SEDIMENTOLOGY OF A HYDROTHERMALLY ALTERED, SILICICLASTIC TIDE-DOMINATED SUCCESSION: A CASE STUDY IN THE LOWER CAMBRIAN MYOBONG FORMATION, KOREA

This study focuses on the facies analysis of the Myobong Formation (Cambrian Series 2; stages 3–4), Taebaek Group, Korea, which dominantly consists of dark-colored, fine-grained siliciclastic sedimentary rocks that experienced extensive hydrothermal alterations. Sangdong mine, one of the largest tungsten mine in the world, is located less than 1 km from the study area. Based on microfacies analysis using large scale (7.6 × 5.2 cm) thin-sections, this study aims to reveal primary sedimentary features that are overprinted by skarn minerals. Twelve sedimentary facies and four facies associations are identified from the Myobong Formation, and the corresponding depositional model is generated. Siliciclastic sedimentation of the lowermost Myobong Formation initiated in an alluvial plain environment (FA 1) during the early transgression of an epeiric platform. With an ensued rise in sea level, the land became submerged, and extensive siliciclastic tidal flat (FA 2) developed. Continued transgression resulted in the deep subtidal environment (FA 3), where carbonate sediments were occasionally supplied from shoal via tidal channels. As water depth shallowed with a decrease in the tidal regime, a biologically active shoreface succession (FA 4) of the uppermost Myobong Formation developed. The entire Myobong Formation is successively overlain by an extensive carbonate platform of the Daegi Formation (Miaolingian). The depositional model of the Myobong Formation is generally comparable to that of the coeval Zhushadong and Mantou formations in the Shandong region, China, which is about 1,000 km apart from the study area. This indicates that comparable depositional environments developed throughout the Sino-Korean Block during the early Cambrian, implying the importance of eustatic control on the initial transgression of the epeiric platform during the Cambrian greenhouse interval. In addition, this study demonstrates the possibility of applying the facies analysis technique to hydrothermally altered sedimentary successions, which would be helpful for future mineral exploration.