• The Korean Journal of Quaternary Research
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• v.25 no.2
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• pp.17-24
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• 2011

We investigated the variation of $CaCO_3$ contents in cores PC1 and PC2 recovered from the continental slope area of the Ulleung Basin in the East Sea. $CaCO_3$ contents of cores PC1 and PC2 varied between 0.6 and 17.2% and between 0.3 and 43.0%, respectively. $CaCO_3$ contents in the upper part of core PC1 corresponding to MIS 1 are less than 5%, whereas those in the lower part of MIS 2 are more than 10%. Such variation of $CaCO_3$ contents in core PC1 confirms the previous results of $CaCO_3$ studies in the East Sea. In core PC2, $CaCO_3$ contents of the upper part are similar to those of core PC1. However, $CaCO_3$ contents in the lower part of core PC2 are more than 40%. According to XRD operation and SEM examination, the high $CaCO_3$ contents in the lower part of core PC2 are more attributable to the authigenic carbonate minerals rather than the biogenic carbonate composition. Such abundant authigenic carbonate minerals are closely related to the dissociation of methan hydrates which were observed in the Ulleung Basin.

• Economic and Environmental Geology
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• v.18 no.2
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• pp.177-184
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• 1985

The carbonate flat pebble conglomerates (CFPC) are interbedded as lenticular bed in the greenish rhythmite of the upper part of $Hwaj{\check{o}}l$ Formation, $Jos{\check{o}}n$ Supergroup. Pebbles are composed mainly of lime-mudstone with small amounts of bioclasts and silt-sized subangular quartz grains. The matrix among pebbles is composed mainly of sparry calcite with relatively much amounts of bioclasts, silt-sized subangular quartz grains and authigenic pyrite crystals or grains. The sparry calcite of the matrix seems to be the results of neomorphism of skeletal sands and bioclasts. The pebbles are well rounded and no plastic deformations are found. Some pebbles show the outer rim of glauconite. CFPC are not associated with any other intertidal features such as stromatolites, flaser bedding and channel structures. Also any features indicative of subaerial exposure such as dessication cracks, fenestrae and so on are not found in the bed. The sedimentological features of CFPC suggest that the following conditions appear to have been necessary for the formation of CFPC : 1) episodic deposition of thin, permeable calcareous beds separated argillaceous beds; 2) preservation of these beds near the sediment-water interface where they could become rapidly cemented; 3) erosion and redeposition of the partially lithified beds by storms or other exceptional erosional events. Eventually storm erosion and redeposition together represent only one of several critical conditions in the genesis of CFPC. The CFPC are very common in Cambrian and lower Ordovician formations, and become very rare in the younger carbonate formations. The expansion of infauna after Ordovician Period eliminated the widespread potential for rapid submarine cementation which is one of the critical factors to form CFPC.

• Journal of the Korean earth science society
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• v.23 no.7
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• pp.575-586
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• 2002

Authigenic minerals found in sandstones and mudrocks of the Lower Hayang Group (Cretaceous) in the central part of the Kyungsang Basin are carbonate minerals (calcite, dolomite), clay minerals (illite, chlorite, C/S, I/S and kaolinite), albite, quartz and hematite. Characteristic diagenetic mineral assemblages are as follows: albite-chlorite (including C/S)-hematite in the Chilgog Formation, albite-illite-calcite in the Silla Conglomerate, illite-chlorite-hematite in the Haman Formation and albite-chlorite-dolomite in the Panyawol Formation, respectively. Among clay minerals reflecting the physical and chemical change of the diagenetic process, illite, the dominant clay mineral, occurs in every formation in the study area. Chlorite occurs mainly in green or gray sandstones and mudrocks, or in sandstones and mudrocks of the Chilogok Formation which contains a high content of volcanic materials. Based on the mineral assemblage, diagenetic minerals are strongly related with source rocks. Judging from the illite crystallinity, diagenesis of sandstones and mudrocks in the study area reached the late diagenetic stage or low grade metamorphisim. The diagenetic process was much influenced by intrusion of the Bulguksa granite, content of organic materials, grain size, and depositional environment rather than burial depth.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.663-666
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• 2005

Gas hydrates are ice-like compounds that form at the low temperature and high pressure conditions common in shallow marine sediments at water depths greater than 300-500 m when concentrations of methane and other hydrocarbon gases exceed saturation. Estimates of the total mass of methane carbon that resides in this reservoir vary widely. While there is general agreement that gas hydrate is a significant component of the global near-surface carbon budget, there is considerable controversy about whether it has the potential to be a major source of fossil fuel in the future and whether periods of global climate change in the past can be attributed to destabilization of this reservoir. Also essentially unknown is the interaction between gas hydrate and the subsurface biosphere. ODP Leg 204 was designed to address these questions by determining the distribution, amount and rate of formation of gas hydrate within an accretionary ridge and adjacent basin and the sources of gas for forming hydrate. Additional objectives included identification of geologic proxies for past gas hydrate occurrence and calibration of remote sensing techniques to quantify the in situ amount of gas hydrate that can be used to improve estimates where no boreholes exist. Leg 204 also provided an opportunity to test several new techniques for sampling, preserving and measuring gas hydrates. During ODP Leg 204, nine sites were drilled and cored on southern Hydrate Ridge, a topographic high in the accretionary complex of the Cascadia subduction zone, located approximately 80km west of Newport, Oregon. Previous studies of southern Hydrate Ridge had documented the presence of seafloor gas vents, outcrops of massive gas hydrate, and a pinnacle' of authigenic carbonate near the summit. Deep-towed sidescan data show an approximately $300\times500m$ area of relatively high acoustic backscatter that indicates the extent of seafloor venting. Elsewhere on southern Hydrate Ridge, the seafloor is covered with low reflectivity sediment, but the presence of a regional bottom-simulating seismic reflection (BSR) suggests that gas hydrate is widespread. The sites that were drilled and cored during ODP Leg 204 can be grouped into three end-member environments basedon the seismic data. Sites 1244 through 1247 characterize the flanks of southern Hydrate Ridge. Sites 1248-1250 characterize the summit in the region of active seafloor venting. Sites 1251 and 1252 characterize the slope basin east of Hydrate Ridge, which is a region of rapid sedimentation, in contrast to the erosional environment of Hydrate Ridge. Site 1252 was located on the flank of a secondary anticline and is the only site where no BSR is observed.

• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.739-752
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• 2006

Deep-sea surface sediments acquired by multiple corer from 69 stations in the Clarion-Clipperton fracture zone of the northeast equatorial Pacific, were examined to understand the correlation of mass physical properties and sedimen-tological processes. The seabed of the middle part ($8-12^{\circ}N$) of the study area is mainly covered by biogenic siliceous sediment compared with pelagic red clays in the northern part ($16-17^{\circ}N$). In the southern part ($5-6^{\circ}N$), water depth is shallower than carbonate compensation depth (CCD). The mass physical properties such as grain size distribution, mean grain size, water content, specific grain density, wet bulk density, void ratio, and porosity of sediments are distinctly different among the three parts of the study area. Surface sediments in northern part are characterized by fine grain size and low water contents possibly due to low primary productivity and high detrital input. Conversely, sediments in the middle part are characterized by coarse grain size and high water contents, which might be caused by high surface productivity and deeper depth than CCD. The sediments show low water contents and high density in the southern part, which can be explained by shallower depth than CCD. Our results suggest that the variations in mass physical properties of sediments are influenced by combined effects including biogenic primary productivity of surface water, water depth, especially with respect to CCD, sedimentation rate, detrital input, and the geochemistry of the bottom water (for example, formation of authigenic clay minerals and dissolution of biogenic grains).