Geological structures in the Tongri-Dogye and Sangdeog areas in the eastern part of the Samcheog Coalfield, Korea

Abstract

The study area, the Tongri-Dogye and Sangdeog areas, is located in the eastern part of the Samcheog Coalfield and consists of Precambrian granitic rocks, Paleozoic sedimentary rocks, and Cretaceous sedimentary and volcanic rocks. The study area is characterized by the E−W trending folds and thrusts, and N−S trending faults. The E−W trending folds and thrusts are well developed and are cut by the N−S trending faults in the study area. The N−S trending faults records two components of fault movements; earlier stage of the west dipping normal fault and later stage of strike-slip fault. A series of these normal faults have a character of step faults and stratigraphic positions are younger toward the west across these faults. Cretaceous volcanic rocks have two phases, extrusive and intrusive phases. Extrusive volcanic rocks are affected by the southwards thrust movement, while others intruded into the thrust sheets. Age of volcanic rocks ranges from 66.9 Ma to 49.2 Ma. These lines of evidences indicate that thrust movement occurs between 66.9 Ma and 49.2 Ma. The Osipcheon Fault, one of the major N−S trending faults in the eastern part of the Samcheog Coalfield, is characterized by strike-slip with dextral movement. Along the Osipcheon fault, the horse tail structures are developed near the tip area in the western part and subparallel faults are dominant in the eastern part of the fault. The Osipcheon Fault is terminated in the Triassic Donggo Formation near the Tongri town. Thrust faults and related structures are also developed along the lateral tip line of the minor thrust such as ramp structures, crescent type anticline, and antiformal stack structures. Along the Osipcheon Fault, minor reverse faults and domino-type extensional faults are developed on the coaly shale beds during the strike-slip faulting.