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High-resolution reconstruction of the paleoenvironmental changes since the Last Glacial by the analyses of highland moor deposits

通过高地沼泽沉积物分析高分辨率重建末次冰期以来的古环境变化

基本信息

批准号：
14380034
负责人：
KATO Shigehiro
金额：
$ 5.31万
依托单位：
Museum of Nature and Human Activities, Hyogo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2005
项目状态：
已结题

项目摘要

Five all-cored sediments were taken at the Ohnuma Moor in the northern part of Hyogo Prefecture, three of which were the oriented samples obtained by newly developed non-magnetic core samplers. Synthetic analyses of the core sediments were performed including petrologic analysis of tephra layers, AMS-^<14>C dating, pollen and diatom analyses, and physical measurements of lightness, grain size, loss on ignition, magnetic susceptibility, and paleomagnetic secular variation (PSV), to clarify the paleoenvironmental changes since the Last Glacial and the formative processes of the moor. More than 65-m thick deposits underlie the Ohnuma Moor. The upper part about 50-m thick is composed mainly of sand and gravels, while the finer sediments about 17-m thick, mainly of clay and peat, comprise the upper part containing six tephra layers of K-Ah, SUk, MsP, Sh, AT, and Nh. Based on the estimated eruption ages of K-Ah and AT and more than 30 AMS-^<14>C dates along with the results of diatom analysis, it is inferred that the Ohnuma Moor originated the depression formed by the large scale landslide at ca.41 ka cal.BP and has been developed as a mire between ca.32 and 29 ka cal.BP and after ca.13 ka cal.BP and as a wetland until ca.32 ka cal.BP and from ca.29 to 13 ka cal.BP. All measured physical properties show the cyclic changes with small amplitude for the time interval from 41 to 13 ka cal.BP without the air fall tephra horizons. The temporal changes are possible to reflect the global climatic changes named the Dansgaadrd-Oeschger Oscillations with Heinrich Events. The PSV can be reconstructed mainly for the period between 35 and 32 ka cal.BP, suggesting the effectiveness of the new sampling method. However, it is necessary to improve it because the core samples were disturbed especially at their uppermost and lowermost parts.

在兵库县北方的大沼摩尔采集了5个全取心沉积物样品，其中3个是用新开发的非磁性岩心取样器获得的定向样品。通过火山灰层的岩石学分析、AMS-^<14>C测年、孢粉和硅藻分析、亮度、粒度、烧失量、磁化率和古地磁长期变化（PSV）等物理测量，阐明了末次冰期以来的古环境变化和摩尔沼泽的形成过程。大沼摩尔下有超过65米厚的沉积物。上部约50 m厚，主要由砂和砾石组成，而较细的沉积物约17 m厚，主要由粘土和泥炭组成，上部含有K-Ah、SUk、MsP、Sh、AT和Nh六个火山灰层。根据K-Ah和AT的喷发年龄和30多个AMS-^<14>C测年沿着，结合硅藻分析结果，推测大沼摩尔起源于约41 ka cal.BP的大规模滑坡形成的洼地，在约32 ~ 29 ka cal.BP和约13 ka cal.BP之后发展为沼泽，在约32 ka cal.BP和约29 ~ 13 ka cal. BP之前发展为湿地。在41 ~ 13 ka cal BP的时间间隔内，所有测得的物理性质都表现出小幅度的周期性变化，没有空气降落火山灰层。这些时间变化可能反映了全球气候变化，称为具有Heinrich事件的Dansgaadrd-Oeschger振荡。PSV主要可以重建为35和32 ka cal.BP之间的时期，表明新的采样方法的有效性。但是，由于岩心样品的扰动特别是在其最高和最低部位，因此有必要对其进行改进。