• Journal of the Mineralogical Society of Korea
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• v.16 no.2
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• pp.151-159
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• 2003

$^{31}$ /P NMR and XRD have been used to study the mineralogical compositions and the phosphorus species in marine sediments near Wolsung nuclear power plant. The core samples with 30cm depth were investigated and no mineralogical changes have been found. The studied marine sediments were composed of quartz, albite, microcline, calcite, and some clay minerals such as illite, smectite, chlorite, and kaolinite. Only orthophosphate-monoester and very small amount of ortho-phosphate-diester were identified as phosphorus species in the studied sample, different from the species reported in other countries. These phosphorus species are mainly from organisms and was exposed to the oxic conditions. The consistent mineralogical compositions as well as the same phosphorus species throughout the entire core samples indicate that the constant oxic condition was kept without any changes in sedimentary conditions or the sediments were deposited with different sedimentary conditions, but later they were disturbed by other activities and exposed to the surface oxic conditions continuously.

• Journal of the Korean earth science society
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• v.27 no.3
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• pp.328-340
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• 2006

In Janghwa-ri of Kanghwa Island morphological changes in four transects, 112 surface, and 2 core sediments were analyzed to understand the seasonal variation of the muddy tidal-flat environment. Sedimentary of facies can be classified into four facies; sand, muddy sand, sandy mud, and silt. During winter, the coarse-grained sediment facies expanded seaward. In the subsurface part of the core sediments, poorly sorted silty sediments dominate the area. According to the Pb-210 isotope analysis, accumulation rates of the tidal flat in Jangwha-ri appear to be $5{\sim}19mm/yr$. In the study area, the result is suggestive of a rapid change in depositional environments in recent years.

• Journal of the Korean earth science society
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• v.30 no.4
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• pp.409-426
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• 2009

In the four sedimentary cores from Yeoja Bay, the analyses of grain size, benthic foraminiferal species compositions, assemblages and statistics were carried out to investigate the effects of late Holocene sea-level change on benthic foraminifera. The core sediments were mainly composed of fine-grained silt and clay. The benthic foraminifera were classified into 27 species of 16 genera, 30 species of 21 genera, 50 species of 29 genera and 52 species of 29 genera in Core YC-1 to 4, respectively. In the result of cluster analysis, it seemed that Group 1 (Core YC-1 and 2) of representative A. beccarii assemblages was deposited in upper bay environment and Group 2 (Core YC-3 and 4) of representative E. clavatum-A. beccarii assemblages was deposited in inner bay environment affected by offshore water. In the result of species composition analysis, the production frequency of A. beccarii was gradually decreased from low layer to upper layer, whereas production frequency of E. clavatum and P.F./T.F. was gradually increased to upward. These change patterns appeared in benthic and planktonic foraminifera seemed to reflect the late Holocene sea-level rise in Yeoja Bay.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.14 no.3
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• pp.127-133
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• 2009

In order to determine organic carbon oxidation by manganese and iron oxides, six core sediments were obtained in slope and basin sediments of Ulleung Basin in East Sea. The basin sediments show high organic carbon contents (>2%) at the water depths deeper than 2,000 m; this is rare for deep-sea sediments, except for those of the Black Sea and Chilean upwelling regions. In the Ullleung Basin, the surface sediments were extremely enriched by Manganese oxides with more than 2%. Maximum contents of Fe oxides were found at the depth of $1{\sim}4cm$ in basin sediments. However, the high level of Mn and Fe oxides was not observed in slope sediment. Surface manganese enrichments (>2%) in Ulleung Basin may be explained by two possible mechanisms: high organic carbon contents and optimum sedimentation rates and sufficient supply of dissolved Manganese from slope to the deep basin. Reduction rates of iron and manganese oxides ranged from 0.10 to $0.24\;mmol\;m^{-2}day^{-1}$ and from 0.30 to $0.57\;mmol\;m^{-2}day^{-1}$, respectively. In Ulleung Basin sediments, $13{\sim}26%$ of organic carbon oxidation may be linked to the reduction of iron and manganese oxides. Reduction rates of metal oxides were comparable to those of Chilean upwelling regions, and lower than those of Danish coastal sediments.

• Economic and Environmental Geology
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• v.36 no.3
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• pp.225-232
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• 2003

Three piston cores. obtained from the northwestern Ulleung Basin of the East Sea, are analyzed to study the tephrostratigraphy of the late Quaternary core sediments and to reveal the comparative characteristics of the tephra layers. The cores consist mainly of the muddy sediments that are partly interbedded with lapilli tephra and ash layers. The muds are further divided into hemipelagic and turbiditic mud facies. The hemipelagic facies is dominated by bioturbated mud and crudely laminated mud, whereas the turbiditic facies includes mainly thinly laminated mud and homogeneous mud, and often alternates with non-turbiditic muds. According to microscopic observation and EDX analysis, three tephra layers of the Ulleung-Oki (U-Oki; ca. 9.3 ka), Aira-Tanzawa (AT: ca. 22~24.7 ka) and Ulleung-Yamato (U-Ym; ca. 25~33 ka) are identified in the study cores. Among these, the U-Oki and U-Ym layers, originating from the Ulleung Island, consist mainly of massive-type glass shards with alkali feldspar. Both of the tephra layers contain a lower content of SiO$_2$ (57~66.5 wt.%) and a higher content of Na$_2$O+K$_2$O (11~16 wt.%) than the AT layer (SiO$_2$=75~78.5 wt.%, Na$_2$O+K$_2$O=6.5~9 wt.%) that consists of typical plane-type and/or bubble-wall glass grains. Compared with that of the U-Ym layer, a sedimentary facies of the U-Oki layer is very thick and contains three stratigraphic units, probably due to relatively large and different supplies of pyroclastic sediments. Thus, the eruption of Ulleung Volcano (ca. 7,300 B.C.) is thought to have had a more powerful effect on depositional environment than the U-Ym eruption.

• The Korean Journal of Petroleum Geology
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• v.10 no.1_2 s.11
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• pp.18-22
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• 2004

To identify and interpret the distribution and the characteristics of the gas hydrate layers in the Ulleung Basin, we have surveyed and gathered the multi-channel seismic data, Chirp sub-bottom profiler, SeaBeam and 12 m piston core samples since 1996. In previous works, high-resolution seismic profiles showed acoustic anomalies such as acoustic void, acoustic turbidity and pock mark which indicate the presence of gas-charged sediments. The patterns of horizontal degassing cracks originated from free methane expansion is the strong indicator of shallow gas-charged sediments in the core samples. The observation of submarine slides and slumps from destabilizing the sediments in the southern part of the Ulleung Basin may also point out that the gas had been released from gas hydrate dissociation during lowstand of sea level. The multi-channel seismic data show BSR, blanking and phase reversal. The gas hydrate layers above which large-scale shallow gases are distributed exist at the depth of about 200 m from the sea-floor with water depth of 2,100 m. From the interpretation of seismic sections in the southern Ulleung Basin, gas hydrate layers occur in the Pleistocene-Holocene sediments. These gas-charged sediments, acoustic anomalies and BSR may be all related to the existence of gas hydrate layers in the study area.

• Journal of the korean society of oceanography
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• v.34 no.3
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• pp.179-183
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• 1999

A light-weight multiple piston corer to meet increasing coring needs in areas where R/V access is limited, is designed and discussed. Hydraulically-damped and spring-driven piston system not only virtually undisturbed surface sediments but also facilitate the recovery and subsequent operation including pore water extraction and core slicing on board the ship. It is designed as compact, light-weight and easy to dissemble that whole gear can be carried by small passenger vehicle yet it permits thick-walled core tube for thermal insulation or large opening core tubes. Because single spring instead of heavy weights of conventional gravity-driven multiple corers is used, this device is very simple and cheap to construct.

• Ocean and Polar Research
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• v.36 no.4
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• pp.395-405
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• 2014

A 570 cm-long sediment core was retrieved at $9^{\circ}57^{\prime}N$ and $131^{\circ}42^{\prime}W$ in 5,080 m water depth from the northeast equatorial Pacific and its stratigraphy was established with $^{10}Be/^9Be$ and paleomagnetic measurements. Successive AF demagnetization reveals eight geomagnetic field reversals. In the reference geologic time scale, the eight reversal events correspond to an age of about 4.5 Ma. However, $^{10}Be/^9Be$-based age yields 9.5 Ma at a depth of 372 cm. Such a large discrepancy in determined ages is attributed to an extremely low sedimentation rate, 0.4 mm/kyr on average, of the study core and resultant loss or smoothing of geomagnetic fields. The composite age model reveals a wide range in the sedimentation rate - varying from 0.1 to 2.4 mm/kyr. However, the sedimentation rate shows systematic variation depending on sedimentary facies (Unit II and III), which suggests that each lithologic unit has a unique provenance and transport mechanism. At depths of 110-80 cm with a sedimentation rate of about 0.1 mm/kyr, ancient geomagnetic field reversal events of at least a 1.8 Myr time span have not been recorded, which indicates the probable existence of a hiatus in the interval. Such a sedimentary hiatus is observed widely in the deep-sea sediments of the NE equatorial Pacific.

• 한국해양학회지
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• v.30 no.5
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• pp.382-389
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• 1995

This study intended to investigate the sedimentation rates of core sediments of the western part of the East Sea using Accelerator Mass Spectrometer (AMS) C-age on the planktonic foraminifera or acid-ex-tracted residue, base-soluble and base-extracted residue fractions. On the basis of the depth-age correlations, the sedimentation rates during the late Holocene period of Cores HP-10, HP-3, 94-9 and 92-3 were 30 cm/kyr, 10 cm/kyr, 11 cm/kyr and 112 cm/kyr, respectively. The sedimentation rates of the westem part of the East Sea, however, seems to be ranged from 11 cm/kyr to 30 cm/kyr, because the rates of the only two cores (Cores HP-10 and 94-9) which were dated at more than three depths are considered to be more reliable. The rates in each core sediment showed good linear relationship with the sample depth, suggesting that the sea-level rise had been finished nearly during the early Holocene period and the general depositional environments had been lasted rather constant during the late Holocene period.

• Journal of the Korean earth science society
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• v.26 no.3
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• pp.276-282
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• 2005

The Quaternary palynoflora from Cheongsu core, drilled on the western part of the Jeju Island, consists mainly of deciduous broad-leaved angiosperms and herbs. Dominant taxa are Pinaceae, Alnus, Castanea/Castanopsis, Ulmus/Zelkova, Chenopodiaceae and Compositae. Based on palynofloral composition, two palynostratigraphic zones are recognized. Zone I is characterized by a predominance of Alnus and Chenopodiaceae, and by the abundance of herbs. Zone II is dominated by conifers and deciduous broad-leaved angiosperms, including Abies, Taxodiaceae-Cupressaceae-Taxaceae, Ulmus/Zelkova and Gramineae. The Cheongsu palynoflora can be correlated with Alnipollenites(Alnus)-Chenopodipollis(Chenopodiaceae)-Compositae Assemblage Zone of the East China Sea and is assigned to the Pleistocene in age. Ecology of main taxa and comparison with the present vegetation of Korea suggest a cool temperate climate and a low relief in the Jeju Island during the deposition of the Cheongsu core sediments.