华南与中南半岛三角洲发育特征之比较

The South China and Indochina Peninsula Deltas——A Comparison

韩江、珠江、红河、湄公河、湄南河三角洲同处东亚季风热带。河流丰水少沙,径流强劲, 洪枯流量比值大,洪泛平原和湿地发育,有珊瑚礁和红树林堆积,平原推进速率较大,出海口门多,这些都是热带三角洲的特色。各三角洲的构造基础都是断陷盆地,由于断陷的幅度和时代不相同,故而第四系的厚度和年龄差异很大。受全球海平面变化的影响,末次冰期以来,各三角洲经历了相似的沉积过程,发育 3期三角洲。所处位置 (湾内或湾外)、滨外陆架坡度、海洋动力等条件,使各三角洲的地貌类型、地面高程、平原推进速率、水下三角洲、水动力类型等有较大的差异。

The five deltas of South China and Indochina Peninsula are all deposited in downfaulted basins. The downfault structure is mainly shown by the red weathering crust on the basement of the Quaternary,island hills on plain,islands off estuary,seismic activity and others.The thickness of Quaternary of Chao Phraya Delta is over 650m but that of Zhujiang Delta is only 63m, showing the different amplitude of downfaulting. The deposits of Early and Middle Pleistocene can be found in the three deltas of Indochina Peninsula but the kown oldest datings are only 52 138 a B P and 45 120 a B P in Hanjiang and Zhujiang Delta,respectively. Since middle stage of the Latest Glacial Period the five deltas have undergone three times of deltaic deposition and two times of discontinuity occurred.The maximum of Holocene transgression is mostly dated at 6 500-5 000 a B P.The advance rate of plain during the past hundred years is 63-120m/a in Zhujiang Delta but that of Chao Phraya Delta is only 4.0m/a. The similarity of the deltas can be enumerated as follows:abundant water and less silt content,composite deposits of several rivers,braided stream,several river mouths,smaller channel curvature,extensive flood plain and wetland,south-westward extending of delta plain,and sedimentary of mangrove. The deltas have following differentiation.The areas of the deltas are quite different.The altitude of plain is larger in the delta inside of estuary.The submerged delta developed in the delta with smaller shelf gradient.The hydrodynamics of the deltas can be recognized as follows:runoff-tidal type of Zhujiang Delta and Chao Phraya Delta,runoff-wave type of Hanjiang Delta and Red River Delta,and runoff-tidal-wave type of Mekong Delta.