• Economic and Environmental Geology
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• v.43 no.4
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• pp.333-341
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• 2010

Fluvial sediments are widely distributed in present and old river-beds of the mid-Keum River, the tributaries of which are the Yugu and Jeongan Rivers. The basement of the mid-Keum River area consists of Mesozoic granites which are easily eroded compared to Precambrian gneisses, which are exposed in the upper-Keum River area. The provenance of the fluvial sediments includes both the Precambrian gneisses and Mesozoic granites, which occur in the catchment of the mid-Keum River. The coarse-grained sediments were probably transported from the river-beds and the overbank floodings of the main Keum River and its tributaries when the climate was warm and wet. The oldest mud deposits were dated at ca. 9,400 yr BP by the radiocarbon method. It has been estimated that the sand deposits below the dated muds were formed in a period from the Late Pleistocene to the Early Holocene. However we have revealed that the major part of the present river-bed sediments was formed at ca. 3,000-6,000 yr BP, i.e., in the mid- to late Holocene, when summer monsoon was very strong due to climatic changes. We have calculated fluvial sedimentation rates of 0.12-0.16 cm/yr and 0.02-0.09 cm/yr for borehole KJ-29 river-bed sediments and borehole KJ-28 floodplain deposits, respectively. We conclude that the sedimentation rate is higher near the present stream channel than near the floodplain.

• Economic and Environmental Geology
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• v.45 no.4
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• pp.407-429
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• 2012

There has been much debates on the geologic age of the sediments of the Domi Basin, since age results varied after research methods and fossil groups. This study carried out palynological analysis and seismic interpretation to establish a stratigraphy and environmental reconstruction mainly based on fossil dinoflagellates and Seismic data from the Domi-1 and Sora-1 wells. The dinocyst assemblages found enabled zonation of the well sediment sequence resulting in 4 ecozones. Index fossils among dinocysts and palynomorphic substances indicate geologic age of the well ranges from Eocene to Pleistocene, and paleoenvironment varies from freshwater to inner-neritic marine. The fossil association also suggests strong relationship to Japanese Tertiary basins in Kyushu area in terms of stratigraphy and basin developmental history.

• Economic and Environmental Geology
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• v.15 no.4
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• pp.177-188
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• 1982

The Chungju and Seosan Groups have been known usually as Precambrian formations in Korea. But their relative and absolute ages have been controvericial problem in relation with other geologic system such as so-called Ogcheon and Yeoncheon Systems in Korea. This study has mainly focused on the corelation of the Chungju Group with the Seosan Group in their stratigraphy, structure, metamorphism, and iron ore deposits. In the process of study, the auther surveyed and reclassified the Chungju and Seosan Groups and corelated with Gyeonggi and Ogch cheon metamorphic belts and got some new data. The Chungju iron-bearing formations showing transtitional relation with the Gyeonggi Gneiss Complex and the Jangamri Formation consisting mainly of pebble bearing calcarious phyllite, should be seperated from the Gyemyeongsan formation which is mainly composed of metavolcanic rocks. The Jangamri Formation and the coaly phyllite, which can be corelated respectively with the Hwaggangri Formation and Changri Formation in Ogcheon Group, are repeated in the Gyemyeonsan and Munjuri Formations with the overturned anticlinal folding(F1). So the Chungju Group which was defined as an indipendant geologic unit from the Ogcheon Group should be limited only on the Chungju iron Formation. The Seosan Group can be classified stratigraphically such as Seosan Formation consisting of iron-bearing quartzite and mica schist, Daesan Formation overlying unconformably on the Seosan Formation and Gyeonggi Gneiss Complex. Taean Formation overlying unconformably on the Daesan Formation should be seperated from Seosan Group. There are many similarity in the stratigrphy, structure, and metamorphic facies between Chungju and Seosan Groups exept the metavolcanic rocks in the Gyemyeongsan and Munjuri Formations and the pebble bearing calcareous phyllite in the Jangamri Formation. The two Groups were deformed with two kinds of differant stages, the first shows $N30^{\circ}-40^{\circ}E$ trend of fold axis, the second $N70^{\circ}-80^{\circ}W$ respectively. The Seosan Formation, which is the lowest formation in Seosan Group and bearing the iron formation, was metamorphosed at 2500 m. y. before. These age is similar with the metamorphic age of Gyeonggi metamorphic belt and with the age of Algoman and Kenoran Orogenies which devide the Precambrian into Archean and Proterozoic Era. So the Seosan Formation, which is included in some migmatitic rocks of Gyeonggi Gneiss Complex, is the oldest formation in Korea and can be corelated with the Anshan Group which bears the oldest iron formation in China. The metamorphic facies of the Precambrian metamorphism in Seosan area is simillar with that of Chungju area, showing high temperature-low pressure amphibolite facies which is corelated with the Gyeonggi metamorphic belt, the oldest metamorphic belt in Korea ($650^{\circ}-680^{\circ}C$, 3.2-4.4 Kb). The high temperature intermediate pressure amphibolite facies in Seosan area with the low temperature-intermediate presure greenschist facies of Taean formation is corelated with that of Ogcheon Group ($590^{\circ}-640^{\circ}$ C, 5.2-6.3 Kb). The Chungju and Seosan iron formations were deposited in Archean, showing geochemical composition of Precambrian iron formations. The Chungju iron formation was mainly formed by the chemical precipitation, on the other hand, the Seosan iron formation was formed by alternated action of chemical and detrital depositions.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.1
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• pp.57-67
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• 2013

In Korea, there are debris-flow disasters induced by typhoon and localized torrential rainfall annually. There are particularly extensive debris-flow disasters in Gangwon-do because of its geomorphological characteristics; the extensive coverage of mountainous region, steep slope, and shallow soil. In this paper, we constructed a GIS database about topological characteristics of debris-flow basin in Gangwon-do by years of field survey. Also, we conducted frequency analysis based on this database with the digital forest type map and the digital soil map. We analyzed frequencies of debris-flow by simple count for topological characteristics, whereas we analyzed by considering an area ratio based on GIS for physiognomic and geologic characteristics. We used slope, aspect, width, depth and destruction shapes for analysis about topological characteristics of debris-flow basin. Also we used attributes of forest physiognomy, diameter, age, and density about physiognomic characteristics, and i n terms of geologic characteristics, we used attributes of drainage class, effective soil depth, subsoil properties, subsoil grave content, erosion class, parent material of soil, and topsoil properties. In consequence, we figured out topographic, forest physiognomic, and geologic characteristics of debris-flow basin. This result is applicable to establish a rational disaster prevention policy as a fundamental information.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.613-624
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• 1997

A study of anisotropy of magnetic susceptibility (AMS) was conducted on the Ordovician-Eocene strata in the Taebaek area. The study area is a northeastern part of the Okchon belt, sometimes called as Paegunsan Synclinal Area. A total of 600 independently oriented samples were collected from 60 sites covering the whole area. With a few exception of late Cretaceous-Eocene volcanic rocks, all the sampled strata are nonmetamorphosed sedimentary rocks, mainly sandstones. Among the 60 sites, 5 sites showed flow lineation lying on the bedding plane, 11 sites showed load foliation parallel to the bedding plane, and 21 sites showed tectonic foliation unrelated to the bedding plane. The tectonic foliations are defined by $k_1-k_2$ ($k_{max}-k_{int}$) anisotropy plane, and are considered as a result of tectonic forces acted perpendicularly to the foliation plane in the geologic past. Regardless of sample-site locations, tectonic force directions defined by $k_3$ ($k_{min}$) axis perpendicular to the tectonic foliation are consistent among the strata of the same geologic age. In the course of geologic time, however, the tectonic force directions showed a clockwise rotation: approximately E-W in the Ordovician sites, NW-SE in the Permian sites, N-S in the Triassic sites, and lastly NE-SW in the late Cretaceous-Eocene sites. The pre-Permian directions showed better clustering in the in-situ (geographic) coordinates, while the younger directions become better clustered after the bedding-tilt correction. It is interpreted that the major tectonic structures of the Taebaek area were controlled by the above-mentioned tectonic forces: The Paegunsan Syncline and the Hambaeksan Fault must have been generated by the NW-SE force of late Permian-early Triassic time. It was then reactivated in the reverse (dextral) sense by the N-S force of Triassic time. The Osipchon Fault in the eastern part of the study area was either generated or reactivated by the NE-SW force of late Cretaceous-Eocene time. The Permo-Triassic NW-SE force should be an expression of the Songnim Disturbance in the Korean peninsula, which is in turn related with the SCB/NCB collision in China.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.674-677
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• 2005

The characteristics of geothermal resources in Korea was roughly estimated using hot springs, 580 geothermal gradients and 338 heat flow data. In the aspect of hot springs with geologic structure, location of hot springs coincide with fault zone, especially younger age of Cretaceous to Tertiary. In the aspect of geothermal gradients, Pohang area shows the highest geothermal gradient anomaly, which is covered with unconsol idated rock of low thermal conductivity preserving the residual heat from igneous activity or radioactivity elements decay. In the aspect of heat flow density, high anomaly can be found along the zone connecting Uljin-Pohang-Busan on the southeastern part of Korean peninsula at which big fault zone as Yangsan fault is well developed.

• Journal of the Korean earth science society
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• v.26 no.2
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• pp.137-148
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• 2005

Five species of graptolites were discovered from the Jigunsan Shale of Taebaeg area, Korea. They are herein described as Archiclimacograptus riddellensis (Harris, 1924), Pseudamplexograptus distichus(Eichwald, 1840), Hustedograptus teretiusculus(Hisinger) sensu Jaanusson, 1960, Hustedograptus vikarbyensis (Jaanusson, 1960), and Hustedograptus sp. The graptolite assemblage from the Jigunsan Shale corresponds to those of the Pseudamplexograptus distichus zone in the Baltic and German areas and the geologic age of graptolites bearing beds of the Jigunsan Shale might be late Middle Llanvirn.

• Economic and Environmental Geology
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• v.19 no.3
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• pp.179-192
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• 1986

In the Bupyeong district, Mesozoic pyroclastic rocks, intrusive breccia, granites and felsic porphyries comprise a volcano-plutonic complex, overlying and intruding the Precambrian Gyeonggi gneiss complex. pyroclastic rocks, consisted mainly of rhyolitic welded tuffs, form a topographic circular structure about 10 kilometers in diameter. Granites and felsic porphyries which intruded the pyroclastic rocks are distributed in the inner side and also along the outer margin of the circular structure. K-Ar ages of two granite bodies(biotite), 162 and $148{\pm}7$ Ma, and that of the intrusive rhyolite (whole rock), $121{\pm}6$ Ma indicate that a series of volcano-plutonic igneous activity occurred between Jurassic and early Cretaceous age. Petrochemical characteristics suggest that the pyroclastic rocks, granites and felsic porphyries were originated from the comagmatic source. From the evidences of field occurrence, petrochemical and geochronological characteristics of igneous rocks and the geologic structures, it is believed that the igneous rocks in the Bupyeong district were formed during a Jurassic to early Cretaceous resurgent caldera evolution.

• Economic and Environmental Geology
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• v.26 no.1
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• pp.83-96
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• 1993

Kwangju granite body located in vicinity of Kwangju city consist of three rock bodies-Kwangju rock body, Jangsung rock body and Youngkwang rock body. Petrochemistry of Kwangju granite is as follows: Kwangju granite body is igneous complex which compose of a series of differential products of a magma. Kwangju granites are divided into four rock facies based on the geologic age, mineralogical and chemical constituents and texture: Triassic hornblende-biotite granodiorite and biotite granite, and Jurassic porphyritic granite and two mica granite. Harker and other variation diagrams of Kwangju granites plot on trend of calc-alkali rock series and range of peraluminous granite. Parental magma type of Kwangju granites correspond to I-type, Syn-Collision type in compressive stress field by collision movement between both rock block. In chondrite normalized REE patterns of Kwangju grnites, LREE enriched than HREE in REE amount and have more steep negative slope with slightly (-) Eu anormaly.

• Economic and Environmental Geology
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• v.55 no.6
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• pp.597-616
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• 2022

The Chungnam basin is a crucial area for studying the Mesozoic crustal evolutionary history of the Korean Peninsula. This study reports the revised geology and new isotopic ages from the northeastern Chungnam Basin based on detailed geological mapping and LA-ICP-MS zircon U-Pb analysis. Our renewed geologic map defines intra-basin, basin-bounding, and basement fault systems closely related to hydrothermal gold-bearing quartz vein injections. Here, we propose the directions of (micro)structural and geochronological future work to address issues on the relationship between the tectonic process, basin evolution, and hydrothermal fluid migration in the southwestern Korean Peninsula.