Yeongwol Group in the Namae section, Yeongwol, Korea: A refined lithostratigraphy of the upper Cambrian to Lower Ordovician sedimentary successions in the western Taebaeksan Basin and its geologic significance

Stratigraphic understanding of the Yeongwol Group in a western division of the Taebaeksan Basin remains unclear due largely to development of complex thrust faults and extensive dolomitization. This study aims to describe lithostratigraphic features of the Namae section, where the upper Cambrian to Lower Ordovician sedimentary successions are continuously exposed without structural discontinuities, and to shed light on their geological values with an emphasis on refinement of lithostratigraphic units and boundaries. The Yeongwol Group in the Namae section consists of the uppermost Machari (14.5 m), Wagok (171 m), Mungok (189.5 m), and lower Yeongheung (38 m) formations in ascending order. This section is the only site to date where three lithostratigraphic boundaries between the formations can be observed in one place. In this section, two lithostratigraphic intervals, including an entire succession of the Wagok Formation and a transitional interval from the upper Mungok to the lower Yeongheung formations, were newly identified. Although the Wagok Formation is mainly composed of massive dolostone, sedimentary structure, carbonate grains, and fossil skeletons are partly preserved in the lower and upper intervals of the formation, allowing us for further paleontologic, stratigraphic, and sedimentologic researches. In addition, the Namae section provides a lithostratigraphic standard for the boundary between the Mungok and Yeongheung formations, which has been ambiguously defined or misinterpreted in previous works. It reveals how and when the peritidal carbonate depositional system of the Yeongheung Formation developed in this region.