長江河口細顆粒物質(zhì)來源豐富、水動力作用活躍,近年來又受到三峽大壩等流域大型工程的影響,因此其水下三角洲沉積層序?qū)ψ匀贿^程(物源變化、潮汐水道地形調(diào)整、風暴潮事件等)和人類活動(航道疏浚等)的響應成為一個重要的科學問題。 本研究對覆蓋長江口水下三角洲的31個站位的沉積物柱狀樣進行了粒度分析和210Pb測定。所獲2468個子樣的粒度分析結果表明,長江水下三角洲表層底質(zhì)的平均粒徑一般細于4Φ,只有CJ03和CJ09站位的表層沉積物為極細砂(3Φ<平均粒徑<4Φ)。長江河物質(zhì)主要是來源于現(xiàn)代流域供給,少數(shù)站位的砂質(zhì)沉積則代表海底侵蝕。柱樣的平均粒徑有四類垂向分布趨勢：向上細化、垂向穩(wěn)定、垂向波動式變化、向上粗化,分別對應于不同的地貌部位和沖淤動態(tài)。沉積物粒度參數(shù)的變化主要受物源豐富程度、沉積過程和流域輸入懸沙物質(zhì)組成等因素的影響。向上變粗類型的沉積物柱樣主要來自南槽口門附近以及北槽挖沙水道附近。向上變細和垂向均一類型的柱樣采集地均為研究區(qū)內(nèi)距河口較遠處。此外,在南支北槽挖沙水道外和在南支北港口門外獲取的柱樣粒度分選極差(2<分選系數(shù)<4),指示長江口南支口門的沉積水動力...

【文章頁數(shù)】：282 頁

【學位級別】：博士

【文章目錄】：
摘要
Abstract
Acknowledgements
Notations
Chapter 1 Introduction
    1.1 The Scientific Problem
    1.2 Purpose of the stuay
    1.3 Hypothesis
    1.4 Themes of research
        1.4.1 Grain size analysis of sediment cores
        1.4.2 Factors affecting grain size distribution
        1.4.3 ²¹⁰Pb dating for sedimentation rates
        1.4.4 Factors affecting the ²¹⁰Pb_ex activities of sediments
        1.4.5 ²¹⁰Pb_ex patterns in relation to sediment dynamics
        1.4.6 Tidal cycle measurements
        1.4.7 Observed variations in relation to sediment dynamical changes
Chapter 2 Literature Review
    2.1 Estuarine processes
        2.1.1 River discharges of freshwater and sediment
        2.1.2 Tides and tidal currents in estuaries
            (a) Tides and tidal currents
            (b) Tidal limit and tidal current limit
        2.1.3 Estuarine circulations
        2.1.4 Formation of turbidity maxima
        2.1.5 Sediment transport patterns
            (a) Sediment resuspension
                Initiation of sediment motion
                Shields curve
            (b) Bottom boundary layer
                Bottom shear stress
                Bottom roughness length
            (c) Sediment transport rate
                Estimation of suspended sediment flux
                Calculation of resuspended flux
            (d) Gravity currents
                Gravity current
                Turbidity current
                Hyperpycnal plume
                Fluid mud
    2.2 River deltas
        2.2.1 Types of river deltas
        2.2.2 Evolution of river deltas
        2.2.3 Sedimentary facies and sequences
        2.2.4 Sediment budget
    2.3 ²¹⁰Pb in deltaic sedimentation
        2.3.1 Analytical techniques
        2.3.2 Spatial distribution patterns
        2.3.3 Vertical distribution in relation to accumulation rate
        2.3.4 Sediment dynamic factors affecting the burial of ²¹⁰Pb
Chapter 3 The Study Area
    3.1 Regional geology and geomorphology
        3.1.1 Geological background
        3.1.2 Geomorphological features
        3.1.3 Estuary and delta evolution
            (a) Evolution under sea level rise
            (b) Land progradation since 2000BP
            (c) Development in the last 100 years
        3.1.4 Holocene sediment systems
    3.2 Hydrodynamics
        3.2.1 Freshwater discharges
        3.2.2 Tides and tidal currents
        3.2.3 Waves
        3.2.4 Estuarine and shelf circulations
        3.2.5 Modern events
            (a) Floods
            (b) Typhoon
    3.3 Sedimentation
        3.3.1 Sediment supply
        3.3.2 Variations of sediment supply
            (a) Mass flux change,in response to natural oscillations
            (b) Sediment flux change,in response to deforestation
            (c) Sediment flux change,in response to dam constructions
            (d) Sediment flux change,in response to dredging navigation channels
        3.3.3 Surficial sediment types and distributions
        3.3.4 Suspended sediment and turbidity maxima
        3.3.5 Sediment transport patterns
        3.3.6 Depocenter and sedimentation rates
    3.4 Biotic influence
Chapter 4 Material and Methods
    4.1 Sampling and sample treatment
        4.1.1 Sampling locations
        4.1.2 Software utilization for geomorphology maps
        4.1.3 Core sample recovery
        4.1.4 Sub-sampling and core description
    4.2 Grain size analysis
        4.2.1 Sample preparetion for grain size analysis
        4.2.2 Measurements of grain size distribution
        4.2.3 Calculation of grain size parameters
        4.2.4 The grading and classification of sediments
    4.3 Water content analysis
        4.3.1 Water content calculation
        4.3.2 Data precision of water content
    4.4 Determination of sedimentation rates
        4.4.1 Sample pretreatment for ²¹⁰pb dating
        4.4.2 ²¹⁰Pb activity and sedimentation rates
        4.4.3 Sediment flux estimations
        4.4.4 Error correction of accumulation rates
            (a) Grain size correction of accumulation rates
            (b) Compaction correction of accumulation rates
                Approach Ⅰ:Standard layer method
                Approach Ⅱ:Removing of compact effecf
    4.5 Fine grain sediment resuspension and transport
        4.5.1 Tidal cycle measurements
        4.5.2 Laboratory analysis and data processing
            (a) SSCs data analysis
                SSCs data analysis of in situ water samples
                SSCs data analysis of calibrated ADCP echo intensity information
                Figure producing of SSCs profile
            (b) Data analysis of bottom boundary layer parameters
            (c) Estimation of sediment re-suspension
            (d) Estimation of suspended sediment flux
Chapter 5 Results
    5.1 Seafloor morphology of the study area
    5.2 Sediment types and distributions
        5.2.1 Description of sediment cores
        5.2.2 Vertical distribution patterns of sediment grain size
        5.2.3 Spatial distribution of vertical patterns
        5.2.4 Sub-sample selection,for ²¹⁰Pb dating
    5.3 Water content and compaction effects
        5.3.1 Water content precision in relation to sub-sampling duration
        5.3.2 Distributions of compaction effects on core lengths
        5.3.3 Compaction effects on core lengths in relation to water content
    5.4 Distribution patterns of ²¹⁰pb activities
        5.4.1 Vertical distribution patterns of ²¹⁰Pb activities
        5.4.2 Horizontal distributions of ²¹⁰Pb decay profile types
        5.4.3 Horizontal distributions of ²¹⁰pb activities
    5.5 Distribution patterns sedimentation rates
        5.5.1 Detailed analysis results of each core sample
            (a) Sediment cores with normal ²¹⁰Pb_ex decay profile
                Core CJ06
                Core CJ08
                Core CJ12
            (b) Sediment cores with unique total 210Pb activity profile
                Core CJ01
                Core CJ04
                Core CJ09
                Core CJ15
            (c) Sediment cores with sectional ²¹⁰Pb_ex decay profile
                Core CJ02
                Core CJ05
                Core CJ07
                Core CJ11
                Core CJ14
                Core CJ16
                Core CJ19
                Core CJ23
                Core CJ24
                Core CJ25
            (d) Sediment cores with topsy-turvy ²¹⁰Pb activity profile(sectional ²¹⁰pb_ex decay and inverse ²¹⁰Pb_ex decay profile)
                Core CJ13
                Core CJ17
                Core CJ18
                Core CJ20
                Core CJ21
                Core CJ22
                Core CJ26
                Core CJ27
                Core CJ28
                Core CJ29
        5.5.2 Horizontal distributions of sedimentation rates
    5.6 Profiles of hydrodynamic observations
        5.6.1 Distribution of SSCs and current velocity components
        5.6.2 Distribution of bottom boundary layer parameters
Chapter 6 Discussion
    6.1 ²¹⁰pb profiles in relation to catchments changes
        6.1.1 Catchment changes over the Changjiang Estuary
            (a) Mass discharge changes
            (b) Deltaic Processes
        6.1.2 ²¹⁰Pb profiles in relation to catchments changes
            (a) 1980s(first period in Fig.3.10)
            (b) After 2003 (third period in Fig.3.10)
            (c) Years in between (second period in Fig.3.10)
    6.2 ²¹⁰Pb distribution patterns in relation to sedimentary processes
        6.2.1 Surficial ²¹⁰Pb in relation to turbidity maximum
        6.2.2 Sedimentary processes represented by ²¹⁰Pb patterns
            (a) Sedimentary processes of Pattern 2
            (b) Sedimentary processes of Pattern 3
            (c) Possible sedimentary processes of Pattern 4
    6.3 Sedimentation rate variations in response to catchments changes
        6.3.1 Variations in sedimentation rates
            (a) Sedimentation rate variations over modern subaqueous delta
            (b) Sedimentation rates over the old Changjiang Delta
            (c) Sedimentation rates over the delta front-transition region
        6.3.2 Sedimentation rates in relation to turbidity maxima
        6.3.3 Sedimentation rates in relation to mass discharge
        6.3.4 Relationships between sedimentation rates and ²¹⁰Pbex

        6.3.5 Distribution of sedimentation rates affected by evolution of biological communities
    6.4 Conditions for the formation of hyperpycnal flow
        6.4.1 Conditions for the generation of hyperpycnal flow
        6.4.2 Possibility of hyperpycnal flow induced by the increase in SSCs within the bottom boundary layer
        6.4.3 Relationship between seabed morphology and sediment gravity flow
    6.5 Factors affecting the distribution of sediment grain size
        6.5.1 Locations on different deltaic facies
        6.5.2 Material source affecting the distribution of sediment grain size
        6.5.3 Possible sedimentation process affecting the distribution of sediment grain size
            (a) Hyperpycnal depositional sequence
            (b) Turbidity currents
        6.5.4 Variation in hydrodynamics affecting the distribution of sediment grain size
            (a) Variation over time
                Hydrodynamic events
                Channel evolution at the Changjiang River mouth
            (b) Variation over the estuary (horizontal hydrodynamic distribution)
        6.5.5 Human activities affecting the distribution of sediment grain size
    6.6 Future sediment retention
    6.7 Hydrodynamics data analysis
        6.7.1 Analyzing parameters of the bottom boundary layer at estuary
        6.7.2 Validity of SSCs data calibrated from echo intensity recorded by ADCP
Chapter 7 Conclusion
    Basic characteristics of sediment core samples
    Vertical distribution patterns
    Distribution of sedimentation rates
    Catchments changes
    Factors affecting the distributions
    Further research in need
References
Appendices
    Appendix 1: Results of regression analyses on excess ²¹⁰Pb activity against depth
    Appendix 2: Sub-sampling duration effects on the precision of the water content data(2009)
    Appendix 3: Relative water content(dimensionless ratio)of sediment cores(2009)(note:Locations shown in Figure 3.7-1)
    Appendix 4: Research articles completed during 2009-2013



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