Geology of South Korea

Dobongsan Peaks (도봉산 정산)

The geology of South Korea includes rocks dating to the Archean and two large massifs of metamorphic rock as the crystalline basement, overlain by thick sedimentary sequences, younger metamorphic rocks and volcanic deposits.[1] Despite the country's small size, its geology is diverse, containing rocks formed during the Precambrian to Cenozoic eras.[2]

## Geologic history, stratigraphy, and tectonics

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The K'yŏnggi Massif and Yongnam Massif lie north and south of the Okch'on-T'aebaeksan Zone respectively. They are both polymetamorphic gneiss and schist complexes from the Precambrian and underlie the entire Republic of Korea. Units range in age from the Archean to the Proterozoic, with metamorphic facies from greenschist to amphibolite grade. Some geologists have attempted to correlate the rocks with North China-North Korea Paraplatform and Yangtze Paraplatform rocks although these categorizations are uncertain.

### Precambrian (–539 million years ago)

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The rate which Precambrian rocks occupy in Korean Peninsula is 40%.[3] The Korea Peninsula formed mostly after the Paleoproterozoic (2,500 to 1,600 million years ago), and Archean rocks appear in some regions.[4]

### Paleozoic (539–251 million years ago)

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Gumunso, where early Paleozoic formation can be found. (Joseon Supergroup Makgol limestone Formation)

Rock formations formed during the Paleozoic are composed of the Joseon Supergroup (lower) and Pyeongan Supergroup (upper).

#### Joseon Supergroup

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

Geologic time scale | Taebaek Area  | Yeongwol Area  | Pyeongnam Area

|
|
|

division  | Formation Name  | Thickness(m)  | Distribution region[10] | Formation Name  | Rock  | Thickness(m)
Ordovician
443.8–485.4 Mya  | upper
great limestone group  | Duwibong limestone | 50  |  | Yeongheung  | shale
limestone | \-  | Sangseo-ri
Mandal
Singok
Jigunsan shale | 50~100  |
Makgol limestone | 250~400  | Taebaek
Dumugol shale (Odu)  | 150~200  | Baegun Mt. Syncline Zone  | Mungok  | limestone
Dolomite | 120~200
Dongjeom Quartzite (Od)  | 50  | Baegun Mt. Syncline Zone
Cambrian
485.4–538.8 Mya  | lower
great limestone formation  | Hwajeol (CEw)
Sesong  | 200~260  | Baegun Mt. Syncline Zone
East Danyang | Wagok  | limestone
Dolomite | 200~500  | Gopung
Daegi(Pungchone limestone) (CEp)  | 150~300  | Baegun Mt. Syncline Zone
Southeast Jeongseon | Machari
(Om)  | shale
limestone
Dolomite | 420  | Mujin
Yangdeok Formation (C)  | Myobong Slate (CEm)  | 80~250  |  | Sambangsan
(cs)  | Sandstone
shale | \-  | heuggyo(C)
Jangsan Quartzite (CEj)  | 150~200  | Baegun Mt. Syncline Zone
Danyang |  |  |  | Junghwa(C)

#### Pyeongan Supergroup

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The border region of Gyeongsang Basin, Yongnam Massif, Okcheon Fold Belt in Sangju Area (using OpenStreetMap)[11][12]

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

The geology and stratigraphy of the Pyeongan Supergroup are as follows.[15]

Geologic time scale | Area

|

period | Epoch | Age | Samcheok | Gangneung | Jeongseon-Pyeongchang | Yeongwol | Danyang | Boeun | Pyeongnam Basin  | Duman Basin
Mesozoic Triassic
201.3–252.17 Mya  | Mid 237–247.2 Mya  | Anisian | Donggo
(Formation)  |  | Bakjisan  |  | Donggo  |  | taejawon  |
Early 247.2–252.17 Mya  | Induan |  | Sangwonsan  |  |
Paleozoic
Permian
252.17–298.9 Mya  | Lopingian 252.17–259.8 Mya  |  |  |  |  |  |  |  | Gobangsan  | Songsang
Guadalupian
259.8–272.3 Mya  | Capitanian | Gohan  | Unbyeolri  | Okgapsan  |  | Gohan  |
Wordian | Dosagok  | Mangdeoksan  |  | Dosagok
Roadian |
Cisuralian
272.3–298.9 Mya  | Cisuralian | Hambaeksan | Hambaeksan |  | Hambaeksan | Hambaeksan | Gyeryongsan
Artinskian | Jangseong  | Jangseong  | Jangseong  | Mitan  | Jangseong  | Jangseong  | Sadong
Sakmarian |  |  | Bamchi  | Bamchi  |  | Bamchi  | Amgi
Asselian |  |  |  | ibseog
Paleozoic
Carboniferous
252.17–298.9 Mya  | Pennsylvanian
298.9–323.2 Mya  | Moscovian | Geumcheon  | Geumcheon  | Geumcheon  | Pangyo  | Geumcheon  |  | hongjeom  |
Manhang  | Manhang  | Manhang  | Yobong  | Manhang  | Manhang
Bashkirian |  |  |

#### Okchon (folded) Zone

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The Okch'ŏn Zone likely formed in mid-Cambrian times with faulting, interpreted from olistolith limestone breccia.

In 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]

### Mesozoic (251–66 million years ago)

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During the Triassic at the beginning of the Mesozoic, as sedimentation continued in the P'yŏngan Supergroup, the Sŏngnim tectonic event affected the Okch'on-T'aebaeksan Zone, although it only caused slight faulting and warping of the major supergroup strata. Geologists have inferred that the event was related to deformation further west in Indonesia.

The event generated dextral strike-slip faulting in intermontane troughs in the Kyonggi Massif, in which the terrestrial sediments of the Taedong Supergroup accumulated. The rocks in the basin include two sequences of conglomerate grading to sandstone, mudstone, and coal beds. The Taedong Supergroup has extensive fossils, particularly crustaceans.

#### Taebo Orogeny

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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

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The Geology map of Daegu City and Gyeongsan City located in the middle of Gyeongsang Basin[17]

The Gyeongsang Basin is a basin that was formed during the Cretaceous.[18] It occupies most of the Yeongnam region and part of the Honam region.

The Gyeongsang Basin is composed of the 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]

### Cenozoic (66 million years ago–present)

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Volcanic activity continued into the Cenozoic ending 50 million years ago. No Paleogene sedimentary rocks have been found onshore. Yangbuk Group conglomerates and alluvial fan sediments gathered in small fault-bounded basins in the Miocene. During the last 2.5 million years of the Quaternary, Jeju and other offshore islands formed from volcanism.

## References

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Wikimedia Commons has media related to Geology of South Korea.

1. ^ Moores, E.M.; Fairbridge, Rhodes W. (1997). Encyclopedia of European & Asian Regional Geology. Springer. pp. 475–482.
2. ^ Hyoun Soo, Lim (2019). "Cretaceous sedimentary basins and volcanic activity in Korea (KOR)". 지질학회지. 55 (5). The Geological Society of Korea: 493–494\. doi:10.14770/jgsk.2019.55.5.493. S2CID 210247110.
3. ^ Seung Ryeol, Lee (2018). "Precambrian Geology of the Korean Peninsula (KOR)". 대한지질학회 학술대회. The Geological Society of Korea: 160.
4. ^ Chang Whan, Oh (2018). "The overview for the tectonic evolution of Korea Peninsular from Paleoproterozoic to Triassic (KOR)". 대한지질학회 학술대회. The Geological Society of Korea: 85.
5. ^ Ryoung Gyun, Kim (2019). "Stratigraphic implications of the Pyeongchang Group (Joseon Supergroup) in Korea (KOR/ENG)". 지질학회지. 55 (6). The Geological Society of Korea: 727–734\. doi:10.14770/jgsk.2019.55.6.727. S2CID 213337130.
6. ^ Yi Kyun, Kwon (2019). "Basin Evolution of the Taebaeksan Basin during the Early Paleozoic (KOR/ENG)". 자원환경지질. 52 (5). The Korean Society of Economy and Environmental Geology: 427–448.
7. ^ Earth Science Introduction (in Korean). The Korean Earth Science Society. 2001. ISBN 8935401854.
8. ^ "Characteristics of rocks and geological structures in the central region of the Korean Peninsula". Korea Institute of Geoscience and Mineral Resources. `{{cite journal}}`: Cite journal requires `|journal=` (help)
9. ^ "Gravity Survey of the Subsurface Geology and Geologic Structure between Samcheog and Taebaek Area". 자원환경지질 = Economic and Environmental Geology. 28 (1). ScienceON: 79–88\. 1995.
10. ^ https://data.kigam.re.kr/mgeo/map/main.do?process=geology_50k Geology map of Korea Institute of Geoscience and Mineral Resources
11. ^ "한반도 지체구조도". Korea Institute of Geoscience and Mineral Resources.
12. ^ "2012~2020년 속리산 일대에서 발생한 지진의 진원 요소 분석". 한국교원대학교, 2021.
13. ^ Mun Gi Kim, Kim (2017). "The stratigraphy and correlation of the upper Paleozoic Pyeongan Supergroup of southern Korean Peninsula - A review (KOR/ENG)". 지질학회지. 53 (2). The Geological Society of Korea: 321–338\. doi:10.14770/jgsk.2017.53.2.321.
14. ^ Hyeong Soo, Kim (2017). "Reassessment of the Pyeongan Supergroup: Metamorphism and Deformation of the Songrim Orogeny (KOR)". 자원환경지질. 52 (5). The Korean Society of Economy and Environmental Geology: 367–379.
15. ^ Mun Gi, Kim (2017). "The stratigraphy and correlation of the upper Paleozoic Pyeongan Supergroup of southern Korean Peninsula - A review (KOR/ENG)". 지질학회지. 53 (2). The Geological Society of Korea: 321–338\. doi:10.14770/jgsk.2017.53.2.321.
16. ^ Moores & Fairbridge 1997, pp. 476–478.
17. ^ "1:50,000 Geology map". KIGAM, Korea Institute of Geology and Mineral. `{{cite journal}}`: Cite journal requires `|journal=` (help)
18. ^ Youngbeom, Cheon (2017). "Geometry and kinematics of fault systems in the Uiseong block of the Gyeongsang Basin, and their roles on the basin evolution (KOR)". 지질학회지. 53 (2). The Geological Society of Korea: 241–264.
19. ^ Hyoun Soo, Lim (2019). "Trace-element composition of the Cretaceous Sindong Group, Gyeongsang Basin, Korea and its implication for provenance (KOR)". 지질학회지. 55 (5). The Geological Society of Korea: 531–549\. doi:10.14770/jgsk.2019.55.5.531. S2CID 210268978.
20. ^ In Sung, Paik (2018). "Bidirectional paleocurrent records in the Jindong Formation of the Gyeongsang Supergroup, Korea : Occurrences and paleoenvironmental implications (KOR)". 지질학회지. 54 (4). The Geological Society of Korea: 321–333\. doi:10.14770/jgsk.2018.54.4.321.
21. ^ In Sung, Paik (2006). "Goseong Formation (Yucheon Group) in the southern part of the Gyeongsang Basin, Korea (KOR)". 지질학회지. 42 (4). The Geological Society of Korea: 483–505.
22. ^ Moores & Fairbridge 1997, pp. 479–481.

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