Fundamental study on the mode of transportation and sedimentation of subaqueous tephras

水下火山灰搬运与沉积方式的基础研究

基本信息

批准号：
63540607
负责人：
KUROKAWA Katsuki
金额：
$ 1.09万
依托单位：
Niigata University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1988
资助国家：
日本
起止时间：
1988 至 1989
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-63540607/
关键词：
Subaqueous tephra Ash flow turbidite The Joetsu Ash The SK020 Ash The Sug-a Ash Facies model Osumilite Andalusite Ash How turbidite Sug-a火山灰層相モデルテフラの堆積構造テフラの粒度特性中央油帯浜忠層西山層

项目摘要

Mode of transportation and sedimentation of subaqueous tephras was investigated especially on those intercalated in the upper Miocene to lower Pleistocene in the Niigata backarc basin, central Japan. They were classified in four categories; (1)subaqueous fallout, (2)ash cloud, (3)subaqueous flow and (4)their epiclastic reworks. Fourteen facies models of these tephras were established in respect to grain-size populations; TypeA1-A5 for silt to medium sand-sized tephras (Population A), TypeB1-B5 for medium sand to granule-sized tephras(Population B) and Type C1-C4 for those containing considerable amounts of pumice clasts larger than granule size(Population C).It is noteworthy that among these subaqueous tephras, subaqueous flows which were directly transformed from subareal ash flows or subaqueous dense ash clouds are not uncommon regardless of their grain-size population; fine-grained ones(TypeA3), medium-grained ones(TypeB4) and coarse- grained-ones(TypeC3). They show inverse-to-normal grading, containing mud balls or rip-ups, and flowed more than 50km with little decrease of thickness. In this research, they are named ash flow turbidites. The Joetsu Ash (Kurokawa and Hirata,1986) is a representative of the ash flow turbidites of TypeB3. It is cordierite-cummingtonite bearing ash of subareal ash flow origin, flowed into water.The basic sequence containing the ash flow turbidites was clarified; the ash flow turbidite unit occupies the base of the sequence (Unit I), overlaid by thin alternations of fine-grained ashes (Unit II) and pumice-rich ashes (Unit III). This sequence suggests the flow differentiation from subareal ash flow or subaqueous ash cloud.Besides, osumilite and magmatic andalusite were found from Pliocene subaqueous tephra (the Sug-a Ash) in the course of this study.

特别研究了中新世上中新世，在日本中部的尼加塔后期更新世，研究了水下tephras的运输方式和沉积。他们分为四类；（1）水下辐射，（2）灰云，（3）水下流动和（4）其上皮逆转。这些tephras的14个相对于晶粒大小的人群建立了。用于淤泥到中等砂尺（种群A），中等砂到中等砂到颗粒大小的tephras（种群B）的TypeA1-A5（种群B）和C1-C4型和含有相当数量的Pumice Clast的pumice大小大于颗粒大小（种群c）的人（种群C）。无论谷物大小如何，浓密的灰云并不少见。细颗粒的（typea3），中等粒度（typeb4）和粗颗粒（typec3）。它们显示出逆向正常的分级，包含泥球或撕裂，流动超过50公里，厚度降低。在这项研究中，它们被命名为灰流浊度。 Joetsu Ash（Kurokawa and Hirata，1986）是TypeB3的灰流浊度的代表。它是圆锥形 - 卷木地岩具有亚氨基灰流的起源，流入水中。灰分流浊度单元占据了序列的底部（单元I），被细粒灰分（IIII单元）和富含Pumice的灰烬（第三单元）覆盖。该序列表明在这项研究过程中，从上新世倒流的Tephra（Sug-A Ash）发现了贝斯河下灰流或水下灰云的流动分化。