화산암-퇴적암 내 단열층서와 그 제어요소 : 백악기 위도화산암의 예

다국어 초록 (Multilingual Abstract)

As brittle deformation structures, fractures reflect multi-stage deformation events in sedimentary basins and determine the permeability of rocks. This study aims to identify differences in the fracture characteristics at different stratigraphic positions, defining fracture stratigraphy and the geologic factors controlling them in volcanic and sedimentary rocks exposed on the northern coast of Wido Island. For this purpose, sedimentary petrological description, fracture sampling, and brittle index calculation were carried out. The brittleness index was calculated based on XRD mineral composition. Linear scanlines at 24 points were set up in different stratigraphic positions to obtain fracture data. The obtained fracture data give information about the orientation and intensity of the fractures, the mutual abutting relationship, and the spatial relationship between the fracture tips and layer boundaries.
The studied outcrop consists of siliciclastic sedimentary units composed of massive / normally graded sandstone and laminated siltstone, and a volcaniclastic sedimentary unit composed of normally graded tuff and bedded tuff. Structural elements within the studied outcrop include bedding planes, soft-sediment deformation structures, normal fault and fracture systems. Notably, the fractures partly control the development of soft-sediment deformation structures. The normal faults have various strikes, do not show fault rocks, and converge downward into the bedding planes of laminated siltstone.
The fracture system consists of six fracture sets distinguished based on orientations, abutting relationships, and relationships to faults: N-S trending set 1, WNW-ESE trending sets 2 and 3, NW-SE — NNW-SSW trending set 4, NE-SW — NNE-SSW trending set 5, and NNE-SSW trending set 6 in chronological order. The fractures are mostly bounded by bed boundaries, except for some set 1 fractures crossing the boundary between bedded tuff and laminated siltstones. When comparing the brittleness index and fracture intensity at measured stratigraphic positions, the following features are noteworthy. (1) The laminated siltstone on top of the cryptocrystalline textured laminated tuff has the highest intensity of fracture system. However, the brittleness index of this position is similar to that of laminated siltstones elsewhere. In other positions, the brittleness index and fracture intensity are roughly proportional. (2) Fracture set 1 develops only in the boundary area between the bedded tuff and the laminated siltstone.
In this study, I interpret the origin of the normal fault and fracture systems and the fracture stratigraphic characteristics in the context of burial and diagenesis of the basin fill. The results will improve the understanding of fracture stratigraphy of volcanic and sedimentary rocks that have experienced heterogeneous lithification during burial.

목차 (Table of Contents)

• 1. 서언 1
• 2. 지질학적 배경 3
• 3. 연구 방법 5
• 3.1. 퇴적암석학적 기재 및 주상도 작성 5
• 3.2. 구조 요소 기재 5
• 3.3. 취성지수 계산 6
• 4. 결과 7
• 4.1. 퇴적암석학적 기재 7
• 4.2. 지질구조 15
• 4.2.1. 연질퇴적변형구조 15
• 4.2.2. 정단층계 18
• 4.2.3. 단열계 21
• 4.2.3.1. 구성 단열군 21
• 4.2.3.2. 퇴적 단위 별 단열계 특성 23
• 4.3. 취성지수 29
• 5. 토의 및 결론 31
• 5.1. 단열 및 정단층계의 기원 31
• 5.2. 단열층서와 취성지수의 관계 33
• 5.3. 유체 흐름에 끼치는 영향 38
• 부록 41
• 참고 문헌 87
• Abstract (in English) 101