三角洲沉积体系(2)

（1）三角洲平原 （DELTA PLAIN）
Lower Delta Plain Sediments
Affected by both fluvial and basinal processes. The width of the lower delta plain is greatest on deltas where tidal range is large.
１．三角洲的亚环境和沉积特征 ２．三角洲的主要类型、沉积相组合、
沉积旋回及演化
1.三角洲的亚环境和沉积特征
两套术语（two sets of terms for deltas） ））
Based on gradient of delta profile（吉尔伯特，美国，1885）: 顶积层或三角洲台地 topset or delta platform 前积层或三角洲斜坡 foreset or delta slope 底积层或前三角洲 bottomset or prodelta
湿地
定义:指海洋和内陆常年有浅层积水或土壤过 湿的地段。
表达湿地的词约有30个左右,但学术上有个比较 统一的名词———沼泽.
在湿地研究影响最大的英语国家中比较普遍的 名词有四五个,如swamp, marsh, bog, moor, fen 等.某些文献中指出其间有些差别,例如swamp 指木本植物多于marsh而排水情况优于bog的一 种湿地; marsh指软、湿、低的草本覆被为主 的有由水过渡到陆的趋势的湿地; marsh土常 多碱性,而bog常多酸性; moor常指较开阔、地 势较高、排水较差、有小灌木丛以致泥炭的湿 地; fen则是英国常用的名词等.
（1）三角洲平原 （DELTA PLAIN）
两个主要单元 （Two principal components of Delta plain ） : 分流河道沉积（Distributary channels）
为沙和粉沙沉积物。横剖面形态为近于对称的透镜体。为向上变 细的沉积序列。
分流河道间沉积（Inter-distributary area）
Sediments:The major sand bodies generated in this environment are bay-fill deposits, which may form thin sand wedges stacked one on top of the other and separated by finer-grained, interdistributary-bay and marsh deposits. In very arid climates, evaporites (蒸发盐) also may be deposited in some parts of the lower delta plain. Deposits of the lower delta plain also commonly include abandoned distributary deposits. These consist of locally derived sands, muds, and organic debris that gradually fill distributary channels after they have been abandoned by the main stream owing to blocking or other processes that cause channel shifting.
The principal depositional environments include braided channels(辫状河道), meandering channels(曲流河道), lacustrine delta fill, backswamps, and floodplain environments such as swamps, marshes, and freshwater lakes(淡水 湖泊) (Coleman and Prior, 1982).
（1）三角洲平原 （DELTA PLAIN）
The subaerial component of deltas is generally larger than the subaqueous component and is divided into an upper delta plain, which lies largely above high-tide level, and a 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.
（1）三角洲平原 （DELTA PLAIN）
Upper Delta Plain Sediments
The upper delta plain lies mainly above tidal influence and is little affected by marine processes, and thus similar to fluvial environments in many respects, except that areas of swamp, marsh and lake are usually widespread and that channels may bifurcate downstream;
Physiographic and Sediment Characteristics of Alluvial Deltaic Systems Variations in sediment input, outflow velocity, wave and current energy, and other factors discussed cause the depositional features of deltas to exhibit a high degree of variability from one delta to another. Nevertheless, all deltas can be divided into subaerial and subaqueous components, each of which can be further subdivided (Fig. 10.15). 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 10 m or so, is
第三章 三角洲沉积体系
DELTA SYSTEMS
第一节 三角洲的环境特点及其沉积作用 第二节 三角洲的沉积特征及沉积模式 第三节 古代三角洲沉积鉴别标志及其
与油气资源的关系
第二节 三角洲的沉积特征及沉积模式
一、曲流河三角洲沉积体系 二、辫状河三角洲沉积体系 三、扇三角洲沉积体系
一、曲流河三角洲沉积
（2）三角洲前缘 (DELTA FRONT)
The subaqueous delta plain constitutes that area of a delta that lies seaward of low tide level and above wave base, and actively receives fluvial sediments. It may extend outward for distances of a few kilometers to tens of kilometers to water depths as much as 300 m. Deposits of the subaqueous delta thus form the base over which subaerial delta deposits prograde as the delta builds seaward. The uppermost part of the subaqueous delta, the delta front, may be dominated by high-energy marine processes, including waves, longshore currents, and tides in some cases.
This plain includes the active distributary system of the delta, as well as abandoned distributary-fill deposits, and may be flanked by marginal-basin or bay-fill deposits. Distributary channels are numerous, but environments between channels make up the largest percentage of the lower delta plain.