• Economic and Environmental Geology
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• v.47 no.4
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• pp.421-430
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• 2014

In this study, a series of autoclave experiments were conducted in order to investigate the geochemical and mineralogical effects of carbon dioxide on deep subsurface environments. High pressure and temperature conditions of $50^{\circ}C$ and 100 bar, which are representative environments for geological $CO_2$ sequestration, were created in stainless-steel autoclaves for simulating the interactions in the $scCO_2$-groundwater-mineral reaction system. Zeolite, a widespread mineral in Pohang Basin where many researches have been focused as a candidate for geological $CO_2$ sequestration, and groundwater sampled from an 800 m depth aquifer were applied in the experiments. Geochemical and mineralogical alterations after 30 days of $scCO_2$-groundwater-zeolite sample reactions were quantitatively examined by XRD, XRF, and ICP-OES investigations. The results suggested that dissolution of zeolite sample was enhanced under the acidic condition induced by dissolution of $scCO_2$. As the cation concentrations released from zeolite sample increase, $H^+$ in groundwater was consumed and pH increases up to 10.35 after 10 days of reaction. While cation concentrations showed increasing trends in groundwater due to dissolution of the zeolite sample, Si concentrations decreased due to precipitation of amorphous silicate, and Ca concentrations decreased due to cation exchange and re-precipitation of calcite. Through the reaction experiments, it was observed that introduction of $CO_2$ could make alterations in dissolution characteristics of minerals, chemical compositions and properties of groundwater, and mineral compositions of aquifer materials. Results also showed that geochemical reactions such as cation exchange or dissolution/precipitation of minerals could play an important role to affect physical and chemical characteristics of geologic formations and groundwater.

• The Journal of the Petrological Society of Korea
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• v.18 no.4
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• pp.315-336
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• 2009

We have studied the orientational characteristics of microcrack frequency, it's length and density in Tertiary crystalline tuff from the northeastern part of the Gyeongsang Basin. 134 sets of microcracks on horizontal surfaces of 3 rock samples from Heunghae-eup were distinguished by enlarged photomicrographs of the thin sections. The variability in patterns among microcrack length-frequency histograms for three rock samples from different altitudes were derived. The pattern of histograms changes progressively from negative exponential form to log-normal form in proportion to altitude. The distribution pattern for rock sample no.1 from lower altitude shows the broad length distribution characterized by higher mean and median, and higher standard deviation. Meanwhile, this distribution pattern corresponds with characteristics of joint length distribution in sedimentary rocks of the lower part of the Gyeongsang Supergroup. The occurrence frequency of shorter microcracks increases toward both NW and NE directions from the $N0{\sim}10^{\circ}W$, with the dominant direction of $N80{\sim}90^{\circ}W$ and $N80{\sim}90^{\circ}E$, respectively. This distribution pattern represents the relative differences in formation timing among microcrack sets and the result of the new initiation of shorter microcracks. Meanwhile, the longest microcracks within $N60{\sim}70^{\circ}W$($L_{max}$:1.18 mm) and $N0{\sim}10^{\circ}W$($L_{max}$:0.80 mm) directions are seen, but this kind of microcracks are very limited in number. Whole domain of the directional angle($\theta$)-frequency(N), length(L) and density($\rho$) chart can be divided into five sections in terms of phases of the distribution of related curves. From the distribution chart, density curve shows five distinct peaks in the WNW-ESE($N70{\sim}80^{\circ}W$), NS~NNE-SSW($N0{\sim}10^{\circ}W$, $N10{\sim}20^{\circ}E$), ENE-WSW($N50{\sim}60^{\circ}E$), and nearly EW($N80{\sim}90^{\circ}E$) directions, respectively. Especially, main directions of faults correspond with the directional angle showing high density. Consequently, these distribution patterns of density curve reflect the representative maximum principal stress orientations suggested in previous studies.

• The Journal of the Petrological Society of Korea
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• v.27 no.3
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• pp.153-171
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• 2018

This study focuses on the investigation of geologic distribution and stratigraphy in the eastern part of Yeongdeok-gun, based on Lidar imaging, detailed field survey, microscopic observations, SHRIMP and LA-MC-ICPMS U-Pb age dating, and a new geological map has been created. The stratigraphy of the study area is composed of the Paleoproterozoic metamorphic rocks consisting of banded gneisses of sedimentary origin and schists ($1841.5{\pm}9.6Ma$) of volcanic origin, Triassic Yeongdeok plutonic rocks ($249.1{\pm}2.3Ma$) and Pinkish granites ($242.4{\pm}2.4Ma$), Jurassic Changpo plutonic rocks ($193.2{\pm}1.9Ma{\sim}188.8{\pm}2.0Ma$) and Fine-grained granites ($192.9{\pm}1.7Ma$), Formations [Gyeongjeongdong Fm, Ullyeonsan Fm. (~108 Ma), Donghwachi Fm.] of the Early Cretaceous Gyeongsang Supergroup and acidic volcanic rocks and dykes erupted and intruded in the Late Cretaceous, Miocene intrusive rhyolitic tuffs ($23.1{\pm}0.2Ma{\sim}22.97{\pm}0.13Ma$) and sedimentary rocks of the Yeonghae basin, and the Quaternary sediments. The Triassic Pinkish granites, Jurassic Changpo plutonic rocks and Fine-grained granites are newly defined plutonic rocks in this study. Miocene intrusive rhyolitic tuffs bounded by the Yangsan Fault, which was first discovered in the north of Pohang city, are believed to play an important role in the understanding of the Miocene volcanic activity and the crustal deformation history on the Korean Peninsula. It is confirmed that The NNE-SSW-striking Yangsan Fault penetrating the central part of the study area and branch faults are predominant in the dextral movement and cutting all strata except the Quaternary sediments.

• Economic and Environmental Geology
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• v.25 no.3
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• pp.337-349
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• 1992

The Tertiary basins in Korea have widely been studied by numerous researchers producing individual results in sedimentology, paleontology, stratigraphy, volcanic petrology and structural geology, but interdisciplinary studies, inter-basin analysis and basin-forming process have not been carried out yet. Major work of this study is to elucidate evidences obtained from different parts of a basin as well as different Tertiary basins (Pohang, Changgi, Eoil, Haseo and Ulsan basins) in order to build up the correlation between the basins, and an overall picture of the basin architecture and evolution in Korea. According to the paleontologic evidences the geologic age of the Pohang marine basin is dated to be late Lower Miocence to Middle Miocene, whereas other non-marine basins are older as being either Early Miocene or Oligocene(Lee, 1975, 1978: Bong, 1984: Chun, 1982: Choi et al., 1984: Yun et al., 1990: Yoon, 1982). However, detailed ages of the Tertiary sediments, and their correlations in a basin and between basins are still controversial, since the basins are separated from each other, sedimentary sequence is disturbed and intruded by voncanic rocks, and non-marine sediments are not fossiliferous to be correlated. Therefore, in this work radiometric, magnetostratigraphic, and biostratigraphic data was integrated for the refinement of chronostratigraphy and synopsis of stratigraphy of Tertiary basins of Korea. A total of 21 samples including 10 basaltic, 2 porphyritic, and 9 andesitic rocks from 4 basins were collected for the K-Ar dating of whole rock method. The obtained age can be grouped as follows: $14.8{\pm}0.4{\sim}15.2{\pm}0.4Ma$, $19.9{\pm}0.5{\sim}22.1{\pm}0.7Ma$, $18.0{\pm}1.1{\sim}20.4+0.5Ma$, and $14.6{\pm}0.7{\sim}21.1{\pm}0.5Ma$. Stratigraphically they mostly fall into the range of Lower Miocene to Mid Miocene. The oldest volcanic rock recorded is a basalt (911213-6) with the age of $22.05{\pm}0.67Ma$ near Sangjeong-ri in the Changgi (or Janggi) basin and presumed to be formed in the Early Miocene, when Changgi Conglomerate began to deposit. The youngest one (911214-9) is a basalt of $14.64{\pm}0.66Ma$ in the Haseo basin. This means the intrusive and extrusive rocks are not a product of sudden voncanic activity of short duration as previously accepted but of successive processes lasting relatively long period of 8 or 9 Ma. The radiometric age of the volcanic rocks is not randomly distributed but varies systematically with basins and localities. It becomes generlly younger to the south, namely from the Changgi basin to the Haseo basin. The rocks in the Changgi basin are dated to be from $19.92{\pm}0.47$ to $22.05{\pm}0.67Ma$. With exception of only one locality in the Geumgwangdong they all formed before 20 Ma B.P. The Eoil basalt by Tateiwa in the Eoil basin are dated to be from $20.44{\pm}0.47$ to $18.35{\pm}0.62Ma$ and they are younger than those in the Changgi basin by 2~4 Ma. Specifically, basaltic rocks in the sedimentary and voncanic sequences of the Eoil basin can be well compared to the sequence of associated sedimentary rocks. Generally they become younger to the stratigraphically upper part. Among the basin, the Haseo basin is characterized by the youngest volcanic rocks. The basalt (911214-7) which crops out in Jeongja-ri, Gangdong-myon, Ulsan-gun is $16.22{\pm}0.75Ma$ and the other one (911214-9) in coastal area, Jujon-dong, Ulsan is $14.64{\pm}0.66Ma$ old. The radiometric data are positively collaborated with the results of paleomagnetic study, pull-apart basin model and East Sea spreading theory. Especially, the successively changing age of Eoil basalts are in accordance with successively changing degree of rotation. In detail, following results are discussed. Firstly, the porphyritic rocks previously known as Cretaceous basement (911213-2, 911214-1) show the age of $43.73{\pm}1.05$ 및 $49.58{\pm}1.13Ma$(Eocene) confirms the results of Jin et al. (1988). This means sequential volcanic activity from Cretaceous up to Lower Tertiary. Secondly, intrusive andesitic rocks in the Pohang basin, which are dated to be $21.8{\pm}2.8Ma$ (Jin et al., 1988) are found out to be 15 Ma old in coincindence with the age of host strata of 16.5 Ma. Thirdly, The Quaternary basalt (911213-5 and 911213-6) of Tateiwa(1924) is not homogeneous regarding formation age and petrological characteristics. The basalt in the Changgi basin show the age of $19.92{\pm}0.47$ and $22.05{\pm}0.67$ (Miocene). The basalt (911213-8) in Sangjond-ri, which intruded Nultaeri Trachytic Tuff is dated to be $20.55{\pm}0.50Ma$, which means Changgi Group is older than this age. The Yeonil Basalt, which Tateiwa described as Quaternary one shows different age ranging from Lower Miocene to Upper Miocene(cf. Jin et al., 1988: sample no. 93-33: $10.20{\pm}0.30Ma$). Therefore, the Yeonil Quarterary basalt should be revised and divided into different geologic epochs. Fourthly, Yeonil basalt of Tateiwa (1926) in the Eoil basin is correlated to the Yeonil basalt in the Changgi basin. Yoon (1989) intergrated both basalts as Eoil basaltic andesitic volcanic rocks or Eoil basalt (Yoon et al., 1991), and placed uppermost unit of the Changgi Group. As mentioned above the so-called Quarternary basalt in the Eoil basin are not extruded or intruaed simultaneously, but differentiatedly (14 Ma~25 Ma) so that they can not be classified as one unit. Fifthly, the Yongdong-ri formation of the Pomgogri Group is intruded by the Eoil basalt (911214-3) of 18.35~0.62 Ma age. Therefore, the deposition of the Pomgogri Group is completed before this age. Referring petrological characteristics, occurences, paleomagnetic data, and relationship to other Eoil basalts, it is most provable that this basalt is younger than two others. That means the Pomgogri Group is underlain by the Changgi Group. Sixthly, mineral composition of the basalts and andesitic rocks from the 4 basins show different ground mass and phenocryst. In volcanic rocks in the Pohang basin, phenocrysts are pyroxene and a small amount of biotite. Those of the Changgi basin is predominant by Labradorite, in the Eoil by bytownite-anorthite and a small amount pyroxene.