Abstract Three sedimentary sequences from a coastal wetland behind a sand barrier, on the west coast of d’Urville Island, New Zealand, were examined using a multi-proxy approach, including sedimentological, geochemical and microfossil (diatom) analyses, with the chronology established using radiocarbon and 210Pb dating. Data show that a brackish lagoon started developing 7300 year ago after formation of the sand barrier in Moawhitu. This was followed by periods of alternating wetland encroachment and open water, displaying spatial variations, until a peatland was established about 1300 cal. yr BP. The wetland was then partially drained in the early 1900s, leading to compaction of the peat near the surface. A coarse layer containing gravel, sand and shells, with a sharp lower contact, in the northern area of the wetland, is attributed to an overwash about 2500-3000 yr BP, most probably a tsunami generated by the rupture of a local or regional fault. The high-resolution continuous record obtained with XRF core scanning revealed a geochemical signature (Ca and S) for the overwash 600 m inland in the middle area of the wetland, while it was absent from the southern site 1.1 km from the shore. This suggests that, except at the northern end of Moawhitu, the sand dune acted as an effective barrier preventing any sediment from overtopping 2500-3000 yr BP, with only a geochemical evidence marking the extent of seawater inundation. No sedimentological or geochemical evidence could be found in the wetland for the 15th century tsunami that had destroyed almost an entire community in Moawhitu, as recounted in Māori oral tradition (pūrākau), although pebbles at the surface of the dune are likely to be linked to this event. Thus, the sand dune appears to have again acted as an effective barrier for the overwash in the 15th century. However, our study suggests that the area might have been impacted by more than one tsunami in the last 3000 years. It also shows that a high-resolution continuous XRF record can provide the evidence for short-term changes (catastrophic or not) that did not leave any clear sedimentological signature, thus providing a better insight of environmental changes in any depositional environment.

中文翻译：

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新西兰沿海湿地 (Moawhitu) 环境变化的 7300 年记录，以及灾难性泛滥（海啸？）的证据

摘要 新西兰 d'Urville 岛西海岸沙障后的沿海湿地的三个沉积序列使用多代理方法进行了检查，包括沉积学、地球化学和微化石（硅藻）分析，并确定了年代学。使用放射性碳和 210Pb 测年。数据显示，7300 年前在 Moawhitu 形成沙障后，一个咸水泻湖开始发育。随后是交替的湿地侵占和开放水域，表现出空间变化，直到泥炭地建立起来大约 1300 卡路里。年 BP。湿地在 1900 年代初期被部分排干，导致地表附近的泥炭被压实。在湿地的北部地区，含有砾石、沙子和贝壳的粗层，具有急剧的较低接触，归因于大约 2500-3000 年 BP 的过度冲洗，最有可能是由局部或区域断层破裂产生的海啸。用 XRF 岩芯扫描获得的高分辨率连续记录揭示了湿地中部内陆 600 m 上冲的地球化学特征（Ca 和 S），而在距海岸 1.1 km 的南部站点则没有。这表明，除了在 Moawhitu 的北端，沙丘充当了防止任何沉积物超过 2500-3000 年 BP 的有效屏障，只有地球化学证据标志着海水淹没的程度。正如毛利人的口述传统 (pūrākau) 所述，15 世纪海啸几乎摧毁了 Moawhitu 的整个社区，在湿地中找不到沉积学或地球化学证据，尽管沙丘表面的鹅卵石很可能与这一事件有关。因此，沙丘似乎再次成为 15 世纪洪水的有效屏障。然而，我们的研究表明，该地区在过去 3000 年中可能受到不止一次海啸的影响。它还表明，高分辨率连续 XRF 记录可以为没有留下任何明确沉积学特征的短期变化（灾难性或非灾难性）提供证据，从而更好地了解任何沉积环境中的环境变化。