Sedimentology of the Jangsan Formation: Pre-vegetation fluvial systems and early Cambrian basin evolution = 장산층의 퇴적학: 식생 발달 이전 하천 시스템과 초기 캄브리아기 분지 진화

다국어 초록 (Multilingual Abstract)

The Jangsan Formation represents the basal siliciclastic succession of the Taebaeksan Basin on the eastern Sino-Korean Craton and preserves an important record of early Phanerozoic basin history. Despite its significance, uncertainties have remained regarding its original composition, depositional environment, and stratigraphic relationships. This doctoral dissertation integrates sedimentary petrology, detrital zircon geochronology, and facies and architectural analysis to establish a revised depositional and stratigraphic framework for the Jangsan Formation and to resolve initial Cambrian basin evolution.
Petrographic and geochemical data demonstrate that the high mineralogical maturity of the sandstone results from diagenetic sericitization of detrital feldspar, indicating that the original sediment was predominantly subarkosic. Detrital zircon age spectra from the basal Taebaek Group indicate that initial sediments were derived from locally restricted basement highs of the Yeongnam Massif. Sediment-routing systems subsequently expanded as paleotopography became progressively inundated during the early Cambrian transgression. As transgression continued, sediment supply 2 from local basement highs diminished, while contributions from more distal sources increased, reflecting the progressive/abrupt expansion of the cratonic basin. Facies, architectural, and paleocurrent analyses show that the Jangsan Formation comprises diverse pre-vegetation fluvial deposits, including flashflood dominated proximal ephemeral streams (FA1), avulsion-driven shallow braided rivers (FA2), migration-dominated deep braided rivers (FA3), and chute-cutoff-dominated distal sandy meandering rivers (FA4). These facies associations and their spatial variation record a progressive evolution of fluvial systems linked to early Cambrian transgression across the antecedent topography.
Collectively, this dissertation provides a revised perspective on the Jangsan Formation and offers a coherent model for cratonic basin evolution associated with the early Cambrian transgression.

국문 초록 (Abstract)

장산층은 중한 지괴(Sino-Korean Craton) 동부의 태백산분지 기저부를 구성하는 규질 쇄설성 퇴적층으로, 한반도 고생대 초기 분지 진화사를 이해하는 데 중요한 기록을 보존하고 있다. 그 중요성에도 불구하고 장산층의 사암 조성, 퇴적환경, 그리고 층서적 관계에 대하여 불확실성이 제기되어 왔다. 본 박사학위 논문은 퇴적암석학, 쇄설성 저어콘 지질연대학, 퇴적상 및 구성요소 분석을 통합하여 초기 캄브리아기 분지 진화 과정을 복원하고 장산층의 퇴적·층서 체계를 규명하는 것을 목표로 하였다.
암석기재학 및 지구화학적 분석 결과, 장산 사암의 높은 조성적 성숙도는 1차 퇴적 특성이 아닌 장석의 견운모화에 의한 속성작용 결과로, 장산층의 원래 퇴적물이 주로 준장석질 사암이었음을 시사한다. 태백층군 기저 퇴적암의 저어콘 연령 스펙트럼은 초기 퇴적물 공급이 영남 육괴에 국한되었으며, 해침이 진행됨에 따라 국지적 기반암의 영향이 감소하고 보다 원거리 공급원의 기여가 증가하여 퇴적물 공급망이 점차 확대되었음을 보여준다. 이는 해침 초기 대륙 내 분지의 확장과 퇴적 시스템의 발달을 반영한다.
퇴적상, 구성요소, 고수류 분석을 통해 장산층은 식생 발달 이전 하천계의 다양한 퇴적체로 구성되며, 홍수 지배 판상류로 형성된 간헐 하천(FA1), 하도 이탈이 우세한 얕은 망상 하천(FA2), 상대적으로 안정된 하도를 유지했던 깊은 망상 하천(FA3), 그리고 수로 절개가 빈번한 사행성 하천(FA4)으로 구분된다. 이러한 퇴적상의 조합과 공간적 분포는 초기 캄브리아기 해침과 선행 지형의 기복에 의해 제어된 하천 시스템의 단계적 진화를 반영한다.
종합적으로, 본 연구는 장산층에 대한 새로운 퇴적학적·층서적 관점을 제시하며, 초기 캄브리아기 해침에 수반된 대륙 내 분지 진화를 설명하는 통합 모델을 제공한다.

목차 (Table of Contents)

• List of Contents
• Abstract 1
• Chapter 1. Introduction 4
• Chapter 2. Diagenetic overprint on sandstone classification: Petrographic and geochemical reassessment of the Cambrian Jangsan Formation, Korea 14
• Abstract 14
• 2.1. Introduction 16
• 2.2. Geological setting and previous work 18
• 2.3. Methods 24
• 2.3.1. Sampling and microscopic observation 24
• 2.3.2. Whole-rock geochemical and mineralogical analysis 31
• 2.4. Results 37
• 2.4.1. Petrographic observation and modal analysis of the framework grains 37
• 2.4.2. Geochemical composition 41
• 2.5. Discussion 42
• 2.5.1. Imbalance between compositional and textural maturity of the Jangsan Formation sandstones 42
• 2.5.2. Origin and formation of the sericite 43
• 2.5.3. Diagenetic evolution of the Jangsan Formation sandstones 49
• 2.5.4. Spatial variability in diagenetic features within the Jangsan Formation and its comparison with other Cambrian sandstone units of the Taebaek Group 52
• 2.5.5. Sandstone classification of the Jangsan Formation and implications for paleoenvironmental interpretation 54
• 2.5.6. Significance of sandstone classification for paleoenvironmental interpretation of basal Cambrian sandstone 56
• 2.6. Conclusions 59
• Chapter 3. Fine-scale provenance variability during the initial Cambrian transgression on the peri-Gondwana margin: Detrital zircon geochronology of the basal Taebaek Group, eastern North China Platform 62
• Abstract 62
• 3.1. Introduction 64
• 3.2. Geological setting 67
• 3.3. Methodology 74
• 3.3.1. Data synthesis 74
• 3.3.2. Sampling strategy 75
• 3.3.3. Analytical methods 79
• 3.4. Results 80
• 3.4.1. Detrital zircon group 80
• 3.4.2. Detrital zircon patterns of the basal Taebaek Group and their variability 83
• 3.5. Discussion 89
• 3.5.1. Sediment provenance of the basal Taebaek Group 89
• 3.5.2. Sediment provenance evolution on the eastern North China Platform during initial transgression 92
• 3.5.3. Regional-scale variability of the sediment source and distribution 94
• 3.5.4. Provenance role of outboard arc complex for SKC and its paleogeographic implications 99
• 3.5.5. Potential for fine-scale provenance variability across Gondwana during the Cambrian transgression 102
• 3.6. Conclusions 103
• Chapter 4. Variability of pre-vegetation fluvial styles in the Cambrian Jangsan Formation, eastern Sino-Korean Craton 107
• Abstract 107
• 4.1. Introduction 109
• 4.2. Geological setting 111
• 4.3. Methods 113
• 4.4. Depositional environments 120
• 4.4.1. Facies and architectural elements 120
• 4.4.2. Facies Association 1 (FA1): Proximal sandy/gravelly ephemeral streams 125
• 4.4.2.1. Description 125
• 4.4.2.2. Interpretation 128
• 4.4.3. Facies Association 2 (FA2): Shallow perennial braided river 131
• 4.4.3.1. Description 131
• 4.4.3.2. Interpretation 134
• 4.4.4. Facies Association 3 (FA3): Deep perennial braided rivers 137
• 4.4.4.1. Description 137
• 4.4.4.2. Interpretation 143
• 4.4.5. Facies Association 4 (FA4): Distal sandy meandering rivers 145
• 4.4.5.1. Description 145
• 4.4.5.2. Interpretation 150
• 4.5. Discussion 152
• 4.5.1. Pre-depositional condition of the eastern Sino-Korean Craton before basin initiation 152
• 4.5.2. Variability of pre-vegetation fluvial systems in cratonic basin during initial transgression 153
• 4.5.3. Paleogeographic implications 160
• 4.6. Conclusions 161
• Chapter 5. Synthesis and integrated basin evolution model 164
• References 170
• Appendix. 207
• 국문초록 245
• 감사의 글 246