Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
권호 표지

Origin, Age and Sedimentation Rate of Mid-Geum River Sediments

금강 중류 하상 퇴적층의 기원과 형성시기 및 퇴적율

  • Oh, Keun-Chang (Dept. of Surficial Environment and Global Change Department, Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Kim, Ju-Yong (Dept. of Surficial Environment and Global Change Department, Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Yang, Dong-Yoon (Dept. of Surficial Environment and Global Change Department, Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Hong, Sei-Sun (Dept. of Surficial Environment and Global Change Department, Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Lee, Jin-Young (Dept. of Surficial Environment and Global Change Department, Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources) ;
  • Lim, Jae-Soo (Dept. of Surficial Environment and Global Change Department, Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources)
  • 오근창 (한국지질자원연구원 지표환경변화연구실) ;
  • 김주용 (한국지질자원연구원 지표환경변화연구실) ;
  • 양동윤 (한국지질자원연구원 지표환경변화연구실) ;
  • 홍세선 (한국지질자원연구원 지표환경변화연구실) ;
  • 이진영 (한국지질자원연구원 지표환경변화연구실) ;
  • 임재수 (한국지질자원연구원 지표환경변화연구실)
  • Received : 2010.05.10
  • Accepted : 2010.08.20
  • Published : 2010.08.28
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Abstract

Fluvial sediments are widely distributed in present and old river-beds of the mid-Keum River, the tributaries of which are the Yugu and Jeongan Rivers. The basement of the mid-Keum River area consists of Mesozoic granites which are easily eroded compared to Precambrian gneisses, which are exposed in the upper-Keum River area. The provenance of the fluvial sediments includes both the Precambrian gneisses and Mesozoic granites, which occur in the catchment of the mid-Keum River. The coarse-grained sediments were probably transported from the river-beds and the overbank floodings of the main Keum River and its tributaries when the climate was warm and wet. The oldest mud deposits were dated at ca. 9,400 yr BP by the radiocarbon method. It has been estimated that the sand deposits below the dated muds were formed in a period from the Late Pleistocene to the Early Holocene. However we have revealed that the major part of the present river-bed sediments was formed at ca. 3,000-6,000 yr BP, i.e., in the mid- to late Holocene, when summer monsoon was very strong due to climatic changes. We have calculated fluvial sedimentation rates of 0.12-0.16 cm/yr and 0.02-0.09 cm/yr for borehole KJ-29 river-bed sediments and borehole KJ-28 floodplain deposits, respectively. We conclude that the sedimentation rate is higher near the present stream channel than near the floodplain.

금강의 지류인 유구천과 정안천은 공주시 일대에서 금강 본류에 합류하는데 금강 중류는 현하상과 구하상에 모래를 많이 포함하는 하천 퇴적물이 널리 분포하고 있다. 금강 중류유역에서는 풍화에 상대적으로 약한 중생대의 화강암이 주요한 기반암이지만 금강 상류로 갈수록 풍화에 강한 선캠브리아기의 편마암이 기반암을 형성한다. 하천퇴적물의 주요 기원암은 연구지역 일대의 유구천과 정안천 하류를 포함하는 금강 중류수계 주변에 분포하는 선캠브리아기의 편마암과 중생대의 화강암이며, 석영과 장석이 우세한 특징을 보인다. 금강중류에 분포하는 조립질 퇴적물은 기후가 온난 다습해지는 기후조건하에서 강우량 증가에 따라 하상을 따라 운반된 퇴적물과 금강 본류와 지류들의 합류부 주변에서 조성된 범람환경하에서 형성되었다. $^{14}C$ 연대분석을 통하여 금강중류 유역의 가장 오래된 니질퇴적층의 연대가 약 9,430 yr BP임을 확인하였으며, 이에 따라 더 하부에 분포하는 사질퇴적층은 플라이스토세말에서 홀로세 초기에 퇴적된 것으로 판단된다. 그러나 대부분 현하상에 분포하는 퇴적층은 3,000-6,000 yr BP로 나타나며, 이는 그 형성시기가 홀로세 중기와 그 이후로서 기후변화로 인해 여름몬순(summer monsoon) 이 강하게 작용했던 시기이다. 금강중류의 하상과 범람원 퇴적층의 퇴적율을 보면, 하상사질층은 KJ-29 시추공에서 0.12 cm/yr-0.16 cm/yr, KJ-28 시추공의 범람원 퇴적층은 0.02 cm/yr-0.09 cm/yr로 각각 산정되었으며, 범람원보다 현하상에 가까울수록 퇴적율이 높게 나타났다.

Keywords

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