• 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.

• Journal of the Korean earth science society
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• v.39 no.5
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• pp.458-472
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• 2018

Pterosaur tracks were discovered recently in the Daegok-ri dinosaur tracksite (Ulsan Metropolitan City Cultural Properties No. 13), Ulju-gun, Ulsan. Those tracks were reported as being the first in the Cretaceous deposits of Ulsan area. This tracksite is located relatively far from the Gyeongsangnam-do coastal area where pterosaur tracks were reported intensively, and there are stratigraphic differences. This study described the pterosaur tracks and trackway of the Daegok-ri tracksite and discussed the spatio-temporal distribution of the Cretaceous pterosaurs in the Korean Peninsula. The pterosaur footprints founded in Daegok-ri can be classified as Pteraichnus ichnosp., followed by the morphological characteristics. Based on the distribution of the pterosaur tracks on the Korean Peninsula including the Daegok-ri pterosaur tracks, it was estimated that the Cretaceous pterosaurs on the Korean Peninsula had survived approximately for 40 million years from 120 Ma (i.e., Early Cretaceous) to 80 Ma (i.e., Late Cretaceous) and inhabited in various sedimentary environments regardless of the basin size and the specific sedimentary environments. Furthermore, the occurrence of the sauropod, ornithopod, theropod, pterosaurs, birds, and crocodyliforms tracks/trackways in the Daegok-ri area represented that the Cretaceous vertebrate ichnodiversity was fairly high.

• Economic and Environmental Geology
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• v.9 no.3
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• pp.127-134
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• 1976

The K-Ar age determined on six granitic rocks samples from the Eonyang- and the northwestern part of Ulsan-quardrangle, Kyeongsang-nam-do, Korea, ranges from $87{\times}10^6$ years to $58{\times}10^6$ years. Three of the samples belong to the upper Cretaceous ($87{\times}10^6-71{\times}10^6years$) and three to the late Cretaceous-early Tertiary ($63{\times}10^6-58{\times}10^6years$) in age. The early Tertiary ages are measured first on the "Younger Granites" in Korea. These two emplacement periods of granitic rocks are representative that the former is correlated to north Kyushu-Seto Inland belt ($95{\times}10^6-75{\times}10^6years$) and the later to Sanin-central Honshu belt ($65{\times}10^6-50{\times}10^6years$), in southwestern Japan.

• Economic and Environmental Geology
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• v.23 no.3
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• pp.343-352
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• 1990

The Cretaceous granites are widely distributed in the studied area, Mungyeong-Sangju, which belongs to the southwestern part of the Ogcheon Folded Belt. The granites are characterized by medium-coarse grained, spotted miaroles, partly flow textures of biotite, aplitic dykes and pegmatitic pockets with druse. From the major compositions, the granites indicate peraluminous, calc-alkaline, salic and late stage products of differentiation. In the view of normative compositions of Qz-Ab-Or and perthitic alkali feldspar, they were formed under 1-4kb and $426^{\circ}-456^{\circ}C$ in acqueous conditions. The K/ Ar biotite age shows $72{\pm}1$ Ma for this grante, corresponding to the igneous activity of the Bulgugsa Disturbance periods in the area. The above results represent that these granite bodies are differentiated from a single magma.

• Journal of the Korean earth science society
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• v.37 no.5
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• pp.295-308
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• 2016

Nine species of fossil plants were described based on the new material collected from the Hasandong Formation. They are as follows: Thallites yabei, Onychiopsis elongata, Cladophlebis denticulata, C. shinshuensis, C. (Eboracia ?) lobifolia, C. (Klukia ?) koraiensis, Brachyphyllum japonicum, Elatocladus tennerima, and Taeniopteris ? sp. cf. T. auriculata. The floristic composition of the Hasandong flora is very similar to that of the Nakdong flora. This means that both floras might have flourished under subtropical warm arid climate. This flora contains both the Tetori-type and Ryoseki-type floras. It is considered that the Hasandong flora is a member of the Mixed-type floras that existed in eastern Eurasia during the Late Jurassic to Early Cretaceous time.

• Economic and Environmental Geology
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• v.24 no.4
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• pp.379-391
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• 1991

The studied Cretaceous granties are widely distributed at the southern Mungyeong area in the southwestern part of Ogcheon Fold Belt. From the mineralogical and geochemical compositions, it is suggested that they show the characteristics of I-type and magnetite-series and formed under the conditions of high oxygen fugacity. The mineral chemistry of plagioclase, alkali feldspar and biotite in the granites by EMPA, was revealed as albite to oligoclase, microcline to microcline perthite and orthoclase perthite, and annite compositions, respectively. The granites have the distribution patterns of enriched LREE and depleted HREE, and show Eu negative anomalies suggesting mainly due to the feldspar fractionation in the residual magma. The geochemical data of Eu, EU/$^*Eu$, Sm and Gd suggest that the granites of the area have more abundant alkali feldspar crystallization than plagioclase. From the geochemical characteristics of Sr/Ba, La/Sm vs. Ce/Yb and other trace element evidences, the granites were the late stage products of differentiation and fractionated from a homogeneous parental granitic magma.

• Journal of the Korean earth science society
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• v.30 no.5
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• pp.565-580
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• 2009

The Yongdong basin developed during Early Cretaceous in the central part of the Korean Peninsula and bounded on the northwest and southeast by northeast trending mega-scale strike-slip Yongdong Fault. An 8 km thick succession of exclusively terrigeneous sediments can be grouped into two mega-sequences. In concert with the migration of depocenter, the upper sequence overlaps the lower and occupies northern part of the basin during basin evolution. Alluvial and lacustrine environments were predominantly formed from early to late stage of the basin formation. Several lines of evidence support that the basin was formed within intra-arc tectonic environments and destroyed by polyphase tectonic force. Schematic evolutionary diagram of the basin is proposed.

• Economic and Environmental Geology
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• v.28 no.1
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• pp.9-17
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• 1995

The Kamkye Cu-Pb-Zn-Au-Ag deposits occur as quartz veins that filled fault-related fractures of NW system developed in the Cretaceous Gyeongsang basin. Three major stages of mineral deposition are recognized: (1) the stage I associated with wall rock alteration, such as sericite, chlorite, epidote and pyrite, (2) the early stage II of base-metal mineralization such as pyrite, hematite, and small amounts of sphalerite and chalcopyrite. and the middle to late stage II of Cu-As-Sb-Au-Ag-S mineralization, such as sphalerite, chalcopyrite, galena with tetrahedrite, tennantite, pearceite, Pb-Bi-Cu-S system, argentite and electrum. (3) the stage III of supergene mineralization, such as covellite, chalcocite and malachite. K-Ar dating of alteration sericite is a late Cretaceous ($74.0{\pm}1.6Ma$) and it may be associated with granitic activity of nearby biotite granite and quartz porphyry. Fluid inclusion data suggest a complex history of boiling, cooling and dilution of ore fluids. Stage II mineralization occurred at temperatures between 370 to $220^{\circ}C$ from fluids with salinities of 8.4 to 0.9 wt.% NaCl. Early stage II($320^{\circ}C$, 2.0 wt.% NaCl) may be boiled due to repeated fracturing which opened up the hydrothermal system to the land surface, and which resulted in a base-metal sulfide. Whilst the fractures were opened to the surface, mixing of middle-late stage II ore fluids with meteoric waters resulted in deposition of Cu-As-Sb-Au-Ag minerals from low temperature fluids(${\leq}290^{\circ}C$). Boiling of ore fluids may be occured at a pressure of 112 bar and a depth of 412 m. Equilibrium thermodynamic interpretation of sphalerite-tetraherite assemblages in middle stage II indicates that the ore-forming fluid had log fugacities of $S_2$ of -6.6~-9.4 atm.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.203-216
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• 2012

Based on the petrologic and age data of the Cretaceous to early Tertiary granites in south Korea, we propose a new tectonic model reflecting their temporal and spatial variations. A number of petrographic and geochemical studies on the granites suggest that they originated from the magma formed by subduction of oceanic crust in continental margin and were emplaced in epizone. The MMEs with various shapes and sizes, which were produced due to the magma mixing caused by the injection of mafic magma from mantle during the crystallization of the granitic magma, are observed in the granites. The distributions of the MMEs and ages of the granites show a distinctive spatio-temporal distribution pattern. The distribution pattern can be explained by a multiple slab window model related to the ridge subduction of Izanagi-Pacific plates during the Late Cretaceous.

• Economic and Environmental Geology
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• v.29 no.4
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• pp.455-470
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• 1996

Mesozoic granitic rocks in the Korean peninsula contain $H_2$, $CH_4$, CO and rare $C_2H_6$. The Jurassic Daebo granites mostly belonging to the ilmenite series are predominated in $CH_4$. Meanwhile, the magnetite series Bulguksa granites of Cretaceous age in the Kyongsang basin and Okchon zone are relatively enriched in $CO_2$. The older granites have a wide variation of $CH_4/CO_2$ ratios (0.1~1.0) compared to those of the younger ones (0.1~0.5). This characteristics of gas compositions suggest that the Jurassic granites are principally derived from the partial melting of metasedimentary rocks with much reducing materials in the lower continental crust. On the other hand, the mantle source granitic magmas might be responsible for the Cretaceous granites characterized by dominant and homogeneous $CO_2$ gas compositions. Liquid-vapor homogenization temperatures of quartz in the Jurassic and Cretaceous granites range from 108 to $539^{\circ}C$ (av. $324^{\circ}C$) and 160 to $556^{\circ}C$ (av. $358^{\circ}C$), respectively. Their salinities are between 0.2 and 16.3 wt.% NaCl for the Jurassic granites and 0.4, and 15.6 wt.% NaCl for the Cretaceous ones. Fluid inclusions with solid daughter minerals lying on or near the halite equilibrium curve represent inclusion fluids from the magmatic stage. The type I and II fluid inclusions which are plotted apart from the equilibrium curve are considered to trap in late hydrothermal alteration stage with a increasing influx of metedric water.