Late Pleistocene to Holocene formation process of Mekong River Delta, South Vietnam

对湄公河下游三角洲11个钻孔的岩心样品进行了详细分析，揭示了后冰期海侵的沉积过程和湄公河三角洲全新世的演化过程。末次盛冰期（LGM）形成的切谷大部分在末次盛冰期（LGM）后海拔上升期间被填满。河间带海拔约为-20 m，被全新世三角洲沉积物不整合覆盖。三角洲沉积物和详细的年代地层分析在沉积物相、潮汐影响、沉积速率以及陆上和水下地形等方面清楚地显示了过去4 kyr的三角洲沉积。随着三角洲的演化，三角洲环境受海浪的影响越来越大，形成了滩脊场、海岸沉积物扩散和三角洲前缘的陡坡面。沿湄公河和河道用单爆仪获得的地震剖面清楚地显示了上更新世沉积物的不整合。不整合面上的冲积沉积层厚度一般为20 ~ 40 m，切谷部分厚度可达70m。湄公河三角洲下游的地形特征是发育了几条活跃和废弃的海滩沙脊。主要描述了这些活跃和残缺的滩脊的地貌和沉积特征，并通过对滩脊石英颗粒的OSL定年进行了年龄测定。在8行海滩脊和1个钻孔岩心中采集了沉积物逻辑学和年代学分析样本。在特拉荣市南部可以观察到八行残迹和活动的沙脊。虽然它们大致与最近的河流和海岸线平行，但在岛的东侧却有独特的发展。特别是四条内陆线在城市的南部汇合，并在北向南方向延长，与最近的河流平行。所有的海滩山脊都向南和向西分化成几个狭窄而低矮的山脊。用光释光测年法测定了海滩残砂的年龄。它们的年龄一般分为两组，即年龄在4岁以上的和年龄在1.2岁以下的。少

Detail analysis of core samples from 11 bore holes in the Lower Mekong River Delta show the sedimentation during the postglacial transgression and the Holocene evolution of the Mekong River Delta. The incised valley that formed during LGM (the Last Glacial Maximum) was mostly filled during the rise of sca-level after the LGM. The interfluvial zones are about -20 m in altitude and are covered unconformably by Holocene deltaic sediments. The deltaic sediments and detailed chlonostratigraphic analyses clearly show the delta progradation for the last 4 kyr in terms of the sediment facies, tide influence, progradation rate, and subaerial and subaqueous topography. As the delta has evolved, the delta environment has become more wave-influenced with the development of a beach-ridge field, longshore sediment dispersal, and a steep face of the delta front. Seismic profiles get by uni-boom along Mekong River and channels show clearly the unconformity within the Upper Pleistocene sediments. The a … More lluvial sediments lying on the unconformity is generally 20 to 40 m in thickness, partly upto 70m in incised valley.Lower part of the Mekong River Delta is topographically characterized by development of several lines of active and relict beach sand ridges. The geomorphologic and sedimentologic features of these active and relict beach ridges were described primarily together with some ages by OSL dating from quartz grains of beach ridges. Samples for sedimento-logic and chlonologic analysis were collected from 8 lines of beach ridges and one boring core. Eight lines of relict and active sand ridges are observed to the south of Tra Vinh City. Although they are arranged generally parallel to the recent river and coast line, are distinctively developed in the eastern side of the island. Especially four lines inland converge to the south of the City, and elongated in the N-S direction parallel to the recent river. All beach ridges are diverged southward and westward to several narrow and low ridges. Some ages are gotten from relict beach sands by OSL dating method. Their ages are classified generally into two groups, that is, sands older than 4 kyr and ones younger than 1.2 kyr. Less