한국지구과학회지 (Journal of the Korean earth science society)

  • 제24권8호
  • /
  • Pages.657-667
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  • 2003
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  • 1225-6692(pISSN)
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  • 2287-4518(eISSN)
한국지구과학회 (The Korean Earth Science Society)
권호 표지

한국 서해 경기만 조간대 퇴적층의 후기 플라이스토세 부정합

Late Pleistocene Unconformity in Tidal-Flat Deposit of Gyeonggi Bay, Western Coast of Korea

  • 정회수 (한국해양연구원 해저환경자원연구본부) ;
  • 유해수 (한국해양연구원 해저환경자원연구본부) ;
  • 서정모 (군산대학교 해양학과) ;
  • 팽우현 (한국해양연구원 해저환경자원연구본부) ;
  • 임동일 (한국해양연구원 해저환경자원연구본부)
  • Jung, Hoi-Soo (Marine Geoenvironment and Resources Research Division, KORDI) ;
  • Yoo, Hai-Soo (Marine Geoenvironment and Resources Research Division, KORDI) ;
  • Seo, Jung-Mo (Department of Oceanography, Kusan National University) ;
  • Paeng, Woo-Hyun (Marine Geoenvironment and Resources Research Division, KORDI) ;
  • Lim, Dhong-Il (Marine Geoenvironment and Resources Research Division, KORDI)
  • 발행 : 2003.12.31
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초록

현세-후기 플라이스토세의 부정합적 경계면을 조사하기 위하여 한국 서해 경기만 조간대에서 심부시추와 탄성파 탐사를 실시하였다. 분석된 모든 시추 퇴적물에서 현세 퇴적층(Unit I) 하부에 놓이는 최대 4m두께의 산화되고, 반고화된 특징을 보이는 황갈색의 산화대층(oxidized-sedimentary layer)이 발견되었다. 이 세립질의 산화대층에서 나타나는 황갈색의 퇴적물 색, 높은 N 값과 낮은 함수율의 준고화된 상태, 동토구조, 스멕타이트 광물의 부재 그리고 높은 퇴적물 화학적 풍화지수(Ba/Sr 비) 등의 다양한 특성은 퇴적물의 대기중 노출과 풍화의 중요한 증거로 제시된다. 탄소동위원소 연대와 함께 이러한 여러 증거들을 고려할 때, Unit II의 상부 산화대층은 초기 현세까지 계속되는 저해수면 동안 대기중에 노출되어 풍화 및 산화작용으로 인하여 퇴적물의 특성이 변질되어 형성된 것으로 해석된다. 따라서 산화대층의 상부 경계면은 현세와 선현세(후기 플라이스토세) 퇴적층을 구분하는 부정합면으로 제시되며, 탄성파 자료에서 나타나는 강한 반사면(prominent near-surface reflector)과 잘 일치한다.

Deep-drilled core sampling and high-resolution seismic survey were carried out to identify a Holocene-late Pleistocene boundary in Gyeonggi Bay, western coast of Korea. Analysis of core sections revealed the existence of an oxidized and semi-consolidated sediment layer, Iying immediately below a Holocene horizon (Unit I) and being developed at the top of a late Pleistocene deposit (Unit II). The oxidized sedimentary layer (uppermost part of Unit II) is characterized by semi-consolidated, yellowish sediments showing signs of desiccation and alteration such as high N value, low water content, periglacial cryogenic structure, depletion of smectite, and high geochemical weathering index (Ba/Sr ratio). This feature, together with radiocarbon ages, suggests that the layer has formed as a result of prolonged subaerial exposure of Unit II sediments during the late Wisconsin sea-level lowstand, producing a regional unconformity. Such unconformitic-bounding surface corresponds to a prominent near-surface reflector (R), which is observed in seismic profiles obtained across the drilled-core sections in the study area. Consequently, the buried oxidized-sedimentary layer associated with the seismic reflector possibly plays a key horizon for the understanding of late Quaternary environmental changes as well as evidence of the emergence of the Yellow Sea shelf during the late Wisconsin sea-level lowstand.

키워드

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