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第三节 滨海沉积相及其特征 第三章 海岸带. 波动底流速的不对称和海岸砂体的特征 沉积相 Sedimentary facies  Each sedimentary environment is characterized by a particular suite of physical, chemical,

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Presentation on theme: "第三节 滨海沉积相及其特征 第三章 海岸带. 波动底流速的不对称和海岸砂体的特征 沉积相 Sedimentary facies  Each sedimentary environment is characterized by a particular suite of physical, chemical,"— Presentation transcript:

1 第三节 滨海沉积相及其特征 第三章 海岸带

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

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) -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)

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15 封闭泻湖 半封闭泻湖 海湾 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 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 m 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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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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