• Journal of the Korean Geographical Society
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• v.28 no.4
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• pp.285-297
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• 1993

For the application of the diffusion equation, slope height and maximum slope angle are calculated from the plotted slope profile. Using denudation rate as a solution for the diffusion equation, an apparent age index can be calculated, which is the total amount of denudation through total time. Plots of slope angle versus slope height and apparent age index versus slope height are useful for determining relative or absolute ages and denudation rates. Mathematical simulation plots of slope angle versus slope height can generate equal denudation-rate lines for a given age. Mathematical simulations of slope angle versus age for a given slope height, for equal denudation-rate at a particular profile site, and for comparing to other sites having controlled ages.

• The Journal of the Petrological Society of Korea
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• v.17 no.2
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• pp.51-56
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• 2008

The geologic age of the Okcheon metamorphic belt, used to be a longstanding puzzle, has been settled down to Neoproterozoic to Paleozoic with discovery of fossils and isotopic age dating of metavolcanic rocks. As isotopic ages become accumulated, there appeared a controversy over the age of peak metamorphism in the Okcheon metamorphic belt, i.e., a single late Permian-early Triassic metamorphism (CHIME allanite age and U-Pb age of metamorphic zircon), or earlier independent presence of early Permian metamorphism (U-Pb age of allanite within garnet porphyroblast). If we compare the isotopic ages that can represent metamorphism, the data for the latter have much larger error than those of the former with some overlap considering the error limits. It means that, the former, supported by two independent ages, is considered a better representation for the age of metamorphism of the Okcheon metamorphic belt. Therefore, I propose the idea of early Permian metamorphism should better be reserved until conclusive evidence appears. The late Permian-early Triassic metamorphic age suggest that the effect of continental collision influenced much of the middle part of Korean Peninsula, namely, the Imjingang belt, the Gyeonggi massif and the Okcheon belt.

• Journal of the Korean Wood Science and Technology
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• v.46 no.3
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• pp.241-252
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• 2018

It was estimated that the Imdang-dong site of Gyungsan was constructed in the 2nd to 4th century based on excavated layers and artifacts. This study was carried out to verify the result using the dendrochronological analysis of six wooden pillars excavated at the site. As a result, it was proven that 6 specimens were not cut at the same age because their tree-ring chronologies were not synchronized each other. And more, it was reconfirmed in wiggle matching dating as confirming two of them were dated to A.D. 94-135 and A.D. 224-289, respectively. It was coincided with the above-mentioned estimated age. In wood identification, most of them were identified as Hovenia dulcis Thunb., Tilia spp., Ulmus spp. which grow usually under cool environment. Based on the result, we could conclude that the climate at that time was cooler than the present.

• The Korean Journal of Zoology
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• v.36 no.1
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• pp.14-20
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• 1993

한국산 도룡농, Hvnobius leechii의 7개 집단에서 mitochondrial DNA(mtDNA)의 변이가 조사되었다. MtDNA의 크기에서의 차이는 관찰되지 않았으나 제한효소 인식 부위에서의 차이가 조사되었다. MtDNA의 절편 양상은 각 집단에서 동일하게 나타났다. 제한 효소로 처리하여 얻어진 절편의 비교에서 종내 변이는 염기 치환에 의하여 발생한 것임이 분석되어졌다. 특히 하동과 제주 집단은 몇개의 제한 효소 인식 위치에서 나머지 5개 집단과 뚜렷한 차이를 보였다. 염기치환율(p값)은 공통 절편 비율(p값)을 토대로 하여 얻어졌으며 그 값은 0.004에서 0.064의 범위 내의 값으로 측정되었다. 하동과 제주 집단을 제외한 5개 집단의 비교에서는 비교적 낮은 침의 염기 치환율을 보였으나 제주와 나머지 집단들과의 비교에서는 염기치환율이 높게 측정되었다. 염기 치환율과 관련지어 염기 분화 연대를 측정한 결과 도룡뇽 7개 집단은 3개의 group으로 나뉘어 졌으며 이들은 약 188만년전에 분화된 것으로 사료되어 진다.

• Journal of the Korean Geographical Society
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• v.39 no.2
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• pp.269-282
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• 2004

Luminescence dating of a coastal dune from the Shindu dunefield on the T'aean Peninsula shows that deposition of the dune structure began about 500-600 years ago. The lower section of the dune has remained stable since then but the upper part yields an age of about 30 years, suggesting reactivation or additional deposition since the 1970's. The two samples that were collected from the lower part of the dune at depths of 3.5 m and 2.0 m below the surface differ by an age interval of about 50-70 years. This indicates a net depositional rate of around 2.5 cm a year which is relatively slow for a coastal dune. Whilst only one dune structure has been dated for the time being and even though the dunefield was probably established much earlier in the Holocene, the OSL ages obtained demonstrate that some dunes in the area could be younger than 1000 years. Such chronologies point to a dynamic environment where the dune structures are not permanently fixed. Sedimentological properties of the dune sands are consistent with those of particles initially deposited under subaqueous conditions and then later transported by wind.

• The Journal of the Petrological Society of Korea
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• v.14 no.1
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• pp.1-11
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• 2005

Sphene U-Pb ages were determined for the granodiorites from Gimcheon, Seongju and Anui areas of the middle Yeongnam massif. The determined ages were in the narrow range of 195.7±2.4∼200.8±1.9(2σ) Ma that are approximately coincident with the boundary between Triassic and Jurassic. Even though the studed plutons are aerially separated, they reveal quite similar major element compositions and almost identical ages, suggesting that they were generated from the similar source materials under the identical tectonic environment and thus they can be considered to form a single suite. Considering the age and spatial distribution of the Triassic to Lower Jurassic plutons of the Yeongnam Massif and Okcheon Belt, it seems that there were episodic changes in tectonic environment in both areas with relatively short intervals. In general, the compressive environment of active continental margin was prevailed. However, the tensional environment of within-plate was also appeared several times intermittently. In conclusion, Yeongnam Massif and Okcheon Belt experienced distinct tectonic environments during Triassic to Lower Jurassic, providing important clue to reveal the crustal evolution of the Korean Peninsula.

• Journal of Korean Society of Forest Science
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• v.103 no.1
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• pp.80-86
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• 2014

$^{210}Pb$ dating was conducted to examine the influence of land use changes in the forest catchment on lake sedimentation. The Kushiro River, into which Lake Takkobu drains under regular flow conditions, contributed to an increased sedimentation rate in sampling point at the lake outflow because turbid water from the Kushiro River flows back into Lake Takkobu during floods. The elevated sediment flux from the catchment dilutes the $^{210}Pb$ concentration in sampling points at the inflow of the Takkobu River and the lake outflow, which causes fluctuations in the $^{210}Pb$ concentrations in sediment cores. The $^{210}Pb$ dating was estimated using the CRS (Constant rate of Supply) model. The dates by the CRS model in Lake Takkobu profiles were in good agreement with the dates by $^{137}Cs$. Sedimentation rates reconstructed for the past 100-150 years suggested that sedimentation rates increased drastically following land use changes. While a natural sedimentation rate of $0.01-0.03g/cm^2/year$ is observed until the 1880s, whereas lake sedimentation accelerated to $0.03-0.09g/cm^2/year$ following land use changes such as deforestation and channelization, between the 1880s and 1940s. In particular, the sedimentation rates have been associated with deforestation, channelization, agricultural development and road construction, since the 1980s, and these rates were about 9-28 times higher than those under natural conditions, leading to accelerated lake shallowing.

• The Journal of the Petrological Society of Korea
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• v.22 no.2
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• pp.83-115
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• 2013

Erroneous fission-track (FT) ages caused by an inappropriate calibration in the initial stage of FT dating were redefined by re-experiments and zeta calibration using duplicate samples. Revised FT zircon ages newly define the formation ages of Yucheon Group rhyolitic-dacitic tuffs as Late Cretaceous to Early Paleocene ($78{\pm}4$ Ma to $65{\pm}2$ Ma) and Gokgangdong rhyolitic tuff as Early Eocene ($52.1{\pm}2.3$ Ma). In case of the Early Miocene volcanics, FT zircon ages from a dacitic tuff of the upper Hyodongri Volcanics ($21.6{\pm}1.4$ Ma) and a dacitic lava of the uppermost Beomgokri Volcanics ($21.3{\pm}2.0$ Ma) define chronostratigraphies of the upper Beomgokri Group, respectively in the southern Eoil Basin and in the Waeup Basin. A FT zircon age ($19.8{\pm}1.6$ Ma) from the Geumori dacitic tuff defines the time of later dacitic eruption in the Janggi Basin. Based on FT zircon ages for dacitic rocks and previous age data (mostly K-Ar whole-rock, partly Ar-Ar) for basaltic-andesitic rocks, reference ages are recommended as guides for stratigraphic correlations of the Miocene volcanics and basements in SE Korea. The times of accumulation of basin-fill sediments are also deduced from ages of related volcanics. Recommended reference ages are well matched to the whole stratigraphic sequences despite complicated basin structures and a relative short time-span. The Beomgokri Group evidently predates the Janggi Group in the Eoil-Waeup basins, while it is placed at an overlapped time-level along with the earlier Janggi Group in the Janggi Basin. Therefore, the two groups cannot be uniformly defined in a sequential order. The Janggi Group of the Janggi Basin can be evidently subdivided by ca. 20 Ma-basis into two parts, i.e., the earlier (23-20 Ma) andesitic-dacitic and later (20-18 Ma) basaltic strata.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2001.06a
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• pp.141-142
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• 2001

남서부 경기육괴의 편마암류로부터 분리된 저어콘(zircon) 입자를 대상으로, 이온현미분석기(ion microprobe)를 사용한 U-Pb 연대를 구하였다. 그 결과는 후기 원생대(약 820 Ma) 뿐만 아니라 오르도비스기에 상당한 화성활동이 한반도에 있었음을 지시한다. 우리 나라 후기 원생대의 화성-변성 활동에 대해 알려져 있는 바는 극히 제한적이어서 후속연구가 필수적이며, 이러한 연구는 한반도의 지체구조적 변천사를 로디니아 초대륙(Rodinia supercontinent)의 생성-분리와 관련해 재조명할 수 있는 기회를 제공할 것이다. 또한 오르도비스기의 화성작용은 그동안 논란이 되어 왔던 소위 “칼레도니아(Caledonian)” 변동 (cf. 조문섭, 2000)에 대한 또 다른 증거를 제공해준다. 저어콘의 연대측정은 서호주의 커튼공업대학교에 설치되어 있는 SHRIMP-II(Sensitive High-Resolution Ion Microprobe-II; 고감도-고분해능 이온현미분석기)를 사용하였으며, 시료 준비 및 분석방법은 기존에 보고된 바와 같다 (e.g., Kinny et al., 1999). 분석된 3개의 암석 시료(1006-5, 8, 9)는 경기육괴의 남서부에 위치한 홍성 지역의 정편마암들이다. 1006-8 시료는 Turek and Kim (1996)이 전통적인 방법을 사용해 687$\pm$5 Ma의 U-Pb 저어콘 연대를 보고한 바 있는 화강암질 편마암 (시료번호, KJ43)에 해당된다. 두 개의 다른 시료는 1006-8 주변에서 산출하는 전형적인 경기육괴의 편마암류로서 화강암질 정편마암이다. 이들 시료로부터 분리된 저어콘 입자들은 대부분 화성기원의 누대구조와 자형의 결정형태를 보여준다. 과성장띠(overgrouth rims)는 1006-5 시료에서 흔하게, 그리고 1006-9 시료에서 매우 드물게 관찰된다. 음극선발광(cathodoluminescence) 영상의 해석을 통해 저어콘 결정의 성장사를 유추하였으며, 이를 바탕으로 이온현미분석 점(spot)을 정하였다. U-Pb-Th 자료는 퍼스(Perth) 저어콘 스탠다드 (CZ3, 564 Ma, $^{206}$Pb/$^{238}$U=0.0914)를 사용하였다. 아래에 기술하는 연대는 모두 $^{206}$Pb/$^{238}$U 연대에 해당된다. 두 개의 화강암질 편마암 시료로부터 구한 U-Pb 저어콘 연대는 각각 812 $\pm$ 14 Ma(1006-8)와 822 $\pm$ 17 Ma(1006-9)로 분석오차 내에서 서로 일치한다. 이 결과는 춘천 및 전곡 지역의 석류석 각섬암에서 보고된 Sm-Nd 전암연대(852 $\pm$ 24 Ma 및 824 $\pm$ 143 Ma; Lee and Cho, 1995; Ree et al., 1996)와 잘 부합한다. 따라서 후기 원생대 기간 중 화성활동이 한반도에서 광범위하게 일어났음을 시사한다. 한편, 1006-9 시료에서는 예외적으로 한 개의 저어콘 입자 주변부(rim)에서 매우 얇은 과성장띠가 관찰되었으며, 두 개의 점 분석으로부터 구한 U-Pb 저어콘 연대는 약 235 Ma이다. 이 띠는 또한 변성기원의 저어콘에서 흔히 관찰되는 작은 W (<0.05) 비를 보인다. 1006-5 시료는 위 두 시료로부터 수 km 떨어진 지점에서 채집하였으나, 저어콘 연대는 상이한 기록을 보여준다. 즉 매우 작은 Th/U (<0.01) 값을 갖는 저어콘의 주변부에서 223 $\pm$ 5 Ma의 연대가 잘 정의되며, 이는 1006-9 시료에서 관찰된 결과와 함께 트라이아스기의 고온변성작용이 백립암상에 가까운, 매우 높은 온도에 달하였음을 지시한다. 한편 저어콘의 중심부는 335-473 Ma의 비교적 넓은 연대 분포를 보인다. 이는 저어콘이 실제 성장한 연대를 지시하기보다는 트라이아스기의 변성작용에 따른 납손실(Pb loss) 그리고 누대 규모보다 더 큰 빔 크기(beam size, 약 30 $\mu\textrm{m}$)의 영향일 것으로 해석된다. 또한 저어콘이 다양한 외래물질로부터 기원했다는 증거가 관찰되지 않으므로, 이 정편마암의 모암은 오르도비스기(약 430-470 Ma)에 관입하였을 것으로 생각된다. 따라서 그동안 논란이 되어 왔던 소위 “칼레도니아” 변동이 한반도 내에 실존하였을 가능성을 시사한다. 이상의 결과를 종합하여 볼 때, 경기육괴의 변성암류는 후기 원생대 이후 다양한 저어콘의 성장사를 기록하고 있음을 알 수 있다: 즉 (1) 후기원생대(약 820 Ma)의 화성작용; (2) 오르도비스기(약 450 Ma)의 화성작용: 그리고 (3) 트라이아스기 (약 223 Ma)의 부분용융을 수반한 고온 변성작용으로 대표된다. 이러한 지질연대는, 옥천변성대에서 얻어진 756 Ma의 저어콘 연대(Lee et al., 1998)와 더불어, 친링-다비-수루(Qinling-Dabie-Sulu) 대륙 충돌대와 양쯔 지괴에서 보고된 지질연대 결과와 잘 부합한다. 따라서 지구연대학적으로 경기육괴가 북중국보다는 대륙충돌대를 포함하는 남중국지괴에 속할 것으로 결론지을 수 있다.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.89-112
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• 2012

The Korean Peninsula consists of three Precambrian blocks: Nangrim, Gyeonggi and Yeongnam massifs. Here we revisited previous stratigraphic relationships, largely based on new geochronologic data, and investigated the crustal evolution history of the Precambrian massifs. The Precambrian strata have been usually divided into lower crystalline basements and upper supracrustal rocks. The former has been considered as Archean or Paleoproterozoic in age, whereas the latter as Paleoproterozoic or later. However, both are revealed as the Paleoproterozoic (2.3-1.8 Ga) strata as a whole, and Archean strata are very limited in the Korean Peninsula. These make the previous stratigraphic system wrong and require reconsideration. The oldest age of the basement rocks can be dated as old as Paleoarchean, suggested by the occurrence of ~3.6 Ga inherited zircon. However, most of crust-forming materials were extracted from mantle around ~2.7 Ga, and produced major portions of crust materials at ~2.5 Ga, which make each massif a discrete continental mass. After that, all the massifs belonged to continental margin orogen during the Paleoproterozoic time, and experienced repeated intracrustal differentiation. After the final cratonization occurring at ~1.9-1.8 Ga, they were stabilized as continental platforms. The Nangrim and Gyeonggi massif included local sedimentary deposition as well as igneous activity during Meso-to Neoproterozoic, but the Yeongnam massif remained stable before the development of Paleozoic basin.