• Economic and Environmental Geology
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• v.33 no.3
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• pp.217-228
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• 2000

We use spectral correlation method to analyze gravity and magnetic anomalies of Euiseong Sub-basin for distribution of rock facies and gelogic structures. The analysis reveals distinct polarity between gravity and magnetic anomaly correlation ; intermediate to mafic intrusives, extrusives, and the Tertiary basin shows positive gravity (+G) and positive magnetic (+M) correlation. Granitic gneiss and felsic volcanics negative gravity 9-G) and negative magnetic (-M) correlation. The Palgongsan granite, felsic to mafic extrusives and Mesozoic granites are characterized by -G and + M correlation. +G and -M correlations in the sedimentary formations are interpreted by uplift of pre-Cretaceous basement rocks . The + G and + M correlation characteristics in northeastern part of Euiseong Sub-basin including the Tertiary sedimentary basin result from the uplift of crustal materials. Major axes of spectrally correlated amomalies have mostly NW-SE or NE-SW directions. The former is due to the intrusives along strike-slip faults, and the latter which is observed in sedimentary formations is related to geological structures of basement associated new insight into the boundary between Euiseong and Milyang Sub-basin.

• Economic and Environmental Geology
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• v.33 no.3
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• pp.229-237
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• 2000

The structure of Euiseong Sub-basin and boundary of sub-basins were examined by analytical aeromagentci anomaly data. Magnetic lineaments have trends of NE-SW, NWW-SEE and NEE-SWW. The NE-SW lineaments in the sedimentary formations and pre-Cretaceous basement are assoicated with the direction of expansion of basin and the lineaments in the volcanic rocks and intrusives indicate the direction of structural weakness ones such as fault, which were major gateways of igneous activities. Euiseong Subbasin is bounded by pre-existing Andong Fault, pre-Cretaceous basement in the west, NE-SW lineament from Jyungsan to Angang, and NW-SE lineament connecting southwestern boundary of Palgongsan Granite and Jeokje Fault. In particular , the NW-SE lineament , which caused upheavel of pre-Cretaceous rocks, on Jeokje Fault is inferred as a boundary between Euiseong and Milyang Sub-basins.

• Economic and Environmental Geology
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• v.27 no.4
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• pp.411-420
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• 1994

Euiseong sub-basin, one of three sub-basins in Kyungsang basin, consists of various sedimentary and igneous rocks of Cretaceous age. Kusandong tuff and Yucheon volcanic rocks from the sub-basin were collected for the anisotropy of magnetic susceptibility (AMS) study. Maximum directions of the AMS for Kusandong tuff and Yucheon volcanic rocks are used to detect possible source areas. Although the dispersion of the maximum directions of the AMS, mainly due to low susceptibility and/or low percent anisotropy of individual specimens, is rather large, it is possible to reveal several source areas for the volcanic rocks. Areas near the Keumseongsan and Hwasan, calderas in the study area, are identified as source areas for Yucheon volcanic rocks, while the western part of Sunamsan, another collapsed caldera in Euiseong sub-basin, is inferred to be the source area for Kusandong tuff. However, it is not possible to determine detailed source areas for groups of Yucheon volcanic rocks of different lithologies, because of poor degree of convergence of the maximum directions of the AMS results from the volcanic rocks. It is also concluded that several episodic volcanic activities centered at Keumseongsan and Hwasan calderas were responsible for the formation of Yucheon volcanic rocks in Euseong area.

• Korean Journal of Remote Sensing
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• v.16 no.1
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• pp.25-36
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• 2000

To evaluate the feasibility of using lineaments for the interpretation of regional geological structures, the extracted lineaments from satellite image and surveyed surface geological features mapped in the field were analyzed for the Euiseong Sub-basin. The lineaments extracted from Landsat-5 TM images show primary directions of N20$^{\circ}$~30$^{\circ}$E, N60$^{\circ}$~70$^{\circ}$E, N60$^{\circ}$~70$^{\circ}$W, which represent the trends of faults, strikes, and joints. In the sedimentary formation in the northern part of Palgongsan Uplift Zone, primary directions of the lineaments are NNE and NWW, and NEE in southern parts. The analysis of satellite lineaments is proved to be very useful to study the large-scale structures and surface geology of the Euiseong Sub-basin, whereas the previous research using brittle tectonics approach was advantaged in the outcrop scale in interpretation.

• Proceedings of the KSEEG Conference
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• 2003.04a
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• pp.184-185
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• 2003

The Cretaceous magmatism in the Gyeongsang Basin, which intruded into the upper crust or extruded throughout ENE-trending volcanic belts in southern Korea, led to the formation of two contrasting metallogeinic provinces: the Haman-Gunbug-Goseong and the Euiseong. The Haman-Gunbug-Goseong metallogenic province in the southwestern portion of the Gyeongsang Basin consists of dominantly nonmarine sedimentary rocks (e.g., the Sindong and Hayang groups) which are rarely intercalated with andesitic pyroclastics and flows. (omitted)

• Economic and Environmental Geology
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• v.38 no.2 s.171
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• pp.143-153
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• 2005

Euiseong subbasin, included in the Kyungsang Basin, was created by the result of volcanic activity in the late Cretaceous, and contacts with Milyang and Youngyang subbasins by Palgongsan and Andong faults, respectively. In this study, geophysical survey is implemented fur investigating surface and subsurface geologic structure in Euiseong subbasin which composed with the complex of volcanic and plutonic rocks. To understand surface geologic feature, IRS satellite image and DEM(Digital Terrain Map) are used for analyzing lineament and its density. The numbers of lineaments show major trend in $N55^{\circ}\~65^{\circ}W$, and aspects of lineament lengths show major trend in $N55^{\circ}\~65^{\circ}W$ and N-S directions. 13 delineate subsurface density discontinuity; Power spectrum analysis was implemented for gravity anomaly data, resulting $4-5{\cal}km$ depth of basin basement and $0.5-0.6{\cal}km$ depth of shallow discontinuity. From the result of power spectrum analysis, 2.5-D modelings were implemented along two profiles of A-A' and B-B', and they show subsurface geology in detail. Analytic signal method for detecting boundaries of magnetic basements show 0.001-130 nT/m values, and high energy area show good correspondency with the boundaries of Palgongsan granite and caldera areas in Euiseong subbasin.

• Economic and Environmental Geology
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• v.32 no.2
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• pp.189-201
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• 1999

Paleomagnetic and rock magnetic investigations have been carried out for the Cretaceous Hanyang Group, exposed in the Yongyang Sub-Basins within the Kyeongsang Basin, eastern South Korea. A total of 452 oriented core samples was drilled from 31 sits for the study. The in-situ site mean direction is more dispersed than the mean direction after bedding correction, indicating that the fold test is positive at 95% confidence level. In addition, the stepwise unfolding of the characteristic remanent magfold test is positive at 95% confidence level. In addition, the stepwise unfolding of the characteristic remanent magnetization reveals that a maximum value of k is observed at 90% unfolding. Furthermore, the rock magnetic investigations and electron microscope observations of the representative samples show that the main magnetic carrier of the Hayang Group is the detrital specular hematite of single and pseudo-single domain sizes with negligible contribution of pigmentary hematite grains. These results collectively imply that the ChRM direction is the primary component acquired at the time of the formation of the strata. Provided the primary nature of the ChRM, a magnetostratigraphic correlation between polarities of the studied formation and the Geomagnetic Time Scale indicates that the Hayang Group in the Yongyang Sub-Basin can be correlated to the Cretaceous Long Normal superchron. The paleomagnetic pole position from this study is significantly different from those of the Hayang group in the Euiseong the Milyang sub-Basins. Rather the paleomagnetic pole position of the Hayang Group of the study area is closer to that of the Quaternary period or present time of the Korean Peninsula. It is hypothesized that the study area might be rotated about 25$^{\circ}$ aticlockwise with respect to the Euiseong and Milyang Sub-Basins after the formation of the strata and aquisition of the ChRM, although there is not enough geologic evidence supporting the rotation hypothesis.

• Economic and Environmental Geology
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• v.27 no.3
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• pp.263-279
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• 1994

Paleomagnetic and rock-magnetic data of Cretaceous sedimentary and volcanic rocks from the Euiseong area indicate that the stable components of remanence are carried by single and pseudo-single domain magnetite, with the exception of the Shinyangdong Formation which has been remagnetized. The Hayang Group, except for the remagnetized Shinyangdong Formation, yields the mean characteristic direction of $D/I=22.5^{\circ}/57.2^{\circ}$ (${\alpha}_{95}=4.6^{\circ}$, N=14 sites) and the pole position is $72.0^{\circ}N$, $206.4^{\circ}E$ ($dp/dm=4.9^{\circ}/6.7^{\circ}$). The Yucheon Group shows two polarities and the mean characteristic direction of $D/I=351.2^{\circ}/60.5^{\circ}$ (${\alpha}_{95}=11.2^{\circ}$, N= 19 sites) and the pole position is $81.3^{\circ}N$, $79.0^{\circ}E$ ($dp/dm=13.0^{\circ}/17.0^{\circ}$). The mean directions of both the Hayang and the Yucheon Groups are supported by the McElhinny's fold test at the 99% confidence level and that of the Yucheon Group by a reversal test at the 95% confidence level. A magnetostratigraphic correlation between polarities of the study formations and the Geomagnetic Time Scale indicates that the Hayang Group can be correlated to the Cretaceous Long Normal Superchron (CLNS), and the Yucheon Group to the boundary between the CLNS and the Polarity Chron 33R or later boundaries between normal and reverse polarities. Comparison of the paleopoles from this study with those from the surrounding areas both within the Gyeongsang basin and in the northeastern Asia indicates that the study area was not undergone significant tectonic rotations with respect to the other parts of the Gyeongsang basin and that the Korean Peninsula was the part of the single terrane of the northeastern Asia at least since the CLNS. The Yucheon Group can be divided into four sub-groups based on the paleomagnetic data, suggesting that there were at least four times of volcanic activities in the study area.

• Economic and Environmental Geology
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• v.30 no.1
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• pp.1-14
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• 1997

The shales from the Euiseong area are interbedded along the bedding in Cretaceous Gyeongsang Supergroup, which are composed mainly of quartz, plagioclase, K-feldspar and associated with trace amount of biotite, muscovite, chlorite, pyrite, hematite, carbonate and clay minerals. The ratio of $Al_2O_3/Na_2O$ and $K_2O/Na_2O$ in shales from the Shindong Group are ranged from 9.16 to 24.32 and from 1.70 to 5.97, and the Hayang Group ranged from 2.76 to 8.89 and from 0.42 to 2.74, which are negative correlated between $K_2O/Na_2O$ and $Al_2O_3/Na_2O$ against $SiO_2/Al_2O_3$ respectively. Those are suggested that controlled of mineral compositions in shales due to substitution and migration of elements by sedimentation and diagenesis. These shale formation were deposited in basin of terrestrial environments originated from the igneous rocks, and the REE of these rocks are not influenced with diagenesis and hydrothermal alterations on the basis of $Al_2O_3$ versus La, La against Ce, Zr versus Yb, the ratios of La/Ce (0.43 to 0.62) and Th/U (1.11 to 10.71). The narrow range in trace and REE element characteristics as Co/Th (0.63 to 1.92), La/Sc (1.98 to 5.90), Sc/Th (0.58 to 1.30), V/Ni (0.90 to 3.25), Cr/V (0.45 to 1.78), Ni/Co (1.88 to 6.67) and Zr/Hf (30.04~60.87) of these shales argues for inefficient mixing of the simple source lithologies during sedimentation. These rocks also show much variation in $La_N/Yb_N$ (6.90 to 17.02), Th/Yb (4.17 to 13.68) and La/Th (1.98 to 5.90), and their origin is explained by derivation from a mixture of intermediate to acidic igneous rocks.

• The Korean Journal of Petroleum Geology
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• v.4 no.1_2 s.5
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• pp.12-19
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• 1996

Directional sedimentary structures (channel structure, cross stratification, and current ripple) were observed in fine to gravelly ye.y coarse sandstones of the Cretaceous Mayans Group (lljig, Hupyeongdong, and Jeomgok formations) in the northeastern part of Euiseong subbasin of Kyongsang basin, Southeast Korea. Large and small scale channel structures are common in all formations. Trough cross-stratification and channel structure frequently occur in the lljig formation (proximal fluvial deposit), whereas planar cross- stratification, cross lamination, and current ripple occur abundantly in the Hupyeongdong and Jeomgok formations (distal braided fluvial to marginal lacustrine deposits). The paleocurrent directions inferred from a statistical analysis of total 43 directional sedimentary structures show a mean azimuth of $290^{\circ}C$ with a standard deviation of $\pm68$. It suggests that the main flow of the paleocurrents moved toward the WNW direction and the source area of the sediments would be located somewhere in the ESE direction beyond the study area.