河口有孔虫的搬运作用及其古环境意义(Ⅰ)

研究微体化石的搬运作用,不仅为区别埋葬群与生物群、正确再造原地的古生物组合所必需,而且可以为古环境研究提供重要信息.早在五十年代初就认识到有孔虫死亡后,其壳体象一般沉积颗粒一样,被水流搬运(Illings,1950),因而需要辨别原地与异地埋葬的微体化石群(Canter,1951;Jones,1958).有孔虫搬运作用的室内试验,始于法国的Berthois et Le Calvez(1960),他们首先探索了浮游有孔虫壳体与石英颗粒在水层中沉降速度的比较.后来,西德Diester(1972)进一步作了沉降试验;美国Berger＆Piper(1972)研究了浮游有孔虫不同种的差异性沉降作用,提出用沉降速度的分级求水流搬运作用的方法;而Yamashiro(1975)则发现用壳体的粒度分析更能指示搬运作用的强度.西德Seibold(1978)也讨论了各种浮游有孔虫沉降速度的差异可能引起的埋葬群动力分选.墨西哥Fok-Pun等(1983)则进一步研究了水介质密度与壳形对沉降速度     

福建东山岛第四纪微体化石群及其地质意义

本文对东山岛9个钻孔70块样品进行了有孔虫和介形虫等微体化石群分析,并参考有关资料,探讨了该岛第四纪地层的沉积时代、沉积相和古环境演变。     

伶仃洋有孔虫生物群和埋葬群的比较及河口沉积作用分析

对伶仃洋沉积物表层中的有孔虫生物群与埋葬群进行了比较分析,有效地分辨出河口湾内拦门沙区的高速沉积带、深槽里的有孔虫异地埋葬分子、东、西槽内陆架咸水作用的差异以及沉积物不同搬运方向等.证明用有孔虫生物群与埋葬群的对比分析可判释出沉积动力环境的更细微的差别和变化,较单纯据死有孔虫群的分析效果要好.     

台湾海峡西岸第四纪有孔虫与地质问题

一、序言台湾海峡西岸的第四纪地质工作,解放前,只是在地质矿产调查,土壤调查时涉及到一些。而第四纪有孔虫的研究工作更是空白。解放后,特别是近几年来,伴随着福建省水文地质,工程地质等工作的开展,积累了相当数量的钻孔和地表资料,出现了系统地研究第四纪地质的新局面。1977—1980年,我们与福建省水文工程地质队协作,对福建沿海一些钻孔中的有孔虫等化石,进行了分析研究。本文主要根据五个钻孔(图1)岩心中的有孔虫、硅藻等化石群特征,参考有关资料,就台湾海峡西岸的福州盆地、闽江口和厦门筼筜港地区的第四纪地层的划分、第四纪海侵层的沉积环境和第四纪地层发育史,进行初步研究。     

江苏中南部潮滩有孔虫特征及其与环境的关系

江苏中南部沿岸潮滩现代表层沉积物样品的定量分析结果表明其有孔虫为混合埋葬群,由原地生活分子和外海的异地分子混合而成,其特点是分异度偏高、丰度变化大、壳径偏小、壳体机械破坏较明显,富含壳径细小的浮游有孔虫。这些特点反映出埋葬群在形成过程中辐射沙洲区强大潮流的搬运作用。在搬运、沉积和埋葬过程中有孔虫壳体经受机械分选和破坏作用。埋葬群与生态环境因素和埋葬环境因素均有密切关系。     

江苏海岸带沉积环境中的有孔虫埋葬群特征

研究结果表明，江苏海岸有孔虫埋葬群可划分为：南部长江河口海岸区，中部辐射沙洲及其娄砂质海岸区和北部海州湾区３大类群。这３类埋葬各自的特点并与当地的沉积环境相对应，各大环境又包含若干亚环境，可依据各亚环境有孔虫埋葬群的特点加以区分。     

西沙晚中新世以来礁相地层中有孔虫动物群的分布及其意义

本文依据西琛1井和西永2井400m以上井段岩心样品中的有孔虫鉴定结果,将西沙礁相地层中的有孔虫分为6个组合段,并依据有孔虫带化石的分布对晚第三纪以来的地层时代进行了划分。并对研究西沙珊瑚礁发育与演化起到一定的作用。     

长江三角洲地区上新世以来的古地理变化

为研究江苏东部沿海平原区第四纪环境变迁,查明第四纪期间的海侵、海退过程,寻求海面变动与湖面变动间的关系,并试图以地磁地层学的方法对当地的第四纪地层进行划分与对比.近年来,中国科学院海洋研究所曾对江苏盐城孔、弶港孔、启东孔和位于长江南岸的嘉定孔(上海市)地层进行了系统分析,包括微体化石群的定性分析(有孔虫、海陆相介形类)、软体动物群鉴定、古地磁系统测量和少量样品的C~(14)测年.为配合沉积环境     

山东省打渔张灌区第四纪有孔虫及其沉积环境的初步探讨

"科学的发生和发展一开始就是由生产决定的"。随着我国地质勘探事业的迅速发展,特别是我国东部平原和浅海地区石油及其他沉积矿藏的勘探开发,有孔虫的研究工作已成为岩相识别、地层对比、恢复古地理及古气候等所依据的重要手段之一,越来越为人们所重视。 1965年,我们承担了山东省打渔张灌溉区(以下简称"灌区")七个钻孔岩芯中的有孔虫分析任务。目的是根据有孔虫在灌区地层中的出现情况,识别其海相层,进而划分出海、陆相地层,以便为探讨灌区土地盐碱化的原因、更合理地利用水利资源、进一步改造灌区的盐碱化土地等,提供必要的参考资料。这一任务已于同年完成,并已将初步分析结果送交有关单位。 为了配合生产单位对我国华北地区第四纪地层进行研究,近来,我们在前一工作的基础上,又将灌区的有孔虫资料进一步分析整理,除对93种底栖有孔虫进行分类记述外,并试图以灌区地层中的有孔虫群与现今渤海沉积物中的有孔虫群进行粗略对比,以便根据有孔虫的区系特点和生态组合等,探讨灌区地层海相层的古沉积环境。 由于在划分灌区地层的海相层和探讨海相层的古沉积环境时,我们仅是以现有有孔虫方面的资料为依据,因此,所讨论的问题必定存在较大的局限性和片面性。     

南海北部新生代晚期浮游有孔虫及其分带

随着石油地质勘探工作的开展,南海北部新生代海相地层被大量钻孔揭露出来,并在其中发现丰富的浮游有孔虫化石,本文通过浮游有孔虫在地层中的分布特征和规律,建立南海北部新生代晚期浮游有孔虫分带序列及其对比.     

Net Sand Transport Direction in a Tidal Inlet, using Foraminiferal Tests as Natural Tracers

The relationship between the flux of exotic benthic foraminiferal tests (i.e. tests which are supplied from open-sea sources alone) in a tidal inlet and that of bulk sediment was analysed, which can be expressed as two first-order linear equations. According to this relationship, in order to determine net sediment transport directions in the entrance, the test concentration in surficial sediments of the tidal basin can be compared against a ‘ critical level ’. The critical level is determined for the conditions that no net transport of bulk sediment is present within the entrance. If the observed concentration (averaged over the tidal basin) is higher than the simulated critical level, then the net sediment transport is directed to landward. This method is applied to the analysis of net sand transport at Christchurch Harbour, a tidal inlet system located in southern England. In this investigation, concentrations of exotic foraminiferal tests in the surficial sediments of the tidal basin and ebb tidal delta area were obtained from the analysis of sea-bed sediment samples. A series of probable critical levels were calculated based upon the data sets with regard to: (1) sediment discharge from the rivers; (2) magnitude of sediment discharge within the entrance during the ebb; (3) the test concentration outside the harbour; (4) the thickness of the moving layer; and (5) two parameters associated with dispersive processes. The results show that the concentration in the tidal basin sediment is higher than a number of simulated critical concentrations for representative cases. Consequently, the high level of the concentration of exotic benthic foraminiferal tests within the harbour should be explained as a result of landward net transport of sands within the entrance.     

Group Settling Velocity of Non-Cohesive Sediment Mixtures

Settling velocity is a fundamental parameter in sediment transport dynamics.For uniform Par-ticles,there are abundant formulas for calculation of their settling velocities.But in natural fields,sedi-ment consists of non-uniform particles.The interaction among particles is complex and should not be neg-lected.In this paper,based on the analysis of settling mechanism of non-cohesive and non-uniform parti-cles,a theoretical model to describe settling mechanism is proposed.Besides suspension concentration andupward turbulent flow caused by other particles,collision among particles is another main factor influ-encing settling velocity.By introducing the collision theory,equations of fall velocity before collision,colli-sion probability,and fall velocity after collision are established.Finally,a formula used to calculate the set-tling velocity of non-cohesive particles with wide grain gradation is presented,which agrees well with theexperimental data.     

The use of grain size trend analysis in macrotidal areas with breakwaters: Implications of settling velocity and spatial sampling density

In a macrotidal environment with offshore breakwaters (Elmer, West Sussex) a new approach for the identification of the sediment transport pathways with grain size trend analysis (GSTA) was undertaken using statistical parameters (mean, sorting and skewness) directly derived from settling velocities distributions. The same samples were analysed with sieving (quarter- and half-phi resolution) and GSTA was performed again in order to directly compare the resultant sediment transport directions derived with the two analytical techniques. Furthermore, both regular and irregular sampling distributions were used to recalculate GSTA. Hydrodynamic data were collected in different locations around the breakwaters and net sediment transport directions were calculated in order to assess the accuracy of the sediment transport pathway directions derived with the different analytical techniques.The accuracy of settling velocity in determining the statistical parameters of the grain size distribution is identified, especially for the fine-medium sand sediments. Settling velocities produced better results than the sieving; the quarter-phi resolution producing the poorer results in comparison with the coarser half-phi resolution. The results for the different spatial sampling strategies are found to depend upon the number of samples utilised; that shows that the accuracy of the GSTA is based upon the ability of representing, adequately, the spatial distribution of the sediment parameters.     

A method of determining proximity of marginal seas to an ocean

On any area of continental shelf the foraminiferal assemblage in the bottom sediment is likely to be composed of an indigenous benthic component and an allochthonous planktonic component sedimented from the water column above. Planktonic forminiferids are essentially oceanic and it seems clear that their presence in shelf sediments is often due to transport from an oceanic source. Evidence from the Celtic Sea, northwestern Gulf of Mexico, Persian Gulf and Andaman Sea shows that with passage away from the ocean there is a reduction in the planktonic—benthic ratio in the bottom sediment, a progressive decrease in size of the planktonic tests and a reduction in diversity of the planktonic assemblage. Thus a study of the relationships between the planktonic and benthic foraminiferids in these areas gives a measure of proximity to or isolation from the ocean. It is suggested that these relationships are useful tools in the interpretation of palaeoecology and in the reconstruction of former patterns of water circulation.     

Origin of grain size spectra of suspension deposited sediment

Hydronamic modification by settling from a turbulent suspension of an originally unsorted sediment produces grain size distributions that correspond to the size characteristics of many natural suspended and bottom sediments. Evaluation of the resulting equations allows parameterization of sediments in terms of three constants describing the source material, transport energy, and reworking history, respectively.     

The influence of particle size of the dispersed mineral fraction on the settlement of marine and estuarine muds

Considering the sedimentation behaviour of suspensions, four states of different sediment-water mixtures are usually distinguished, these being (in increasing concentration) dilute suspensions, concentrated suspensions, fluid muds and mud deposits. As the concentration values delimiting these states vary considerably from one cohesive sediment to another, a procedure for their quantitative determination is proposed here. This paper deals mainly with the effects of hindered settling in interacting concentrated suspensions and of sedimentation in fluid muds. In contrast to the settling velocity of individual particles in a dilute suspension, which must be studied statistically as a stochastic variable denoted W, hindered settling and sedimentation velocities can be described by a scalar denoted V, as solids at any particular level of concentrated suspensions and fluid muds settle at the same velocity. On the basis of settlement tests carried out in this study and published data on organic-rich cohesive sediments, a concentration-dependent empirical law for a permeability coefficient (k) has been generated for cohesive sediments, using data from ten estuarine and nine marine environments, based on the one-dimensional Kynch theory of sedimentation. Based on the median diameters of the dispersed mineral fraction, the main provenances of the sediments are: fine to very fine clay from tropical marine/estuarine environments, medium clay to very fine silt from estuaries in western France, and fine to coarse silt from marine (harbour) environments in the Normandy region of France. A general trend for the influence of the grain size of the mineral fraction on the permeability coefficient has been established. It is demonstrated that the concentrations delimiting the different states of sediment-water mixtures can also be related to the grain size of the mineral fraction. Thus, hindered settling and sedimentation processes of muds, similar to the marine and estuarine cohesive sediments considered in this paper, can be studied as generic problems parameterized through a defined median diameter of the dispersed mineral fraction. Results for Loire estuary sediments are presented separately, based on specific tests to analyse the influence of experimental conditions on settlement. Moreover, the concentration values delimiting the different sediment-water mixture states have been largely established for this estuary.     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.