• Economic and Environmental Geology
• /
• v.56 no.6
• /
• pp.831-846
• /
• 2023

The Jucheon-Pyeongchang area in the northwestern Taebaeksan Zone of the Okcheon fold-thrust belt preserved several thrust faults placing the Precambrian basement granite gneisses of the Gyeonggi Massif on top of the Early Paleozoic Joseon Supergroup and the age-unknown Bangrim Group. Especially, the thrust faults in the study area show the closed-loop patterns on the map view, showing older allochthonous strata surrounded by younger autochthonous or para-autochthonous strata. These basement-involved thrusts including Klippes will provide important information on the hinterland portion of the fold-thrust belt. For defining Klippe geometry in the thrust fault terrains of the Jucheon-Pyeongchang area by older on younger relationship, the stratigraphic position of the age-unknown Bangrim Group should be determined. The Middle Cambrian maximum depositional age by the detrital zircon SHRIMP U-Pb method from this study, together with field relations and previous research results suggest that the Bangrim Group overlies the Precambrian basement rocks by nonconformity and underlies the Cambrian Yangdeok Group (Jangsan and Myobong formations). The structural geometric interpretation of the Pyeongchang area based on newly defined stratigraphy indicates that the Wungyori and Barngrim thrusts are the same folded thrust, and can be interpreted as a Klippe, having Precambrian hanging wall granite gneisses surrounded by younger Cambrian strata of the Joseon Supergroup and the Bangrim Group. Further detailed structural studies on the Jucheon-Pyeongchang area can give crucial insights into the basement-involved deformation during the structural evolution of the Okcheon Belt.

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

• The Journal of the Petrological Society of Korea
• /
• v.23 no.2
• /
• pp.105-117
• /
• 2014

The Ogcheon and Joseon Supergroups are distributed in the Bonghwajae area, Jecheon-si, Chungcheongbuk-do, Korea which is located in the northeastern fore-end of the Ogcheon Metamorphic Zone. This paper researched the geological structures based on the geometric and kinematic characteristics and the forming sequence of the major multi-deformed rock and microstructures. Most of regional foliations are not the S0 bedding but the S0-1 composite foliations defined by the preferred orientation of stretching minerals, some are recognized as the S0-1-2 composite foliations by the preferred orientation of insoluble opaque minerals and cleavage lamella. The geological structures were formed at least by three phases of deformations i.e. NNE-SSW trending D1, E-W trending D2, N-S trending D3 compressions. The S0-1 composite foliation, which shows a similar zone-distribution trend of the constitution strata of the Ogcheon and Joseon Supergroups, trended WNW before D2 deformation, but it was reoriented into N-S which was parallel to the trend of S2 foliation by D2 deformation, and it was rearranged into NW, NE, N-S trends as it is now by D3 deformation. The structural characteristics of each deformation phase and the deformation history are very similar to those in the eastern domain of Busan area into which the Ogcheon and Joseon Supergroups in this area are extended as NNW trend. It is expected to be very valuable data in interpreting the tectonic evolution of the northeastern fore-end of the Ogcheon Metamorphic Zone.

• The Korean Journal of Petroleum Geology
• /
• v.5 no.1_2 s.6
• /
• pp.16-26
• /
• 1997

The Yemi Breccia has been reported as a separate formation near Yemi area, Kangwondo. This formation overlies the Maggot Formation of the Joseon Supergroup unconformably, and is overlain by the Goseong Shale conformably. Based on the field observation and textural examination of the Yemi Breccia, the breccia beds are interpreted as soluton-collapse breccia beds, which were formed by the dissolution of the pre-existing evaporites. The evaporites were precipitated during the deposition of the upper part of the Maggot Formation. Therefore, the Yemi Breccia should not be regarded as a separate formation, instead, it should be considered to be a upper part of the Maggot Formation. This implies that the overlying Goseong Shale and Goseong Limestone can be correlated with the Jigunsan and Duwibong Formtions, respectively.

• The Journal of the Petrological Society of Korea
• /
• v.24 no.4
• /
• pp.291-305
• /
• 2015

Microbialites are defined as rocks formed by microbial organisms. After their first appearance around 3.5 billion years ago, microbialites occur in various depositional environments throughout geological periods. Microbial organisms form microbialites by trapping and binding detrital sediments and/or precipitating carbonate cements, resulting in formation of various microstructures and mesostructures. Four major types of microbialites are distinguished based on their mesostructures: stromatolite, thrombolite, dendrolite, and leiolite. In the geological records, occurrences of microbialites are influenced by calcium carbonate saturation of seawater and interaction of microbialites with metazoans. Stromatolites mainly flourished during the Precambrian, and diminished as level of atmospheric carbon dioxide declined. On the other hand, thrombolites, mainly formed by calcified microbes, began to flourish from the Neoproterozoic. As metazoans diversified in the Phanerozoic, proportion of the microbialites within sedimentary record declined. Since then, microbialites only occasionally flourished during the Phanerozoic, such as shortly after mass-extinction events. In the Korean Peninsula, microbialites occur in the Neoproterozoic Sangwon System, the Early Paleozoic Joseon Supergroup, and the Cretaceous Gyeongsang Supergroup, which form different shapes according to their age and depositional environments. By performing detailed studies on these Korean microbialites, it is possible to understand how microbes affected geological records and sedimentary environments, as well as their interaction with other organisms.

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

• Economic and Environmental Geology
• /
• v.49 no.3
• /
• pp.167-179
• /
• 2016

Water quality of Oseepchun, Dogye area, was investigated quantitatively for its origin and hydrogeochemistry in relation to the influence of groundwater. Groundwater appears to be the principal source of Oseepchun from the water-quality monitoring data including redox potentials, composition of dissolved ions and their correlations, hydrogen and oxygen stable isotopic ratios, and the distribution and occurrence of contaminants. Water-quality type of the surface water was grouped by the water-rock interactions as $Ca-HCO_3$ type originated from carbonated bed-rocks in the Joseon Supergroup, (Ca, Mg)-$SO_4$ type related with dissolution of surfide minerals in coal beds of Pyeongan Supergroup, and (Ca, Mg)-($HCO_3$, $SO_4$) type of the mixed one. Locally water pollution occurs by high $SO_4$ from mine drainage and $NO_3$ from waste-treatment facility. Intensive precipitation in summer has no effect on the water type of Oseepchun, but increases the inflow of nitrate and chloride originated from land surface. Results of this study direct that groundwater-surface water interaction is intimate, and thus surface-water resource management should begin with groundwater characterization.

• Journal of the Korean earth science society
• /
• v.42 no.2
• /
• pp.175-184
• /
• 2021

Fold axis of fold, a representative ductile deformation structure, is important for collecting information on the 3D fold structure and the orientation of maximum horizontal principal stress at the time of deformation. For this reason, several fold axis measurement methods based on the fold-related structural elements have been suggested and used even in areas where it is impossible to measure it directly. Thus, these various measurement methods are briefly introduced here, and the measured data with different methods are compared to estimate these methods' reliability. For this purpose, we acquired fold axes at six sites across the Manhang formation of the Pyeongan supergroup and limestones of the Joseon supergroup in Danyang, Chungcheongbuk-do, where fold structures are well developed. The data from the different methods are generally consistent, indicating practical applicability. Most of the fold axes from the measured sites show NNNE or NE trends indicating WNW-ESE or NW-SE trending maximum horizontal principal stress, except for the one site with a WNW trend. The WNW-ESE trending fold axis might be related to a different orogeny or secondary folding. The minor difference in the trends between N-NNE and NE was interpreted as being due to different scale; however, further research is needed to confirm this.

• Journal of the Korean earth science society
• /
• v.28 no.3
• /
• pp.367-373
• /
• 2007

A geoacoustic modeling has been developed to predict sound transmission through the submarine layers of sediment and rock. It demands a geoacoustic model with the measured, extrapolated, and predicted values of geoacoustic parameters controlling acoustic propagation. In the coastal areas of Okgye and Bukpyeong, the East Sea, the marine succession consists of Quaternary/Tertiary deposits and acoustic basement. The basement of Okgye coastal area is indicative of siliciclastics of the Pyeongan Group in Paleozoic, and the average velocities of P-wave and S-wave are 4276 m/s and 2400 m/s, respectively. The basement of Bukpyeong coastal area is indicative of limestone of the Joseon Supergroup in early Paleozoic, and the average velocities of P-wave and S-wave are 5542 m/s and 2742 m/s, respectively.

• Journal of the Mineralogical Society of Korea
• /
• v.9 no.1
• /
• pp.1-6
• /
• 1996

Woolastonite from Susan occurs as intercalations in limestone beds of Lower Paleozoic Joseon Supergroup. It is a thermal metamorphic product of impure limestone. Electron microprobe analysis shows that it is considerably pure wollastonite. It has triclinic cell with a=7.932$\AA$, b=7.328$\AA$, c=7.069$\AA$, $\alpha$=89.995$^{\circ}$, $\beta$=$95.255^{\circ}$, and $ \Upsilon=103.367^{\circ}$.Dissolution behaviors of wollastonite have been studied conducting three different dissolution experiments; two different reactions with HC1 (one batch and one re-initialization experiment) and one traction with distilled water. In the batch type powder wollastonite-HCl reaction, pH of solution rapidly increases in the early stage and then its rate of increase slows down to reach plateau resulting in parabolic relationship with time. It is represented by the early rapid rise and fall in pH giving a sharp pH-edge and succeeding slow rise in the re-initialization experiment. The early rapid rise in pH is due to the rapid sorption of H- in solution to oxygens on the reactive surface of wollastonite and the fall in pH means that all reactive surface sites are occupied by H- ions and no more H- adsorption occurs. The slow rise in pH following the pH- edge is due to the dissolution of wollastonite as evidenced by the correlation of pH variation and cation concentration. Dissolution of powder wollastonite in HCl shows linear trend with time. Si is dissolved predominantly over Ca at a constant rate. Ca is dissolved predominantly in the very early stage. Dissolution rate of coarse-grained wollastonite fragments in distilled water is parabolic with times howing a rapid reaction in the early stage and a slow reaction in the advanced stage. The Ca/Si ratio in solution is high in the case of coarse-grained wollastonite fragment as compared with powder wollastonite. The coarse-grained wollastonite fragment-water (acid) reaction resulted in the solution with an elevated constant pH value (alkaline) giving an important significance on the environmental view point.