• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.66-73
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• 2001

Yangsan fault in the southeastern part of Korean peninsula has been locally reactivated along a prexisted fault during the late Pleistocene time. Geomorphological evidence of the reactivation is revealed at the northern segment(Yugye-ri, Tosung-ri areas) of the Yangsan fault. The reactivation is distinctively characterized by fault gouge and fracture zone with high frequency in the Yugye-ri area. Obique slip separation of the area is about three meters of the middle terrace. The cumulative vertical displacement is recognized after the formation of the middle terrace. Age of the reactivated faulting is constrained to during the formation of dissected valley deposits. Average vertical slip based on paleo-event is inferred to about 0.5-0.7 meter in this area.

• 한국석유지질학회:학술대회논문집
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• autumn
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• pp.2-16
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• 1999

This study includes structural analysis of the northern Pattani Basin, areal description of depositional facies, and their spatial relationships using 3-D seismic and well data. Well log data indicate that the representative depositional facies of the studied intervals are sandy, fluvial, channel-fill facies encased in shaly floodplain deposits. Seismic responses were predicted from a synthetic seismogram using a model of dominant depositional facies. Peak-to-trough amplitude and instantaneous frequency seismic attributes are used in depositional facies interpretation. Three Intervals A, B and C are interpreted on the successive stratal surfaces. The shallowest interval, A, is the Quaternary transgressive succession. Each stratal surface showed flow pattern variation of fluvial channel facies. Two transgressive cycles were identified in interval A. Interval B also indicated fluvial facies. Depositional facies architectures are described by interpreting seismic attributes on the successive stratal surfaces.

• Journal of the Korean earth science society
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• v.44 no.4
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• pp.264-274
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• 2023

The Korea Strait comprises a continental shelf in a shallow sea that experienced glacio-eustastic sea-level changes during the Quaternary period. A long core of 76.6 m in length was acquired at the South Sea Drilling Project site (SSDP-101; 34°19.666'E and 128°16.335'N) with a 60 m water deep. The uppermost massive sand beds were interpreted as sandy sediments of the nearshore marine sand ridge in the shallow sea during the transgression of sea level, whereas the lower parts of alternating sandy and muddy beds were interpreted as deposits in marsh, estuary, and tidal flat environments. A three-layered geoacoustic model was reconstructed for the sedimentary succession in the high-resolution seismic profile based on a 140-grain size and sediment type of core SSDP-101. For the actual underwater simulation and experiments, the in-situ P-wave speeds were calculated using the sound speed ratio of the Hamilton method.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.3
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• pp.142-151
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• 2001

Detailed interpretation of some high-resolution seismic profiles in Yosu Strait reveals that Late Quaternary deposits consist of three allostratigraphic units (UH, LH, PL) formed by fluvial and tidal controls. The top mud unit, UH, thins onshore, and overlies the backstepping modem Seomjin delta deposits, which is interpreted as a transgressive systems tract (757) related to Holocene relative sea-level rise. The unit LH below the unit UH is composed of delta, valley- and basin-fill facies. The delta facies (Unit $LH_1$) occurs only in Gwangyang Bay and shows two prograding sets retrogradationaly stacked, thus it is also interpreted as a transgressive systems tract(757). On the contrary, the valley- and basin-fill facies (Unit $LH_2$), interpreted as 757, occur between the units UH and PL (Pleistocene deposits) in Yosu Strait. The bounding surface between UH and $LH_2$ can be interpreted as a tidal ravinement surface on the basis of trends thinning toward inner bay and becoming young landward. Furthermore its geomorphological pattern is similar to that of recent tidal channels. This allostratigraphy in'ffsu Strait suggests that two 757 deposits (UH and $LH_2$), divided by tidal ravinement surface, have been formed in Yosu Strait, whereas in Gwangyang Bay backstepping delta deposits ($LH_1$) without tidal ravinement surface have been formed during Holocene sea-level rise. These characteristics indicate that different stacking patterns could be formed in these two areas according to different increasing rate of accommodation space caused by different geomorphology, sediment supply and tidal-current patterns even in the same period of Holocene sea-level rise.

• The Korean Journal of Quaternary Research
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• v.4 no.1
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• pp.41-57
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• 1990

Gravel shapes of the terrace gravel sequences are compared with the present river gravels and beach gravels in the Pohang and its surrounding areas. Seventeen gravel textural parameters are divided into 5 groups based on R-mode factor analysis. Among them, three parameters (RDm, MPSm, SZstd) are selected for a test of discriminant possibility of palaeoenvironment of the terrace gravel deposits. Marine gravels are in the range of 0.49 to 0.75 in mean roundness, 0.46 to 0.78 in mean maximum projection sphericity and 0.39 to 1.85 in standard deviation of size, whereas river gravels are 0.28 to 0.51 in mean roundness, 0.66 to 0.72 in mean maximum projection sphericity and 1.04 to 1.81 in standard deviation of size. For practical access to the palaeoenvironment discrimination, a bivariant diagram between mean roundness and mean maximum projection sphericity is the most effective. The marine terrace gravels are plotted within the variation range of present beach gravels and show 0.49 to 0.71 in mean roundness and 0.59 to 0.66 in mean maximum projection sphericity. The gravels of river terrace vary within the range of gravels derived from present river bed and are characterized as 0.36 to 0.48 in mean roundness and 0.66 to 0.71 in mean maximum projection sphericity.

• Economic and Environmental Geology
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• v.56 no.3
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• pp.343-363
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• 2023

Sulawesi island, as a global producer of nickel resources, is leading the rapid growth of nickel industry of Indonesia. Nickel laterite deposits in Sulawesi was formed by lateritization of the world-scale East Sulawesi Ophiolite (ESO) under the active tectonic setting and tropical rainforest climate. In this paper, exploration cases for nickel laterite deposits in five regions of Sulawesi are reported. Regional characteristics on nickel laterite deposits in Sulawesi are understood based on various exploration activities such as outcrop, trench and pit survey, petrological observation, geochemical analysis, and interpretation of drilling data, etc.. In the northeastern part of 'Southeast-Arm', which is a strategic location for nickel industry of Indonesia, ESO is extensively exposed to the surface. In the Morombo and Morowali regions, typical high-grade saprolite-type orebodies with a thickness of 10 to 20 m occur. The cases showed that topographic relief tends to regulate Ni-grade distribution and orebody thickness, and that high grade intervals tend to occur in places where joints and garnierite veins are dense. In the Tinanggea and South Palangga regions in the southern part of the Southeast-Arm, overburden composed of Neogene to Quaternary deposits is a major factor affecting the preservation and profitability of nickel laterite deposits. Despite the overburden, high-grade saprolite-type orebodies composed of Ni-bearing serpentine with garnierite veins occur in a thickness of around 10 m to secure economic feasibility. In contrast, in the Ampana region in the northern part of 'East-Arm', low-grade nickel laterite deposits with immature laterite profile was identified, which is thought to be the result of active denudation due to tectonic uplift. Exploration cases in this paper will help to understand characteristics and controlling factors on nickel laterite deposits in Sulawesi, Indonesia.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.8 no.1
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• pp.35-43
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• 2003

Recent geomorphological changes and late Quaternary depositional sequences of Gwangyang Bay are studied based on bathymetric maps, surface sediments, and seismic profiles. As a result of the reclamation of coastal area for an industrial complex construction, the coastline of Gwangyang Bay has rapidly been changed and the area of it has now been reduced by about 25 ％ in the last 30 years. In addition, the bottom topography is actively modified by dredging for navigation channels. In surfical sediment distribution, the western part of Gwangyang Bay is dominated by mud facies, whereas the eastern part of the Bay is dominated by sand-mud mixing facies. Depositional sequences above the basement are divided into two units: Unit I in upper layer and Unit II in lower one. These depositional units are unconformably bounded by middle reflector-M. Unit II, mostly occupying the channel areas, is interpreted as fluvial-origin deposits during sea-level lowstand. Unit I typically shows a progradational pattern from the Seomjin River mouth to the Yeosu Strait, which is interpreted as deltaic deposits supplied from the Seomjin River during the Holocene sea-level highstand. The shallow gas within the sediments Is widely distributed in most area, and locally exposed onto the sea-bed due to dredging.

• Journal of the Korean Geographical Society
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• v.33 no.3
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• pp.447-454
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• 1998

As a widespread tephra erupted 24 to 25 KA, Aira-Tn Ash, or AT, provides an invaluable datum for stratigraphic study of late Pleistocene in Northeast Asia. AT can be identified from their tonal characteristic and morphology (the so­called bubble-wail feature), as well as typical refractive index. First reported in 1983, its presence was confirmed from many palaeolithic deposits distributed throughout Korea. It forces us to reconsider the age of prominent Pleistocene deposits. At the famous archaeological site of Chon-gok-ni, presence of AT lends a firm support that sedimentation and deposition of lithic assemblage were in fact a late Upper Pleistocene event, thus, throwing a new question at archaeologists to explain why such archaic-looking tools were continued to be made. Discovery of AT at Chongdongjin is more surprising, since the coastal terrace has been regarded by many as an early Lower Pleistocene eustatic feature. It implies strongly that we need to devise a new scheme for Quaternary stratigraphy. In the absence of reliable datum and marker for Quaternary research, efforts must be given to search for and identify AT and other widespread tephras.

• Journal of the Korean Geophysical Society
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• v.5 no.4
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• pp.271-281
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• 2002

Interpretation of high-resolution seismic profiles collected from the inner shetf of the Korea Strait reveals that the shelf sequence in this area consists of three sedimentary units (I, II, and III in a descending order) formed after the last glacial maximum. Lower two units (II and III) represent the transgressive systems tract formed during the Holocene transgression, Unit III above the sequence boundary is interpreted to be the transgressive estuarine deposit, whereas Unit ll above the ravinement surface forms a thin transgressive sand which consists of the sediment produced through shoreface erosion and winnowing during the transgression. Unit I above the maximum flooding surface is the highstand systems tract consisting mainly of recent muds derived from the Nakdong River.

• The Korean Journal of Quaternary Research
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• v.17 no.2
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• pp.33-38
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• 2003

This study is conducted to examine the data of climate or environmental change in the northeastern Asia during the last glacial maximum. A remarkable feature of the 18,000 BP biome reconstructions for China is the mid-latitude extention of steppe and desert biomes to the modem eastern coast. Terrestrial deposits of glacial maximum age from the northern part of Yellow Sea suggest that this region of the continental shelf was occupied by desert and steppe vegetation. And the shift from temperate forest to steppe and desert implies conditions very much drier than present in eastern Asia. Dry conditions might be explained by a strong winter monsoon and/or a weak summer monsoon. A very strong depression of winter temperatures at LGM. has in the center of continent has influenced in northeast Asia similarly. The vegetation of Hokkaido at LGM was subarctic thin forest distributed on the northern area of middle Honshu and cool and temperate mixed forest at southern area of middle Honshu in Japan. The vegetation landscape of mountain- and East coast region of Korea was composed of herbaceous plants with sparse arctic or subarctic trees. The climate of yellow sea surface and west region of Korea was much drier and temperate steppe landscape was extended broadly. It is supposed that a temperate desert appeared on the west coast area of Pyeongan-Do and Cheolla-Do of Korea. The reconstruction of year-round conditions much colder than today right across China, Korea and Japan is consistent with biome reconstruction at the LGM.