Infilling and flooding of the Mekong River incised valley during deglacial sea-level rise
Infilling and flooding of the Mekong River incised valley during deglacial sea-level rise
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DOI：
10.1016/j.quascirev.2010.02.022
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发表时间：
2010-06
影响因子：
4
通讯作者：
R. Tjallingii;K. Stattegger;A. Wetzel;P. Phách
中科院分区：
文献类型：
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作者：
R. Tjallingii;K. Stattegger;A. Wetzel;P. Phách
越南东南陆架断谷充填沉积物从河流沉积到海相沉积的突变，准确地记录了距今（BP） 14ka后的冰期海侵。海侵后沉积以浅海相碳酸盐砂为主。这种沉积物成分的变化在高分辨率x射线荧光（XRF）岩心扫描记录中被准确地标记出来。在洪水之前，河口的河流沉积物迅速堆积，几乎完全填满了湄公河切割的山谷。然而，在河口水系淹没后，谷地的堆积率明显下降。这也影响了越南东南部大陆架较深部分的沉积物供应。湄公河流域填海与东亚地区潮下和潮间沉积记录的海平面历史对比表明，切谷填海记录中保存的海侵面是一个强有力的海平面指标。东亚海平面记录显示，在13.0 ~ 9.5 kaBP期间，该流域几乎完全被河流沉积物填满，海平面持续上升，约为10 mm/yr。在陆架较浅的部分，大量的沉积物改造和在充填最后阶段河口条件的建立使海侵面准确测年复杂化。然而，切谷填充物记录和陆上钻探地点表明，在9.5 ka至8.5 kaBP之间，从现代越南海岸线到柬埔寨低地的陆架发生了巨大而迅速的洪水。这部分陆架的快速泛洪与低陆架梯度和东亚海平面从低于现代海平面34 ~ 9 m （mbsl）上升的强烈加速有关，对应于熔体水脉冲（MWP） 1C的海平面跳变。
The abrupt transition from fluvial to marine deposition of incised-valley-fill sediments retrieved from the southeast Vietnamese shelf, accurately records the postglacial transgression after 14ka before present (BP). Valley-filling sediments consist of fluvial mud, whereas sedimentation after the transgression is characterized by shallow-marine carbonate sands. This change in sediment composition is accurately marked in high-resolution X-ray fluorescence (XRF) core scanning records. Rapid aggradation of fluvial sediments at the river mouth nearly completely filled the Mekong incised valley prior to flooding. However, accumulation rates strongly reduced in the valley after the river-mouth system flooded and stepped back. This also affected the sediment supply to deeper parts of the southeast Vietnamese shelf. Comparison of the Mekong valley-filling with the East Asian sea-level history of sub- and inter-tidal sediment records shows that the transgressive surface preserved in the incised-valley-fill records is a robust sea-level indicator. The valley was nearly completely filled with fluvial sediments between 13.0 and 9.5 kaBP when sea-level rose rather constantly with approximately 10 mm/yr, as indicated by the East Asian sea-level record. At shallower parts of the shelf, significant sediment reworking and the establishment of estuarine conditions at the final stage of infilling complicates accurate dating of the transgressive surface. Nevertheless, incised-valley-fill records and land-based drill sites indicate a vast and rapid flooding of the shelf from the location of the modern Vietnamese coastline to the Cambodian lowlands between 9.5 ka and 8.5 kaBP. Fast flooding of this part of the shelf is related with the low shelf gradient and a strong acceleration of the East Asian sea-level rise from 34 to 9 meter below modern sea level (mbsl) corresponding to the sea-level jump of melt water pulse (MWP) 1C.