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(1) , 36, 3 , 225-232, 2003 Econ. Environ. Geol., 36(3), 225-232, 2003.

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(3) . . . . Stratigraphy of Late Quaternary Core Sediments and Comparative Study of the Tephra Layers from the Northwestern Ulleung Basin of the East Sea Myong-Ho Park1, Il-Soo Kim2* and Byong-Jae Ryu1 1. Petroleum Marine Resources Research Division, Korea Institute of Geoscience and Mineral Resources, Gajeong-dong 30, Yuseong-gu, Daejeon 305-350, Korea 2 Department of Earth System Sciences, Yonsei University, Shinchon-dong 134, Seodaemun-gu, Seoul 120-749, Korea. 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 SiO2 (57~66.5 wt.%) and a higher content of Na2O + K2O (11~16 wt.%) than the AT layer (SiO2 = 75~78.5 wt.%, Na2O + K2O = 6.5~9 wt.%) that consists of typical plane-type and/or bubblewall 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.. Muddy sediments, tephra layer, glass shards, Ulleung Basin, late Quaternary.

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(49) . . Description of the three piston cores and inferred stratigraphic correlation. The 14C ages of tephra and DLM (Dark Laminated Mud layer) are taken from Machida and Arai (1983), Oba et al. (1991) and Bahk et al. (2002). Symbols on the right side of the column represent sedimentary facies: BM bioturbated mud, HM homogeneous mud, LM laminated mud, CLM crudely laminated mud, TL lapilli tephra layer, and AL ash layer. M, S, and G indicate mud, sand, and gravel, respectively.. EF 3XY*!=" eMN µí?@ /" ©+0 ²@!= '()*[ V V V V V V V ! Y?@ /0 ²@ e 2!-)* %++V'++ 56 @ '()* _+!" wÅL + µí?@ /0 (%V('% 56 @ 0$. '. 56 @. %%. % 56 @. %. % 56 @. . (%. %%. +BC7!+. ('% 56 @. % 56 @. '. %%'. '%% 56 @. %% 56 @. 3XY*!=" eI + + Y. ¿ k [ 0 0 ¿ ! IJ KLC *: |u0 U ²@!=8 * *+ ?"< ²@U" í: * * _+! V n 3XY*+ Y?@ / 0 + G!= * e ! +" 3XY*[ 5 ". "5 " +BC7!+%. . +BC7!+' . 2!45. . +BC7!+ '. 2!45. . 2!-). 2!45. 2!-).

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(53) . . *. +BC7!+%. '( 5. +BC7!+'. /. SEM microphotographs of two representative volcanic glass shards: Pumice-type glass shards of the Ulleung-Oki (a) and Ulleung-Yamato (b) tephra layers; (c) and (d) bubble-wall shards of Japanese origin..

(54) . . Classification of the glassy tephra layers based on the total alkali-silica plot after Le Bas et al. (1986): U-Oki Ulleung-Oki (open circles), U-Ym Ulleung-Yamato (closed triangles), and AT Aira-Tanzawa ashes (open diamonds).. e+ : {N L?@ /0 **[ HKu e : © k lD /M9 Õ N Ö§¢ ! °~ : { K[ no 0Å ©+0 * *!= X>C : © W [ õ '+ ./2!45*Võ ' ./2!-)* fg õ * Võ * ,;: fgMN h?0 +U [ fg[ * *+ ~a " a bcbN ^ >C k &:Ô0 c¾9 * : © ! W [ õ fg õ ,;: fgMN h?@ 8 '()*! ·IJ V ![ ,;: fgk |u0 +" *+ à bcb N ^ >?¤k §0 != |" }U + *[ 8 * *! ·IJ eMN $ f ID /0 EF 3XY* 3XY*[ 3 L! Ï+& "#I$ ?" w~ 8 * *! W " ® EI$ h?0 +" % *+ ® E L bcbN ^ C k §0. Distribution of the Ulleung-Oki (U-Oki, open circles), Ulleung-Yamato (U-Ym, closed triangles), and Aira-Tanzawa (AT, open diamonds) ashes in the diagram of Na2O versus K2O. The diagram shows the more sodic and potassic characters of the Ulleung tephra layers than those of AT ash layers..

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(58) . Major characteristics of the Ulleung-Oki, Aira-Tanzawa and Ulleung-Yamato tephra layers found in the study cores. Tephra layers. Ulleung-Oki. 14. C absolute ages Thickness of layers Pumiceous fragments Morphology of glass shards SiO2 Na2O + K2O Classification of volcanic rocks Stratigraphic sequence. 56 @. . . . $ 2!-). G. 0 . . 5). . *k KLÔ 8 >+ (::) 3X>+¤k &:Ô0 12.

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(62) . . . . . . . 5 @ . . . . . . F. (. %. ) . (( ) . +BC7!+'. ca. 25~33 ka 1.5~3 cm present massive 57~66.5 wt.% 11~16 wt.% trachytic to phonolitic one unit. k *= ·! +¿I¸0 +U [ *= ·" ²@ + ¬ V Gw + ^ ?D /¤k §0 ÕÓÖ§¢ ! I~ 8 u * *[ E a©k lD / M e : {& u w~ EF *[ +9 a© Z {" ? ¯M K : {N L?@ /0 W ! I~ * *[ V fg V fgMN h?@ ~a a L+ M *[ V fg V ,;: fgMN h?@ à L+ 0 ²@!= *[ e I &I MN 3?@ /M (::) K 3X>N ^ KLC '()*+0 w~ *[ * ·IJ eMN ý[ * %´ lD / M * 38 ? ¯"0 3 ! I~ % *[ ® E L bcbN ^ > ?@ KLC k , Â /M9 * %´9 m Åek D-0~ *k KLÔ 3X >+ eMN ¬d¤k , Â /0 +" *+ ¡¢ 3! §. þ8 c/ ¬d¤k & :Ô0 . +. %+ ) . . (. . (. 1. 2!-). . 2!45. . . *. . . . %. . ''% ./. 2!-). . -. 2!45. ' ./. - 3. &-. . *. %. -. % ./. '%. ./ . %. 2!-). . . . 2!45. . 2!-). . . 2!45. . -). Ulleung-Yamato. ca. 22~24.7 ka 0.4~1.2 cm not present plane or bubble-wall 75~78.5 wt.% 6.5~9 wt.% rhyolitic one unit. . ²@ [ è Õé+ M N L Aê ëz a© 3XY { Ä+ Y?@ 9úû0 C e[ y ô + ì: + ¬ì: + õ + Z [ + e +0 è Õé!= ?" î[ aïðî âÎ+ +D /0 *= ·" ! ,-ß '()* Æ Þk +¿I¸0 ²@!= hC '()*[ * * V * V +0 ã&N % ²@ U != µ¶C . Aira-Tanzawa. ca. 9.3 ka 10~14 cm present massive 57.5~66 wt.% 12~15.5 wt.% trachytic to phonolitic three units. &I '()* [ k f ID / ¯M § *:& ü§I$ C0 +U [ e · I &I '()* *= '. " K 3Z. . 2!. *. . . . ) . 2!45. +BC7!+%. =:. . % ) . . 2!45. . +6 ! +¿C ²@ [ != ÂØID /" “& I+01+é 2_ Ç µ ” E¡MN ÀÁ?0 Ö§¢ ! J¾ N 83 © A à Õ 4Y5 6!$ 7_ 080 ± `k v_ 4 D- uÊ ä_9 . 1=;. .

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