Abstract Having developed in the later Quaternary Period, the Mui Ne dunefield, representing the upper-most portion of a major coastal barrier complex in SE Vietnam, formed by wind regimes associated with the Asian monsoon climate. The barrier complex is 100 km long and higher than 150 m in elevation but despite its large dimensions, research on its geomorphological and geological characterization is limited. Several active dune fields extend 2–10 km landwards from the coast while the rest of the barrier surface is stabilized. We applied ground-penetrating radar (GPR) and quartz optically-stimulated luminescence (OSL) dating to the transverse dunes of the Mui Ne dunefield to characterize the morphostratigraphy and recent aeolian sedimentation history. Currently the dunes have a relief of typically 5–10 m and a wavelength of 50–100 m. They are driven by the northeasterly winter monsoon winds and reversed with minor relief in response to the southwesterly summer monsoon. GPR profiles and OSL ages define three morphostratigraphic units: the modern, Holocene, and Pleistocene dune units. The GPR data of the modern dune unit is dominated by a series of steep reflections that dip exclusively towards the west reflecting the winter monsoon and is punctuated by reactivation surfaces. Evidence for the wind reversal is not preserved in the sediment successions but is represented by reactivation surfaces. Thus a subunit bounded by the reactivation surfaces defines annual deposition. The preservation potential of a subunit varies with the migration rate of the transverse dune, and in the fastest migrating dunes, approximately one subunit was preserved every year (1.1 ± 0.6 subunit/yr). The modern dunes are generally younger than 100 years and have migrated WSW at net rates of 0.6–2.5 m/yr. The Holocene dune unit is as thick as the modern unit although it spans a period, ten times longer, reflecting the lower preservation potential of the transverse dunes as sedimentary records, due to erosion associated with their migration. The rate of dune migration suggests that an aeolian contribution of coastal sands has occurred following the sea level highstand of the Middle Holocene, accounting for the extent of the active dunefields. This mode of the barrier accumulation is considered as an analogue for earlier highstand events. However, the dunefields only cover a fraction of the entire barrier. It is thus inferred that barrier formation occurred over a long period, probably encompassing several glacial-interglacial cycles. Sand accumulation during the lowstand, either by transport of sand from the subaerially exposed shelf and/or reworking of sand emplaced during the prior highstand, may contribute significantly to the barrier development.

中文翻译：

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季风气候下海岸沙丘地层的季节控制，美奈沙丘，越南东南部

摘要 在第四纪后期开发的美奈沙丘是越南东南部主要沿海屏障复合体的最上部，由与亚洲季风气候相关的风况形成。屏障复合体长 100 km，海拔高度超过 150 m，但尽管规模很大，但对其地貌和地质特征的研究有限。几个活跃的沙丘区从海岸向陆地延伸 2-10 公里，而屏障表面的其余部分是稳定的。我们应用探地雷达 (GPR) 和石英光学受激发光 (OSL) 测年对美奈沙丘的横向沙丘进行测年，以表征形态地层学和最近的风成沉积历史。目前，沙丘的起伏通常为 5-10 m，波长为 50-100 m。它们受到东北冬季季风的驱动，并随着西南夏季风的轻微缓解而逆转。GPR 剖面和 OSL 年龄定义了三个地层单元：现代、全新世和更新世沙丘单元。现代沙丘单元的 GPR 数据主要是一系列陡峭的反射，这些反射完全向西倾斜，反映了冬季季风，并被重新激活的表面所打断。风向逆转的证据没有保留在沉积层序列中，而是由再活化表面表示。因此，以再活化表面为界的亚基定义了年沉积。一个亚基的保存潜力随横向沙丘的迁移速度而变化，在迁移速度最快的沙丘中，每年大约保存一个亚基（1.1±0.6 个亚基/年）。现代沙丘通常小于 100 年，并且以 0.6-2.5 米/年的净速率迁移 WSW。全新世沙丘单元与现代单元一样厚，尽管它跨越一个时期，长十倍，反映了横向沙丘作为沉积记录的较低保存潜力，这是由于与其迁移相关的侵蚀。沙丘迁移的速度表明，在中全新世海平面高位之后发生了沿海沙的风成作用，说明了活动沙丘的范围。这种屏障积累模式被认为是早期高位事件的类似物。然而，沙丘只覆盖了整个屏障的一小部分。因此推断屏障的形成是在很长一段时间内发生的，可能包括几个冰期-间冰期循环。