Abstract Two 40 m-long sediment cores BL01 and SC02 were drilled in the lower Mekong River Delta plain and compared to high-resolution seismic profiles from the adjacent shelf documenting the presence of two depositional sequences (SQ1, SQ2) for the past 140 kyr. SQ2 is a fourth-order sequence and covers a complete sea-level cycle of 120 kyr. SQ1 is a fifth-order sequence comprising a sea-level half cycle in the past 20 kyr. These two sequences are bounded by the sequence boundaries (SB1, SB2) and the topographic surface. The transgressive systems tract (TST2) of SQ2 was probably formed during the sea-level rise from the Marine Isotope Stage (MIS) 6 lowstand to the MIS 5e highstand, indicated by riverine-estuarine and shallow-marine sediments. The regressive systems tract (RST2) of SQ2 corresponds to the sea-level lowering from MIS 5e to 3 with deltaic and alluvial plain sediments prevailing. These sediments were then gradually exposed to tropical subaerial processes to generate the formation of patchy reddish-orange stiff sandy silt and clay. The overlaying sequence SQ1 contains the lowstand systems tract (LST1), TST1, and RST1. LST1 consists of deltaic sediments at the shelf edge deposited during the MIS 2 sea-level lowstand. TST1 includes retrograding-fluvial, estuarine, and shallow-marine sediments deposited during the deglacial sea-level rise 19-8 cal kyr BP and the maximum flooding period 8-6 cal kyr BP before the advance of the modern Mekong River Delta. RST1 comprises the modern delta-facies association formed during the past 8 kyr and is restricted to the water depth of 25 m.

中文翻译：

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过去 140 kyr 越南南部湄公河三角洲和邻近陆架的沉积层序

摘要 在湄公河三角洲下游平原钻探了两个 40 m 长的沉积岩心 BL01 和 SC02，并与记录过去 140 kyr 存在两个沉积序列（SQ1、SQ2）的相邻陆架的高分辨率地震剖面进行比较。SQ2 是一个四阶序列，涵盖了 120 kyr 的完整海平面循环。SQ1 是包含过去 20 kyr 海平面半周期的五阶序列。这两个层序以层序边界（SB1、SB2）和地形表面为界。SQ2的海进系统域（TST2）可能是在海平面从海洋同位素阶段（MIS）6低位上升到MIS 5e高位期间形成的，以河流-河口和浅海沉积物为标志。SQ2的回归系统域（RST2）对应于海平面从MIS 5e下降到3，三角洲和冲积平原沉积物占主导地位。这些沉积物随后逐渐暴露于热带地下过程，形成斑片状的红橙色硬质砂质淤泥和粘土。叠加序列 SQ1 包含低位系统域 (LST1)、TST1 和 RST1。LST1 由 MIS 2 海平面低位期间沉积的陆架边缘的三角洲沉积物组成。TST1 包括在冰消期海平面上升 19-8 cal kyr BP 和现代湄公河三角洲推进之前的最大洪水期 8-6 cal kyr BP 期间沉积的逆流河流、河口和浅海沉积物。RST1 包括在过去 8 kyr 期间形成的现代三角洲相组合，并且限于 25 m 的水深。