Holocene Environmental History in and around the Paleo-Nagareyama Bay, Central Kanto Plain
Holocene Environmental History in and around the Paleo-Nagareyama Bay, Central Kanto Plain
复制标题
中关东平原古流山湾及周边地区全新世环境史
DOI：
10.4116/jaqua.28.61
复制
发表时间：
1989
期刊：
影响因子：
--
通讯作者：
T. Takano
中科院分区：
文献类型：
--
作者：
K. Endo;M. Kosugi;M. Matsushita;N. Miyaji;R. Hishida;T. Takano
在东京北部长山市的Sakagawa低地(古长山湾)，对全新世古环境的持续历史进行了调查。在这一地区，绳索海侵的海水侵入了在上一次冰川期间被深度解剖的山谷。~(14)C测年、Tephra鉴定、颗粒成分分析、硅藻分析和孢粉分析表明，沉积物记录了一些重要的古地理变化证据，特别是海平面和植被的变化。通过对一些化石组合垂直变化的比较，认为6、500、5、300、4、500和3,500a.B.P.是全新世环境史上共同和重要的界线。这些年龄与关东平原中部根据65个14C测年绘制的相对海平面变化曲线的转折点相对应。关东平原全新世环境历史为：1)7,500-6,500yB.P.：海平面迅速上升，形成深水内湾。在海湾周围的阶地上，以栎类为主的暖温带阔叶落叶林占主导地位，其次是栎类和栎类等透明叶乔木。2)6,500-5,300yB.P.：海平面稳定在+3m，潮滩发育，大片牡蛎礁形成。这些沙质物质不仅从周围的梯田运来，还从该地区的主要水体--古奥库托乔海湾运来。4)4,500-3,500yB.P.：海平面恢复稳定，形成了牡蛎礁。沼泽和由Alnus组成的沼泽林覆盖了这片海域。(5)3,500年B.P.-现在：由于海平面下降到-1-2米，海域面积从3,500年B.P.逐渐退化到1800年B.P.。在这一阶段的前半部分，阶地上以亮叶林为主，山谷中以赤杨沼泽林为主。然而，当海平面上升到0米时，赤杨沼泽林在1800年前突然消失了。1800yB.P.以后，柳杉和水生植物的花粉急剧增加。
The continuing history of paleoenvironments in the Holocene was investigated in a small valley, the Sakagawa lowland (Paleo-Nagareyama Bay), situated in Nagareyama City, north of Tokyo. In this area, the seawater of the Jomon transgression invaded the valley, which had been deeply dissected during the last glaciation. 14C dating, tephra identification, grain-component analysis, diatom analysis, and pollen analysis showed that the sediments recorded some important evidence of paleogeographic changes, especially in sea-level and vegetation.As a result of the comparison in vertical changes among some fossil assemblages, the ages 6, 500, 5, 300, 4, 500, and 3, 500y.B.P. were recognized as common and important boundaries in Holocene environmental history. Moreover, such ages correspond to the turning points in the relative sea-level change curve which was drawn based on 65 14C dates obtained in the central Kanto Plain.The Holocene environmental history of the area is as follows:1) 7, 500-6, 500y.B.P.: Sea-level rose rapidly and a deep inner bay formed. On terraces surrounding the bay, the warm-temperate broad-leaved deciduous forest mainly composed of Quercus (Lepidobalanus) was dominant, along with lucidophyllous tress such as Castanopsis and Quercus (Cyclobalanopsis).2) 6, 500-5, 300y.B.P.: Sea-level was stable at +3m, the tidal flat developed, and oyster reefs were formed over a wide area.3) 5, 300-4, 500y.B.P.: About 5, 300y.B.P., sea-level was abruptly lowered to +2-+1m, and sand layers covered the reef. Those sandy materials were transported not only from the surrounding terraces, but also from the Paleo-Okutokyo bay, the major body of water in the area. The broad-leaved deciduous forest continued to be dominant on the terraces.4) 4, 500-3, 500y.B.P.: The sea-level was stable again, and oyster reefs were formed. Marshes accompanied by swamp forests composed of Alnus covered the sea area. Lucidophyllous forest, mainly of Quercus (Cyclobalanopsis), because dominant.5) 3, 500y.B.P.-Present: The sea area regressed gradually from 3, 500y.B.P. to 1, 800y.B.P. due to the lowering of the sea-level to -1--2m. During the early half of this stage, lucidophyllous forest was dominant on the terraces, and Alnus swamp forest developed in the valley. Alnus swamp forest, however, disappeared suddenly at 1, 800y.B.P., when the sea-level rose to 0m. After 1, 800y.B.P., Cryptomeria and aquatic plant pollen increased dramatically.