Geology of South Korea

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Dobongsan Peaks (dobongsan jeongsan) Geology of South Korea - Dobongsan Peaks (dobongsan jeongsan) (3578202462).jpg
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]

Contents

Geologic history, stratigraphy and tectonics

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)

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

Paleozoic (539–251 million years ago)

The 'Gumunso(ko:gumunso)' - The place where early Paleozoic formation exists. (Joseon Supergroup Makgol limestone Formation) Gumunso.jpg
The 'Gumunso(ko:구문소)' - The place where early Paleozoic formation exists. (Joseon Supergroup Makgol limestone Formation)

The rock formation which is formed during Paleozoic is composed of Joseon Supergroup (lower) and Pyeongan Supergroup (upper).

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]

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

Pyeongan Supergroup

The border region of Gyeongsang Basin, Yongnam Massif, Okcheon Fold Belt in Sangju Area (using OpenStreetMap) Sangju earthquake.jpg
The border region of Gyeongsang Basin, Yongnam Massif, Okcheon Fold Belt in Sangju Area (using OpenStreetMap)

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]

Geologic time scale Area
period Epoch Age Samcheok Gangneung Jeongseon-Pyeongchang Yeongwol Danyang Boeun Pyeongnam BasinDuman Basin
Mesozoic Triassic
201.3–252.17 Mya
Mid 237–247.2 Mya Anisian Donggo
(Formation)
BakjisanDonggotaejawon
Early 247.2–252.17 Mya Induan Sangwonsan
Paleozoic
Permian
252.17–298.9 Mya
Lopingian 252.17–259.8 MyaGobangsanSongsang
Guadalupian
259.8–272.3 Mya
Capitanian GohanUnbyeolriOkgapsanGohan
Wordian DosagokMangdeoksanDosagok
Roadian
Cisuralian
272.3–298.9 Mya
Cisuralian Hambaeksan Hambaeksan Hambaeksan Hambaeksan Gyeryongsan
Artinskian JangseongJangseongJangseongMitanJangseongJangseongSadong
Sakmarian BamchiBamchiBamchiAmgi
Asselian ibseog
Paleozoic
Carboniferous
252.17–298.9 Mya
Pennsylvanian
298.9–323.2 Mya
Moscovian GeumcheonGeumcheonGeumcheonPangyoGeumcheonhongjeom
ManhangManhangManhangYobongManhangManhang
Bashkirian

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]

Mesozoic (251-66 million years ago)

In the Triassic at 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

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 Geology map of Daegu City and Gyeongsan City located in the middle of Gyeongsang Basin daegujijil.jpg
The Geology map of Daegu City and Gyeongsan City located in the middle of 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]

Cenozoic (66 million years ago-present)

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.

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