三角洲与河口湾

Early river-mouth bar
Later river-mouth bar and distributary channels
Байду номын сангаас
Formation of river-mouth bar and
distributaries
河流入海的河口区，水流展宽和潮流的顶托作用使 流速骤减，河流底负载下沉而堆积成水下浅滩。
Principal categories of delta facies
Upper delta plain 上部三角洲平原: migratory channel deposits– braided-channel and meandering-channel deposits; lacustrine delta-fill and floodplain deposits Lower delta plain 下部三角洲平原: bay-fill deposits(interdistributary bay, crevasse splay, natural levee, marsh); abandoned distributary-fill deposits Subaqueous delta plain 水下三角洲平原: distributarymouth bar deposits (Prodelta distal bar, distributary-mouth bar); river-mouth tidal-range deposits; subaqueous slump deposits Prodelta 前三角洲: seafloor seaward of the subaqueous delta
Mississippi Delta
2
3
4
1
5
6
7
Six stages of mouth bar development
Development stages of the Huanghe delta. The Holocene Huanghe delta is divided into ten superlobes. The estimated age of each superlobe is 1: 6000-5000 yrBP 2: 5000-4500 yrBP 3: 4500-3400 yrBP 4: 3400-3000 yrBP 5: 3000 yrBP-602 BC 6: 602 BC-11AD 7: 11 AD-1048 8: 1048-1128 9: 1128-1855 10: 1855-present (Xue, 1993).
The subaqueous delta plain lies seaward of the lower deltaic plain below low-tide water level and is characterized by relatively open marine faunas.
The uppermost part of the subaqueous delta, lying at water depths down to 10m or so, is commonly called the delta front. The remaining seaward of the subaqueous delta is called the prodelta, or prodelta slope.
Multi-stage development of deltas
Mississippi River Delta: seven subdeltas Huanghe River Delta: nine subdeltas Changjiang River Delta: six subdeltas 三角洲的增长和向海的推进可以有很高的速 度，例如长江每年平均增长速度为40m，黄 河多年平均则为300—400m，密西西比河三 角洲小于50m—100m。
delta extension
分支河道不断向海延伸，河床坡度减小，流速减缓，河床 淤高。坡度减小至一定程度泄流不畅，洪水季节洪流冲决 天然堤，呈散流倾泻于滨海平原或叉道间海湾，流速骤减， 沉积物逐渐淤积而成决口扇滩，从而使三角洲在横向上逐 渐扩大。
河水冲决天然堤后，取道于较大坡度的新河床入海。旧河 道淤塞，泥砂供应断绝，加之海浪的改造和侵蚀，使原来 的三角洲废弃，而在其旁侧新河道入海处，新的三角洲开 始发育成长。随着时间的推移，三角洲的废弃和发育相互 转化，交替出现，结果各三角洲彼此连接和部分叠合，形 成三角洲复合体。
Sediment components of delta system
The subaerial component of deltas is generally larger than the subaqueous component and is divided into:
- upper delta plain: lies largely above high-tide level
- lower delta plain: lying between low-tide mark and the upper limit of tidal influence
The upper delta plain is commonly the oldest part of the delta and is dominated by fluvial processes. The lower delta plain is exposed during low tide but is covered by water during high tide. Thus, it is subjected to both fluvial and marine processes.
第五章 三角洲与河口湾
一、三角洲研究历史及世界主要三角洲 二、三角洲的分类与沉积过程 三、三角洲的发育与沉积特征 四、建设性与破坏性三角洲 五、河口湾
Characteristics of fluvial-, tide-, and wave-dominated deltas
Delta development
Huanghe Delta
Controls of delta formation
河流的作用 蓄水体(海、湖水)的密度与河水密度的差异 蓄水体的水动力作用 河口区海底地形 蓄水盆地的构造特征
Principal components of a delta system
Subfacies of a delta
浅滩淤高、增大，露出水面，形成新月形河口砂坝， 水流从砂坝顶端分成两股，形成两个分支河道(分 流河道)，并向外侧扩展。分支河道向前发展，在 河口处又会出现的次一级河口砂坝；这一过程的不 断重复，就形成了一个喇叭形向海延伸的多叉道河 网系统，三角洲的雏形随之形成。
Formation of crevasse slay and