【正文】 第三章 三角洲沉積體系DELTA SYSTEMS 第一節(jié) 三角洲的環(huán)境特點(diǎn)及其沉積作用 第二節(jié) 三角洲的沉積 特征及沉積模式 第三節(jié) 古代三角洲沉積鑒別標(biāo)志及其 與油氣資源的關(guān)系 第二節(jié) 三角洲的沉積特征及沉積模式 一、曲流河三角洲沉積體系 二、辮狀河三角洲沉積 體系 三、扇三角洲沉積體系 一、曲流河三角洲沉積 １．三角洲的亞環(huán)境和沉積特征 ２．三角洲的主要類型、沉積相組合、 沉積旋回及演化 兩套術(shù)語(yǔ) （ two sets of terms for deltas） ）） Based on gradient of delta profile（ 吉爾伯特 ，美國(guó)， 1885） : ? 頂積層或三角洲臺(tái)地 topset or delta platform ? 前積層或三角洲斜坡 foreset or delta slope ? 底積層或前三角洲 bottomset or prodelta 推薦使用的術(shù)語(yǔ) Based on deltabuilding processes: ? 三角洲平原 delta plain 上部 高潮面以上 下部 低潮面以上 ? 三角洲前緣 delta front 浪基面以上 ? 前三角洲 prodelta 浪基面以下 水上三角洲 水下三角洲 所有三角洲都可以分為水上三角洲（三角洲平原：又分上部和下部）和水下三角洲（三角洲前緣和前三角洲） 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 ponents, each of which can be further subdivided (Fig. ). The subaqueous delta plain lies seaward of the lower deltaic plain below lowtide 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 monly called the delta front. （ 1）三角洲平原 （ DELTA PLAIN） The subaerial ponent of deltas is generally larger than the subaqueous ponent and is divided into an upper delta plain, which lies largely above hightide level, and a lower delta plain, lying between lowtide mark and the upper limit of tidal influence. The upper delta plain is monly 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。 Sedimentation on the upper delta is dominated by distributarychannel migration and associated fluvial sedimentation processes such as channel and pointbar deposition, overbank flooding, and crevassing into lake basins. The principal depositional environments include braided channels(辮狀河道 ), 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). Therefore, upper deltaplain sediments are predominantly fluvial sands, gravels, and muds that may be closely associated with lacustrine, swamp, and marsh deposits. 濕地 ? 定義 :指海洋和內(nèi)陸常年有淺層積水或土壤過(guò)濕的地段。 ? 表達(dá)濕地的詞約有 30個(gè)左右 ,但學(xué)術(shù)上有個(gè)比較統(tǒng)一的名詞 ——— 沼澤 . ? 在濕地研究影響最大的英語(yǔ)國(guó)家中比較普遍的名詞有四五個(gè) ,如 swamp, marsh, bog, moor, fen等 .某些文獻(xiàn)中指出其間有些差別 ,例如 swamp指木本植物多于 marsh而排水情況優(yōu)于 bog的一種濕地 。 marsh指軟、濕、低的草本覆被為主的有由水過(guò)渡到陸的趨勢(shì)的濕地 。 marsh土常多堿性 ,而 bog常多酸性 。 moor常指較開闊、地勢(shì)較高、排水較差、有小灌木叢以致泥炭的濕地 。 fen則是英國(guó)常用的名詞等 . （ 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. This plain includes the active distributary system of the delta, as well as abandoned distributaryfill deposits, and may be flanked by marginalbasin or bayfill deposits. Distributary channels are numerous, but environments between channels make up the largest percentage of the lower delta plain. These environments include actively migrating tidal channels, natural levees, interdistributary bays(分流間灣 ), bay fills (crevasse splays), marshes, and swamps (Coleman and Prior, 1982). Sediments:The major sand bodies generated in this environment are bayfill deposits, which may form thin sand wedges stacked one on top of the other and separated by finergrained, interdistributarybay and marsh deposits. In very arid climates, evaporites (蒸發(fā)鹽 ) also may be deposited in some parts of the lower delta