Geochemical Study of the Jigunsan Shale: A Sequence Stratigraphic Application to Defining a Middle Ordovician Condensed Section, Taebacksan (Taebaeksan) Basin

직운산 세일층의 지화학적 연구: 태박산분지 오오도비스 중기 응축층 규명을 위한 시퀀스층서학적 적용

  • 유인창 (경북대학교 지질학과) ;
  • 유선영 (경북대학교 지질학과) ;
  • 손병국 (한국지질자원연구원 석유해저자원본부)
  • Published : 2009.02.28


A 30-m-thick Middle Ordovician Jigunsan Shale exposed along the southern limb of the Backunsan (Baekunsan) Syncline, Taebacksan (Taebaeksan) basin, has been simply considered as a transgressive shale sequence onlapped the underlying Maggol platform carbonates. Results of this study, however, suggest that majority of the Jigunsan Shale be interpreted as a regressive shale sequence downlapped onto a thin (ca. 240 cm) marine stratigraphic unit consisting of organic-rich (>3 wt.% of TOC) black shales in the lower Jigunsan Shale, which was accumulated at the time of maximum regional transgression. Detailed stratigraphic analysis in conjunction with XRD, XRF, and ICP-MS as well as Rock-Eval pyrolysis allows the thin marine stratigraphic unit in the Jigunsan Shale to define a condensed section that was deposited in a distinctive euxinic zone formed due to expansion of pycnocline during the early highstand phase. As well, a number of stratigraphic horizons of distinctive character that may have sequence stratigraphic or environmental significance, such as transgressive surface, maximum flooding surface, maximum sediment starvation surface, and downlap surface, are identified in the lower Jigunsan Shale. In the future, these stratigraphic horizons will provide very useful information to make a coherent regional stratigraphic correlation of the Middle Ordovician strata and to develop a comprehensive understanding on stratigraphic response to tectonic evolution as well as basin history of the Taebacksan Basin.


Jigunsan shale;sequence stratigraphy;condensed section;paleoredox;pycnocline


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