Interpretation of the Deformation History and Basin Geometry in the Southeastern Margin of the Yeongdong Basin

다국어 초록 (Multilingual Abstract)

The Yeongdong Basin is interpreted as a small-scale terrestrial sedimentary basin formed by pull-apart opening associated with the sinistral strike-slip movement of the Yeongdong Fault during the Early Cretaceous. While numerous studies have addressed the formation of the Yeongdong Basin, research on its post-depositional structural deformation and subsequent evolutionary processes remains insufficient. In particular, the southeastern margin of the basin exhibits a characteristic arcuate basin-margin geometry, suggesting the possibility of post-depositional deformation; however, no specific studies have been reported on this feature. This study aims to reconstruct the structural evolution of the southeastern Yeongdong Basin area and elucidate the formation mechanism of the arcuate basin boundary based on the distribution and deformation characteristics of various geological structures, including faults, basin fills, and dikes. The results of the study indicate that the major faults in the study area can be categorized into NE-striking and NNW-striking fault groups, where structural movements during basin formation and after the completion of deposition were concentrated. The structural evolution of the southeastern margin area is summarized into the following three stages based on major stress events: (1) Sinistral strike-slip movement of the NE-striking faults and normal faulting of the NNW-striking faults under N–S to NNW–SSE compression and orthogonal extension; (2) NW-striking normal faulting and dike intrusion under NE–SW extension; (3) Reverse reactivation of the NE-striking faults, sinistral strike-slip reactivation of the NNW-striking faults, and associated folding and bedding-parallel slip of basin fills under NW–SE compression. These stress events are interpreted to correspond to the early and late basin expansion stages and the subsequent basin inversion stage, respectively. Notably, the NW–SE compression associated with basin inversion is linked to regional uplift and denudation events that commenced in the Late Cretaceous along the East Asian continental margin, with their final timing constrained to the range of 59–51 Ma in this area. During this period, the basement block on the southeastern side of the arcuate boundary was significantly uplifted by thrusting over the basin fills, with the reverse reactivation of the Yeongdong Fault system playing a key role. Consequently, the currently observed arcuate basin-margin geometry is inferred to be an erosional boundary of the reverse faults exposed by continuous differential erosion and denudation following the structural inversion.

목차 (Table of Contents)

• I. Introduction 1
• 1.1. Background 1
• II. Geological Setting 5
• 2.1. General Geology of the Yeongdong Basin 5
• 2.2. Geology of the Study Area 8
• III. Results of Geological Survey and Analysis 11
• 3.1. Topographic Analysis 11
• 3.2. Geometric and Kinematic Characteristics of Faults 13
• 3.2.1. Strike-slip Kinematics of the NE-striking Fault Group 14
• 3.2.2. Reverse Kinematics of the NE-striking Fault Group (Surface Survey) 17
• 3.2.3. Reverse Kinematics of the NE-striking Fault Group (Trench Survey) 21
• 3.2.4. Normal Kinematics of the NNW-striking Fault Group 26
• 3.2.5. Strike-slip Kinematics of the NNW-striking Fault Group 30
• 3.3. Distribution and Associated Deformations of Basin Fills 34
• 3.3.1. Basement Area with Basin Fill Outliers 35
• 3.3.2. Domain I 35
• 3.3.3. Domain II 36
• 3.3.4. Domain III 36
• 3.3.5. Domain IV 37
• 3.3.6. Domain V 39
• 3.4. Paleostress Reconstruction 42
• IV. Discussion 45
• 4.1. Comprehensive Interpretation of Structural Evolution 45
• 4.1.1. Dn: Syn-rift Sinistral Strike-slip Faulting 46
• 4.1.2. Dn+1: Stress Regime Transition Associated with Magmatism 49
• 4.1.3. Dn+2: NW–SE Compression and Regional Uplift 51
• 4.2. Origin of the Basin-Margin Geometry and Inferred Contact Relationships 55
• V. Conclusions 61
• References 63