• Economic and Environmental Geology
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• v.42 no.6
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• pp.627-634
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• 2009

Redefining the difference among the Yamaguchi's 'so-called Yeoncheon system,' north Korean's 'Rimjin System' and Yeoncheon Group of national geological map, authors tried to avoid a possible misunderstanding of concept between Yeoncheon Group and Imjingang fold Belt. As a tool of preliminary geological mapping and or N-S reconnaissance of the whole Yeoncheon Group, an interpretation technique of satellite image from various angles has been applied to understand the geometrical attitude of strike and dip of random spot, and a further concept like as cross section.

• The Journal of the Petrological Society of Korea
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• v.4 no.1
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• pp.1-19
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• 1995

In order to characterize the petrogenesis of the E-W trending Imjinganag belt, we studied the metamorphic rocks of the Yeoncheon Group near its type locality, Yeoncheon - Cheongok area, belonging to the southern part of this fold-thrust belt. The Samgot Formation of the Yeoncheon Group consists of calc-silicate and metapsammitic rocks together with amphibolite and amphibole gneiss. Layers of these metamorphic rocks concordantly occur in a wide area with its length greater than 15 km along their strike direction. Major mineral assemblages of the amphibolite are hornblende + plagioclase ${\pm}$ garnet ${\pm}$ diopside ${\pm}$ biotite ${\pm}$ quartz. Accessory rutile and ilmenite are characteristically replaced by titanite. Metamorphic temperatures and pressures estimated from the garnet - hornblende - plagioclase - quartz geothermo-barometers are 632-$736^{\circ}C$ and 7.9-11.1 kbar, respectively. Thus, the regional metamorphism of the study area belongs to the upper amphibolite facies. Furthermore, Sm-Nd and Rb-Sr data of garnet, plagioclase, and whole rock of an amphibolite define mineral isochrons of $231{\pm}30$ Ma and $222{\pm}24$ Ma, respectively, suggesting the Triassic metamorphism. These results are consistent with P-T conditions and metamorphic ages reported in the Shandong Peninsula, and support the hypothesis that the Chinese collision belt may extend into the Imjingang belt in the Korean Peninsula.

• The Journal of the Petrological Society of Korea
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• v.24 no.2
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• pp.107-124
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• 2015

The 'Imjin System' (or Rimjin System) was established in 1962 as a new stratigraphic unit separated from the Upper Paleozoic Pyeongan System based on the discovery of brachiopods and echinoderms of possible Devonian age. Subsequent discoveries of the Middle Devonian charophytes confirmed the Devonian age of the system. The Imjin System is distributed in the Imjingang Belt between the Pyongnam Basin and the Gyeonggi Massif, spans from the eastern areas including Cholwon-gun of the Gangwon Province, Gumchon-gun, Phanmun-gun, and Tosan-gun of the Hwanghaebuk Province, to the western areas of Gangryong-gun and Ongjin-gun of the Hwanghaenam Province, and includes the Yeoncheon Group (metamorphic complex) to the south. Unlike the lower Paleozoic strata in the Pyongnam Basin which solely produce marine invertebrate fossils, the Imjin System yields diverse non-marine plant and algal fossils. Brachiopods of the system are similar to those from the Devonian of the South China Block and include taxa endemic to the platform, implying a close paleogeographic affinity to the South China Block. The Imjin System is generally considered as of Middle to Late Devonian in age, although there have been suggestions that the system is of the Middle Devonian to Carboniferous in age. North Korean workers postulated that the Imjin System was deposited in the current geographic position, where the "Imjin Sea" (an extension of the South China Platform) was located during the Devonian. The Imjin System displays strong local variations in stratigraphy and its thickness. It has recently been reported that the strata are repeated and overturned by thrust faults in many exposures. The Yeoncheon Group a southward extension of the Imjin System, also experienced intense tight folding and contractional deformation. Northward decrease in metamorphic grade within the system suggests that the northern part of the Gyeonggi Massif and the Imjingang Belt are probably an extension of the Dabie-Sulu Belt between the South China and Sino-Korean blocks, and the Imjin System is an remnant of accretion resulted from the collision between the two blocks. In order to understand tectonic evolution and Paleozoic paleogeography of eastern Asia, further studies on stratigraphic, sedimentologic and tectonic evolution of the Imjin System involving scientists from the two Koreas are urgently needed.

• Economic and Environmental Geology
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• v.18 no.3
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• pp.277-288
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• 1985

Mineral composition and grain size analyses of the sandstone from the Early Jurassic Daedong Group distributed in Mungyeong, Daecheon, Kimpo and Yeoncheon areas were made for the study of provenances and depositional environments. The most of the analyses are obtained from Mungyeong area, with some preliminarly works from Daecheon, Kimpo and Yeoncheon areas. All sandstones from the study area are characterized by high content of quartz ranging from 59.8 to 87.2 percent of total constituents. Many of quartz which has rounded dust ring seems to come from aeolian sediments. Content of feldspar is very low except Daecheon area where it ranges from 1.8 to 10.0 percent. Sandstones from Mungyeong, Kimpo and Yeoncheon areas are classified as quartz and quartzose arenite/wacke, while those from Daecheon area are classified as quartzose and lithic arenite/wacke. According to the character of the sandstones, provenance could be quartzose sandstone and quartzite. Results of grain size analysis of C-M and sorting versus skewness suggest that depositional environment seems to be fluvial, while log-probability curve pattern lacustrine environment. It is hard to derive a definite conclusion of sedimentary environment by the grain size analysis.

• Economic and Environmental Geology
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• v.8 no.2
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• pp.73-87
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• 1975

Regional unconformities have been used as boundaries of major stratigraphic units in Korea. The term "synthem" has already been propsed for formal unconformity-bounded stratigraphic units of maximum magnitude (ISSC, 1974). The unconformity-based classification of the strata in the cratonic area in Korea comprises in ascending order the Kyerim, $Sangw{\check{o}}n$, $Jos{\check{o}}n$, $Py{\check{o}}ngan$, Daedong, and $Ky{\check{o}}ngsang$ Synthems, and the Cenozoic Erathem. The unconformites separating them from each other are either orogenic or epeirogenic (and vertical tectonic). The sub-$Sangw{\check{o}}n$ unconformity is a non-conformity above the basement complex in Korea. The unconformities between the $Sangw{\check{o}}n$, $Jos{\check{o}}n$, and $Py{\check{o}}ngan$ Synthems are disconformities denoting late Precambrian and Paleozoic crustal quiescence in Korea. The unconformities between the $Py{\check{o}}ngan$, Daedong, and $Ky{\check{o}}ngsang$ Synthems are angular unconformities representing Mesozoic orogenies. The bounding unconformities of the $Ky{\check{o}}ngsang$ Synthem involve non-conformable parts overlying the Jurassic and late Cretaceous granitic rocks.

• 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.