Comparison study about formation mechanism of frost cracks and sun cracks, cause of stratigraphic disturbance on the last glacial stage

裂缝是旧石器时代地层扰动的原因之一。我通过实地观察和实验室分析，比较了朝鲜半岛的土楔、本州的干裂浇铸和北海道的冰楔浇铸。我从结构和形成机制方面考察了霜裂和干裂的差异和过渡特征。在朝鲜半岛上更新世，包括在朝鲜半岛的土壤楔块中，在裂缝的上限附近发现了圆形石英和其他小于极细砂粒的圆形矿物。因此，圆形矿物可能起源于风成黄土。此外，裂缝填充物中含有较大比例的来自AT火山灰的火山玻璃。我认为大多数上部裂缝是在末次冰期高潮前后形成的。将上更新世划分为裂缝期、火山玻璃期、深色带、深红褐色带等4个时期。裂缝的结构和形成因素在局部观测和未受扰动的地表观测中，除顶部外，朝鲜半岛的土楔和本州的干燥裂缝仅为雨水形成的泥纹。这种裂缝现象是在北海道伴随活动层的冰楔铸件中没有发现的结构。关于冰楔铸模的主要成因取决于冻结，土楔和干裂铸模受到末次冰期寒冷条件的影响，但由于干燥而收缩被认为是形成的主要因素。因此，这些裂缝是不同于所谓土楔的另一种裂缝。

This research was on cracks, which are one of the causes of disturbance in Paleolithic strata. I compared soil wedges in the Korean Peninsula, desiccation crack casts in Honshu, and ice wedge casts in Hokkaido by observation in the field, and some laboratory analysis. I examined differences and transitional characteristics in frost cracks and desiccation cracks with respect to structure and formation mechanism.1. Correlation of the Upper Pleistocene in the Korean PeninsulaIn the Upper Pleistocene, including in soil wedges from the Korean Peninsula, round quartz and other round minerals of less than very fine sand grain size were recognized near the upper limits of the cracks. Thus, the round minerals may have originated as aeolian loess. In addition, it became clear that volcanic glasses which came from AT volcanic ash are included comparatively large portion in the crack fillers. I suggest that most upper cracks were formed before and after the climax of the last glacial stage. Furthermore, I made up Upper Pleistocene into four period with cracks, volcanic glasses, the dark color zone, the dark reddish-brown zone and so on.2. Structure and a formation factor of cracksIn both local observations and observations of undisturbed surfaces, except for the top portion, soil wedges on the Korean Peninsula and desiccation cracks on Honshu were only mud veins made visible by rainwater. This crack phenomenon is a structure not found in the ice wedge casts accompanying with the activity layer in Hokkaido. With regard to the fact that the main origin of the ice wedge casts depends on freezing, the soil wedges and desiccation crack casts were influenced by the chilly conditions of the last glacial stage, but it is thought that shrinking due to drying was the main factor in formation. It is concluded, therefore, that these cracks were another cracks which were different from so-called soil wedges.