• The Journal of the Petrological Society of Korea
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• v.27 no.1
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• pp.25-36
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• 2018

The volcanic rocks around Mieukdo Island, Tongyeong, are classified as lower andesitic rocks (Jusasan Subgroup) and rhyolitic rocks (Unmunsa Subgroup), and upper andesitic rocks (Yokji Subgroup) and rhyolitic rocks (Saryang Subgroup). We confirmed their eruption timings and stratigraphic relationships, based on SHRIMP U-Pb zircon dating for zircons from major stratigraphic units of the subgroups. By the SHRIMP U-Pb dating, the samples yield the concordia ages of $88.95{\pm}0.44Ma$(n=11) in Punghwari Tuff and $82.56{\pm}0.95Ma$(n=10) in Chudo Tuff of the lower andesitic rocks, and $73.01{\pm}0.75Ma$(n=11) in Dara Andesite of the upper andesitic rocks. And then samples show a concordia age of $71.74{\pm}0.47Ma$(n=14) in Namsan rhyolite dyke of the upper rhyolitic rocks and an apparent age of $70.7{\pm}3.5Ma$ in granodiorite dyke, These data confirm the eruption or injection timings of the units and allow them to distinguish chronostratigraphy of Jusasan, Unmunsa, Yokji and Saryang Subgroups around the Mireukdo Island. In addition, the subgroups give a clue that can make a chronostratigraphical correlation with different volcanic units of the Late Cretaceous Yucheon Group in the Gyeongsang basin.

• Economic and Environmental Geology
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• v.49 no.3
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• pp.181-191
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• 2016

We estimate the eruption history and magmatic eruptive volumes of each rock units to evaluate the volcanic eruption scale and volcanic hazard of the Ulleung Island. Especially, Maljandeung Tuff represents about 19~5.6 ka B.P. from $^{14}C$ dating, and Albong Trachyandesite, about 0.005 Ma from K-Ar dating in recent age dating data. These ages reveal evidences of volcanic activities within the last 10,000 years, indicating that the Ulleung Island can classify as an active volcano with possibility of volcanic eruption near future. Accumulated DRE-corrected eruptive volume is calculated at $40.80km^3$, within only the island. The calculated volumes of each units are $3.71km^3$ in Sataegam Tuff, and $0.10km^3$ in Maljandeung Tuff but $12.39km^3$ in accounting the distal and medial part extended into southwestern Japan. Volcanic explosivity indices range 1 to 6, estimating from the volumes of each pyroclastic deposits. The colossal explosivity indices are 5 in Sataegam Tuff, and 6 in Maljandeung Tuff in accounting the distal and medial part. Therefore, it is necessary for appropriate researches regarding possibility of volcanic eruption of the island, and establishment system of the evaluation and preparation for volcanic hazard based on the researches is required.

• Journal of the Korean earth science society
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• v.41 no.4
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• pp.367-380
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• 2020

LA-MC-ICP-MS zircon U-Pb dating was conducted to constrain the timing of fossil formation and the depositional age of the uppermost Jinju Formation located in Natural Monument No. 534 (Tracksite of Pterosaurs, Birds, and Dinosaurs in Hotandong, Jinju), and 87 Cretaceous, 1 Precambrian, and 2 Jurassic zircons were obtained from 90 valid analytical points. Most Cretaceous zircons were found to have a youngest graphical peak age of ca. 106.5 Ma, suggesting the depositional age of the uppermost Jinju Formation. Based on this study and previous works, the average sedimentation rate of the Jinju Formation was calculated to be approximately 0.17-0.31 mm/year in the Milyang Subbasin, and the Cretaceous zircons of the uppermost Jinju Formation seem to have originated mainly from the western or northwestern parts of the Gyeonggi Massif. Unlike the Nakdong and Hasandong formations of the Sindong Group, most zircons analyzed in the uppermost Jinju Formation were Cretaceous. This suggests that volcanic activity occurred in the area closer to the Gyeongsang Basin due to the roll-back of subducting paleo-Pacific Plates during the Jinju period.

• Journal of The Geomorphological Association of Korea
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• v.24 no.3
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• pp.83-103
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• 2017

Sand deposit with shell units is exposed in Hasa-ri, Yeonggwang-gun, Jeonnam province. We investigated the characteristics of sand sediment topography in the Yeonggwang coastal area to collect evidence of the paleo-environmental change. We performed analysis on particle characteristics, chemical composition, and the age of deposition of sediments. The deposit comprise moderately well sorted medium and fine sand ($1.00{\sim}2.19{\varphi}$). Various sedimentary structures can be observed. Geochemical characteristics change by depth and the degree of variation with depth is small. The results obtained from OSL dating show that sand layers below shell units are deposited 0.32-0.43 ka. As the elevation of the shell unit far mean high water levels or highest high water level, the extensive shell layers could only have been deposited during storm surge conditions. Aeolian processes are discounted due to the size of clasts and the location at which they occur. Results of age dating of the surrounding deposits indicate shell deposits formed after around 300 years age. There is a distinct difference between sedimentary layers including dark brown-black layer. The sedimentary characters such as particle size and geochemistry show difference with depth. It is presumed that depositional environmental in Hasa-ri has changed several times before. This study is expected to contribute to finding an evidence about occurrence of storm surges.

• Journal of the Mineralogical Society of Korea
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• v.26 no.3
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• pp.161-174
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• 2013

The geology of the weondong deposit area consists mainly of Cambro-Ordovician and Carboniferous-Triassic formations, and intruded quartz porphyry and dyke. The skarn mineralized zone in the weondong deposit is the most prospective region for the useful W-mineral deposits. To determine the skarn-mineralization age, U-Pb SHRIMP and K-Ar age dating methods were employed. The U-Pb zircon ages of quartz porphyry intrusion (WD-A) and feldspar porphyry dyke (WD-B) are 79.37 Ma and 50.64 Ma. The K-Ar ages of coarse-grained crystalline phlogopite (WD-1), massive phlogopite (WDR-1), phlogopite coexisted with skarn minerals (WD-M), and vein type illite (WD-2) were determined as $49.1{\pm}1.1$ Ma, $49.2{\pm}1.2$ Ma, $49.9{\pm}3.6$ Ma, and $48.3{\pm}1.1$ Ma, respectively. And the ages of the high uranium zircon of hydrothermally altered quartz porphyry (WD-C) range from 59.7 to 38.7 Ma, which dependson zircon's textures affected by hydrothermal fluids. It is regarded as the effect of some hydrothermal events, which may precipitate and overgrow the high-U zircons, and happen the zircon's metamictization and dissolution-reprecipitation reactions. Based on the K-Ar age datings for the skarn minerals and field evidences, we suggest that the timing of W-skarn mineralization in weondong deposit may be about 50 Ma. However, for the accurate timing of skarn mineralization in this area, the additional researches about the sequence of superposition at the skarn minerals and geological relationship between skarn deposits and dyke should be needed in the future.

• Journal of Conservation Science
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• v.18 s.18
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• pp.97-104
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• 2006

Absolute ages for three pieces of organic materials such as wood and shell were determined with radio-carbon concentrations and two potsherds with thermoluminescence measurements. Radiocarbon contents of each sample were compared with those of modern standard oxalate(NBS SRM4990C) and calculated radiocarbon ages of them. Quartz grains with diameter of $90\sim150{\mu}m$ were extracted from potsherds and used for measuring the archaeodose. Annual dose were calculated with measuring the alpha count rates and water contents and analysing $K_2O$ concentration of both potsherds and soils. Radiocarbon ages of organic materials were in the ranges of $4\sim2C$ BC and Quartz grain techniques for thermoluminescence dating showed 170 BC ud 210 BC respectively. It was found that the results of radiocarbon dating and TL dating were accorded with each other. But the deviations of TL dating have shown 13% and 20% respectively. It need to reduce the deviations.

• Journal of the Korean Geographical Society
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• v.40 no.6 s.111
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• pp.716-729
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• 2005

In the Yeongpyeong River, one of the branches of Hantan River, there 4 fluvial terraces are identified. During the Quaternary, lava flow from Hantan River had gone 4.5km into upstream Part of the Yeongpyeong River and damed its entrance, and resultantly its lower basin had become a lava-damed paleolake. This study deals with fluvial terrace surface classification, stratigraphic analysis, deposits analysis, and OSL age dating in from Gungpyeongri to Seongdongri in lower reach of Yeongpyeong River, in order to identify Seomorphological Process of the terrace landforms relating to duration of lava-damed paleolake. Terrace surface T4, named Baekeuiri Formation, has been located under Jeongok lava layer to indicate pre-lava river bed. Terrace surfaces T3 and T2 are supposed to be formed during paleolake time, based on $3{\~}4m$ thick sand deposits including pebble and cobble layers, and clay and silt layers intersected with sand ones in nearly horizontal bedding. Terrace T1 is estimated to be formed as post-lake fluvial terrace after dissection of lava dam, based on the more fresh phase of deposits and very low height from present riverbed. The results of the OSL age dating for the T3 deposit layers indicate approximately $33{\~}40ka$, and still lake phase at that time.

• Journal of the Mineralogical Society of Korea
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• v.24 no.3
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• pp.179-188
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• 2011

In order to investigate absolute age of marine sediment in the KR5 region, northeastern Pacific, we measured the Be isotope ($^{10}Be$ and $^{9}Be$) of box core (BC08-02-13) sediment with depth. Core sediment is divided into three sedimentary facies (Facies I, Facies II, FaciesIII). Facies I mainly consists of brown to dark brown (10YR4/3) homogeneous mud with high water content. Facies II shows brownish yellow (10YR6/6) color. The unconformity is recognized at the boundary between Facies I and Facies II, Facies III consists of very dark brown (10YR2/2) mud. Many bioturbated burrows are observed at FaciesII and FaciesIII. Based on Be dating results, FaciesIII and Facies II had been deposited before 3.7 Ma and 2.3 Ma, respectively. After 2.3 Ma, the upper part of Facies II was eroded due to the change of sedimenary environment. Facies I has been deposited since 1.8 Ma. The unconformity located at the boundary between Facies I and Facies II may be driven by the envrionmental change due to the migration of Intertropical Convergence Zone.

• Economic and Environmental Geology
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• v.48 no.6
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• pp.501-508
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• 2015

The purpose of this study is to provide an inquiry into paleovegetation (paleoenvironment), eruption age and inferred emplacement temperature of pyroclastic deposit using charcoal occurred in the Quaternary Nari Caldera, Ulleung Island. In order to obtain the data, we carried out species identification and tree-ring analysis, radiocarbon dating for the charcoal. This sample was collected from pumiceous deposit in lowermost member(Member N-5) of the Nari Tephra Formation, which corresponds to the wood branch that has well preserved the tree-ring structure. Speciation and outermost tree-ring of wood reveal Picea spp. and $263+{\alpha}$ years. The calibrated ages from the center(pith) to the outermost tree-ring are $20,260{\pm}230$, $19,995{\pm}245$, and $19,975{\pm}265cal\;BP$, respectively, which are accordant with the tree-ring position. The youngest age, <19,710 cal BP would have implications for the eruptive age of Member N-5. Our results indicate that Picea spp. is the paleovegetation representing that Nari Caldera was under cold and wet climate conditions during the late Pleistocene. Based on the silky luster, brittleness, color, and streak of charcoal, etc., the lowest emplacement temperatures of pyroclastic flow are interpreted to have been at least as high as $350{\sim}500^{\circ}C$.

• Journal of the Korean Chemical Society
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• v.40 no.2
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• pp.101-108
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• 1996

The chemical characteristics and age dating of the thermal springwater developed recently in Chullabukdo were investigated. The temperature range of the thermal springwater was found 27∼29$^{\circ}C$, indicating a low temperature thermal springwater. The concentration of $F^-$ ion in the springwater was found relatively high in the range of 2∼3 ppm, but $NO_3^-$ ion was nearly not detected. The concentration range of $SO_4^{2-}$ ion was 0.02∼23 ppm, among which $SO_4^{2-}$ content of $Y_3$ was found very high compared to that of other springwater, since this site is known as a sulfur spring. $HCO_3^-$ ion content was found 2∼5 times higher than that of groundwater. $Y_1,\;Y_3,\;Y_5,\;Y_2,\;Y_4,\;and\;Y_8$, were classified as $HCO_3^-$ type, $Y_6$ as $CI^-$type, and $Y_7$, as no domonant type by classification diagram for anion and cation facies. From the results of age dating on the basis of the mean tritium level of precipitation and thermal springs, $Y_1$ was identified as the oldest thermal spring (-89 years) and $Y_7$ was identified as -89 years and $Y_7$ was -1 year using dispersive model. The results calculated by two models agreed well each other.