Joseon Supergroup

From the early Cambrian to the Ordovician in the early Paleozoic, the Joseon Supergroup was formed, and it distributed in the Pyeongnam Basin and Okcheon Fold Belt. The early Paleozoic Joseon Supergroup in Korea has been divided into Taebaek, Yeongwol, Pyeongchang, Yongtan and Mungyeong groups, depending on the sequence of lithology.^[5] Taebaek group that located in Taebaek, Samcheok is composed of Jangsan, Myobong, Daegi, Sesong, Hwajeol, Dongjeom, Dumugol (Dumu-dong), Makgol (Makgol), Jigunsan, Duwibong Formation. Yeongwol group is composed of Sambangsan, Machari, Wagok, Mungok, Yeongheung Formation.^[6] The geological table of the Joseon Supergroup is as follows.^[7][8][9]

Pyeongan Supergroup

From Carboniferous to Triassic, The Pyeongan Supergroup was formed, and it distributed in the Pyeongnam Basin and Okcheon Folded Zone.^[13][14]

The geological table and stratigraphy of the Pyeongan Supergroup are as follows.^[15]

Okchon (folded) Zone

The Okch'ŏn Zone likely formed in mid-Cambrian times with faulting, interpreted from olistolith limestone breccia. By contrast to the Chŏsun Supergroup, the Okch'ŏn Supergroup crops out in the central Okch'on-T'aebaeksan Zone with thick sequences of metasedimentary and metavolcanic rocks. Some geologists have interpreted the supergroup as a series of nappe formations that took shape in a Cambrian intracratonic basin. Above the volcanic and sedimentary sequence in the middle part of the supergroup are jumbled rocks formed from submarine debris flows during rifting and contain granite, gneiss, quartzite, limestone, mudstone and basic volcanic rock fragments.

At first, the Taebo orogeny was credited with the folding, thrusting and metamorphism but Cluzel, Jolivet and Cadet in 1991 named the Okch'on orogeny to explain Silurian and Devonian deformation.

South Korea has no Silurian or Devonian sedimentary rocks, but sedimentation began again on a sinking paralic platform inland from the proto-Japan as it formed beginning in the Carboniferous. The P'yŏngan Supergroup outcrops northeast of the Okch'on Zone, subdivided into the Hongjom Formation gray mudstone, limestone and mudstone, Sadong Formation sandstone, mudstone and coal seams, Kobangsan Formation coarse terrestrial sandstone and mudstone, and Nogam Formation green sandstone and mudstone. ^[16]

Taebo Orogeny

The Taebo orogeny in the Jurassic is broadly similar to the Yenshanian tectonism in China, although its effects are believed to have been less dramatic. The event ended with the batholith intrusions of the Taebo granites which outcrop over 30 percent of the country.

Gyeongsang Basin

The Gyeongsang Basin is the basin that is formed at Cretaceous.^[18] it occupies most of the Yeongnam region and part of Honam region.

The Gyeongsang Basin is composed of Gyeongsang supergroup, which consists of Sindong, Hayang, Yucheon group, and Bulguksa Granite. The Sindong Group is the lowest stratigraphic sequence in the Cretaceous Gyeongsang Basin and comprises three stratigraphic units: the Nakdong, Hasandong, and Jinju Formation in ascending order.^[19] Hayang group is mid group of Gyeongsang supergroup.^[20] Yucheon group is the top group of Gyeongsang supergroup.^[21]

Kyŏngsang rocks are intruded by microlite, diorite and granodiorite from the late Cretaceous. ^[22]