Holocene evolution of the Song Hong (Red River) delta system, northern Vietnam
Holocene evolution of the Song Hong (Red River) delta system, northern Vietnam
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DOI：
10.1016/j.sedgeo.2005.12.004
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发表时间：
2006-05-15
影响因子：
2.8
通讯作者：
Kitamura, Akihisa
中科院分区：
文献类型：
--
作者：
Tanabe, Susumu;Saito, Yoshiki;Kitamura, Akihisa
位于南海北部湾西岸的宋洪（红河）三角洲，是全新世宋洪河排沙的结果。三角洲平原上游的河流沉积盆地并不大。三角洲平原包括在+2-3 in（6-4 cal. kyr BP）海平面高位期间形成的露出的潮坪/红树林坪，以及分别位于三角洲平原的向陆和向海两侧的海滩-山脊滨海平原，其中直的到叶状的海滩山脊。三角洲为我们提供了机会，全面研究河口形态动力学与泥沙排放和海平面变化的关系。根据1999-2001年在三角洲平原采集的7个30-70 m长的沉积物柱样和101个放射性碳年代学资料，描述了松洪三角洲体系的全新世演化和河口地貌动力学特征。从上到下依次为由砾质砂和杂色粘土组成的河流沉积物、由贝壳和木屑组成的潮汐河口沉积物和由砂和泥组成的三角洲沉积物，其中砂和木屑的含量向上增加。通过应用层序地层学概念，可以在砾石砂-斑粘土边界处识别海侵面，并且可以在河口-三角洲沉积物边界处识别最大海泛面。低水位体系域、海侵体系域和高水位体系域分别记录了15、15-9和9-0 cal. kyrBP的沉积物。河口从湾头向海湾延伸，其形态从漏斗形（9-6 cal. kyr BP）到直形（6-2 cal. kyr BP），最后到叶状（2-0 cal. kyr BP）。从漏斗形到直线海岸的形态变化被解释为与从潮汐主导的湾头设置到波浪影响的开放海岸设置的水文制度转变密切相关。海平面上升的停止在6卡尔。kyr BP可能只发挥了很小的作用，在河口形态的变化，因为降水速率从22到4米/年减速。而不是在那个时候加速。河口形态动力学从笔直到叶状的变化主要是由于人为砍伐森林导致宋洪河上游的宋洪沉积物排放量从17-27吨（9-2万年BP）增加到4900万吨/年（2-0万年BP）。沿着宋洪河上游。(c)2005 Elsevier B. V.保留所有权利。
The Song Hong (Red River) delta, located on the western coast of the Gulf of Bac Bo (Tonkin) in the South China Sea, formed as a result of the Song Hong sediment discharge throughout the Holocene. The river's sedimentary basin upstream from the delta plain is not large. The delta plain comprises emerged tidal/mangrove flats formed during the sea-level highstand at +2-3 in (6-4 cal. kyr BP) and a beach-ridge strandplain, with straight-to-lobate beach ridges, on the landward and seaward sides of the delta plain, respectively. The delta affords us the opportunity to examine river-mouth morphodynamics comprehensively in relation to sediment discharge and sea-level changes. In this paper, we describe the Holocene evolution of the Song Hong delta system and the river-mouth morphodynamics on the basis of seven sediment cores, each 30-70 rn long, taken from the delta plain during 1999-2001 and 101 radiocarbon dates obtained from the core sediments.Sediments from the seven cores, consisting of incised-valley fills since the last glacial maximum, can be divided, in ascending order, into fluvial sediments composed of gravelly sand and mottled clay, tide-influenced estuarine sediments containing shell and wood fragments, and deltaic sediments composed of tide-influenced sand and mud deposits, in which the contents of sand and wood fragments increase upward. By applying sequence stratigraphic concepts, a transgressive surface can be identified at the gravelly sand-mottled clay boundary, and the maximum flooding surface can be identified at the estuarine-deltaic sediments boundary. The lowstand systems tract, transgressive systems tract, and highstand systems tract record similar to 15, 15-9, and 9-0 cal. kyr BP, respectively.During the past 9 kyr, the majority of the sediment discharged by the Song Hong accumulated in the incised valley and enhanced progradation at the river mouth. The river mouth prograded from the bay head toward the gulf, and its morphology changed from funnel-shaped (9-6 cal. kyr BP) to straight (6-2 cal. kyr BP) and finally to lobate (2-0 cal. kyr BP). The morphological change from a funnel-shaped to straight coast is interpreted to have been closely related to a hydrologic regime shift from a tide-dominated bay-head setting to a wave-influenced open-coast setting. The cessation of the sea-level rise at 6 cal. kyr BP may have played only a small role in the change of river-mouth morphology because the progradation rate decelerated from 22 to 4 m/yr. instead of accelerating at that time. The river-mouth morphodynamic change from straight to lobate was largely caused by an increase in the Song,Hong sediment discharge from 17-27 (9-2 cal. kyr BP) to 49 million t/yr (2-0 cal. kyr BP) as a result of anthropogenic deforestation along the upper reaches of the Song Hong. (c) 2005 Elsevier B.V. All rights reserved.