Quaternary Tephra Studies in the Hokkaido District, Northern Japan
Quaternary Tephra Studies in the Hokkaido District, Northern Japan
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日本北部北海道地区的第四纪火山灰研究
DOI：
10.4116/jaqua.30.379
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发表时间：
1991
期刊：
影响因子：
--
通讯作者：
K. Okumura
中科院分区：
文献类型：
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作者：
K. Okumura
20世纪80年代北海道第四纪温度年代学研究的关键问题是缺乏广泛的标志温度，以及在14C方法范围之外缺乏明确的年代学资料。近10年来，随着B-Tm （<1ka）、Aso-4 （70ka）、Toya （90ka）和KHb （100ka）等一系列显著分布广泛的毡层的发现，这些问题在全新世和晚更新世得到了部分解决。Aso-4层和Toya层的发现使北海道的温度年代学与本州和九州的温度年代学联系起来。同时，北海道大部分地区除德胜平原周边地区外，早更新世至中更新世地层资料仍不足，无法建立全面的年代地层学。本文对北海道东部地区的地层地层进行了介绍，以总结北海道地区第四纪地层的研究进展，并勾勒出北海道地区第四纪地层的轮廓。通过地层修正和玻璃碎片显微探测技术的广泛应用，对北海道爆发活动历史最悠久的阿干火山和库察罗火山的火山碎屑流沉积地层进行了修正和关联。引入了与北海道东部产气相岩相特征不同的介入性气相岩，作为早更新世至中更新世时期的标志岩。中更新世泥岩的年代学资料仍然很少，但揭示了它们与主要海侵的地层位置。研究了玻璃碎片和砾石矿物组合中钾含量的时间和区域变化，从而对早更新世至中更新世未确定的温层的起源火山和年龄有了总体认识。
The critical problems remaining for the study of the Quarternary tephrochronology of Hokkaido in the 1980s were the lack of extensive marker tephras and of well-defined chronological data beyond the range of 14C method. In the last ten years, these problems were partly solved for the Holocene and Late Pleistocene with the recognition of a number of remarkable wide-spread tephra-layers including B-Tm (<1ka), Aso-4 (70ka), Toya (90ka) and KHb (100ka). The finding of Aso-4 and Toya layers enabled to correlate the tephrochronology of Hokkaido with that of Honshu and Kyushu. Meanwhile, information on Early to Middle Pleistocene tephras is still insufficient for establishing a comprehensive chrono-stratigraphy in most of Hokkaido, with the exception of the region around the Tokachi Plain.The tephrostratigraphy in eastern Hokkaido is described in this paper in order to summarize recent progress and to show the outline of Quaternary tephras in Hokkaido. The stratigraphy of pyroclastic flow deposits from Akan and Kutcharo volcanoes, which have the longest history of explosive activities in Hokkaido, has been revised and interrelated through stratigraphic revision and extensive application of microprobe techniques to glass shards. Intervening airfall tephras with different petrographic characteristics from tephras occurring in eastern Hokkaido are introduced as possible marker tephras of Early to Middle Pleistocene age.Chronological data for Middle Pleistocene tephras are still very few, but their stratigraphic positions in relation to major transgressions are revealed. Temporal and regional variation of potassium content in glass shards and maffic mineral assembrage is examined to give general ideas of source volcanoes and ages of unidentified tephra layers of Early to Middle Pleistocene.