to develop a diatom‐based tidal‐level transfer function. The results suggest that there is highly significant correlation between the diatom assemblages and water levels from mean high water of neap tides to highest astronomical tide (p = 0.01, 99 random permutations). A weighted average (WA) transfer function is thus established, and the predictive ability of this transfer function is highly satisfactory. Finally, this transfer function is applied successfully to estimate palaeotidal‐levels from fossil diatom data recorded in late Holocene coastal sequences. Copyright © 1999 John Wiley & Sons, Ltd.     

Late Holocene relative sea-level changes and the earthquake deformation cycle around upper Cook Inlet,Alaska

Multiple peat-silt couplets preserved in tidal marsh sediment sequences suggest that numerous great plate boundary earthquakes caused the coast around Cook Inlet, Alaska, to subside over the past 3500 years. Field and laboratory analyses of the two youngest couplets record the well-documented earthquake of AD 1964 and the penultimate one, approximately 850 cal yr BP. Diatom assemblages from a range of modern day estuarine environments from tidal flat through salt marsh to acidic bog produce quantitative diatom transfer function models for elevation reconstructions based on fossil samples. Only nine out of 124 fossil assemblages analysed, including previously published data for the AD 1964 earthquake, have a poor modern analogue. Calibration of fossil samples indicate co-seismic subsidence of 1.50±0.32 m for AD 1964, similar to measurements taken after the earthquake, and 1.45±0.34 m for the ∼850 cal yr BP earthquake. Elevation standard errors for individual fossil samples range from ∼0.08 m in peat layers to ∼0.35 m in silt units. Lack of a chronology within fossil silt units prevents identification of changes in the rate of recovery and land uplift between the post-seismic and inter-seismic periods. However, preservation of multiple peat-silt couplets indicates no net emergence over multiple earthquake cycles. Glacio-isostatic movements from Little Ice Age glacier advance and retreat explains a ∼0.15 m relative sea-level oscillation recorded within the peat layer subsequently submerged as a result of the AD 1964 earthquake. Before both this and the ∼850 cal yr BP earthquake, diatom assemblages suggest pre-seismic relative sea-level rise of ∼0.12±0.13 m, representing possible precursors to great earthquakes.     

Assessing the performance of a foraminifera-based transfer function to estimate sea-level changes in northern Portugal

We assessed the performance of a transfer function model for sea-level studies using salt-marsh foraminifera from two estuaries of northern Portugal. An independent data set of 12 samples and 13 sub-fossil samples from a core were used to evaluate if reconstructions and errors derived from current models are adequate. Initial transfer function models provided very strong results as indicated by cross-validation (component 2; r² = 0.80-0.82; RMSEP ranged from 10.7 to 12.3 cm) and improved its performance by ca. 10% when sample size reached ca. 50. Results derived using an independent test data set indicate that cross-validation is a very effective approach and produces conservative errors when compared to observed errors. We additionally explored the possible effect of transforming the concentration data into percent in the error estimations by comparing the results obtained based on the use of both concentration and compositional data. Results indicate that this type of transformation does not affect the performance of the transfer function. Results derived from a reconstruction of sub-fossil samples from a core indicate that high-resolution sea-level reconstructions are possible, but show that depositional environments have to be selected carefully in order to minimize the impact of possible taphonomical loss.     

四川南江地区上震旦统灯影组混积层系特征及成因

陆源碎屑和碳酸盐混积层系是一种沉积机理特殊而又有重要意义的沉积现象。四川南江新立村下震旦统灯影组剖面碎屑岩-碳酸盐岩混积层系发育良好。在该剖面上共识别出4类混积层系岩石组合类型:细砂岩-泥晶白云岩组合(Ⅰ)、粉砂岩-泥晶白云岩组合(Ⅱ)、粉细砂岩-含粉砂白云岩组合(Ⅲ)、含砾砂岩-白云岩组合(Ⅳ)。通过岩石类型、岩石组合特征的分析,显示出灯影组二段上部-三段由下向上发育混积中潮坪、潮下浅滩、潮道、低潮坪4种沉积亚相,而混积层系主要产出于混积中潮坪和潮道亚相。微量元素指示研究地层整体形成于氧化环境,但发生混积层位的形成环境相对缺氧。根据当时海平面变化和大地构造演化,认为灯影组陆源碎屑和碳酸盐混积层系的出现与桐湾运动Ⅰ幕之后海平面下降导致的陆源碎屑输入增强有关。     

Scale considerations in using diatoms as indicators of sea‐level change: lessons from Alaska

This paper assesses variations in quantitative reconstructions of late Holocene relative sea‐level (RSL) change arising from using modern diatom datasets from different spatial scales, applied to case studies from Alaska. We investigate the implications of model choice in transfer functions using local‐, sub‐regional‐ and regional‐scale modern training sets, and produce recommendations on the creation and selection of modern datasets for reconstructing RSL change over Holocene timescales in tidal marsh environments comparable with those in Alaska. We show that regional modern training sets perform best in terms of providing fossil samples with good modern analogues, and in producing reconstructions that most closely match observations, where these are available. Local training sets are frequently insufficient to provide fossil samples with good modern analogues and may over‐estimate the precision of RSL reconstructions. This is particularly apparent when reconstructing RSL change for periods beyond the last century. For reconstructing RSL change we recommend using regional modern training sets enhanced by local samples. Copyright © 2012 John Wiley & Sons, Ltd.     

A new Late Holocene sea-level record from the Mississippi Delta: evidence for a climate/sea level connection?

A detailed relative sea-level (RSL) record was constructed for the time interval 600–1600 AD, using basal peat to track sea level and containing 16 sea-level index points that capture ～60 cm of RSL rise. The study area is in the Mississippi Delta where the spring tidal range is ～0.47 m, the impact of ocean currents on sea-surface topography is limited, and crustal motions are well constrained. Age control was obtained by AMS ¹⁴C dating and most ages represent weighted means of two subsamples. Sample elevations were determined by combining differential GPS measurements with optical surveying. All index points were plotted as error boxes using 2σ confidence intervals for the ages, plus all vertical errors involved in sampling and surveying, as well as the indicative range of the samples. A striking clustering of sea-level index points between ～1000 and ～1200 AD suggests a possible acceleration in the rate of RSL rise. Removal of the long-term trend (0.60 mm yr^?1) allows for the possibility of a sea-level oscillation with a maximum amplitude of ～55 cm. However, given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out. Comparison of the new RSL record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes, including the Medieval Warm Period and the Little Ice Age. However, given the error margins associated with this reconstruction, it is stressed that this causal mechanism is tentative and requires corroboration by high-resolution sea-level reconstructions elsewhere.     

Modern diatom assemblages from Chilean tidal marshes and their application for quantifying deformation during past great earthquakes

Tidal marsh sediments from south‐central Chile provide evidence for multiple great earthquakes. Diatom transfer functions, statistical models of the relationship between species preserved in the sediment and elevation, provide quantitative estimates of coseismic vertical land‐level change associated with individual earthquakes. However, in south‐central Chile, our ability to quantify land‐level change is currently limited by a lack of understanding of the environmental variables controlling the distribution of diatoms, an essential prerequisite for converting variations in fossil diatom assemblages into quantitative estimates of past elevation changes. We present a new modern diatom dataset for the region and explore the implications of the scale of the dataset used in transfer function models on the reconstructions of land‐level change. Modern training sets containing samples from a regional scale are superior to sub‐regional and local‐scale training sets, providing closer estimates for known deformation during the great 1960 Chilean earthquake, a higher proportion of good modern analogues and uncertainty terms up to 42% smaller than previously published reconstructions. Copyright © 2017 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.

     

Reconstruction of recent sea-level change using testate amoebae

Proxy-based sea-level reconstructions place the instrumentally observed rates of recent sea-level rise in a longer term context by providing data that extend the instrumental sea-level record into past centuries. This paper presents the first sea-level reconstructions based on analyses of testate amoebae, to test their ability to produce high-precision reconstructions of past sea level. We present two reconstructions for the past 100 yr from sites in Maine (USA) and Nova Scotia (Canada) based on short cores from salt marshes, and modern training data from North America and the United Kingdom. These are compared with tide-gauge records and reconstructions based on foraminifera from the same cores. The reconstructions show good agreement with both the tide-gauge data and the foraminifera-based reconstructions. The UK data perform well in predicting known elevations of North American surface samples and produce sea-level reconstructions very similar to those based on the North American data, suggesting the methodology is robust across large geographical areas. We conclude that testate amoebae have the potential to provide robust, higher precision sea-level reconstructions for the past few centuries if modern transfer functions are improved and core sites are located within the main zone of testate amoebae occurrence on the salt marsh.