Impact of reworked foraminifera from an eroding salt marsh on sea-level studies, New Zealand
Impact of reworked foraminifera from an eroding salt marsh on sea-level studies, New Zealand
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来自侵蚀盐沼的改造有孔虫对新西兰海平面研究的影响
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
B. Hayward
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文献类型：
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作者：
B. O. Figueira;B. Hayward
利用全新世有孔虫进行的海平面定量重建通常是基于同一地点现代盐沼有孔虫潮汐高程相关带的高程传递函数估计。由于最近海平面上升超过沉积物供应，许多新西兰盐沼正在受到积极侵蚀，因此很难在其向海末端找到不受侵蚀影响的现代模拟研究的样带。在新西兰南岛的怀卡瓦港，我们发现来自侵蚀河岸的改造盐沼有孔虫已经与原位动物大量混合：(1)在沼泽向海的沙滩上；(2)在80 cm高的堤岸顶部的春季潮汐沼泽（连同堤岸下沙中的中潮有孔虫）；(3)侧向输送到附近的低海拔非侵蚀芦苇沼泽。河岸富含有机物的纤维状盐沼泥被侵蚀破坏，大块的石块坍塌到较低的沙平面上，在那里，原有的残余动物与新殖民的低海拔盐沼有孔虫混合在一起。这些研究表明，受侵蚀的盐沼可能导致有孔虫试验的大量改造和混入现代动物群，从而影响它们在海平面重建中的应用。这项研究促使我们重新审视了卡特林斯湖附近的部分岩心序列，并重新解释了先前推断的地震位移（5-4.5 ka），而不是侵蚀和崩塌的盐沼岸的结果。
Quantitative sea-level reconstructions using Holocene foraminifera are usually based on transfer function estimates of elevation derived from the tidal-elevation-related zonation of modern salt marsh foraminifera at the same site. Many New Zealand salt marshes are actively eroding as a result of recent sea-level rise exceeding sediment supply, making it difficult to find transects for modern analogue studies that are unaffected by erosion at their seaward ends. At Waikawa Harbour, South Island, New Zealand we show that reworked salt marsh foraminifera from the eroding bank have been mixed in significant quantities with in situ faunas: (1) in the sand flat seaward of the marsh; (2) in the spring tidal marsh on top of the 80-cm-high bank (together with mid tide foraminifera from the sand below the bank); and (3) transported laterally into a nearby non-eroding rush marsh at lower elevation. The fibrous organic-rich salt marsh mud of the bank has been undermined by erosion and large blocks have collapsed to a lower level on the sand flat where the in situ relict faunas are being mixed with newly colonised lower elevation salt marsh foraminifera. These studies show that eroding salt marshes may result in substantial reworking and mixing of foraminiferal tests into the modern faunas thereby compromising their use in sea-level reconstructions. This study prompted us to revisit part of a cored sequence at nearby Catlins Lake and reinterpret a previously inferred earthquake displacement (5–4.5 ka) to be the result of an eroding and collapsing salt marsh bank instead.