Field measurements of weathering rates of bedrocks under erosional terrace surfaces

目的是建立表示基岩风化速率的经验公式，定义为dz/dt，其中Z是垂直于地表方向的风化物质厚度，t是自新鲜基岩表面最后一次被侵蚀以来所经过的时间。这些数据是在日本东京附近古老的河流和海洋侵蚀阶地表面下的基岩风化物质获得的。所研究的阶地1)划分为21个年代为70~7万年的阶地序列，年龄假定为t；2)由第三系沉积岩组成；3)覆盖0.2~3m厚的砾石或砂岩。采用试验坑、钻孔和地震勘探相结合的方法，在14个阶地系列的56个站点上调查了风化剖面，并将其划分为4个不同风化级别的风化带：高度风化带(H)、中度风化带(M)、轻度风化带(S)和微弱风化带(F)。通过孔径分布和渗透硬度的差异确定了四个区域之间的边界。从梯田单板底部到四个带每个底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‘s与t之间的关系表示为Z=alphat^&lt；β&gt；其中α和β为常数。Z_H、Z_M和Z_S的SLPHA值分别为0.48、1.2和3.2 mm/年，而β值在三个不同的带上几乎一致，为0.75。这一事实表明，风化速率dz/dt随时间t的增加而减小。

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.