• The Journal of the Petrological Society of Korea
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• v.17 no.1
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• pp.1-15
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• 2008

The metasedimentary rocks of the Nampo Croup consisting of metaconglomerates, metasandstones, phyllites are exposed in the area of the Daechcon beach and Maryangri, Seocheon-gun. Their typical metamorphic assemblages of Bt-Mus-Grt-Qtz (${\pm}Pl{\pm}Chl$) and Bt-Mus-Qtz (${\pm}Pl{\pm}Chl$) indicate that they have been under intermediate P/T type metamorphism and were metamorphosed to garnet zone grade of amphibolite-facies during the Daebo Orogeny. Pressure-temperature conditions of peak metamorphism estimated from geothermobarometries are $560{\sim}595^{\circ}C$, $6.9{\sim}8.2\;kb$ respectively. The results of K-Ar biotite age determination are $143.2{\pm}3.6\;Ma$, $122.6{\pm}2.4\;Ma$ and $124.8{\pm}2.4\;Ma$ and the last two ages are considered as the results of later-stage thermal perturbation. On the bases of the formation age of Daedong Supergroup of $187{\sim}172\;Ma$ (Han et al., 2006; Jeon et al., 2007) combined with the results of this study, the hypothetical model of tectonometamorphic evolution of the study area during Daebo Orogeny is proposed. Crustal thickening resulted from folding and duplexing of thrusts in the area initiated at around 175 Ma just after sedimentation of Nampo Croup. And then rapid cooling by normal faulting due to crustal extention followed immediately after the peak metamorphism to the closure temperature of biotite.

• 한국지구과학회:학술대회논문집
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• 2002.09a
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• pp.59-59
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• 2002

• Journal of the Korean earth science society
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• v.23 no.7
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• pp.616-616
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• 2002

• 한국지구과학회:학술대회논문집
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• 2010.04a
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• pp.99-100
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• 2010

충남 서부에 위치한 보령 지역은 트라이아스기 후기로 알려진 육성 기원의 남포층군이 널리 분포하고 있다. 남포층군은 하부로부터 하조층, 아미산층, 조계리층, 백운사층 및 성주리층으로 구분된다. 남포층군에서 산출되는 화석의 대부분은 식물 화석이며, 기타 이매패 화석, 어류 화석, 곤충의 유충 화석, 패갑류(conchostracans) 등의 화석이 산출되고 있지만, 양적으로 극히 적다. 이들 화석 중에서 체계적으로 연구가 된 것은 식물 화석뿐이고, 나머지 화석들은 전문 연구가의 부재 등에 의해 극히 미미한 연구 수준에 머물러 있다. 이번의 연구를 통해서 아미산층에서 채집된 곤충화석은 모두 107점이고, 그중에서 유충 화석이 94점, 날개 화석이 14점이다. 이들의 분류학적 연구 결과, 아미산층의 곤충화석군은 소시목, 강도래목, 날도래목, 하루살이목, 잠자리목, 바퀴벌레목, 벌목, 매미목을 비롯한 8목 11종에 이르는 유시류의 곤충들로 구성된다. 이들은 현재까지 우리나라에서 발견된 곤충화석 중 시대적으로 가장 오래된 화석이다. 유충 화석은 모두 수서 곤충의 유충화석이다. 이들의 유충은 수중생활에 적응하여 지상생활을 하는 성충과 형태적으로 큰 차이가 있는 불완전변태류 또는 외시류이다. 날개 화석은 수서곤충의 성충의 날개이고 일부는 육상 생활을 하는 곤충의 날개가 포함되어 있다. 아미산층에서 나온 곤충화석에는 육상에서 생활하는 매미목과 바퀴목도 있는데 이들은 불완전변태류에 속한다. 그러나, 똑같은 육상생활자이면서도 벌목은 완전변태류 또는 내시류에 속하는 것도 있다. 따라서 아미산층에서 산출된 곤충화석군에는 불완전변태류와 완전변태류가 섞여 있는 특징을 보인다. 이들은 실제로 같은 시대에 비슷한 장소에서 함께 생활을 했던 생물군집이지만, 서로 살던 장소가 다른 집단들이 섞여 있다는 것은 육상생활자의 일부가 죽은 후 수류에 의해 퇴적분지로 유입되어 매몰된 혼합집단으로 볼 수 있다. 현생의 하루살이목, 강도래목 등은 대표적인 유수성 곤충이고, 잠자리, 노린재 등은 대표적인 정수성 곤충으로 알려져 있다. 이들이 지층에 밀집하여 산출되는 것으로 보아 살던 장소에서 많은 퇴적물의 유입에 따른 급격한 매몰에 의해 화석화된 것으로 판단된다. 동아시아의 중생대 초기에서 보고된 곤충 화석은 양적으로도 수적으로도 그리 많지 않다. 그중에서 일본의 Mine에서 보고된 화석군이 가장 대표적이며 바퀴류(Blattaria)와 딱정벌레(Coleoptera)의 화석이 가장 큰 비율을 차지하지만, 아미산층 곤충화석군과의 공통종은 한 종도 없다. 아미산층의 곤충화석군은 비록 다양성은 쥐라기의 곤충상에 비해 떨어지지만 조성적으로는 쥐라기의 곤충상에 매우 유사하다. 육상에 사는 곤충이 화석으로 보존되기 어렵다는 것을 감안하면 아미산층에서 산출된 곤충화석은 학술적으로 매우 귀중하고 큰 의미가 있다. 보령 지역의 곤충화석은 중생대의 쥐라기와 백악기를 거쳐 현재로 이어지는 곤충 진화사의 잃어버린 고리를 이어줄 수 있는 귀중한 자료로 평가된다.

• Journal of the Korean earth science society
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• v.29 no.6
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• pp.466-473
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• 2008

This study deals with the morphological characteristics and structure of organ fossils of Neocalamites carrerei such as rhizomes, aerial leafy stems, and cones collected in situ from the Amisan Formation of Nampo Group. Judging from the size of some extant Equisetum and paleoclimate of Daedong flora, it is considered that the size of Neocalamites carrerei was probably very large. The cone of Neocalamites takahashii (Kon'no) is closely associated with the leaves of Neocalamites carrerei. It indicates that two organ fossils mentioned above probably belong to the same species. Comparing with very abundant occurrence of aerial leafy stems and rhizomes in the Amisan Formation, cones are very rare. This fact implies that Neocalamites reproduce not only by spore reproduction, but also by asexual reproduction. Neocalamites largely differ in the leaf form and size from Equisetum.

• Journal of the Korean earth science society
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• v.35 no.3
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• pp.161-167
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• 2014

Recently, a winged insect fossil the Mecoptera has been discovered for the first time in the Late Triassic Amisan Formation in the Boryeong area, Chungnam, Korea. The fossil is classified as Mesopsyche dobrokhotovae based on the characteristics of wing venation. Insect fossils which belong to this Genus show worldwide distribution in the Late Triassic, making it possible to estimate that they thrived in this period. Extant Mecoptera survive in humid environments by hanging onto tree leaves or stems and eating other small insects. Compared to the ecology of extant Mecoptera, the presence of the fossil Mecoptera indicates that the paleoenvironment in Nampo Group was very similar to the present during the Late Triassic Period. Mesopsyche dobrokhotovae is the first Mecoptera occurrence and one of the oldest insect fossil occurrences in Korea.

• Journal of the Korean earth science society
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• v.22 no.2
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• pp.105-111
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• 2001

Seven specimens of raindrop imprints are discovered from the Late Triassic Amisan Formation of Nampo Group distributed in the Myeongam area of Boryeong-City, Chungcheongnam-do. The raindrop imprints are interpreted to had been formed in lacustrine environments under subtropical humid climate during the lowered period of the surface of the water by temporally or seasonally arid climate. The raindrop imprints are the first finding in the Lower MesozoicNampo Group, Korea.

• Journal of the Korean earth science society
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• v.36 no.2
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• pp.181-189
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• 2015

A large number of fossil conchostraca used in this study were collected from the Amisan Formation distributed in the western part of Chungnam, Korea. These fossils were densely discovered in several horizons of the Amisan Formation, and might have flourished in the fresh water environment of subtropical climate. The fossil conchostraca from the Amisan Formation were classified into four species belonging to three genera as follows: Euestheria kawasakii, E. shimamurai, Sphaerestheria koreanica, and Cyclestherioides rampoensis. Out of four species, the last species was previously described from the Amisan Formation, and the other three species were newly found. Based on the fossil conchostraca, it is inferred that the geological age of the Amisan Formation falls under the Late Triassic Period.

• Economic and Environmental Geology
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• v.19 no.1
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• pp.67-83
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• 1986

Oriented hand samples were collected from Gobangsan Formation and Nogam Formation in the north of Danyang and south of Yeongchun, from Bansong Group in and around Danyang, from Nampo Group in Chungnam Coalfield, from Gyeongsang Supergroup distributed from Waegwan through Daegu to Gyeongsan and from Daegu to Goryong, and from volcanic flows in Jeongog area and Jeju Island to study the paleomagnetism of southern Korea since Permian. Stepwise alternating field and thermal demagnetization experiments were carried out to determine optimum fields and temperatures. Observed mean paleomagnetic directions are as follows: $D=331.5^{\circ}$, $I=25.1^{\circ}$, $a95=12.8^{\circ}$ for Permian, $D=325.6^{\circ}$, $I=46.1^{\circ}$, $a95=11.8^{\circ}$ for Triassic, $D=313.4^{\circ}$, $I=43.1^{\circ}$, $a95=16.0^{\circ}$ for early Jurassic, $D=41.3^{\circ}$, $I=64.6^{\circ}$, $a95=4.5^{\circ}$ for early Cretaceous, $D=28.3^{\circ}$, $I=58.1^{\circ}$, $a95=2.3^{\circ}$ for late Cretaceous, $D=2.0^{\circ}$, $I=55.8^{\circ}$, $a95=6.6^{\circ}$for Quaternary. To describe the tectonic translocation of southern Korean block, northern Eurasian continental block was used as a reference frame. For each age since Permian the expected northern Eurasian field directions in terms of paleolatitude and declination were calculated. The paleolatitudes of Permian ($13.2^{\circ}N$) and early Jurassic ($25.1^{\circ}N$) obtained from the study area are quite different from those of Permian ($66.0^{\circ}N$) and early Jurassic ($68.1^{\circ}N$) which are expected for northern Eurasia. The declinations of Permian ($331.5^{\circ}$) and early Jurassic ($313.4^{\circ}$) are also quite different from those of the Permian ($56.6^{\circ}$) and the early Jurassic ($47.5^{\circ}$) expected for northern Eurasia. The Cretaceous paleolatitude is similar to the expected within error limit, but the declination for the same period is significantly different from that of the expected for the northern Eurasia. From the above evidences it is suggested that the south Korean land mass had moved from low latitude in Permian to north and sutured to northern continental block since early Jurassic. The relative rotations of early Cretaceous($27.4^{\circ}$) and late Cretaceous($10.8^{\circ}$) to northern Eurasian continent reveal that the Korean land mass might be rotated clockwise in two different times, probably in late Early Cretaceous and in Tertiary.