## 5 Discussion  
### Types and Conditions for the Formation of Deformation Bands  
Deformation bands can be classified into categories: kinematics and deformation mechanisms [2; 3]. The two classifications are not completely independent but rather related in some cases. For example, compactional shear bands (CSBs [4; 53]), shear-enhanced compaction bands (SECBs [6; 54; 55]) and pure compaction bands (PCBs [54]) could only form as cataclastic deformation bands [3; 53; 55]. Since the formation of cataclastic deformation bands is accompanied by volume reduction of the pore space in deformation bands, the cataclastic bands are considered as CSBs, SECB or PCBs formed under contractational settings [3]. In some of the present deformation bands, since the grain sizes of the host sandstones are significantly reduced by cataclasis, they could be considered as cataclastic deformation bands. Hence, these deformation bands could be classified as CSBs, SECBs or even PCBs. Some shear bands from outcrop sample KT2 occurred as conjugate sets. This fact precluded these deformation bands from pure compaction bands (PCBs). The difference between the CSBs and SECBs is in the shear versus compaction ratio (S/C): when the S/C is greater than one, it is called as CSBs, while it is called as SECBs when it is around one [4; 6]. The S/C ratio can be inferred from the shear strain inferred from the direct measurements of displacement along deformation bands and the compaction ratio from the difference in porosity between the host and deformation bands (e.g., [6]). In the present study, we have not made any such analyses to infer the ratio of S/C. On the other hand, the dihedral angle between conjugate deformation bands could be used to distinguish the types of deformation bands. According to a review of the dihedral angle between conjugate deformation bands [3], it varies between 40 to 75\({}^{\circ}\) for CSBs, while it is in the range of 70 to 100\({}^{\circ}\) for SECBs. Therefore, the present conjugate deformation bands with the dihedral angle of c. 60\({}^{\circ}\) are most reasonably interpreted as CSBs. Although the present deformation bands formed in the borehole core sample B6_8.2 m can be classified as cataclastic bands, almost all of the deformation bands in outcrop samples KT1, 2 and 3 could be classified as phyllosilicate bands with little cataclasis [2]. We could not interpret why cataclastic bands formed in the borehole core samples while phyllosilicate bands formed in the outcrop samples. However, it could be ascribed to the difference in the amount of strain as mentioned below (i.e., higher strain in the borehole core samples than in the outcrop samples). In sample KT2, cataclasis occurred in the conjugate deformation bands (Figure 7b,c), while it little occurred in other deformation bands, which are only defined by the preferential orientation of altered biotite grains (phyllosilicate bands, Figure 7a). Therefore, it seems that the phyllosilicate bands could have developed into the cataclastic conjugate bands due to strain hardening associated with grain interlocking with increasing strain (e.g., [2]). In fact, altered biotite grains were also preferentially orientated along the cataclastic conjugate bands (Figure 7b,c), which perhaps occurred before the onset of cataclasis. To discuss the mechanism for the formation of deformation bands, we investigated the formation conditions and phyllosilicate contents because the mechanisms were dependent on the two factors [2]. The temperature and pressure (i.e., depth) conditions could be first inferred from the burial depth of the strata, where the deformation bands were inferred to