The first geological map of Korea, with a scale of 1:1,000,000,
was published in 1928. Geological maps with a scale of 1:250,000 covering the
whole Republic were published in 1974. The Geological Survey of Korea started
to publish geological quadrangles with a scale of 1:50,000 from 1961. The Geological
Society of Korea was established in 1947, the Korea Institute of Mining Geology
in 1968, and the Paleontological Society of Korea in 1984. The Geological Survey
of Korea was renamed the Korean Institute of Geology, Mining and Materials (KIGAM)
in 1991.
Geological Overview
Korea is a mountainous peninsula extending south-southeast from the northeastern
part of the Chinese mainland. The north-northwest, south-southeast trend forms
the Taebaek range along the east coast. The east coast shows typical features
of an uplifted topography, chiefly a relatively straight shoreline, whereas
the west coast has the features of a submerging shoreline. Throughout the country,
mountains are not high, rarely exceeding 1,200 meters, but they are found almost
everywhere. The terrain is rugged and steep and only near the west and southwest
coasts are extensive flat alluvial or diluvial plains and more subdued rolling
hilly lands.
Korea consists largely of the Precambrian rocks, such as
granite gneisses and other metamorphic rocks. Two separate blocks of the
Paleozoic strata are found in South and North Korea. The one in the South
covers the Taebaek range, and the one in the North occurs near Pyongyang.
The Mesozoic strata are found in the southeastern part of the peninsula
and the Cenozoic strata are limited to some small areas scattered around
the peninsula. The Jurassic and Cretaceous granites have intruded upon
the older rocks in a northeast-southwest direction in some places, but
show no specific trend in others.
Unlike nearby Japan, Korea is a stable landmass with no active volcanoes
and rare earthquakes, although the Ulleungdo and Jejudo are volcanic islands.
Mt. Baekdusan in the North is capped with a caldera lake, and Mt. Hallasan
on Jejudo island also has a small crater lake. |
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Geological Map of the Korean Peninsula |
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Earthquakes
Nearly 1,800 earthquakes are recorded in various historical documents of past
dynasties from A.D. 2 to 1907 and more than 200 have been scientifically recorded
since 1905 on the Korean Peninsula. Thus, the total number of recorded earthquakes
in Korea is a little more than 2,000 of which only 48 were destructive. This
number is far lower than those recorded in Japan but higher than in Manchuria.
Japan is located on the Circum-Pacific Earthquake Belt. Korea and Manchuria
are located some distance from it, but Korea is nearer to the belt. Thus, seismicity
in Korea is much stronger than in Manchuria, but much weaker than in Japan.
In Korea, earthquakes occurred mainly on faults or tectonic planes, which, viewed
on the surface, are river courses. However, in recent years, earthquakes took
place frequently along mountain ranges. South Korea is a comparatively stronger
seismic area than North Korea, and the west half of the Korean Peninsula has
shown stronger seismicity than the eastern half.
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Gwaneumgul cave in Gangwon-do
Province |
Baengnyeongdo island
in the Yellow Sea |
|
The downstream basins of the major rivers flowing into the Yellow Sea show a
much denser distribution of earthquake epicenters than the middle and upper
stream basins. Frequent seismicity occurs in both the lower and middle stream
basins of Nakdonggang river. The southwestern edge of the Gyeonggi Massif, located
in the central part of the peninsula, or the northern margin of South Korea,
has shown much stronger seismicity than the inland and northeastern coastal
areas. Almost the entire area of the Okcheon belt has shown frequent seismicity.
The southwestern region of the Taebaeksan Block of the Yeongnam Massif has shown
a more frequent seismicity and the northeastern edge of the Jirisan Block of
the Yeongnam Massif, a southwestern continuity of the Taebaeksan block have
shown relatively more frequent seismicity than other areas. The entire area
of the Gyeongsang Basin, occupying the southeastern edge of the Korean Peninsula,
has shown greater frequency and particularly both the eastern and western edges
have historically shown an intensive seismicity. The Chugaryeong Graben running
through the central zone of the Gyeonggi Massif in the north-northeast to south-southwest
directions, has shown a more frequent seismicity in both past and present times.
Tectonic and Geological Provinces
The Korean Peninsula lies within the Korea-China Heterogen. Generally speaking,
the Precambrian basement of the Peninsula is tectonically related to that of
Manchuria and China. The Pyeongbuk-Gaema Massif forms the southern part of the
Liao-Gaema Massif of southern Manchuria, and the Gyeonggi and Sobaeksan massifs
of the peninsula can be compared to the Shandong and Fujian Massifs of China.
The Paleozoic sediments, lying on the Precambrian Massifs in the Pyeongan and
Okcheon basins, have much in common with those in the Yellow River and Yangtze
basins. On the other hand, the Mesozoic rocks of the Gyeongsang Basin in the
southeastern part of the peninsula can be said to extend toward the southwestern
tip of Japan across the Korea Strait. The Pohang Tertiary sedimentary rocks,
distributed mainly in the southeastern corner of the land, lie on Mesozoic rocks.
Precambrian Geology
The Precambrian geology of Korea is yet to be fully explored. The 1:250,000
scale geological maps published in 1974 offer a more detailed Precambrian stratigraphy
of South Korea. In general, the Gyeonggi and Yeongnam Massifs belong to a low-pressure
face series, and the Okcheon Metamorphic Belt to an intermediate pressure series.
Precambrian Sequence of South Korea |
Gyeonggi Massif |
Yeongnam Massif |
Yeoncheon System |
Granite |
Granite Gneiss |
Jirisan Gneiss
Other Gneisses |
Chuncheon System Granite Gneiss |
Yulli System |
Gyeonggi Metamorphic Rock Complex |
Yeongnam System |
|
Yeoncheon System: This system, belonging to the Gyeonggi Massif, is distributed
around Seoul extending to Yeoncheon-gun in a northeasterly direction. The system
is divided into upper and lower parts. The lower part is composed of biotite-quartz-feldspar
schist, marble, lime-silicate, quartzite, and graphite schist, and the upper
part is of mica-quartz-feldspar schist, mica schist, quartzite, augen gneiss,
and garnet-bearing granitic gneiss.
Precambrian Granite Gneiss
This gneiss is also known as grey granite gneiss or Goguryeo granite. Outcrops
of it cover one-third of the surface of Korea, and are especially prevalent
in Pyeongan-do and Hamgyeongnam-do provinces. Goguryeo granite also intruded
the Yeoncheon System in the Gyeonggi Massif.
Sangwon System: This system was first observed in the northern part of
Korea, Sangwon, Pyeongannam-do province and Hwanghae-do province in central
Korea. Collenia fossils have been found in the limestone interbedded in the
system. The presence of Collenia suggests that the system belongs to the Proterozoic
Era.
Paleozoic Erathem
Paleozoic sediments in Korea are represented by the lower Paleozoic Joseon Supergroup
and the upper Paleozoic Pyeongan Supergroup. The Joseon Supergroup consists
of the Cambrian to Middle Ordovician sedimentary rocks, the Pyeongan Supergroup,
the Middle Carboniferous to Permian, and the Unidentified Triassic sedimentary
rocks. Lower Silurian limestone was found with conodonts in 1980.
The Upper Ordovician, Devonian and Lower Carboniferous systems have yet to be
discovered.
Cambro-Ordovician Strata
The Cambro-Ordovician Joseon Supergroup is widely distributed in the limestone
plateau in northwest Korea. There are many other localities with scattered patches
of the Joseon Supergroup. The Joseon Supergroup has been divided into two parts
according to its lithology, the Samcheok Group and the Sangdong Group. These
groups are conformable to each other. The Samcheok Group overlies the Precambrian
rocks, but they do not conform.
Samcheok Group: The Samcheok Group is divided into the Jangsan, Myobong,
Pungcheon and Hwajeol formations in Gangwon-do province. The Jangsan Formation
consists mainly of white quartzite that is pebbly throughout, but it starts
with thin basal conglomerates. The overlying Myobong formation, which is predominated
by greenish grey slates, follows Jangsan with alternating zones of quartzite
and slate at its base. The average thickness of each of these two formations
is about 200 meters.
Sangdong Group: The Sangdong Group, distributed in Gangwon-do province,
which is located in the east central part of Korea, is a sequence of thick limestone-rich
sediments, as is the case with the strata in northern Korea. The strata have
been divided into four formations. The lowest stratigraphic unit of the Sangdong
Group is the Dongjeom Quartzite which also overlies the Hwajeol formation. The
Dumugol limestone is of a lesser worm-eaten appearance. The Makgol and Duwibong
limestones consist of gray limestones. A bed of fossiliferous shale, known as
the Jigunsan shale, is intercalated between the two limestones. Trilobite, cephalopod,
graptolite and other fossils are found in the limestones of the Sangdong Group.
Recently, a variety of conodonts have been identified in these strata.
Appendix: Geological Formations of the Korean Peninsula
Generalized Geological Sequence |
Age |
Period |
Systems or supergroup |
Group of formation |
Cenozoic |
?/td>
| Quarternary
Tertiary |
Yeonil, Janggi |
Mesozoic |
Cretaceous
Jurassic
Triassic |
Gyeongsang
Daedong
Pyeong-an |
Bulguksa intrusions
Silla
Sindong Nakdong
Bansong
Nogam, Mt. Gobangsan |
Paleozoic |
Permian
Carboniferous
Devonian
Silurian
Odovician
Cambrian |
Joseon
|
Sadong
Hongjeom
(Absent)
Hoedong-ri
Great Limestone
Yangdeok |
Proterozoic |
?/td>
| Sangwon |
Guhyeon
Sadanggwi(in North Korea)
Jigyeon |
Archeozoic |
?/td>
| Granite Gneiss
Yeoncheon |
?/td>
|
|
Middle Paleozoic Strata
Middle Paleozoic strata from the Upper Ordovician to the Lower Carboniferous
are not known to exist. However, the existence of the Lower Silurian Hoedong-ri
formation has been established by the finding of Silurian conodont fauna. Some
formations in the Okcheon Supergroup are thought to be middle Paleozoic in age
by some geologists, although no conclusive evidence has been found to substantiate
this claim.
Carboniferous-Triassic Strata
Carboniferous-Triassic strata of the Pyeongan Supergroup, distributed exclusively
overlying the Middle Ordovician unconformably, are found roughly in four locations
in North Korea, and three areas in Gangwon-do and Chungcheongbuk-do provinces
in South Korea.
Gomok Group: The main rocks of this group are slightly metamorphosed
green, red, gray or mottled sandstone and shale with some light-colored limestone.
Most of the shale are characterized by dark fine ottrelite. The limestone beds
are fossiliferous with primitive fusulinids and other foraminiferas, corals,
brachiopods and others. The presence of fusulinids indicates the age of the
group to be Moscovian of Middle Carboniferous. The Gomok Group is about 220
meters thick on average.
Cheoram Group: The Cheoram Group is characterized by somewhat metamorphosed
gray to dark-gray sandstone, shale, coaly shale, coal beds, and dark grey limestone
beds. Three or more coal beds are intercalated in the upper part of the series,
and are an important source of anthracite. Upper Moscovian fusulinids are found
in the Samcheok and the Danyang coalfields, while Sakilometersarian fusulinids
are found in the Yeongwol coalfield. The thickness of the Cheoram Group averages
150 meters.
Hwangji Group: The group locally overlies the Cheoram Group conformably,
and is composed mainly of white quartzites intercalating some black shale. The
age of the group is Middle to Late Permian, possibly even extending to Triassic.
The thickness of the Tosagok and Gohan formations is about 880 meters. The upper
part of the group (Donggo formation) is composed mainly of green arkose sandstone
with some conglomerate beds. The age of the Donggo formation has not been clarified
by fossils, though it has been thought to be Triassic because of its thickness.
This formation is 400-2,000 meters thick.
Mesozoic Erathem
The lower Mesozoic is represented by the Donggo formation of the upper part
of the Pyeongan Supergroup. The rest of the Mesozoic sediments in Korea are
represented by the middle Mesozoic Daedong Supergroup and the upper Mesozoic
Gyeongsang Supergroup.
The Daedong Supergroup represents the Jurassic, and the Gyeongsang the Cretaceous.
In the Jurassic Period, a deformation known as Daebo Orogeny took place. This
mountain forming process was the most intensive on the Korean Peninsula, which
caused all earlier formations to fold, thrust and fault drastically.
Daedong Supergroup
The Daedong Supergroup is not widely distributed in Korea. Long, narrow, and
patchy, it is scattered with or without distributional relationship with the
Pyeongan Supergroup, though showing deformations as does the latter. It is subdivided
into the Lower Nampo, Upper Nampo and Bansong groups in South Korea, which consist
mainly of conglomerates, milky white pebble-bearing arkosic quartzose sandstone,
black sandy shale, coaly shale, and coal. The Daedong Supergroup near Pyongyang
in North Korea is subdivided into the Sunyeon and Yugyeong series, which consist
of conglomerate, sandstone, and shale ranging up to 1,300 meters in thickness.
Subdivision of the Paleozoic Strata (Samcheok Coal Field) |
Classic |
|
Proposed |
Age |
|
Pyeongan System |
Green Series |
|
Donggo Formation |
Triassic |
Mt. Gobangsan Series(Mt. Gobangsan) |
Hwangji Group |
Gohan Formation Dosagok Formation |
|
Sadong Series |
Cheoram Group |
Hambaek Formation Jangseong Formation |
Permian |
Hongjeom Series |
Gomok Group |
Geumcheon Formation Manhang Formation |
Carboniferous |
Hiatus: Late Ordovocian to Early Carboniferous (Except Lower Silurian) |
Joseon System |
Great Limestone Series |
Duwibong Formation Makgol Formation Dumugol Formation Dongjeom Quartzite |
Sangdong Group |
|
Ordovician |
Hwajeol Formation Pungcheon (Daegi) Formation |
Samcheok Group |
|
|
Yangdeok Series |
Myobong Formation Jangsan Formation |
Samcheok Group |
|
|
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Plutonism in the Jurassic Period
Most of the granite bodies, except the Cretaceous ones, intruded during the
Jurassic Period. In South Korea, granite batholiths show a characteristic distribution
trend north northeast-south southwest (the so-called Sinan). Most of these granite
bodies are biotite granites, while some are hornblende granites.
Gyeongsang Supergroup: The Gyeongsang Supergroup is distributed across
a wide area within the Gyeongsang-do province in the southeastern part of Korea.
Animal fossils indicate that sediments were deposited in shallow water environments.
They are of fresh to brackish water genera. No marine fossils have been found.
The Gyeongsang Basin was formed subsequent to the Daebo Orogeny and can be divided
into three minor basins: the Yeongyang, Uiseong, and Miryang basins. The Gyeongsang
Supergroup is composed of the Sindong and Hwayang groups and the Bulguksa Intrusives.
Plutonism in Cretaceous Period
The biotite granite intruded in the Gyeongsang Supergroup is called Bulguksa
Granite. The radiogenic isotope ages of intrusions are dated to be Late Cretaceous
to Early Tertiary. A remarkable characteristic of the Plutonism of this period
is that the granites are not of an orogenic production.
Sindong Group: This group is distributed in the western part of the Gyeongsang-do
province and is subdivided into three formations. It consists mainly of shales,
sandstones, conglomerates, and one or two thin coal seams. The formations of
the group have gentle monotonous eastward dip in contrast to the marked deformation
of the Jurassic and Pre-Jurassic rocks. Ripple marks and sun cracks are found
in many localities of the group, indicating that the group was formed in shallow-water
environment. Animal fossils indicative of the Early Cretaceous age are prevalent.
They include Viviparus, Hydrovia, Bulimus, Itometamia, Brotiopsis, Anisus, Trigonioides,
Plicatounio, Nakamuranaia, Schistodesmus, and Estherites. Plant fossils include:
Group 1, Cladophlebis browniana, Onychiopsis mantelli, Ruffordia goepperti,
and Nilssonia schaumbur gensis; Group 2, Cladophlebis lobifolia, Coniopteris
hymenophylloides, Dictyozamites falcatus, Ptilophyllum pecten, and Nilssonia
compta. The Group 1 indicates Early Cretaceous and Group 2 Middle Jurassic.
Because the Sindong Group overlies granite gneiss unconformably, its relationship
to the Daedong System cannot be determined.
Hayang Group: This group, widely distributed throughout the Gyeongsang-do province,
consists of conglomerates, sandstone, shale, and volcanic rock such as andesite,
basalt, rhyolite, and tuff, especially in the upper part of the group. The thick
basal conglomerates form the boundary dividing the groups from the underlying
Sindong Group. The Cheokgang-ri formation in South Korea and the Daebo Series
near Pyongyang in North Korea are correlated to the Hwayang Group. The former
overlies the Pyeongan Supergroup, and the latter Daedong System unconformably.
The Hayang Group has more ripple marks and sun cracks than the Sindong Group,
but the latter is more fossiliferous. Plant fossils found in this group indicating
the whole range of the Cretaceous period are Filicales, Cycadales, Coniferales,
and Angiospermae. Bones, eggs and tracks of dinosaurs have also been found in
the Hayang sediments.
Cenozoic Geology
Neogene Tertiary Strata are distributed across small areas along the eastern
coast of the Korean Peninsula. They are, from north to south, the Gilju-Myeongcheon
Basin in North Korea, and the Bukpyeong, Yeonghae, Pohang and the Ulsan basins
in South Korea. The rocks are poorly lithified sandstone, shale, conglomerate,
lava, and sill. An alternation of land and marine deposits is characteristic
of the strata.
Bongsan Series: This series is distributed throughout the Hwanghae-do
and Pyeongannam-do provinces of North Korea, and consists of an alternation
of shale and sandstone, conglomerate, and coal seams. Fossils indicating the
late Eocene include Colodon, Caenolophus, Desmatotherium and Portianotherium
(animal fossils), and Populus, Platanus and Vipurunus (plant fossils). The series
is about 350 meters thick.
Yeongdong Series: This series is distributed in Hamgyeongbuk-do province,
North Korea, and consists of sandstone, shale, interbedded coal seams, and alkali-basalt
in the lower part of the series. Plant fossils indicating Middle to Late Oligocene
include Pinus, Glyptostrobus, Sequoia and Juglans. The series is 80 meters thick.
Yangbuk Group: This group is distributed in Gyeongsangnam-do province,
South Korea, and consists of conglomerates, volcanic rocks, sandstone, shale,
and coal seams alternating with tuff. Plant fossils indicating the early to
middle Miocene include Sequoia, Salix, Carpinus, Alnus, Populus, Betula, Fagus,
Fagophyllum, Castanea, Colylus, Zenthoxyl-on, Planea, Ficus, Uities, Acer and
Juglans. The series is approximately 1,400 meters thick.
Yeonil Group: This is distributed throughout Yeonil, South Korea, and
consists of conglomerate (200 meters thick) and thick shale (400 meters thick).
Fossils indicating the Miocene include Turborotaria, Globigerina and Globigerinoides,
which are all foraminifers; Caridium, Solen, Lucina, and Potamides, which are
all marine mollusks, from the sandstone; Leda, Cardium, Dosinia, Ostrea and
Pecten which are from the shale; and Salix, Quercus, Cinnamomum, Sapindus and
Aagus, which are all plant fossils, from the upper part of the shale.
Seogwipo Formation: This formation is distributed in Jejudo island off
southwestern Korea. The formation consists of sandstone and mudstone. Fossils
indicating the late Pliocene Era include marine mollusks and foraminifers.
General Tertiary Stratigraphy |
Tertiary |
Pliocene |
Seogwipo Formation |
Miocene |
Yeonil Group Yangbuk Group |
Oligocene |
Yeongdong Series |
Eocene |
Bongsan Series |
|