Middle to late-Holocene decreased fluvial aggradation and widespread peat initiation in the Ishikari lowland (northern Japan)
Middle to late-Holocene decreased fluvial aggradation and widespread peat initiation in the Ishikari lowland (northern Japan)
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DOI：
10.1177/0959683616646189
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发表时间：
2016-06
期刊：
影响因子：
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通讯作者：
Y. Ishii;K. Hori;A. Momohara;Toshimichi Nakanishi;W. Hong
中科院分区：
文献类型：
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作者：
Y. Ishii;K. Hori;A. Momohara;Toshimichi Nakanishi;W. Hong
本研究调查了海平面和气候变化的影响减少河流加积和随后广泛的泥炭启动中晚全新世在石狩低地，这是一个沿海洪泛平原形成的冰后期海平面变化。通过引入一种新的方法来分别评估有机质和碎屑沉积物的输入率，我们证明，泥炭开始形成时，河流沉积速率显着下降（小于0.6毫米/年），而植物宏体化石分析表明，降低水位也是重要的泥炭启动。这种沉积环境的变化可能与决口扇的突然废弃有关。泥炭萌生的集中年龄约为5600-5000、4600-4300和4100-3600 calBP，表明外源控制促进了决口扇的废弃，不同的萌生年龄可以通过石狩河及其支流的不同河流响应来解释。决口扇的废弃可能是由于海平面下降或降水减少。虽然在日本沿海低地没有报道过与泥炭起源相一致的亚千年海平面波动，但来自中国的石笋（代表东亚夏季风（EASM）的强度）记录的开始年龄和降水量减少的密切比较表明，降水量减少导致了决口扇的放弃。我们的研究结果可能表明，类似的河流响应可能是常见的其他沿海洪泛区受东亚夏季风影响。
This study investigated the influence of sea-level and climate changes on the decreased fluvial aggradation and subsequent widespread peat initiation in the middle to late-Holocene in the Ishikari lowland, which is a coastal floodplain formed in response to the postglacial sea-level change. By introducing a new approach to separately evaluate the rates of organic and clastic sediment input, we demonstrated that the peat began to form when the fluvial sedimentation rate was significantly decreased (less than 0.6 mm/yr), while plant macrofossil analysis suggested that lowering of water level is also important to the peat initiation. Such changes in sedimentary environment may be associated with the abrupt abandonment of crevasse splays. The concentrated ages of the peat initiation around 5600–5000, 4600–4300, and 4100–3600 cal. BP suggest that an allogenic control promoted the abandonment of crevasse splays, and different onset ages can be explained by different fluvial responses of the Ishikari River and its tributaries. The abandonment of crevasse splays could result from sea-level fall or decreased precipitation. While submillennial sea-level fluctuations coincident with the peat initiation have not been reported in coastal lowlands of Japan, the close comparison of the onset ages and decreased precipitation recorded in a stalagmite from China, which represents the strength of the East Asian summer monsoon (EASM), suggests that decrease in precipitation led to the abandonment of crevasse splays. Our results may indicate that similar fluvial responses might be common in other coastal floodplains affected by the EASM.