From mountain source to ocean sink – the passage of sediment across an active margin, Waipaoa Sedimentary System, New Zealand
From mountain source to ocean sink – the passage of sediment across an active margin, Waipaoa Sedimentary System, New Zealand
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DOI：
10.1016/j.margeo.2009.12.010
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发表时间：
2010-04
期刊：
影响因子：
2.9
通讯作者：
L. Carter;L. Carter;A. Orpin;S. Kuehl
中科院分区：
文献类型：
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作者：
L. Carter;L. Carter;A. Orpin;S. Kuehl
美国和新西兰联合发起的从源头到汇的倡议旨在揭示从山脉到深海塑造景观的构造、气候和其他过程。在世界范围内选定的两个重点区域中，新西兰东北部的怀保阿沉积系统被确定为中纬度、高沉积物输入系统的一个例子。它位于西风带内，横跨澳大利亚板块和太平洋板块的会聚带。因此，构造和气候驱动因素是突出的，它们对WSS的影响是可以破译的，正如本期《海洋地质学》特刊中介绍的一套从源到汇的研究报告所述。WSS在几个时间和空间尺度上受到强迫，它们共同表现为叠加长期行为变化(构造抬升和海平面变化)的短期事件(风暴、地震和火山喷发)。总体而言，WSS正在经历隆升，这是自上一次冰盛期以来造成山谷切割的原因。隆升既是渐进的，也是间歇性的，后者与断层和俯冲相关的地震有关。这种地震活动破坏了地形的稳定，再加上频繁的风暴，产生了大量的泥沙。当这些沉积物通过系统时，一部分被沿海平原和中大陆架局部下沉形成的圈闭捕获，那里隔离了大厚度的全新世和可能更古老的沉积物(例如，沿海平原下约200米)。然而，大量的泥沙仍然到达大陆斜坡，在峡谷头部和斜坡盆地中堆积，其他沉积物在物质流中沿斜坡重新分布。大型火山喷发还通过火山灰落下的直接输入和火山破坏陆地植被后加剧的侵蚀影响沉积物通量。频繁的不同强度的风暴在泥沙的产生和转移中起着关键作用。重大事件，如1988年的气旋博拉，淹没了大陆架的沉积物，但可识别的洪水沉积只在当地保存下来，证明了大陆架物理和生物混合制度的有效性。尽管有风暴、地震和火山喷发，WSS最大的扰动，至少在过去的2400年里，一直是人类对该景观的森林砍伐。由此产生的沉淀物的流入超过了大陆架的存储能力。现代陆架没有像在人类时代之前那样捕获90%的河流输入，而是只保留了~25%，其余的逃逸到斜坡和其他地方。
The joint US–NZ Source-to-Sink initiative aims to unravel the tectonic, climatic and other processes that shape the landscape from the mountains to deep ocean. Of the two focus areas chosen world-wide, the Waipaoa Sedimentary System (WSS) of north-eastern New Zealand was identified as an example of a mid-latitude, high sediment input system. It resides within the westerly wind belt and extends across the convergence zone of the Australian and Pacific plates. Accordingly, the tectonic and climatic drivers are prominent and their influences on the WSS are decipherable as is documented in the suite of Source-to-Sink studies presented in this special issue of Marine Geology. The WSS is forced at several temporal and spatial scales, which collectively appear as short-term events (storms, earthquakes, and volcanic eruptions) superimposed on long-term, behavioural shifts (tectonic uplift, and eustatic sea level change). Overall, the WSS is undergoing uplift, which has been contributing to valley incision since the Last Glacial Maximum. Uplift is both gradual and intermittent, the latter relating to fault- and subduction-related earthquakes. Such seismic activity destabilises the landscape and, together with frequent storms, generates large amounts of sediment. As this sediment passes through the system, part is captured in traps formed by local subsidence of the coastal plain and middle continental shelf where large thicknesses of Holocene and probably older sediment are sequestered (e.g., ~200 m under the coastal plain). Nevertheless, substantial sediment still reaches the continental slope to accumulate in canyon heads and slope basins with other deposits redistributed down-slope in mass flows. Major volcanic eruptions also affect the sediment flux via direct input from ash-fall and by enhanced erosion following volcanic destruction of terrestrial vegetation. Frequent storms of varying intensity play a key role in the generation and transfer of sediment. Major events such as the Cyclone Bola of 1988, inundated the shelf with sediment, but identifiable flood deposits were preserved only locally, attesting to the effectiveness of shelf physical and biological mixing regimes. Despite the storms, earthquakes and volcanic eruptions, the largest perturbation of the WSS, at least in the last ~2400 years, has been the human deforestation of the landscape. The resultant influx of sediment overwhelmed the shelf’s storage capacity. Instead of capturing 90% the fluvial input, as in pre-human times, the modern shelf retains only ~25%, the remainder escaping to the slope and elsewhere.