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第三章 海岸带 第三节 滨海沉积相及其特征.

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Presentation on theme: "第三章 海岸带 第三节 滨海沉积相及其特征."— Presentation transcript:

1 第三章 海岸带 第三节 滨海沉积相及其特征

2 波动底流速的不对称和海岸砂体的特征

3 沉积相 Sedimentary facies
Each sedimentary environment is characterized by a particular suite of physical, chemical, and biological parameters that operate to produce a body of sediment characterized by specific textural, structural, and compositional properties. Such distinctive bodies of sediments or sedimentary rock are defined as sedimentary facies: 一定沉积环境中形成的沉积岩石与古生物的组合. Lithofacies 岩相 are distinguished by physical characteristics such as color, lithology, texture, and sedimentary structures. Biofacies 生物相are defined on the basis of paleontologic characteristics.

4 沉积环境和沉积相关系

5 主要的沉积环境

6 滨海沉积相特征 海岸带是波浪和水流强烈作用的地带;水动力变化决定了沉积物的分布和地貌特征,而沉积物的分布和地貌特征反过来又影响水动力条件。
海岸带生物组合受温度、盐度控制显著,在海岸带不同地区具有不同的组合类型。 滨海沉积相划分主要决定于水动力条件、沉积物性质、生物组合和地貌特征。

7 几个术语 Beach 海滩– A gently sloping accumulation of coarse sediment along a lake or ocean shoreline. The beach extends from the low-water line landward to where there is a change in morphology, such as a cliff, dunes, or permanent vegetation. Mainland Beach – long, narrow accumulations of sand aligned parallel to the shoreline and attached to land. Barrier island障壁岛– An elongate body of coastal sand separated from the mainland by a body of water. Barrier-island beaches – similar to mainland beaches but are separated from land by a shallow lagoon, estuary, or marsh, and also commonly dissected by tidal channels or inlets.

8 大陆海滩

9 海滩-近岸带的地貌类型 The beach is divided into the backshore, foreshore and shoreface. Backshore 后滨 extends landward from the beach berm 后滨阶地 above high-tide level and commonly includes back-beach dune deposits. Foreshore 前滨 mainly encompasses the intertidal (littoral) zone between low-tide and high-tide levels. Shoreface 临滨 extends from about low-tide level to the transition zone between beach and shelf sediments, that is, to fair-weather wave base at a depth of about 10-15m. Nearshore 近滨:including foreshore and shoreface Offshore 远滨/远滨 covers the area from the fair-weather wave base to the continental shelf break.

10 近滨 远滨

11 障壁岛和障壁岛海滩

12 障壁岛的形成机制 Shoal and longshore-bar aggradation, that is, upward building and eventually emergence of offshore bars 沙坝加积 Spit segmentation by breaching and detachment of spits oriented parallel to the coast 沙嘴分割 Mainland ridge engulfment owing to submergence and drowning of shoreline-attached beaches 大陆脊-海滩沉陷 Welding or veneering of Holocene dune, beach, and foreshore sand into and over pre-Holocene topographic highs 全新世沉积汇聚 Lateral shifting of coastal sands during transgression to form the barrier island 海侵中海岸沙侧向迁移 -Reineck and Singh(1980)

13 障壁岛的组成单元 The sandy barrier-island chain itself (the subtidal to subaerial barrier-beach complex) The enclosed lagoon, estuary, or marsh behind it (the back-barrier, subtidal-intertidal region) The channels that cut through the barrier and connect the back-barrier lagoon to the open sea (the subtidal-intertidal delta and inlet-channel complex)

14 沙坝/障壁岛-泻湖沉积体系

15 封闭泻湖 海湾 半封闭泻湖 半封闭泻湖

16 沙坝-泻湖的各沉积单元 半封闭泻湖

17 沙嘴拦截出的泻湖 海湾-泻湖 半封闭泻湖

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19 封闭泻湖

20 河北昌黎的海岸沙丘

21 向海

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24 沉积背景 Beach and barrier-island complexes are best developed on wave-dominated coasts where tidal range is small to moderate (<4m). 波控,小到中潮的海岸 Beach is the most dynamic of all depositional environments Microtidal: 0-2m tidal range 小潮 mesotidal 中潮: 2-4 m tidal range, macrotidal 大潮: >4m tidal range Barriers are generally absent on macrotidal coasts; extremely tidal range causes wave energy to be dispersed and dissipated over too great a width of shore zone to effectively form barrier. 同三角洲沉积环境的差别:动力环境—海洋作用为主,风

25 现代海滩和障壁岛沉积相特征 Overall geometry and lithofacies: a narrow body of sediments elongated parallel to the depositional strike, or strike of the shoreline; mainly composed of sand of hundreds of meters broad, up to hundreds of kilometers long, and 10-20m thick (Reineck and Singh, 1980). Beach sediments may be interrupted along its length by deltaic, estuarine, bay, and other deposits where these features cut across the beach. Sands of the barrier beach grade landward into back-barrier sediments that may include washover sands, tidal-delta sands and muds, lagoonal silts and muds, and sandy, muddy tidal-flat and marsh deposits.

26 海滩沉积相特征 后滨:中-细砂;受间歇性的风暴潮和风的作用;向陆缓倾;水平纹层;甲壳类 动物掘穴构造发育;风成槽状交错层理。
前滨: 中细沙,往复水流形成平行纹层, 向海缓倾 (2-3º);沉积层薄,重矿物富集层常见,和石英质砂层交替。 临滨:可分上、中、下三部分,对应于涌浪带、破浪带和碎浪带。

27 Upper-shoreface/surf zone: dominated by strong bidirectional translation waves and longshore currents. Sediments range from fine sand to gravel. Structures consist primarily of multidirectional trough cross-bed sets, but also include low-angle, bidirectional cross-beds and subhorizontal plane beds.

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29 Middle-shoreface/breaker-zone deposits also form under high-energy conditions owing to breaking waves and associated longshore and rip currents. Sediments consist mainly of fine- to medium-grained sand with minor amount of silt and shell material. Structures can be highly complex, depending on the presence or absence of longshore bars, and can include landward-dipping ripple cross-laminations; and seaward- and landward-dipping low-angle planar bedding; subhorizontal plane laminations, and seaward- and landward-dipping trough cross-beds. Trace fossils consisting of vertical burrows are common.

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31 Lower-shoreface/shoaling-zone deposits form under relatively low-energy conditions and grade seaward into open-shelf deposits. They are composed dominantly of fine to very fine sand but may also contain thin layers of silt and mud. Small-scale cross-stratification and planar, nearly horizontal laminatd bedding are the main sedimentary structures present. Such deposits may contain abundant plant materials, mica flakes, and other hydraulically light particles. Laminae in lower shoreface deposits tend to be obliterated by bioturbation, and suspension-feeder and deposit-feeder traces.

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33 理想的海滩沉积层序 进积的全新世低能海滩

34 障壁岛后的沉积相特征

35 海侵-海退的障壁岛沉积相特征


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