• Economic and Environmental Geology
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• v.52 no.5
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• pp.347-356
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• 2019

Various studies regarding the sedimentary environment, depositional age, provenance, and metamorphic history have been carried out on the Taean Formation in the western part of Gyeonggi Massif, since the unique detrital zircon age pattern was revealed. This review paper introduces the previous researches on the Taean Formation and discusses the depositional age and provenance. The Taean Formation was traditionally regarded as a Precambrian stratigraphic unit, but recently it is interpreted to be a middle or upper Paleozoic formation due to the occurrence of large amounts of Early to Middle Paleozoic detrital zircons. The Taean Formation consists of metasandstone, argillaceous schist, and phyllite which are mainly made up of quartz and mica. The protoliths are interpreted as turbidites deposited in deep sea fan environment. The Taean Formation has been interpreted to be deposited between the Devonian to Triassic ages given the age differences between detrital zircons and intrusive rocks. There are two opinions that the deposition age is close to the Devonian or the Permian period. The provenance of this formation is supposed to be South China block, Chinese collisional belt, or Gyeonggi Massif. Given the available detrital zircon ages of the Taean Formation and other Korean (meta)sedimentary rocks, the Taean Formation shares major source rocks with Yeoncheon Group and Pibanryeong Unit of the Okcheon Supergroup, but their source regions are not entirely consistent. Considering the existing hypotheses about the depositional timing and provenance, we put weight on the possibility that the Taean Formation was deposited between Permian and Early Triassic periods. However, further studies on the stratigraphy and sedimentary petrology are needed to clarify its definition and to elucidate the provenance.

• Korean Journal of Mineralogy and Petrology
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• v.34 no.1
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• pp.69-81
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• 2021

The exposed rocks in the Zacatecas state include mainly Mesozoic sedimentary and volcanic, Cenozoic volcanic and plutonic rocks. Paleozoic metamorphic rocks found in the northwestern portion of the state are considered as the most ancient rocks. These rocks correspond to the Caopas Formation which underlays the Later Paleozoic Rodeo Formation. The Mesozoic sequences are represented by a marine sedimentary sequence of the Later Triassic and the red beds of the Triassic-Jurassic Nazas Formation. The marine sediments of the Upper Jurassic overlay the Nazas Formation or metamorphic rocks from the Paleozoic. The Cretaceous sequences comprises marine sedimentary rocks in the north and northeast, and a volcanosedimentary set in the center and southeast. The Cenozoic is represented by volcanic nondifferentiated rocks, intrusive igneous rocks of acid and intermediate composition, and continental conglomerates with evaporitic sediments. The Quarternary sequences includes basalts, piedmont deposits, alluviums and occasionally, layers of evaporites and saltpeter. Furthermore, a great diversity of mineral deposits of both metallic and nonmetallic types occur in Zacatecas state. The rocks composing these deposits are extremely varied and include formations from Paleozoic to Tertiary. The mineralization age of ore deposits corresponds to the Tertiary in approximately 90%, and their genesis is mainly considered as epigenetic.

• The Journal of the Petrological Society of Korea
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• v.26 no.3
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• pp.235-254
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• 2017

We investigate the geological history that formed geology and landscapes of the Juwangsan National Park and its surrounding areas. The Juwangsan area is composed of Precambrian gneisses, Paleozoic metasedimentary rocks, Permian to Triassic plutonic rocks, Early Mesozoic sedimentary rocks, Late Mesozoic plutonic and volcanic rocks, Cenozoic Tertiary rhyolites and Quaternary taluses. The Precambrian gneisses and Paleozoic metasedimentary rocks of the Ryeongnam massif occurs as xenolithes and roof-pendents in the Permian to Triassic Yeongdeok and Cheongsong plutonic rocks, which were formed as the Songrim orogeny by magmatic intrusions occurring in a subduction environment under the northeastern and western parts of the area before a continental collision between Sino-Korean and South China lands. The Cheongsong plutonic rocks were intruded by the Late Triassic granodiorite, which include to be metamorphosed as an orthogneiss. The granodiorite includes geosites of orbicular structure and mineral spring. During the Cretaceous, the Gyeongsang Basin and Gyeongsang arc were formed by a subduction of the Izanagi plate below East Asia continent in the southeastern Korean Peninsula. The Gyeongsang Basin was developed to separate into Yeongyang and Cheongsong subbasins, in which deposited Dongwach/Hupyeongdong Formation, Gasongdong/Jeomgok Formation, and Dogyedong/Sagok Formation in turn. There was intercalated by the Daejeonsa Basalt in the upper part of Dogyedong Formation in Juwangsan entrance. During the Late Cretaceous 75~77 Ma, the Bunam granitoid stock, which consists of various lithofacies in southwestern part, was made by a plutonism that was mixing to have an injection of mafic magma into felsic magma. During the latest Cretaceous, the volcanic rocks were made by several volcanisms from ubiquitous andesitic and rhyolitic magmas, and stratigraphically consist of Ipbong Andesite derived from Dalsan, Jipum Volcanics from Jipum, Naeyeonsan Tuff from Cheongha, Juwangsan Tuff from Dalsan, Neogudong Formation and Muposan Tuff. Especially the Juwangsan Tuff includes many beautiful cliffs, cayon, caves and falls because of vertical columnar joints by cooling in the dense welding zone. During the Cenozoic Tertiary, rhyolite intrusions formed lacolith, stocks and dykes in many sites. Especially many rhyolite dykes make a radial Cheongsong dyke swarm, of which spherulitic rhyolite dykes have various floral patterns. During the Quaternary, some taluses have been developed down the cliffs of Jungtaesan lacolith and Muposan Tuff.

• Economic and Environmental Geology
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• v.6 no.2
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• pp.81-114
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• 1973

The purpose of the present study is to clarify the stratigraphy and geologic structure of the Great Limestone Series by means of study on fossil conodonts and detail investigation of geologic structure. In recent years very few geologists in Korea argue without confident evidences against the age and stratigraphy of the Great Limestone Series which have been rather well established previously in most parts of the regions although it is ambiguous and has not been studied in other areas. Five type localities in the Kangweon basin where the Great Limestone Series is well cropped out were chosen for the study. Total 26 genus and 66 species of conodont were identified from 290 samples collected and treated. From the study on conodonts the age of each formations of the Great Limestone Series has been determined as follows: The Great Limestone Series of Duwibong type Duwibong limestone: Caradocian (mid-Ord.) Jikunsan shale: Landeilian (mid-Ord.) Maggol limestone: Llanvirn-Llandeilian (mid-Ord.) Dumugol: Arenigian (Ord.) Hwajeol: Upper Cambrian The Great Limestone Series of Yeongweol type Mungok (Samtaesan) : Ordovician Machari: upper Cambrian The Great Limestone Series of Jeongseon type Erstwhile Jeongseon limestone: mid-Ord. The erstwhile Jongseon Limestone formation in Jeongseon district is separated into Hwajeol, Dongjeom, Dumudong, and Maggol formations which were cropped out repeatedly by folding and faulting, but Maggol is predominant in areal distribution. Yemi Limestone Breccia bed is not a single bed but distributed in several horizons so that it bears no stratigraphic significance. The limestone bed above Yemi Limestone Breccia, which was believed by some geologists to be much younger than Ordovician, is identified to be Maggol and its age is determined to be mid-Ordovician. Sambangsan formation in Yeongweol district was believed to be Cambrian age and lower horizon than Machari formation by Kobayashi, but C. M. Son believed that it might belong to later than Ordovician and lies above the Great Limestone Series of Yeongweol type. It was identified to be upper Cambrian and lies beneath the Machari formation and above the Daeki formation, the lower most horizon of the Great Limestone Series. The age of Yeongweol type Choseon system is contemporaneous with that of Duwibong type Choseon system. The difference in lithofacies is not due to lateral facies change, but due to the difference in its depositional environment. The Yeongweol type Choseon system is believed to be deposited in the small Yeongweol basin which was separated from the main Kangweon sedimentary basin. Judging from these facts it is definitely concluded that there exists no Gotlandian formation in the regions studied. Structurally the Kangweon basin comprises five basins and two uplifted areas. These structures were originated by at least two crustal movements, that is, Songrim disturbance of Triassic and Daebo orogeny of Jurasic age.

• Economic and Environmental Geology
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• v.1 no.1
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• pp.35-46
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• 1968

Some of geologists in Korea recently postlated that Okchon system previously known to be precambrian age was the metamorphosed sediments of post-Chosen (Ordovician and pre-Kyeongsang (late Jurassic to Cretaceous) periods, or even definitely of Triassic period simply on the basis of the fact that Okcheon system overlies the Great Limestone series of Chosen system of Camber-ordovician age, and of other few assumptions of minor importance. As a result of such correlation, thick series of metasediments and Okcheon system of unknown age were established in this particular region and vaguely correlated to Paleozoic and Mesozoic sediments. Recent study done by the author reveled that: 1) only the upper Okcheon bed of S. Nakamura was true Okcheon system, and the middle and lower Okcheon beds were excluded, because they were correlated to Cambrian and Permian sediments resfectively, 2) Sangnaeri, Seochangri, and rengam formations of unknown age, and Baekhwasan, Jobong, and Ihwaryeong formations of Okcheon system of also unknown age were the metamorphosed Yangdeok system of Cambrian age, all of these formations were differentiated by the previous workers and were equivalent to the middle Okcheon system of S. Nakamure, and. 3) These metamorphosed Yangdeok system overlaid apparently the Great Limestone series in forms of overthrust and klippe which were produced by the orogeny took place during post-Daedong and pre-Kyeongsang period (probably middle to the Jurassic). The Sobaeksan Range, folded mountain Chains was also formed by this orogeny. Thus, Okcheon system newly defined by the author is precambrain age and consists in ascending order of Kemyenogsan, Hyangsan dolomite, and Daehangsan quartzite formation which were previously classified into metasediments of unknown age, and Munjuri, and Hwangkanri, formations which were differentiated into Okcheon system unknown age by the previous workers, but are of reversed sequence. Myeongori and Bukrori formations of Okcheon System are regard by the author as part of Hwangkanri formation. Few other assumption of minor important taken by the previous workers as their positive evidences are carefully explained that they were misinterpreted.

• Economic and Environmental Geology
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• v.48 no.4
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• pp.287-299
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• 2015

The metapsammite distributed in the Yeongam-Gangjin area had been classified into age-unknown Yongamsan Formation, Seologri Formation and age-unknown Seogisan Formation, and these formations are reported as each other different formations. These formations have been renamed Precambrian Galdu or Permian Songjong Formations. In this study, we present detrital zircon SHRIMP U-Pb age data from the metapsammite to examine deposition time and stratigraphy. The analyzed U-Pb zircon ages dominantly reveal Paleoproterozoic ages of ca. 1.87Ga and the youngest detrital grains are constrained by the age of 246-265 Ma. The youngest age indicates late Permian or early Triassic for the deposition time. Therefore, the metapsammite in the Yeongam-Gangjin area is considered to be the upper formation of the late Paleozoic Pyeongan Group which is correlated with the Gohan-Donggo Formations or Nokam Formation of the Samcheock coal field and the Cheonunsan Formation of the Hwasun coal field. The metapsammite of the study area is the late Paleozoic Pyeongan Group by the zircon age rather than Precambrian Galdu and Permian Songjeong Formations are no longer meaningful. Therefore, we propose the upper Paleozoic 'metapelite' and 'metaspammite', or original formation name defined by 1:50,000 geological maps, instead of Galdu and Songjeong Formations.

• Economic and Environmental Geology
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• v.25 no.1
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• pp.87-96
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• 1992

Paleomagnetic study on the sedimentary rocks in the Choongnam Coal Field has been carried out to determine the direction of declination and inclination of NRM and position of paleomagnetic pole, and to investigate the geotectonism and geomagnetic stratigraphy of the sedimentary rocks in the Daedong Group. As a result of paleomagnetic study, the study area can be divided tectonically into two blocks by Baegunsa fault, namely northwestern and southeastern blocks. Site mean declination and inclination of Baegunsa and Seoungjuri Formations in the northwestern block are $23.2^{\circ}$ and $54.9^{\circ}$, respectively. Those of Amisan, Jogyeri, Baegunsa and Seoungjuri Formations in the southeastern block show normal direction with declination and inclination of $-22.1^{\circ}$ and $11.2^{\circ}$, and reversed direction with those of $158.5^{\circ}$ and $-12.6^{\circ}$, respectively. Average paleomagnetic pole position in the northwestern block is located at $212.9^{\circ}E$ and $71.1^{\circ}N$, and that in the southeastern block at $345.7^{\circ}E$ and $53.3^{\circ}N$. This difference suggests relative rotation of about $45^{\circ}$ between two blocks. The paleolatitude of Daedong Group at the time of sedimentation is $5.6^{\circ}N$ much lower than present latitude of $37.7^{\circ}N$. Compared with worldwide Mesozoic paleomagnetic polarity stratigraphy, Amisan Formation is correlated with the lower boundary of Nuanetsi reversal zone in Graham interval, and Baegunsa and Seoungjuri Formations are correlated with just upper part of the upper boundary of Nuanetsi reversal zone, and their geologic ages are Late Triassic to Early Jurassic. The position of paleomagnetic pole acquired from Daedong Group in the study area is different from those in other places. This may be attributed to the different tectonic movement by Daebo Orogeny occurred after the deposition of Daedong Group.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.129-150
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• 2012

The tectonic evolution of the Central Ogcheon Belt has been newly analyzed in this paper from the detailed geological maps by lithofacies classification, the development processes of geological structures, microstructures, and the time-relationship between deformation and metamorphism in the Ogcheon, Cheongsan, Mungyeong Buunnyeong, Busan areas, Korea and the fossil and radiometric age data of the Ogcheon Supergroup(OSG). The 1st tectonic phase($D^*$) is marked by the rifting of the original Gyeonggi Massif into North Gyeonggi Massif(present Gyeonggi Massif) and South Gyeonggi Massif (Bakdallyeong and Busan gneiss complexes). The Joseon Supergroup(JSG) and the lower unit(quartzose psammitic, pelitic, calcareous and basic rocks) of OSG were deposited in the Ogcheon rift basin during Early Paleozoic time, and the Pyeongan Supergroup(PSG) and its upper unit(conglomerate and pelitic rocks and acidic rocks) appeared in Late Paleozoic time. The 2nd tectonic phase(Ogcheon-Cheongsan phase/Songnim orogeny: D1), which occurred during Late Permian-Middle Triassic age, is characterized by the closing of Ogcheon rift basin(= the coupling of the North and South Gyeonggi Massifs) in the earlier phase(Ogcheon subphase: D1a), and by the coupling of South China block(Gyeonggi Massif and Ogcheon Zone) and North China block(Yeongnam Massif and Taebaksan Zone) in the later phase(Cheongsan subphase: D1b). At the earlier stage of D1a occurred the M1 medium-pressure type metamorphism of OSG related to the growth of coarse biotites, garnets, staurolites. At its later stage, the medium-pressure type metamorphic rocks were exhumed as some nappes with SE-vergence, and the giant-scale sheath fold, regional foliation, stretching lineation were formed in the OSG. At the D1b subphase which occurs under (N)NE-(S)SW compression, the thrusts with NNE- or/and SSW-vergence were formed in the front and rear parts of couple, and the NNE-trending Cheongsan shear zone of dextral strike-slip and the NNE-trending upright folds of the JSG and PSG were also formed in its flank part, and Daedong basin was built in Korean Peninsula. After that, Daedong Group(DG) of the Late Triassic-Early Jurassic was deposited. The 3rd tectonic phase(Honam phase/Daebo orogeny: D2) occurred by the transpression tectonics of NNE-trending Honam dextral strike-slip shearing in Early~Late Jurassic time, and formed the asymmetric crenulated fold in the OSG and the NNE-trending recumbent folds in the JSG and PSG and the thrust faults with ESE-vergence in which pre-Late Triassic Supergroups override DG. The M2 contact metamorphism of andalusite-sillimanite type by the intrusion of Daebo granitoids occurred at the D2 intertectonic phase of Middle Jurassic age. The 4th tectonic phase(Cheongmari phase: D3) occurred under the N-S compression at Early Cretaceous time, and formed the pull-apart Cretaceous sedimentary basins accompanying the NNE-trending sinistral strike-slip shearing. The M3 retrograde metamorphism of OSG associated with the crystallization of chlorite porphyroblasts mainly occurred after the D2. After the D3, the sinistral displacement(Geumgang phase: D4) occurred along the Geumgang fault accompanied with the giant-scale Geumgang drag fold with its parasitic kink folds in the Ogcheon area. These folds are intruded by acidic dykes of Late Cretaceous age.

• The Journal of the Petrological Society of Korea
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• v.16 no.3
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• pp.162-179
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• 2007

Macheon Layered Intrusion (MLI) which intruded into Precambrian gneiss complex of the northern Jirisan area, southeastern part of Youngnam (or Sobaeksan) Massif, is a layered mafic-ultramafic complex of Triassic age (ca. 223 Ma). The MLI is divided into Layered Series and Laminated Series. Layered Series is subdivided into Central Zone (Lower Zone) consisting of olivine gabbros and Peripheral Zone (Middle or Upper Zone) consisting of hornblende gabbros based on the type of cumulus texture and the main mafic phase. The Central Zone of Layered Series comprises thinly laminated olivine gabbros and uniform or thickly laminated coarse olivine gabbros which consist of mela-gabbro, troctolite, leuco-troctolite, and anorthositic rocks. Laminated Series is also subdivided into quartz-bearing biotite-pyroxene gabbros and homblende diorite and both have variable amount of interstitial quartz and microcline. Laminated series display moderately to slightly developed igneous lamination which is defined by the planar alignment of lath-shape plagioclases. Chilled margin of quartz-bearing biotite-pyroxene gabbro with surrounding Precambrian gneisses insists shallower intrusion of more felsic cognate magma evolved in the deep a little later. Rocks of Layered Series have orthocumulus to adcumulus olivine, adcumulus to intercumulus plagioclase, and intercumulus to heteradcumulus pyroxene and hornblende. Magmatic modally grading, folding, and cross-lamination are not rarely occurred in thinly layered rocks. These textural characteristics define main mechanisms of the formation of layered and laminated structure in mafic-ultramafic rocks of Macheon Layered Intrusion are gravity settling and in-situ crystallization associated with slumping and density current.

• The Journal of the Petrological Society of Korea
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• v.10 no.2
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• pp.82-94
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• 2001

The main geological structure of the Ogcheon belt in the Buunnyeong area, Mungyeong, which consists of three stratigraphic sequences, Joseon and Pyeongan Supergroups and Daedong Group, is characterized by the development of ESE-vergence structural unit (Dangok unit) and WNW-vergence structural units (Samsil and Bugongni units) onto an autochthonous unit (Buunnyeong unit). Three phases of deformation are recognized in this area. The lent phase of deformation coourred under the WNW-ESE compression, forming an upright-open fold (Buunnyeong-I fold) with NNE axial trend in the Buunnyeong unit. The second phase of deformation also under the WNW-ESE compression formed the Dangok, Samsil and Bugongni units, resulting in the further closing of the Buunnyeong-I open fold, the elongation of pebbles in the conglomerate rocks of a basal sequence of the Daedong Group, recumbent folds (Buunnyeong-II fold) and drag folds (Dangok fold) with NNE axial trend in the Buunnyeong and Dangok units, respectively. The third phase of deformation formed kink folds with its axis p1unging subvertically. The first and second phases of deformation took place before and after the deposition of the Daedong Group of the Upper Triassic -Lower Jurassic, respectively. These first two deformation events, which occurred under the same WNW-ESE compressional field, produced the regional NNE trend of geological structure in the Joseon and Pyeongan Supergroups of this area.