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Field measurements of weathering rates of bedrocks under erosional terrace surfaces

侵蚀阶地表面基岩风化速率的现场测量

基本信息

批准号：
03680213
负责人：
SUZUKI Takasuke
金额：
$ 1.15万
依托单位：
CHUO 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：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

项目摘要

The aim is to establish the empirical equations to express the rates of weathering of bedrocks defined as dZ/dt, where Z is the thickness of weathered materials in the direction perpendicular to ground surface and t is the time elapsed since the surface of fresh bedrock was last eroded. The data were obtained for the weathered materials of bedrocks under the dated fluvial and marine erosional terrace surfaces arount Tokyo, Japan. The studied terraces are 1)divided into the 21 sequential series ranging from 70 to 70,000 yr.B.P.in the age assumed to be equal to the time t, 2)composed of the Tertiary sedimentary rocks, and 3) covered with gravels or sand veneer ranging from 0.2 to 3 m thick.The weathering profiles were investigated at 56 sites on 14 series of the terraces with the combined methods of test pits, borings and seismic prospectings, and were divided into four weathering zones different in weathering grades : highly weatheredzone (H), moderately (M), slightly (S) and faintly (F). The boundaries between the four zones were confirmed by the differences in the pore-size distribution and penetration hardness. The thickness of weathered materials from the base of terrace veneer to each base of the four zones are denoted as Z_H, Z_M, Z_S and Z_F, respectively.The relationships between these Z's and t are expressed as Z=alphat^<beta>, where alpha and beta are constatns. The values of slpha are 0.48, 1.2 and 3.2 mm/yr for Z_H, Z_M and Z_S, respectively, whereas beta shows an almost uniform value of 0..75 for the three different zones. This fact indicates that the weathering rates, dZ/dt, decrease with the time t.

目的是建立表达基岩风化速率的经验方程，定义为dZ/dt，其中Z是风化物质在垂直于地表的方向上的厚度，t是自新鲜基岩表面上次被侵蚀以来经过的时间。这些数据是针对日本东京周围古老的河流和海洋侵蚀阶地表面下的基岩风化材料获得的。研究的阶地1）分为21个连续系列，年龄范围为70至70,000年，假设年龄等于时间t，2）由第三纪沉积岩组成，3）覆盖有厚度为0.2至3 m的砾石或砂饰面。采用组合测试方法对14个系列阶地的56个地点进行了风化剖面调查。坑, 根据风化程度不同，分为强风化带（H）、中风化带（M）、轻度风化带（S）和弱风化带（F）4个风化带。四个区域之间的边界通过孔径分布和渗透硬度的差异来确定。从露台单板基部到四个区域的每个基部的风化材料厚度分别表示为Z_H、Z_M、Z_S和Z_F。这些Z与t之间的关系表示为Z=alphat^<beta>，其中alpha和beta是常数。 Z_H、Z_M 和 Z_S 的 slpha 值分别为 0.48、1.2 和 3.2 mm/yr，而 beta 对于三个不同区域显示几乎统一的值 0..75。这一事实表明，风化速率 dZ/dt 随着时间 t 的增加而降低。