• The Korean Journal of Quaternary Research
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• v.17 no.2
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• pp.165-165
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• 2003

A borehole core ECSDP-102 (about 68.5 m long) has been investigated to get information on paleoenvironmental changes in response to the sea-level fluctuations during the period of late Quaternary. Several AMS $\^$14/C ages show that the core ECSDP-102 recorded the depositional environments of the northern East China Sea for approximately 60 ka. The Yangtze River discharged huge amounts of sediment into the northern East China Sea during the marine isotope stage (MIS) 3. In particular, $\delta$$\^$13/Corg values reveal that the sedimentary environments of the northern East China Sea, which is similar to the Holocene conditions, have taken place three times during the MIS 3. It is supported by the relatively enriched $\delta$$\^$13/Corg values of -23 to -21$\textperthousand$ during the marine settings of MIS 3 that are characterized by the predominance of marine organic matter akin to the Holocene. Furthermore, we investigated the three Holocene sediment cores, ECSDP-101, ECSDP-101 and YMGR-102, taken from the northern East China Sea off the mouth of the Yangtze River and from the southern Yellow Sea, respectively. Our study was focused primarily on the onset of the post-glacial marine transgression and the reconstructing of paleoenvironmental changes in the East China Sea and the Yellow Sea during the Holocene. AMS $\^$14/C ages indicate that the northern East China Sea and the southern Yellow Sea began to have been flooded at about 13.2 ka BP which is in agreement with the initial marine transgression of the central Yellow Sea (core CC-02). $\delta$$\^$18/O and $\delta$$\^$13/C records of benthic foraminifera Ammonia ketienziensis and $\delta$$\^$13/Corg values provide information on paleoenvironmental changes from brackish (estuarine) to modem marine conditions caused by globally rapid sea-level rise since the last deglaciation. Termination 1 (T1) ended at about 9.0-8.7 ka BP in the southern and central Yellow Sea, whereas T1 lasted until about 6.8 ka BP in the northern East China Sea. This time lag between the two seas indicates that the timing of the post-glacial marine transgression seems to have been primarily influenced by the bathymetry. The present marine regimes in the northern East China Sea and the whole Yellow Sea have been contemporaneously established at about 6.0 ka BP. This is strongly supported by remarkably changes in occurrence of benthic foraminiferal assemblages, $\delta$$\^$18/O and $\delta$$\^$13/C compositions of A. ketienziensis, TOC content and $\delta$$\^$13/Corg values. The $\delta$$\^$18/O values of A. ketienziensis show a distinct shift to heavier values of about 1$\textperthousand$ from the northern East China Sea through the southern to central Yellow Sea. The northward shift of $\^$18/O enrichment may reflect gradually decrease of the bottom water temperature in the northern East China Sea and the Yellow Sea.

• Journal of the Korean earth science society
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• v.24 no.1
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• pp.46-60
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• 2003

In Namyang Bay of western Korea, macrotidal-flat deposits are divisible into three late Quaternary units: Unit M1 of upper marine mud, Unit T1 of middle siderite-bearing terrestrial clay, and Unit M2 of lower marine mud. Unit M1 represents typical Holocene intertidal mudflat deposits, showing a coarsening-upward textural trend. It probably resulted from the continual retrogradation of tidal flat during the mid-to-late Holocene sea-level rise. Reddish brown-color Unit T1 consists of homogeneous clay with abundant freshwater siderite grains and plant remains. Unit T1 is clearly separated from the overlying Unit M1 by a sharp lithologic boundary. Radiocarbon age, siderite grains and lithologic features indicate that Unit T1 is originated from freshwater bog or swamp deposition infilling the localized topographic lows during the early Holocene age. Overlain unconformably by early Holocene swamp clay, Unit M2 is orange to yellow in color and mottled, suggesting significant degree of weathering during the sea-level lowstand. Such subaerial oxidation is confirmed in the vertical profiles of geotechnical properties, clay mineral assemblages and magnetic susceptibility. Unit M2 appears to be correlated with the upper part of the late Pleistocene tidal deposits developed along the western Korean coast. The sedimentary succession of the Namyang-Bay tidal-flat deposit provides stratigraphic information for the Holocene-late Pleistocene unconformity and also permits an assessment of the preservation potential of the late Pleistocene marginal marine deposit along the western coast of Korea.

• 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.33 no.3
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• pp.242-258
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• 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
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• v.44 no.4
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• pp.303-312
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• 2011

Analysis of high-resolution seismic profiles from the southeastern continental shelf of Korea reveals that the Holocene transgressive deposits consist of five sedimentary units characterized by retrograding or backstepping depositional arrangements. Unit I, forming a linear sediment body along the shelf margin, is an ancient beach/shoreface deposit formed during the early stage of transgression. During the transgression, the paleo-channels were backfilled with fluvial or coastal-plain sediments, forming Unit II as an incised-channel fill deposit. The near-surface sediment was reworked and eroded by shoreface erosion, forming a thin lag of sands (Unit III) on the midshelf. During the middle stage of the transgression, the shoreline may have stabilized at around 70 - 80 m below the present sea level for some period of time to allow the formation of sand ridge systems (Unit IV). Unit V in the inner shelf was deposited in an estuarine environment during the middle to late stage of transgression. Such transgressive stratigraphic architecture is controlled by a function of lateral changes in the balance among rates of relative sea-level rise, sediment input and marine processes at any given time.

• 한국해양학회지
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• v.29 no.4
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• pp.357-365
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• 1994

The sediments on the continental shelf off the west coast (middle part) of Korea are divided into northern sandy deposits and southern muddy sediments, respectively. The sandy sediments consist dominantly of quartz and feldspar grains, representing mature-stage sediment in composition. Further-more, the presence of iron-stained quartz grain and glauconite does indicate that the sediments are similar to the relict sediments on the outer shelf of Yellow Sea and East China Sea. These sandy sediments are interpreted as a basal sands that were deposited during the transgression period due to sea-level rise after to last glacial maximum (LGM). The tidal deposits in the Namyang Bay, the west coast of Korea are divided vertically into the upper layer of muddy sediments and the lower layer of sandy sediments. the upper layer sediments contain abundant rock fragments, and are interpreted as the modern tetragenous sediments. The lower layer sediments, on the other hand, are rich in quartz and feldspar grains, representing high index of sediment maturity ratio. the lower layer sandy deposits show the presence of iron-stained.

• Journal of the Korean Geographical Society
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• v.32 no.1
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• pp.15-30
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• 1997

This paper concerns the Holocene environmental change with vegetational history and sea-level fluctuation at Ilsan area by the analytical data of pollen, sedimentary facies and $C^14$-dating. The hypothetic palaeogeographic maps of the vegetation cover have been reconstructed with the reference to the periods of pollen zone. The environmental characteristics from the pollen zonation have been summerized as follows. 1)Pollenzone I(3.75~5.75m) showed the period of Alnus-and EMW-dominance. The study area was very humid under the influence of the transgression spreading widely from the rapid sea-level rise during the period(8,000~4,200y.BP). 2)Pollen zone II(5.75~6.35m) has been influenced by the fall of the sea-level and ground water surface. This zone(4,200~2,300y.BP) represented the period of spore~ and NAP-dominance with the increase of Pinus. 3) Pollen zone III(6.35~6.55m) has reflected the influence of the transgression and human interferences together. This zone(2,300~1,800y.BP) represented the period of NAP-dominance. The boundary between Subzone Ilb and Pollen zone III represents the same characteristics as what Weber says Grenzhorizont.

• 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.

• Journal of the Korean association of regional geographers
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• v.17 no.5
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• pp.521-535
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• 2011

This study intended to explain the relationship between climate change and magnetic susceptibility of estuarine sediment. Data of OSL dating and magnetic susceptibility from estuarine tidal sediment were compared with various climate change data. During the last Holocene, the intense of magnetic susceptibility related with weaker Siberian High and stronger Asian Summer Monsoon. It is explained that high precipitation and runoff made much fluvial sediment input to the estuary. From the early to mid Holocene, there is no clear relationship between climate change and MS because of the much coastal sediment input caused by rapid sea level rise and the formation of upland soil and coastal marsh. These results contribute to reconstruct paleo-environmental changes of west coast of Korea, in the way of using benefit of ubiquitous estuarine tidal flats and relatively useful magnetic susceptibility methodoloy.

• Journal of The Geomorphological Association of Korea
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• v.26 no.4
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• pp.33-45
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• 2019

The shore platforms at Dok-do could be an important and clear indicator showing dimensional reduction of Dok-do. Especially flat type shore platforms are distributed in the southern coast of Dok-do island, composed of weak rocks against erosional resistance like interbedded lapilli tuff and massive tuff breccia. The distribution of shore platform is partially related to the wind direction at Dok-do island. The primary SW- and secondary SE winds are representative among wind directions at Dok-do, maintaining from spring to the autumn. Therefore, wide shore platforms could be developed by waves approaching from SW and SE directions in the southern coast of Dok-do. The sea stacks like Gunham-rock, Neopdeok-rock, Keungaje-rock and Jakeungaje-rock on the western coast are also considered to be formed by wave erosion from the SE direction. The shore platforms in the southern coast of Dok-do island were developed since ca. 7,000 yr. BP, when sea level raised almost to the present level. The average extension speed of shore platform was calculated to 4.0mm/y, because the broadest shore platform with the width ca. 28m was extended for ca. 7,000 years. The width's dimension of shore platform at Dok-do reflects a slow extension rate in the present, although erosional process will be faster with the sea level rise in the future.