The geology of South Korea includes rocks dating to the

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth Earth ...

and two large massifs of

metamorphic rock Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...

as the

crystalline basement In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The baseme ...

, overlain by thick sedimentary sequences, younger metamorphic rocks and volcanic deposits. Although extent is small, Geology is diverse, and there are diverse rocks that were formed during the

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

Era in the Korea Peninsula.

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 Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

and

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...

complexes from the

and underlie the entire Republic of Korea. Units range in age from the

to the

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...

, with

metamorphic facies A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures.Essentials of Geology, 3rd Edition, Stephen Marshak The assemblage is typical of what is formed in conditions corresponding ...

from

greenschist Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite ...

amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky ...

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%. It is confirmed that Korea peninsula is formed mostly after

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

(2,500 to 1,600 million years ago) and Archean rocks appear in portion region.

Paleozoic (539–251 million years ago)

The rock formation which is formed during

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

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 South Pyongan Province (Phyŏngannamdo; ) is a province of North Korea. The province was formed in 1896 from the southern half of the former Pyongan Province, remained a province of Korea until 1945, then became a province of North Korea. Its ca ...

Basin and Okcheon Fold Belt. The early Paleozoic Joseon Supergroup in Korea has been divided into

Taebaek Taebaek () is a city in Gangwon province, South Korea. Its name is shared with that of the Taebaek Mountains. Situated at an elevation of , Taebaek is the highest city in South Korea. Attractions Manggyeongsa Temple in Hyeol-dong, at an elevation ...

Yeongwol Yeongwol County (''Yeongwol-gun'') is a county in Gangwon Province, South Korea. It is well known as the place where King Danjong, the sixth king of Joseon Dynasty, was exiled when he was forced to abdicate by his uncle, who became Sejo of Joseon ...

Pyeongchang Pyeongchang (; in full, ''Pyeongchang-gun'' ; ) is a county in the province of Gangwon-do, South Korea, located in the Taebaek Mountains region. It is home to several Buddhist temples, including Woljeongsa. It is about east southeast of Seou ...

, Yongtan and

Mungyeong Mungyeong ( ko, 문경 ' ()) is a city in North Gyeongsang Province, South Korea. The local government, economy, and transportation networks are all centered in Jeomchon, the principal town. Mungyeong has a lengthy history, and is known today for ...

groups, depending on the sequence of lithology. Taebaek group that located in

Samcheok Samcheok () is a city in Gangwon-do, South Korea. History Ancient age & Three Kingdom * It was called "Siljikguk or Siljikgokguk" * 102 under the rule of Silla ( Pasa 23rd) * 468 under the rule of Goguryeo ( Jangsu 56th) * 505 The name changed ...

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. The geological table of the Joseon Supergroup is as follows.

Pyeongan Supergroup

From

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

, The Pyeongan Supergroup was formed, and it distributed in the

Basin and Okcheon Folded Zone. The geological table and stratigraphy of the Pyeongan Supergroup are as follows.

Okchon (folded) Zone

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

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...

. 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 In geology, a nappe or thrust sheet is a large sheetlike body of rock (geology), rock that has been moved more than or above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision z ...

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 The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

and

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

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

. The

P'yŏngan Pyeong-an Province (, ) was one of Eight Provinces of Korea during the Joseon Dynasty. Pyeong'an was located in the northwest of Korea. The provincial capital was Pyeongyang (now Pyongyang, North Korea). History Pyeong'an Province was formed in ...

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.

Mesozoic (251-66 million years ago)

In the

at beginning of the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

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 Intermontane is a physiographic adjective formed from the prefix " inter-" (''signifying among, between, amid, during, within, mutual, reciprocal'') and the adjective "montane" (inhabiting, or growing in mountainous regions, especially cool, moi ...

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 Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted t ...

in the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

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 The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

. it occupies most of the

Yeongnam Yeongnam (Hangul: 영남, ; literally "south of the passes") is a region that coincides with the former Gyeongsang Province in what is now South Korea. The region includes the modern-day provinces of North and South Gyeongsang and the self-go ...

region and part of

Honam Honam (; literally "south of the lake") is a region coinciding with the former Jeolla Province in what is now South Korea. Today, the term refers to Gwangju, South Jeolla and North Jeolla Provinces. The name "Jeonla-do" is used in the names of th ...

region. The Gyeongsang Basin is composed of Gyeongsang supergroup, which consists of Sindong, Hayang, Yucheon group, and Bulguksa

Granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

. The Sindong Group is the lowest stratigraphic sequence in the Cretaceous Gyeongsang Basin and comprises three stratigraphic units: the Nakdong, Hasandong, and

Jinju Formation The Jinju Formation () is an Early Cretaceous geologic Formation (geology), formation in South Korea.microlite Microlite was once known as a pale-yellow, reddish-brown, or black isometric mineral composed of sodium calcium tantalum oxide with a small amount of fluorine. Its chemical formula is. Today it is a name of a group of oxide minerals of a similar ...

diorite Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-silic ...

and

granodiorite Granodiorite () is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...

from the late Cretaceous.

Cenozoic (66 million years ago-present)

Volcanic activity continued into the

ending 50 million years ago. No

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

sedimentary rocks have been found onshore. Yangbuk Group conglomerates and alluvial fan sediments gathered in small fault-bounded basins in the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

. During the last 2.5 million years of the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

, Cheju and other offshore islands formed from volcanism.

References

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