| 초록 | Upper Jurassic sediments between the Daedong and Gyeongsang Systems have not yet been known in south Korea. But the Myogog Formation distributed in the area of Jaesan-myeon, Bonghwa-gun, North Gyeongsang Province, was clarified as upper Jurassic. The Myogog Formation, more than 150 meters thick, is bounded by a thrust fault on the side of Wonnam Formation and is overlain unconformably by the lowermost part of the Nagdong Series of lower Cretaceous. The Myogog Formation is composed mainly of black to dark greenish gray shales, and dark to light gray arkose sandstones. The non-marine fossils, Trigonioides, Plicalounio, Unio, Corbicula and Viviparus， and some fossil plants, Onychiopsis, Adianlites, etc. are found in the Myogog Formation. These fossils indicate that the formation is to be of upper Jurassic to lower Cretaceol1s in age. The Myogog Formation is strongly folded and thrusted, whereas the rocks of Nagdong Series overlying the Myogog formation is monoclinal with gentle dip. So far, the so-called Daebo disturbance has been known to have taken place during late Jurassic to early Cretaceous. But the fact that the oronized Myogog Formation of upper Jurassic is overlain by the almost l1ndistl1rbed Nagdong Series of lower Cretaceous limits the time of the movement to the end of late Jl1rassic. Here, the Nagdong orogeny is proposed for the movement. As for the disturbace which took place just before the Myogog Formation was formed, the Myogog movement is proposed. |
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