• Journal of the Korean Geophysical Society
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• v.2 no.2
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• pp.91-99
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• 1999

A high-resolution seismic profile acquired across the northeastern boundary of the Pungam Basin, one of the Cretaceous sedimentary basins in Korea, has been interpreted to delineate subsurface geological structures across the basin boundary. We identified boundary faults and unconformity surfaces of the basin and divided sediment body into three seismic depositional units (Units I, II, and III from youngest to oldest). Inferred from fault geometry and type, northeastern part of the Pungam Basin has been formed by a strike-slip fault whereas the normal faults near the boundary were formed by transtensional movement along a fault zone. A 350-400 m thick sediment layer is overlying the Precambrian gneiss. Bedding planes of Unit III are dipping westward and are closely related to an anticline in the acoustic basement. Unit II is also tilted westward, suggesting that the eastern part of the fault zone was uplifted after deposition of lower part of the sedimentary body. Afterward, the uplifted sediment layers were eroded and transported to the western part of the basin. Chaotic reflection pattern of sedimentary Units II and III may suggest that strike-slip movement along the fault zone deformed basin-filled sediments.

• Economic and Environmental Geology
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• v.31 no.6
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• pp.519-526
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• 1998

A high-resolution seismic survey was conducted at the northeastern boundary of Pungam basin, one of the Cretaceous sedimentary basins in Korea. A 100 kg weight was used as an energy source and was found to be better than a sledge hammer in mapping deeper geologic structures. Several processing techniques such as f-k filtering, predictive deconvolution, and time-variant filtering are useful to enhance the signal-to-noise ratio by suppressing unwanted seismic energy. Four seismic units are recognized where many vertical faults are developed. The boundary fault between sedimentary rocks and Precambrian gneiss is identified along with a fracture zone of approximately 30 m wide. Bedding planes of the sedimentary rocks dipping westward are interpreted to be limbs of a syncline or volcanic flow. There faults and tilted bedding planes indicate that the basin had undergone significant tectonic deformation.

• Journal of the Korean Geophysical Society
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• v.2 no.3
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• pp.201-208
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• 1999

A high-resolution seismic profile acquired across the middle part of the Pungam Basin, one of the Cretaceous sedimentary basins in Korea, has been interpreted to delineate subsurface geological structures. Boundary faults, intrusive bodies, and unconformity surfaces are identified on the seismic section. Basin fills are divided into five depositional units (Units I, II, III, IV, and V in descending order). The normal faults were formed by transtentional movement along a sinistral strike-slip fault zone. Unconsolidated sediments, a weathered layer, and sedimentary layers overly the Precambrian gneiss. The granite body intruded at the southeastern part contacts the adjacent sedimentary rocks by a near-vertical fault. Granitic intrusions caused tectonic fractures and normal faults of various sizes. An andesitic intrusive body indicates post-depositional magmatic intrusions. Continuous strike-slip movements have deformed basin-filling sediments (Units I and II).

• Journal of the Korean Geophysical Society
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• v.9 no.1
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• pp.37-45
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• 2006

Velocity structures were defined in the vicinty of the 140-m deep test borehole in the pungam basin through simultaneous inversion of surface seismic refraction and far-ofset VSP traveltime data. Seismicenergy generated at the surface by a seisgun was recorded both at 42 surface locations at 3-m intervalsalong the profiles in the N20E and its orthogonal directions and at 71 m depth in the borehole. Forthe ofset VSP study, seismic energy was generated by a 5 kg sledgehamer at the surface in the horizontal ofset range of -19.5∼+19.5 m from the borehole. The seismic signals were detected at 9∼99 m depths with 1∼2 m intervals and recorded for 204 ms per shot. After shot static corrections,first-arrival times picked from both the surface refraction and borehole records were simultaneouslyinverted to yield velocity tomograms. The tomograms indicate that a 1.5 m thick soil layer with velocities les than 500 m/s overlies basements having a velocity range of 3,067 ∼5,717 m/s. Within the basements,∼4 m and deeper than 71 m. The high-velocit yzones may be due to conglomerates intercalated with sandstones and siltstones. No evidence for large-scale fracture zones or faults is detected near the borehole

• 한국지구물리탐사학회:학술대회논문집
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• 2006.06a
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• pp.125-130
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• 2006

Both surface seismic and far-offset VSP data were recorded alongtwo mutually perpendicular profiles in the Pungam basin. The first-arrival times were simultaneously inverted using the tomography method. For the surface data, seismic energy was generated by a 5-kg sledgehammer at 48 stations and detected by 21 surface geophones at 3 m intervals and one 3-component geophone in test borehole for the purpose of static corrections. For the VSP data, seismic waves generated by the sledgehammer on the ground were detected by a 3-component borehole geophone in a depth range of $9{\sim}99\;m$. Delay times of the hammer data were corrected using the seisgun data before the inversion to yield velocity tomograms. The tomograms indicates that the soil layer with velocities less than 750 m/s averages 1.8 m thick. The velocity varies from 5353 m/s at the depth range of $31{\sim}40\;m$ to 4262 m/s at the depth range of $65{\sim}73\;m$. Compared with core samples, the relatively large variation in velocity may due to lithology changes and fracture effects with depth.

• The Journal of Engineering Geology
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• v.8 no.2
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• pp.163-173
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• 1998

Suite of log analysis techniques consisting of geophysical well log, geological core log, and physical core log have been made to understand the well log responses and to determine the lithology of a test borehole-PABH1 located in Pungam sedimentary basin, Sosok, Hongchon-gun, Kangwon Province. Geological core logging has been precisely made over the cores taken between 64 and 124 meters, and 11 groups of rock types were deduced. Using the core samples divided by 11 groups, geophysical property measurements consisting of resistivity, natural gamma and density were made. Each rock group in the area is shown to have its characteristic physical response from geophysical well log and geophysical core logs. The outstanding physical responses particularly shown from siltstone, coarse sandstone to conglomerate, and granitic gneiss in the area were effectively used as keybeds in correlating the geophysical well logs to the result of geological core logs.

• The Journal of Engineering Geology
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• v.8 no.1
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• pp.87-98
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• 1998

Multiple logging techniques consisting of geophysical logs, care logs, physical property measurements on core samples have been adopted on a test borehole drilled in the Pungam basin ; a small Cretaceous sedimentary basin located in Sosok area, Hongchon-gun, Kangwon Province, Korea. This study has been made to solve the problem of mismatches between the results of geophysical log and core log analyses. And the cause and range of depth errors as well as logging responses were studied. The result shows that the depth error caused by geophysical log is so small that it can be used as a reliable depth criterion in the borehole. The analysis of physical property measurements is also shown as very effective in determining the real depth and the geology of the borehole.

• The Journal of Engineering Geology
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• v.14 no.4 s.41
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• pp.401-416
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• 2004

We have collected shale specimens from the Pungam Basin in Kangwon province and investigated change of physical properties by freezing and thawing in water as well as in acidic fluid. The temperature range was $-20{\pm}2^{\circ}C\~15{\pm}2^{\circ}C$. Specimens were frozen for 12 hours and thawed in water for 8 hours. Then, they were saturated in the vacuum chamber for 4 hours to make specimens fully saturated. This procedure was 1 cycle. We have measured absorption, ultrasonic velocity, shore hardness, slake durability and uniaxial compressive strength at every 5th cycles. The physical properties increased or decreased as freezing and thawing cycles increased. Uniaxial compressive strength decreased by 0.40MPa per cycle in water and by 0.48MPa in acidic fluid. Elastic constant also decreased by 0.21GPa per cycle in water and by 0.30GPa in acidic fluid. Absorption increased by $0.29\%$ and $0.37\%$ per cycle in water and acidic fluid, respectively. These results indicate that decrease in uniaxial compressive strength, elastic constant and absorption by freezing and thawing in acidic fluid is more rapid than in water. Ultrasonic velocities, shore hardness and slake durability show no differences in water and acidic fluid. When we compared our results with the temperatures in the Hongchon during the winter season, $6\~12$ cycles may be equivalent to 1 year.

• The Journal of Engineering Geology
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• v.8 no.3
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• pp.261-273
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• 1998

Multiple well log analysis technique consisting of geophysical well log and geological core log has been made to analysis the discontinuities of a test borehole-PABH1 located in Pungam sedimentary basin, Sosok, Hongchon-gun, Kangwon Province. Well log methods consist of normal resistivity log, focussed log, single point resistance log, SP log, gamma log, natural gamma log as well as acoustic televiewer log and borehole television log. Core scanning technique was used as an aid for geological core log. The analysis was made by comparing firstly the televiewer and core discontinuities, and then the results from conventional geophysical log analysis were compared to those from core log and acoustic televiewer log. Fractures deduced from the acoustic televiewer log coincide well with discontinuities shown on the core and conventional geophysical logs. Particularly close coincidence could be observed between fractures derived from acoustic televiewer and conventional geophysical log analysis. It has been noted that the geophysical logs such as, caliper, resistivity, density and high resolution gamma gamma curves are effective in delineating the fractures. For example the ratio between density and resistivity (BRD/SHN) provides also an alternative indicator for discerning the fracture condition in the study area.

• Journal of the Mineralogical Society of Korea
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• v.21 no.1
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• pp.1-15
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• 2008

The Cretaceous Gajok gold-silver deposit within porphyry granite is located nearby the Cretaceous Pungam basin at the northeastern area in Republic of Korea. The Gajok gold-silver deposit is distinctively composed of a multiple-complex hydrothermal veins with comb, crustiform chalcedony quartz and vug textures, implying it was formed relatively shallower depth. The hypogene open-space filling veins could be divided into 5 paragenetic sequences, increasing tendency of Ag-rich electrum and Ag-phases with increasing paragenetic time. Electrum with high gold contents (${\sim}50$ atomic % Au) as well as sphalerite with high FeS contents (${\sim}6$ mole % FeS) are representative ore minerals in the middle stage. The late stage is characterized by silver-phase such like native silver and/or argentite, coexisting with Ag-rich electrum ($10{\sim}30$ atomic % Au) and Fe-poor sphalerite (< 1 mole % FeS). The ore-forming fluids evolution started at relatively high temperature and salinity (${\sim}360^{\circ}C$, ${\sim}7\;wt.%$ eq. NaCl) and were evolved by dilution and mixing mechanisms on the basis of fluid inclusion study. The gold-silver mineralization proceeded from ore-forming fluids containing greater amounts of less-evolved meteoric waters(${\delta}^{18}O$; $-0.6{\sim}-6.7\;%o$). These results imply that gold-silver mineralization of the Cretaceous Gaiok deposit formed at shallow-crustal level and could be categorized into low-sulfidation epithermal type, related to Cretaceous igneous activity.