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Evidences of Soil-Forming Processes and Groundwater Movement Obscuring Sedimentary Structures: A Trench Profile in Yongjang-li, Gyeongju, South Korea
퇴적구조 관찰 시 유의해야 할 토양화 및 지하수 유동 흔적: 경주 용장리 트렌치 단면의 예
Econ. Environ. Geol. 2019 Dec;52(6):519-28
Published online December 31, 2019;
Copyright © 2019 the Korean society of economic and environmental gelology.

Soh-joung Yoon*

Korea Institute of Geoscience and Mineral Resources, Daejeon, South Korea
Received December 24, 2019; Revised December 24, 2019; Accepted December 24, 2019.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
In 2017, Korea Institute of Geoscience and Mineral Resources (KIGAM) has excavated a trench at Yongjang-li in the city of Gyeongju to examine the evidence of fault movement related with the 2016 earthquake in unconsolidated sediments. In the trench profile, the author has observed the features of ongoing soil-forming processes and groundwater movement overlapped on the sedimentary layers. The soil formation was in its initial stage, and most of the original sedimentary layers could be observed. The color changes depending on the redox conditions and by the Mn/Fe oxide precipitation, however, were the most significant features obscuring the sedimentary records. The dark Mn oxide precipitates formed at the groundwater levels often concealed the sedimentary unit boundaries. The groundwater levels varied depending on the particle sizes of the sedimentary layers contacting the groundwater, and thus the Mn oxide precipitates have formed at varying depths. The groundwater could move upward along the narrow pores in the fine-textured sedimentary layer more than a few meters showing the gray color indicating a reducing condition for iron.
Keywords : Yangsan fault zone, soil horizon, soil water movement, Fe/Mn redox conditions, manganese oxide precipitates


December 2019, 52 (6)