东亚和南亚典型大河三角洲晚第四纪地层结构及成因对比

A comparative study on the Late Quaternary stratigraphic architecture and formation of megadeltas in East and South Asia

  • 摘要: 通过整理东亚、南亚典型河口三角洲末次冰消期以来演化历史的研究进展,对比各河口晚第四纪地层结构、沉积体系演替和三角洲开始建造的时间,分析其沉积历史的主要控制因素。结果显示,末次冰消期以来各河口具相似的地层结构和演变过程,即早全新世下切古河谷充填和河口湾发育,中—晚全新世三角洲建造,该过程主要受海平面变化的控制。但是各河口地层结构和沉积历史也存在差异,其中以三角洲开始建造的时间差别最为明显。对比发现这种差异与流域地貌、基岩以及河口沉积盆地的差别有关。流程短、流域基岩易侵蚀的河流,入海泥沙量大,其三角洲开始建造的时间显著早于其他河流,其中以恒河三角洲最为典型。另外,以珠江三角洲为典型,其半封闭、基底浅的河口沉积盆地特征,也有助于中全新世湾顶三角洲的建造。

     

    Abstract: Based on the researches on the evolution of megadeltas in East and South Asia since last deglaciation, we carried out a comparative study on the Late Quaternary stratigraphic architecture, sedimentary systems and the initiation time of megadeltas at large river mouths of the region. Major control factors on deltaic evolution are revealed and discussed. Our data suggests that all the river mouths in the region seem having experienced similar evolutionary history, including the infilling of incised palaeo-valleys and estuaries in Early Holocene, and deltaic progradation in Middle to Late Holocene, controlled by the sea-level change. However, there are some differences in the stratigraphic architecture and sedimentary history from river to river. The most remarkable difference is the time of delta initiation, which is related to the geomorphology and geology of the drainage basin and the sedimentary basin at river mouths. Those rivers having short flow paths and erosive bedrocks in the drainage basin, such as the Ganges-Brahmaputra, usually produce a huge amount of sediment load. As a result, the time of the delta initiation was obviously earlier than other rivers. The Pearl River delta is another example. It has a semi-closed shallow sedimentary basin which is beneficial to the formation of delta in the Middle Holocene.

     

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