南西部地方의 諸岩石에 나타나는 風化穴의 成因과 形成時期

Abstract

Tafoni and gnammas were investigated in 10 sites(fig.1) including Uychon basin(fig.2) and Mokpo(fig.3) in the southwestern part of Korea.

Weathering hollows are developed on boulders, tors and inselbergs in mountains, piedmonts and stepped basins. But they are grown partly on bedrocks around coastal areas and corestones on hills. They are well developed on granite, conlomerate and tutt breccia, but smaller ones are developed on gneiss, tuff and xenolith(table 1). The boulders, of which flared slopes with tafoni developed, are located on the transitions between High -level straths ( etch sur- faces?) and Intermediate-level terraces (Climatic terraces) in Uychon stepped basin (fig. 4 and 5). Tafoni of 5 height levels(90m, 75m, 55m, :30m, 1. 5m a. s. 1.) are developed on the tuff ,breccia in Mokpo(fig.6). The conclusions are as follows: 1) Most of tafoni in the study area had been initiated on weathering fronts by subsurface weathering, and they were fossilized or the forming rates were reduced after exposure by the denudation of regolith. 2) Gnammas were originated on weathering fronts by subsurface weathering. After exposure by stripping of regolith, they have been enlarged by the contact of bedrocks and water. 3) Most of weathering hollows had been initiated at Interglacial ages, and they were changed after exposure by denudation of regolith at Glacial ages.

As the weathering hollows were formed locally with subsurface water or partly under microclimate, they may not be used as paleoclimatic indicators. According to the facts mentioned above, the weathering hollows can be used as the indicators for the denudation chronology in the southwestern part of Korea.