• The Journal of the Petrological Society of Korea
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• v.2 no.1
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• pp.1-8
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• 1993

We report on kyanite newly found in the Yongduri gneiss complex of the Chuncheon-Hongcheon area, central Gyeonggi massif. Major mineral assemblage of quartzofeldspathic gneisses in the study area consists of biotite+ garnet+ sillimanite + plagioclase+ quartz${\pm}$kyanite${\pm}$K-feldspar${\pm}$muscovite. Kyanite occurs in four samples, and coexists with sillimanite in three of these samples. In most cases, kyanite is anhedral to subhedral, ranges up to Imm in the maximum dimension, and occurs as metastable relict grains. These observations indicate that the Yongduri gneiss complex has experienced a medium-pressure type metamorphism, followed by low-pressure type one belonging to the sillimanite+K-feldspar zone. Average temperature and pressure of the peak metamorphism are $683{\pm}62^{\circ}C$ and 4.9-5.5 kbar, respectively, when the existing chemical data are re-interpreted. In conjunction with the finding of kyanite in the Cheongpyeong-Gapyeong area (Lee and Cho, 19921, this study demonstrates that kyanite may occur regionally in central Gyeonggi gneiss complex. Moreover, the persistence of kyanite even after the high-T metamorphism of the sillimanitetK-feldspar zone suggests that the central Gyeonggi massif has experienced a tectonometamorphic evolution characterized by a rapid uplift.

• The Journal of the Petrological Society of Korea
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• v.2 no.2
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• pp.95-103
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• 1993

The geology of the talc ore deposits in the Chungju area consists of the Kyemyeongsan Formation, the Munjuri Formation, the Daehyangsan Quartzite, the Hyangsanni Dolomite, and the basic rocks of the Ogcheon belt. The talc ore occurs in the Hyangsanni Dolomite near the Daehyangsan Quartzite The mineral assemblages in the Hyangsanni Dolomite are \circled1calcite-tremolite-talc-quartz, \circled2calcite-talc-quartz, \circled3tremolite-calcite-dolomite, and \circled4calcite-dolomite-phlogopite-chlorite. Talc has almost the ideal composition($X_{Mg}$=Mg/(Fe+Mg)=0.98). Talc was formed in siliceous dolomite by the medium-pressure type regional metamorphism. The evidences for contact metamorphism and/or hydrothermal reaction are not clear. The metamorphic grade of the Hyangsanni Dolomite and its adjacent pelitic or basic rocks near the deposits corresponds to epidote-amphibolite facies or greenschist facies based on the, mineral assemblages of \circled1hornblendebiotite-muscovite-epidote-quartz \circled2biotite-chlorite-quartz, and \circled3hornblende-actinolite-plagioclasequartz. The formation of the talc deposits were caused by the following reactions due to greenschist facies metamorphism of siliceous-dolomitic rocks in the Hyansanni Dolomite. (I) 3 dolomite+4 quartz+$H_2O$= talc+ 3 calcite +3 $CO_2$; (11) 3 tremolite+ 2 $H_2O$+ 6 $CO_2$= 5 talc+ 6 calcite + 4 quartz. The minimum temperature of the talc-tremolite-quartz assemblage is about $434^{\circ}C$ from calcite thermometry and the carbon dioxide mole fraction in metamorphic fulid($X_{$CO_2$}$) is about 0.1 at assumed pressure, 3 kbar.

• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.52-65
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• 1996

Precambrian metamorphic rocks of the Cheongpyeong-Yangpyeong area, central Gyeonggi massif, comprise gneiss, schist, quartzite and amphibolite. Mineral, assemblages of pelitic gneisses are characterized by biotite + cordierite + garnet + sillimanite + K-feldspar + plagioclase + quartz together with minor muscovite, spinel and corundum, and represent the granulite facies metamorphism. In particular, kyanite occurs as fine-grained relict phase inside plagioclase of three gneiss samples. Metamorphic conditions are estimated from garnet-biotite and garnet-cordierite geothermometers in conjunction with garnet-$Al_2SiO_5$-quartz-plagioclase (GASP) and garnet-rutile-$Al_2SiO_5$-ilmenite (GRAIL) geobarometers. They are 700-$850^{\circ}C$ and 3.2-8.3 kbar, and 580-$690^{\circ}C$ and 2.1-3.2 kbar, respectively, when the core and rim compositions of garnet are use. Garnet of the GASP assemblage increases rimward in the Fe and Mn contents but decreases in the Mg content, whereas its Ca content does not vary significantly. Together with the occurrence of relict kyanite and the result of P-T estimates, compositional zoning patterns of garnet indicate a clockwise P-T history. Moreover, the preservation of high-pressure minerals such as kyanite in plagiocalse, even after the medium-pressure granulite facies metamorphis, suggests a rapid change in P-T conditions.

• Korean Journal of Ecology and Environment
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• v.41 no.3
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• pp.367-373
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• 2008

A freshwater bivalve (Unio douglasiae) was examined to assess the filtering rate (FR) on the cyanobacterial assemblage in a hypertrophic lake. Animal U. douglasiae used in the present study was collected using a hand-operated dredge from the North Han River (Gapyeong, Korea). The FR was measured at different feeding conditions such as feeding interval (1, 4, 7, and 24 h), mussel size (4.2$\sim$8.1 cm, n=23), prey concentration (506.7, 409.8, 327.5, 199.7 and 88.6 ${\mu}g\;L^{-1}$), and mussel density (0.5, 1.0 and 1.5 indiv. $L^{-1}$). On the applied feeding interval, the maximum FR (0.21 L $g^{-1}h^{-1}$) and minimum feces production (FP, 0.12 mg $g^{-1}h^{-1}$) were observed at 1 and 24 hr, respectively. Both weight-based FR and FP were not correlated with the mussel size, and the values lied in a limited range with some degree of variation. Likewise, no significant relations between FR and FP were observed in the mussel size. The FR values were negatively correlated with food concentration, but positively with FP. For the food concentrations, the maximum FR (0.41 L $g^{-1}h^{-1}$) and FP (0.16 mg $g^{-1}h^{-1}$) were 88.6 ${\mu}gL^{-1}$ and 327.5 ${\mu}gL^{-1}$, respectively. These results indicate that U. douglasiae collected from the North Han River, although the filtering rate were slightly less than Keum River mussel, may be applied as a strategic bio-filter to mitigate cyanobacterial bloom in eutrophic lake.

• Korean Journal of Ecology and Environment
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• v.53 no.2
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• pp.148-155
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• 2020

In this study, we analyzed the effects of the presence or absence of weirs on fish assemblages in wadeable streams (Stream order 1^st~4^th). More specifically, we investigated these effects by evaluating the differences in stream size. The results showed differences in the fish assemblages in third or higher order streams (PERMANOVA, P<0.005). The presence or absence of weirs mainly affected variables such as the number of species the individuals, and species richness index, whereas no difference was observed in the populations of exotic, endemic, and endangered species. A SIMPER analysis showed that the common species Zacco platypus, Zacco koreanus, and Pungtungia herzi are dominant in their corresponding streams (contribution>5%), and that these are the main contributors to differences among the fish assemblages. All these species showed high relative abundances at the sites with weirs. Altered environments by the presence of weirs provided these species with concentrated habitats. In summary, this study analyzed the effects of weirs on fish assemblages on a broad, nationwide, scale, and these results can effectively aid future studies on the specific effects of weirs.

• Korean Journal of Environmental Biology
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• v.37 no.2
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• pp.204-216
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• 2019

To evaluate the biological integrity of aquatic ecosystems, we developed Korean multimetric diatom index (KMDI) using metrics that many researchers have been previously described, and compared to single-metric diatom index such as trophic diatom index (TDI) and diatom assemblage index to organic pollution (DAIpo). For the biological and environmental data, we investigated the epilithic diatoms, water quality and the land-use for 923 sites in Korean streams between 2013-2017, and estuaries between 2010-2017, respectively. Five appropriate metrics were selected according to the following steps; 1) extraction of 300 potential metrics (biological, chemical, physical, and geographical) based on previous references, of these, 2) 46 samples having high separation power were selected, 3) the selected metrics were each tested for variability, redundancy, and sensitivity to the environments, finally 4) construction of multi-metric diatom index comprising single type metrics such as TDI, DAIpo, % motile diatoms, % Achnanthes / (Achnanthes+Navicula), and % number of Gomphonema species. The biological integrity of the 233 sites from the Geum River basin were independently investigated using KMDI. Collectively, the new KMDI showed high sensitivity and explanatory power for environmental factors such as land-use, biochemical oxygen demand, total nitrogen, and electric conductivity. However, it had slightly higher biological integrity for the same sites as compared to single type diatom metrics. Finally, more data accumulation from all over Korea and the development of acceptable diatom metrics were required.

• 한국해양학회지
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• v.28 no.3
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• pp.241-258
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• 1993

To investigate the sedimentary environments on the coastal areas of Imja to Nakweol islands which show very complex shorelines and several zonal sand ridges in NE-SW direction, southwestern coast of Korea, a total of forty samples were taken by a grab sampler and sedimentological and micropaleontological studies on those samples were carried out. The present study area are classified into muddy sandy gravel, sand, city sand, sandy silt and silt facies. With statistical moment parameters such as mean, sorting, skewness and ketosis for the sediments in the study area, the sediments are generally categorized as shallow sedimentary facies. The characters that are observed in quartz grains among the sandy sediments of the study area imply the existence of high energy environments, temporal exposures in atmosphere and the mixing of clastic sediments of the several different origins. In the sediments of the study area, one genera belonging to six silicoflagellata species and five genera belonging to five nannoplankton species were detected. On the basis of the micro-organism assemblage, the study area seems to be influenced by active reworking dominantly under warm water masses. In addition, organic matter ad carbonate contents in the sediments did not show a definite relation with the occurrences of the micro-organisms in the study area.

• Korean Journal of Ichthyology
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• v.28 no.2
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• pp.100-109
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• 2016

Species composition and distribution characteristics of fish were determined by monthly underwater visual census from September. 2013 to August, 2014 at Yeongunri off Tongyeong, Korea. The study area was divided into five habitat types by depth and substrate: (1) sand bottom as depth of 0~2 m, (2) seagrass bed of 2~5 m, (3) rocky outcrop of 0~2 m, (4) rocky bottom of 2~5 m, (5) sandy mud bottom of 5~8 m. A total of 1,673 individuals belonging to 43 species in 26 families were recorded during the study period. The number of species tended to decrease after October, 2013 and increase from March, 2014 showing the highest number in October (autumn), and lowest in January (winter). In terms of the number of species, Gobiidae was the most dominant family (7 species), followed by Scorpaenidae (4 species). Embiotocidae was the most abundant (26.1% in total number of individuals), followed by Scorpaenidae (19.9%) and Gobiidae (19.3%). The dominant species were Sebastes inermis (19.2%), Ditrema temminckii (13.1%), and Neoditrema ransonnetii (12.9%). The number of species and abundance were relatively high at the depth between 2 and 5 m on seagrass bed and rocky bottom, whereas they were lower at the depth between 0 and 2 m on the sand bottom, suggesting that seagrass beds and rocky bottoms provided the diverse habitats for various fish species in this sea.

• Journal of the Mineralogical Society of Korea
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• v.28 no.3
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• pp.221-231
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• 2015

Precambrian Jirisan gneiss complex suffered retrograde metamorphism ranging from granulite facies to the amphibolite facies and/or greenschist facies. Intrusive anorthositic rocks in gneiss complex are influenced by late metamorphism. Mafic mineral in anorthositic rock composed mainly of amphiboles, which can anticipate the information about metamorphic conditions and metamorphic facies. Amphiboles from anorthositic rock show subhedral to anhedral in shape and mostly blueish green and/or green in colour in plane polarized light. Some of brownish amphiboles show zonal texture with brownish to blueish green in color from core to rim. Reaction parts in clinopyroxene which exchange with amphibole. It suggests retrograde metamorphism and/or alteration. Amphiboles composing anorthositic rocks can be classified into two types depending on the size and occurrence of amphibole. The first type is microcrystalline amphibole occurring matrix [Group I: ferrohornblende]. The second type is amphibole with 1 mm or larger in size, which is usually occurred in the boundary between opaque mineral and plagioclase [Group II: ferropargasite]. Electron microscopic analyses base on the $Al^{vi}$ composition in amphiboles suggest that the metamorphic pressure of anorthositic rock was low with 5 kbar or less. Ti compositional range in amphibole and representing hornblende+ plagioclase+garnet+biotite+chlorite mineral assemblage suggest that metamorphic facies of anorthositic rock is in amphibolite facies.

• Journal of the Mineralogical Society of Korea
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• v.21 no.1
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• pp.67-83
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• 2008

The sericite ore deposits formed in the Precambrian granitic rock at the Bonghwa area, Kyungsangbuk-do, South Korea. The geochemical and mineralogical characteristics of sericite occurred in Daehyun and Seonghwang mine were analyzed using petrographic microscope, XRD, EPMA, XRF and ICP. An alteration mechanism was also studied. Sericitization occurred within the granitic rock by hydrothermal alteration. From the careful study on the occurrence and mineral assemblage, four alteration zone were clearly identified. These zones reflect progressive hydrothermal alteration process. All sericites belong to $2M_1$ polytype and their mineralogical and geochemical properties are close to illite. The sericite ores show various colors, but the characteristics of major element compositions and crystal structures are not different. The trace element analysis, however, indicates that the difference in color attribute to the abundance of Cr and Ti: bluish green colored sericite are enriched in Cr and blackish green colored sericite enriched in Ti. The formation of sericite ore deposit in the granitic rocks are closely relate to fracture system such as fault and joint. It is considered that the sericite ore deposits in this area were formed by very simple hydrothermal alteration occurred along the fracture zones in granitic rocks with absence of other hydrothermally altered minerals such as kaolin and pyrophyllite.