Sedimentological and palynological analysis of sediment cores from the northeastern Vietnamese Mekong River Delta

Three radiocarbon-dated sediment cores from the northeastern Vietnamese Mekong River Delta have been analysed with a multiproxy approach (grain size, pollen and spores, macro-charcoal, carbon content) to unravel the palaeoenvironmental history of the region since the mid Holocene. During the mid-Holocene sea-level highstand a diverse, zoned and widespread mangrove belt (dominated by Rhizophora) covered the extended tidal flats. The subsequent regression and coeval delta progradation led to the rapid development of a back-mangrove community dominated by Ceriops and Bruguiera but also represented locally by e.g. Kandelia, Excoecaria and Phoenix. Along rivers this community seems to have endured even when the adjoining floodplain had already shifted to freshwater vegetation. Generally this freshwater vegetation has a strong swamp signature but locally Arecaceae, Fabaceae, Moraceae/Urticaceae and Myrsinaceae are important and mirror the geomorphological diversity of the delta plain. The macro-charcoal record implies that natural burning of vegetation occurred throughout the records, however, the occurrence of the highest amounts of macro-charcoal particles is linked with modern human activity.

针对越南北部湄公河三角洲的3根经放射性碳定年（radiocarbon-dated）的沉积物岩芯（sediment core），本研究采用多代用指标法（multiproxy approach）开展分析，涵盖粒度、孢粉、大炭屑及碳含量等指标，以期阐明该区域自全新世中期以来的古环境演化历史。在全新世中期海平面高水位期，以红树属（Rhizophora）为优势类群的多样、分带且分布广泛的红树林带覆盖了广阔的潮滩。随后发生的海退与同期三角洲进积作用，推动了以角果木属（Ceriops）和木榄属（Bruguiera）为优势类群的后红树林群落快速发育，局部区域还伴生有秋茄属（Kandelia）、海漆属（Excoecaria）及刺葵属（Phoenix）等类群。沿河区域的该后红树林群落即便在相邻泛滥平原已转变为淡水植被的情况下，仍得以存续。总体而言，这类淡水植被具有显著的沼泽特征，但局部区域棕榈科（Arecaceae）、豆科（Fabaceae）、桑科/荨麻科（Moraceae/Urticaceae）以及紫金牛科（Myrsinaceae）占据重要生态位，反映了三角洲平原的地貌多样性。大炭屑记录显示，整个岩芯序列中均存在自然植被燃烧事件，但炭屑颗粒含量峰值的出现则与现代人类活动密切相关。