Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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A Study on Sedimentology of the Mesozoic Munamdong Formation, Northeastern Gyeonggi Massif, Korea

경기육괴 북동부에 분포하는 중생대 문암동층의 퇴적학적 연구

  • Choi, Young-Gi (Exploration Business Department, Korea Resources Corporation(KORES)) ;
  • Ryu, In-Chang (Department of Geology, Kyungpook National University)
  • 최영기 (한국광물자원공사 전략탐사실) ;
  • 유인창 (경북대학교 지질학과)
  • Received : 2014.08.09
  • Accepted : 2014.10.25
  • Published : 2014.10.28
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Abstract

The Munamdong Formation is a small scale sedimentary deposit which is located in Yuljeonri, Naemyeon, Hongcheon Gangwon-do. In order to understand the depositional environment and its sequential change in the formation, sedimentary facies analysis was conducted. The result indicates that the Munamdong Formation began to be deposited in alluvial fan system accompanying volcanic activity and gradually deposited in lake system. As well, U-Pb, K-Ar and $^{40}Ar/^{39}Ar$ ages are determined from the Munamdong Formation. The SHRIMP U-Pb Phanerozoic Eon age of the detrital zircons in the middle part of the Munamdong formation yields $229.8{\pm}2.5Ma$. The K-Ar and $^{40}Ar/^{39}Ar$ ages of the volcanic rock in the lowermost part of the Munamdong formation are $203.7{\pm}3.9Ma$ and $227.4{\pm}8.4Ma$ respectively. These results confirm that the Munamdong Formation was deposited during the Late Triassic, indicating that the basin might be formed due to post-collisional rifting or collapsing.

문암동층은 강원도 홍천 율전리 일대에 불규칙한 형태로 분포하는 소규모 퇴적암층이다. 분지의 형성과 발달사를 규명하기 위하여 야외조사를 통해 퇴적상 분석을 실시하여 퇴적환경과 이의 순차적인 변화를 해석하였다. 퇴적상 연구에 따르면 문암동층은 전체적으로 하부의 화산활동을 수반하는 선상지 환경에서 상부의 호수 환경으로 점차 전이하는 환경 변화를 보인다. 분지의 형성시기와 퇴적시기를 규제하기 위하여 문암동층 구간내의 시료에 대하여 U-Pb, K-Ar 및 $^{40}Ar/^{39}Ar$ 연대측정방법으로 절대연령측정을 실시하였다. 문암동층의 중부구간 사암시료의 쇄설성 저어콘에 대한 SHRIMP U-Pb 현생이언 연대결과는 $229.8{\pm}2.5Ma$이며, 문암동층 기저의 시료에 대한 K-Ar과 $^{40}Ar/^{39}Ar$ 연령은 각각 $203.7{\pm}3.9Ma$ 그리고 $227.4{\pm}8.4Ma$로 측정되었다. 이러한 결과는 문암동층의 퇴적 시기가 트라이아스 후기인 것을 확인해 주며 분지는 충돌 후 열 개작용 또는 붕괴에 의해 형성되었던 것을 지시한다.

Keywords

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