• Journal of the Mineralogical Society of Korea
• /
• v.27 no.3
• /
• pp.159-168
• /
• 2014

Holocene plaeoenvironmental changes were interpreted by grain size and mineral analyses of a piston core (HB 13-2), obtained along the western slope of the Hupo Basin, Korea. The core sediments are characterized by two discrete, sedimentary facies: upper unit (0-0.4 mbsf) dominated by bioturbation structures with weak lamination, and lower unit (0.4-3.3 mbsf) characterized by intensified bioturbation toward bottom. Analysis of sensitive grain size and sortable silt demonstrated that the inflow of the Tsushima Warm Current (TWC) into the Hupo Basin strengthen from the period of sediment deposition over 0.82 mbsf. The minerals of the core sediments are composed mainly of quartz, microcline, orthoclase, albite and clay minerals including chlorite, kaolinite and illite. No noticeable changes of the mineral percentage was observed according to the grain size and depth of the samples. The integral breadth (${\Delta}^{\circ}2{\theta}$) of clay minerals from 1.4 mbsf to top layer shows an increasing trend, which clearly means climate warming from the period of sediment deposition above 1.4 mbsf. This interval correlates with the Holocene climate optimum at Mid Holocene.

• Journal of the Korean earth science society
• /
• v.33 no.3
• /
• pp.242-258
• /
• 2012

The Yellow Sea has sensitively responded to high-amplitude sea-level fluctuations during the late Quaternary. The repeated inundation and exposure have produced distinct transgression-regression successions with extensive exposure surfaces in Kyeonggi Bay. The late Quaternary strata consist of four seismic stratigraphic units, considered as depositional sequences (DS-1, DS-2, DS-3, and DS-4). DS-1 was interpreted as ridge-forming sediments of tidal-flat and estuarine channel-fill facies, formed during the Holocene highstand. DS-2 consists of shallow-marine facies in offshore area, which was formed during the regression of Marine Isotope Stage (MIS)-3 period. DS-3 comprises the lower transgressive facies and the upper highstand tidal-flat facies in proximal ridges and forced regression facies in distal ridges and offshore area. The lowermost DS-4 rests on acoustic basement rocks, considered as the shallow-marine and shelf deposits formed before the MIS-6 lowstand. This study suggests six depositional stages. During the first stage-A, MIS-6 lowstand, the Yellow Sea shelf was subaerially exposed with intensive fluvial incision and weathering. The subsequent rapid and high amplitude rise of sea level in stage-B until the MIS-5e highstand produced transgressive deposits in the lowermost part of the MIS-5 sequence, and the successive regression during the MIS-5d to -5a and the MIS-4 lowstand formed the upperpart of the MIS-5 sequence in stage-C. During the stage-D, from the MIS-4 lowstand to MIS-3c highstand period, the transgressive MIS-3 sequence formed in a subtidal environment characterized by repetitive fluvial incision and channel-fill deposition in exposed area. The subsequent sea-level fall culminating the last glacial maximum (Stage-E) made shallow-marine regressive deposits of MIS-3 sequence in offshore distal area, whereas it formed fluvial channel-fills and floodplain deposits in the proximal area. After the last glacial maximum, the overall Yellow Sea shelf was inundated by the Holocene transgression and highstand (Stage-F), forming the Holocene transgressive shelf sands and tidal ridges.

• Economic and Environmental Geology
• /
• v.43 no.4
• /
• pp.333-341
• /
• 2010

Fluvial sediments are widely distributed in present and old river-beds of the mid-Keum River, the tributaries of which are the Yugu and Jeongan Rivers. The basement of the mid-Keum River area consists of Mesozoic granites which are easily eroded compared to Precambrian gneisses, which are exposed in the upper-Keum River area. The provenance of the fluvial sediments includes both the Precambrian gneisses and Mesozoic granites, which occur in the catchment of the mid-Keum River. The coarse-grained sediments were probably transported from the river-beds and the overbank floodings of the main Keum River and its tributaries when the climate was warm and wet. The oldest mud deposits were dated at ca. 9,400 yr BP by the radiocarbon method. It has been estimated that the sand deposits below the dated muds were formed in a period from the Late Pleistocene to the Early Holocene. However we have revealed that the major part of the present river-bed sediments was formed at ca. 3,000-6,000 yr BP, i.e., in the mid- to late Holocene, when summer monsoon was very strong due to climatic changes. We have calculated fluvial sedimentation rates of 0.12-0.16 cm/yr and 0.02-0.09 cm/yr for borehole KJ-29 river-bed sediments and borehole KJ-28 floodplain deposits, respectively. We conclude that the sedimentation rate is higher near the present stream channel than near the floodplain.

• Journal of the Korean earth science society
• /
• v.40 no.1
• /
• pp.24-36
• /
• 2019

In the mid-eastern Yellow Sea, glacio-eustatic sea-level fluctuations and a regional tectonic subsidence have combined to represent an aggradational stacking pattern of sedimentary units during late Pleistocene-Holocene. The accumulated sediments are divisible into two-type units of Type-A and Type-B in high-resolution air-gun seismic profiles and the deep-drilled core of YSDP-105. Type-A unit largely comprises clast-rich coarse-grained sediments of non-marine to paralic origin, whereas Type-B unit consists mostly of tidal fine-grained sediments. Based on a bottom model of the sedimentary units, this study suggested a geoacoustic model of long-coring bottom layers at the YSDP-105 drilling site of the mid-eastern Yellow Sea. The geoacoustic model of 64-m depth below the seafloor with four-layer geoacoustic units was reconstructed in continental shelf strata at 45 m in water depth. For actual modeling, the geoacoustic property values of the models were compensated to in situ depth values below the seafloor using the Hamilton modeling method. We suggest that the geoacoustic model will be used for geoacoustic and underwater acoustic experiments of mid- and low-frequency reflecting on the deep bottom layers in the mid-eastern Yellow Sea.

• Ocean and Polar Research
• /
• v.29 no.4
• /
• pp.411-418
• /
• 2007

We studied the bottom morphology and sedimentary environments of the Masan Bay using high-resolution Chirp seismic profiles and sediments data. According to deep-drilled core samples (up to 20 m thick) penetrated into the weathered rock basement, the sediments consist largely of three sediment types: the lower sandy gravel facies (Unit I) of 1-4 m in thickness, the middle sandy mud and/or muddy sand facies(Unit II) of 1-2 m thick and the upper mudfacies (Unit III) of over 10 m in thickness. The sedimentary column above the acoustic basement can be divided into two major sequences by a relatively strong mid-reflector, which show the lower sedimentary sequenc e(T) with parallel to subparallel internal reflectors and the upper sedimentary sequence(H) with free acoustic patterns. Acoustic basement, the lower sedimentary sequence (T), and the upper sequence (H) are well correlated with poorly sorted massive sandy gravels (Unit I), the sand/mud-mixed sediment (Unit II), and the muddy facies(Unit III), respectively. The acoustic facies and sediment data suggest that the Masan bay is one of the most typical semi-enclosed coastal embayments developed during the Holocene sea-level changes. The area of the Masan Bay reduced from about $19\;km^2$ in 1964 to about $13\;km^2$ in 2005 by reclamation, and its bottom morphology changed as a result of dredging of about $2{\times}10^7\;m^3$.

• Journal of the Korean earth science society
• /
• v.23 no.8
• /
• pp.697-706
• /
• 2002

Authigenic siderite grains, ranging 100 to 250-${\mu}$m in diameter, are abundant in an about 8,600-year-old sediment layer in Namyang Bay, west coast of Korea. The siderites exhibit the aggregated spherulitic morphology with well-developed rhombs on the grain surfaces. They consist mostly of FeCO$_3$ (average, 65%) and MnCO$_3$ (average, 22%) with low Mg/Ca ratio (less than 0.4) in their bulk composition. A series of compositional ternary discrimination diagrams, together with high Mn and low Mg contents, show that only meteoric porewater was involved in siderite precipitation, assuming that depositional environment of host sediment is an organic-rich freshwater system. Considering a series of results such as radiocarbon age, authigenic Mn-rich siderite and lithological features, siderite-hosting sediment (unit Tl) is interpreted as freshwater swamp or bog deposition, infilling the topographic depressions that locally existed before the formation of mid-to-late Holocene tidal deposits. Center-to-margin compositional variation within individual grain is very systematic; Mn and Ca decrease towards the margin of a siderite grain, while Fe and Mg increase. It suggests that the spherulitic siderites were precipitated in this sedimentary layer in a series during the early diagenesis of MnOx-FeOx reduction under steady-state.

• The Journal of Engineering Geology
• /
• v.10 no.2
• /
• pp.52-74
• /
• 2000

The basement rock of upper stream of Keum River Valley consists of Precambrian gneiss which is resistant to weathering. That of mid and lower stream valley, however, is mainly composed of Mesozoic granites which are vulnerable to weathering. The upstream part of Geum River Basin is typified by the deeply-incised and steep meandering streams, whereas mid and lower part is characterized by wide floodplain and gently dipping river bottom toward the Yellow Sea. In particular flooding deposits, in which are imprinted a number of repetitions of erosion and sedimentation during the Holocene, are widely distributed in the lower stream of Geum River Basin. For understanding of erosions in the mid and lower stream of Geum River Basin, the rate of erosion of each small basins were estimated by using the data of field survey, erosional experiments and GIS ananlysis. It was revealed that erosion rate appeared highest in granite areas, and overall areas, in this field survey were represented by relatively high erosion rates. By implemeatation of remote sensing and imagery data, the temporal changes of river bed sediments for about last 11 years were successfully monitored. Observed as an important phenomenon is that the river bed has been risen since 1994 when an embankment (Dyke) was constructed in the estuarine river mouth. From the results derived from the detailed river bed topographical map made in this investigation, the sedimentation of the lower river basin is considered to be deposited with about 5 cm/year for the last 11 years. Based on this river bed profile analysis by HEC-6 module, it is predicted that Geum River bed of Ganggyeong area is continuously rising up in general until 2004. Although extraction of a large amount of aggregates from Gongju to Ganggyung areas, the Ganggyung lower stream shows the distinct sedimentation. Therefore, it is interpreted that the active erosions of tributary basins Geum drainage basins can affect general river bed rising changes of Geum River.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.19 no.2
• /
• pp.131-146
• /
• 2014

High-resolution seismic profiles coupled with sediment sampling were analyzed to investigate the acoustic characters and distribution patterns of the late Holocene sediments in Gamak Bay of the South Sea, Korea. The mean grain size of surficial sediment lies around $6.3{\sim}9.7{\Phi}$. Sediments in the bay consist of silt and clay with progressive decrease toward the inner bay. The seismic sedimentary sequence overlying the acoustic basement can be divided into two sedimentary units (GB I and II) by a prominent mid-reflector (Maximum Flooding Surface; MFS). The acoustic basement occurs at the depth between 20 m and 40 m below the sea-level and deepens gradually southward. The GB I, mostly occupying the channel-fill, is characterized by reflection-free seismic facies. It can be formed as late Transgressive System Tract (TST), interpreted tidal environment deposits. MFS appears at the depth of about 15~28 m below the sea-level and is well defined by even and continuous reflectors on the seismic profile. The GB II overlying MFS is composed of acoustically transparent to semitransparent and parallel internal reflectors. GB II is interpreted as the Highstand System Tract (HST) probably deposited during the last 6,000 yrs when the sea level was close to the present level. Especially, it is though that the GB II was subdivided into two layers (GB II-a and II-b) by a HST-reflector and this was classified by wind, sea water flux, and tidal current.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.6 no.3
• /
• pp.152-163
• /
• 2001

Based upon the sedimentological, geochemical and micropaleontological analyses of two sediment cores from the Antarctic Peninsula (AP), three distinct lithological units can be recognized: (1) ice-proximal an/or ice-distal diamictons in the lower part of the cores, accumulated just seaward of the grounding line of the ice shlef until 11,000 yrs BP; (2) diatomaceous mud between 6,000 and 2,500 yrs BP in the middle part, resulted from a large influx of organic materials by enhanced production of open marine condition; (3) diatomaceous sandy mud since 2,500 yrs BP, characterized by an increase in sand content and decrease in TOC and diatom abundance in the lower layers, which reflects the formation of more extensive and seasonally persistent sea ice. Based on the C-14 radiocarbon dating, the sub-ice shlef deposition of the diamicton on the AP western shelf completed around 11,000 yrs BP. Colder condition was reinstated between 12,800 and 11,600 BP with a dropin TOC content and diatom abundance, which is coincident with the Younger Dryas event in the North Atlanticregion. At this time, the ice shelf, that is now absent in the study area, appears to advance as evidenced by an abrupt increase in sea-ice taxa. A climatic optimum is recognized between 9,000 and 2,500 BP, coincide witha mid-Holocene climatic optimum 'Hypsithermal Warm Period' from the other Antarctic sites. During this time, diatomaceous mud accumulated by a large influx of organic materials by enhanced production occurred in openmarine condition. Around 2,500 BP, diatomaceous sandy mud reflects the formation of more extensive and seasonally persistent sea ice, coincident with the onset of the Neoglacial in the Antarctic. Our results provide evidence of climatic change from the Antarctic Peninsula`s western shelf that helps in determining the existence and timing of Holocene milennial-scale climatic events in the Southern Hemisphere.

• The Korean Journal of Quaternary Research
• /
• v.21 no.2
• /
• pp.69-73
• /
• 2007

Inorganic geochemical and mineralogical analyses from the trench sediments of the Hwayang wetland were carried out to verify the wet/dry conditions during 6000 - 5000 yr BP and abnormal event of 6300 yr BP of Korean west coast. Lithostratigraphy, mineralogy and major element concentrations of the sediments of the trench indicate that during 6000 - 5000 yr BP, a wet/dry conditions might be repeated at an interval of 200 years. Carbonate minerals precipitated with the decrease of water depth in the lake or wetland after about 6000 yr BP. On the other hand, the sediments coarser in mean grain size and larger in standard deviation were corresponded with periods of 6300 yr BP and 6230 yr BP. Especially, such a feature of grain size distribution of 6300 yr BP appears in other wetlands situated in the west coast, e.g., Hwangsan wetland and Cheollipo coastal wetland. During the period, the coarse sediments seem to have been delivered by a high energy like storming.