• The Journal of the Petrological Society of Korea
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• v.26 no.1
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• pp.73-82
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• 2017

We determined SHRIMP U-Pb ages of the detrital zircons separated from the Bangnim Group of the Pyeongchang area to constrain its depositional age. As the result, the minimum age group yielded $^{206}Pb/^{238}U$ age of $450.3{\pm}4.2Ma$ (n=3), suggesting depositional age younger than Late Ordovician. Therefore, the Bangnim Group cannot be a Precambrian sedimentary formation but is younger than Myobong Formation of the Early Paleozoic Joseon Supergroup of the Taebaeksan basin. Such a depositional age implies that the Bangnim Group and structurally overlying Jangsan Quartzite should be in fault contact, suggesting that the Jangsan Quartzite, Myobong Formation and Pungchon Limestone thrusted over the Bangnim Group. The zircon U-Pb age distribution pattern of the Bangnim Group resembles those of the Early Paleozoic Myobong and Sambangsan Formations of the Taebaeksan basin and seemingly Middle Paleozoic Daehyangsan Quartzite and the Taean Formation. However, detrital zircon U-Pb age patterns of the Late Paleozoic Pyeongan Supergroup are quite distinct from them, suggesting drastic change in provenance of the detrital zircon supply. Therefore, we suggest that the Bangnim Group was deposited before the Pyeongan Supergroup.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.11a
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• pp.21-38
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• 1999

• Economic and Environmental Geology
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• v.49 no.5
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• pp.349-360
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• 2016

This study determined mineralogical characteristics and discussed the meaning of mineralogical changes of the lower Choseon Supergrouop in the Weondong area based on the field geological investigation and the drilling core description using X-ray diffraction (XRD) mineral quantification and Scanning Electron Microscopy (SEM) observation. 100 samples with depth were collected from the core (250 m long) at a site in the study area. Especially, to investigate the changes from the upper Daegi Formation to the lower Hwajeol Formation, the samples were collected closely with the interval of about 0.3 m at this section. All samples were made into power using mortar for XRD. Mineral quantitative analysis was executed using Relative Intensity Ratio (RIR) method with corundum as an internal standard phase. Calcite, $2M_1$ illite and quartz are main constituents in most of samples. Dolomite and siderite are significantly observed in the Sesong Formation. As the results of quantitative analysis for the major minerals, the upper Daegi Formation is dominated by calcite with over 80%. The Sesong Formation includes high percentage of dolomite and siderite with the intercalation of thin layers containing high calcite and $2M_1$ illite contents. Hwajeol Formation is characterized by the alternation between thin layers of $2M_1$ illite and quartz-dominated layer (IQDL) and calcite-dominated layer (CDL). IQDL is more frequent in the lower part, whereas CDL is more common in the upper part. The boundary between Daegi Formation and the Sesong Formation is distinct, whereas the boundary between the Sesong Formation and the Hwajeol Formation tends to be changed gradually in mineralogy. The result of SEM observation shows that quartz and $2M_1$ illite are detrital, and a significant amount of calcite also shows detrital form with some recrystallized one, indicating that the repeated influx of terrestrial materials had changed the mineralogy of the shallow sea depositional environment in the early Paleozoic era.

• Economic and Environmental Geology
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• v.43 no.6
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• pp.637-648
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• 2010

The Songbong Formation (so-called Bangrim Group), correated to the lower part of Choseon Supergroup, unconformably overlies the Precambrian Gyeonggi massif at northeastem tip of the Ogcheon belt The contact relationship between the Choseon Supergroup and the Yeongnam massif is also known as an unconformity at northeastem part of the Ogcheon belt. lt implies that the Gyeonggi and Yeongnam massifs were probably connected each other before the Early Paleozoic. Three deformational phases are recognized in the study area, The first phase is the north-northeastward ductile thrusting, which places Precambrian granite of the Gyeonggi massif over the Paleozoic rocks of the Ogcheon belt. The second phase is characterized by the southeastward thrusting and deformation partitioning along the Nuruhaji compartment fault. The third phase is the reactivation of the Nuruhaji Fault into dextral strike-slip fault with over a few kilometers displacement.

• 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.

• The Journal of the Petrological Society of Korea
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• v.27 no.1
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• pp.67-72
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• 2018

The K-Ar ages of a sericite quartz schist in the lower Jangsan Formation along the Okdong fault zone reported by Yun (1983) have attracted attention again because of their potential to constrain the depositional timing of the Jangsan Formation. The oldest age of $562{\pm}2Ma$ among three reported K-Ar ages in the schist led to the claim that the depositional period of the lowermost Jangsan Formation in the Joseon Supergroup is late Neoproterozoic. Its depositional age is important for understanding the tectonic evolution of the Korean Peninsula including the formation and evolution histories of its sedimentary basins. Thus, the reliability and geological meaning of three K-Ar ages in the original paper (Yun, 1983) were revisited in the review. Quartz grains in the analyzed sample contain a considerable amount of excess Ar, and therefore it is inappropriate to use the ages as a basis for a depositional age constraint of the Jangsan Formation. The timing of mylonitization in the schist is recalculated as ~170 Ma.

• Economic and Environmental Geology
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• v.52 no.1
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• pp.49-64
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• 2019

SHRIMP U-Pb ages were analyzed for the detrital zircons separated from the Jangsan Formation of the Lower Paleozoic Joseon Supergroup in the Taebaeksan Basin and the Mungyeong area. Similar to the previously reported from Taebaeksan basin, the detrital zircons show strong peaks near the age of about 1.8-2.0 Ga and about 2.5 Ga. This indicates that the detrital zircons of the Jangsan Formation originated from the basement rocks of the Korean Peninsula. Although the age of the basement rocks on the Korean Peninsula is mainly concentrated in the 1.8-2.0 Ga, the age of about 2.5 Ga is clearly visible in the Jangsan Formation, suggesting that the age distribution of the basement rocks exposed to the surface at that time may be somewhat different from now. The detrital zircons of age-unknown Geumsusan Formation distributed between Danyang and Jecheon also show the U-Pb age distribution with a strong peaks around 1.8-2.0 Ga and 2.5 Ga, which is very similar to that of the Jangsan Formation, suggesting a possibility that the two formations are likely to be correlated.

• Economic and Environmental Geology
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• v.49 no.6
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• pp.433-444
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• 2016

The U-Pb ages of detrital zircons from the Baengnyeong Group were determined by LA-MC-ICPMS, yielding condensed age population in the range from 1100 Ma to 1800 Ma corresponding to the Mesoproterozoic to late Paleoproterozoic. However, detrital zircons of ca.1800-2000 Ma or ca. 2500 Ma ages, which appear frequently in the lower Paleozoic Joseon Supergroup and the upper Paleozoic Pyeongan Supergroup are lacking in the Baengnyeong Group. Such characteristics are identical to those of the Neoproterozoic Sangwon System of North Korea, suggesting that the Baengnyeong Group might be the southwestern extension of the Sangwon System. The zircon age distribution patterns from the Impi Formation in the Gunsan area closely resemble those of the Baengnyeong Group, implying possible correlation of the Impi Formation to the Sangwon System. Therefore, the Mesoproterozoic detrital zircons reported from the Hwangangni Formation of the Okcheon Metamorphic Belt and the Myobong, Sambangsan and Sesong Formations of the Taebaeksan Basin might be derived from the provenances within the Korean peninsula.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2002.10a
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• pp.17-30
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• 2002

삼척-도계지역 일대에 분포하는 조선누층군의 풍촌층 석회석은 품위 및 암상에따라 상부고품위대와 하부석회암대로 분대가 가능한데, 이는 삼척-태백간을 북북동으로 흐르는 오십천을 경계로 서쪽에 분포하는 풍촌층과 비교할 때 다소간의 암상차이를 보인다. 즉, 풍촌층의 특징중에 하나인 중부백운암대가 본 역 일대에서는 백운암화가 미약하여 비교적 소폭으로 확인되며, 상부백색대 역시, 발달정도가 미약한 특징을 보인다. 시추탐사결과 확인된 삼척-도계지역의 풍촌층 상부고품위대는 일반적으로 상부백색대$(\pm15m)$ - 백운암대$(\pm5m)$ - 암회색대$(\pm50m)$로 구분되는 것으로 나타났다. 각각의 품위는 상부백색대 : CaO $53_4\~55.6\%$, 백운암대 : MgO $3.0\~18.4\%$, 암회색대 : CaO $50.4\~54.2\%$로 나타나 제철용으로의 사용이 가능하나 백운암대에 대한 선별채광이 부분적으로 요망된다. 이들 석회석은 오십천대단층의 수반단층인 수조의 NNE계열 정단층들에 의해 빈번히 단절되어 있으며 일부지역에서는 EW향의 역단층에 의해 규제되기도 한다. 상기 제단층들은 석회암층을 단절시킬 뿐만 아니라 단층각력, 단층점토, 암맥 등의 불순대를 수반하므로 개발에 장애요소가 되고 있다. 상부고품위대 부존표고는 지역에 따라 다소 차이가 있으나 200ML 내외에서 대부분 확인이 가능하며 지표노출 규모는 작은 편이나 $10^{\circ}$이하의 완경사로 화절층 하부에 부존되어 있어 갱도 채광에 적합한 형태를 이루고 있다.

• Proceedings of the KSEEG Conference
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• 2002.10a
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• pp.17-30
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• 2002

삼척-도계지역 일대에 분포하는 조선누층군의 풍촌층 석회석은 품위 및 암상에따라 상부고품위대와 하부석회암대로 분대가 가능한데, 이는 삼척-태백간을 북북동으로 흐르는 오십천을 경계로 서쪽에 분포하는 풍촌층과 비교할 때 다소간의 암상차이를 보인다. 즉, 풍촌층의 특징중에 하나인 중부백운암대가 본 역 일대에서는 백운암화가 미약하여 비교적 소폭으로 확인되며, 상부백색대 역시, 발달정도가 미약한 특징을 보인다. 시추탐사결과 확인된 삼척-도계지역의 풍촌층 상부고품위대는 일반적으로 상부백색대($\pm$15m) - 백운암대($\pm$15m) - 암회색대($\pm$50m)로 구분되는 것으로 나타났다. 각각의 품위는 상부백색대 : CaO 53.4~55.6%, 백운암대 : MgO 3.0~l8.4%, 암회색대 : CaO 50.4~54.2%로 나타나 제철용으로의 사용이 가능하나 백운암대에 대한 선별채광이 부분적으로 요망된다. 이들 석회석은 오십천대단층의 수반단층인 수조의 NNE계열 정단층들에 의해 빈번히 단절되어 있으며 일부지역에서는 EW향의 역단층에 의해 규제되기도 한다. 상기 제단층들은 석회암층을 단절시킬 뿐만아니라 단층각력, 단층점토, 암맥 등의 불순대를 수반하므로 개발에 장애요소가 되고 있다. 상부고품위대 부존표고는 지역에 따라 다소 차이가 있으나 200ML 내외에서 대부분 확인이 가능하며 지표노출 규모는 작은 편이나 $10^{\circ}$이하의 완경사로 화절층 하부에 부존되어 있어 갱도 채광에 적합한 형태를 이루고 있다.