Economic and Environmental Geology (자원환경지질)

The Korean Society of Economic and Environmental Geology (대한자원환경지질학회)
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Stratigraphy of the Central Sub-basin of the Gunsan Basin, Offshore Western Korea

한국 서해 대륙붕 군산분지 중앙소분지의 층서

  • Kim, Kyung-min (Department of Geology, Kyungpook National University) ;
  • Ryu, In-chang (Department of Geology, Kyungpook National University)
  • Received : 2017.12.13
  • Accepted : 2018.06.15
  • Published : 2018.06.28
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Abstract

Strata of the Central sub-basin in the Gunsan Basin, offshore, western Korea were analyzed by using integrated stratigraphy approach. As a result, five distinct unconformity-bounded units are recognized in the basin: Sequence I (Cretaceous or older(?)), Sequence II (Late Cretaceous), Sequence III (late Late Cretaceous or younger(?)), Sequence IV (Early Miocene or older(?)), Sequence V (Middle Miocene). Since the late Late Jurassic, along the Tan-Lu fault system wrench faults were developed and caused a series of small-scale strike-slip extensional basins. The sinistral movement of wrench faults continued until the Late Cretaceous forming a large-scale pull-apart basin. However, in the Early Tertiary, the orogenic event, called the Himalayan Orogeny, caused basin to be modified. From Late Eocene to Early Miocene, tectonic inversion accompanied by NW strike folds occurred in the East China. Therefore, the late Eocene to Oligocene was the main period of severe tectonic modification of the basin and Oligocene formation is hiatus. The rate of tectonic movements in Gunsan Basin slowed considerably. In that case, thermal subsidence up to the present has maintained with marine transgressions, which enable this area to change into the land part of the present basin.

통합층서적 접근을 통하여 서해 대륙붕 군산분지 중앙소분지의 퇴적층을 분석하였다. 분석 결과, 음향 기반암 상부에서부터 시퀀스 I (Cretaceous or older(?)), 시퀀스 II (Late Cretaceous), 시퀀스 III (late Late Cretaceous or younger(?)), 시퀀스 IV (Early Miocene or older(?)), 시퀀스 V (Middle Miocene) 등 5개의 시퀀스로 분대된다. 후기 쥐라기 말부터 탄루 단층대를 따라 주향이동 단층들이 발달하면서 소규모 열개 분지들이 형성되었고 이후 후기 백악기까지 지속된 분지단층들의 좌수향 이동에 의해 대규모의 인장력을 받게 되어 소규모 열개 분지들은 대규모의 인리형 분지로 확장되었다. 하지만 이후 팔레오세 말부터 시작되는 히말라얀 조산운동의 영향으로 변형이 되기 시작하고, 후기 에오세-전기 마이오세에 동중국에는 남북 주향의 습곡을 수반하는 강한 지구조운동이 나타나 구조 역전 현상이 일어났다. 지구조운동이 완화되면서 심한 습곡으로 인해 생긴 요철부를 부분적으로 채우며 퇴적층이 형성되고, 이후 광역적인 침강과 함께 플라이오세 및 제4기에 걸친 해침의 결과로 수평적인 양상의 퇴적층이 만들어졌으며, 현재와 같은 안정된 대륙 연변부 침강분지로 전이되었다.

Keywords

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