## 6 Conclusions  
From the field structural analyses at outcrops and microstructural and microchemical analyses of deformation bands that occurred in the study area, we have reached the following conclusions. 1. In the study area, the geologic structure of the Eocene Urahoro Group is characterized by a folded belt with a wavelength of 1-2 km. The strata generally dip either east or west at moderate angles. However, there is one flexure structure in the eastern part of the study area consisting of the Shakubetsu Formation, which trends NNE-SSW to NE-SW. The northwestern limb of the flexure very steeply dips SE at 75\({}^{\circ}\) to almost vertically, while the southeastern limb dips south at 6\({}^{\circ}\) (almost horizontally). 2. Deformation bands in this area only developed in the Shakubetsu Formation around the flexure, which contains mudstones and coal layers other than sandstones, not in the uppermost unit of the Shitakara Formation, which solely consists of sandstones. Therefore, it could be inferred that strain was localized in the weak Shakubetsu Formation, resulting in the development of flexure and deformation bands with increasing NW-SE trending shortening in the folded belt. This shortening deformation mostly occurred after the deposition of the Atsunai Formation dated c. 7 Ma. 3. The temperature conditions for the formation of deformation bands were inferred to be c. 50 \({}^{\circ}\)C from the vitrinite reflectance values (%R\({}_{\rm O}\)) of the coal layers (c. 0.5). The deformation bands could have formed at the maximum burial depth, which was inferred to be as much as c. 2.7 km from the thickness of the overlying strata. The depth estimate conforms to the one (1.5-2.5 km) inferred from the inferred temperature conditions, assuming the geothermal gradient of 20 \({}^{\circ}\)C in a froare region and surface temperature of 0-20 \({}^{\circ}\)C. The deformation bands were inferred to have originated as phyllosilicate bands, which developed into the cataclastic bands with increasing strain in the Shakubetsu Formation with c. 10 vol.% of phyllosilicate. 4. In the cataclastic bands, the detrital grains in host sandstones are crushed into sizes less than one-half to one-fifth of the original ones, and the asperities are flaked during the formation of deformation bands. The latter fact could be revealed by a higher circularity of detrital grains in the deformation bands than in the host parts. 5. Reactive transport or structural diagenesis was significant in the present sandstones with deformation bands, some of which were characterized by the alignment of phyllosilicate (i.e., phyllosilicate bands). Here, the detrital biotite and chlorite grains were fractured along the cleavages and were altered (or weathered) to vermiculite and further to kaolinite. Also, authigenic smectite grew in the pore space created by fracturing in detrital grains. Since the deformation-induced weathering could have significantly reduced the internal friction and permeability of rocks in the study area, the landslide was probably triggered by heavy rainfall in such weathered rocks. **Author Contributions:** Conceptualization, H.K. and T.T. ; methodology, H.K. ; software, H.K. ; validation, H.K. and T.T. ; formal analysis, H.K. and T.T. ; investigation, H.K. and T.T. ; resources, T.T. ; data curation, H.K. ; writing--original draft preparation, T.T. ; writing--review and editing, H.K. and T.T. ; visualization, H.K. and T.T. ; supervision, T.T. ; project administration, T.T. ; funding acquisition, T.T. All authors have read and agreed to the published version of the manuscript. This research was funded by JSPS KAKENHI, Grant Number 21H01181, to [PERSON]. Not applicable. **Data Availability Statement:** All the data used in the study are described in the paper.