Journal of the Geological Society of Korea (지질학회지)

The Geological Society of Korea (대한지질학회)
권호 표지

Diatom floras of the Ulleung Basin: implication for Late Quaternary paleoenvironment

규조화석군집을 이용한 동해 울릉분지의 후기 제4기 고환경 연구

Ryu, Eun Yeong;Ryu, Byeong Jae;Yun, Hye Su;Lee, Seong Ju
류은영;류병재;윤혜수;이성주

  • Published : 20030000

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Abstract

Late Pleistocene diatom flora from Core 00GHP-01 drilled in the southwestern margin of the Ulleung Basin, East Sea, was analysed for paleoenvironmental reconstruction(e.g., paleocurrent and salinity). Core sample(00GHP-01) yielded abundant and diversified diatom species, from which six assemblages and two barren zones are recognized. Assemblage zones reveal history of the Tsushima Current. 1) Pseudoeunotia doliolus Assemblage Zone(AZ), 502-410 cm in depth, is dominated by P. doliolus together with tropical Pacific species, which indicates inflow of high saline and warm water, and rising of sea-level. 2) Paralia sulcata AZ(410-360 cm) is characterized by the predominance of P. sulcata and brackish -benthic species indicative of the falling of sea-level at the beginning of the glacial period. 3) Rhizosolenia hebetata var. hiemalis AZ(360-280 cm) reflects that a significant amount of fresh water from Korean and Chinese rivers had flowed into the East Sea. Moreover, an influx of cold water from the Okhotsk Sea may be considered. The productivity in diatom assemblages appears to be low during the glacial period. 4) Paralia sulcata-Cyclotella striata-Thalassiothrix longissima AZ(260-100 cm) documents a minor inflow of the Tsushima Current into the East Sea. The tropical species(e.g., Hemidiscus cuneiformis), which occurred only in this assemblage zone, probably indicates a time of sea-level rise during the period of Pleistocene/Holocene boundary(ca. 230 cm). 5) Paralia sulcata-Thalassionema nitzschioides AZ(100-40 cm) indicates low salinity in surface water. In addition, associated fresh water and extinct species may indicate an influx of terrigenous material by the erosion of shores during the stages of lowering sea level. 6) Pseudoeunotia doliolus- Thalassionema nitzschioides AZ(28-0 cm) is interpreted as relatively warm-water conditions that influenced high productivity, similar to surface-water condition of modern environments. 7) Two barren zones are recognized at depths of 270cm and 30cm, below sea floor. Such barren zones may have resulted from intensification of bottom water activities such as erosion and corrosion associated with a climatic cooling. It could be concluded that the Ulleung Basin was influenced by relatively strong Tsushima Current twice during the deposition of both lowermost(502-400 cm) and uppermost(28-0 cm) intervals, and relatively weak Tsushima Current at the middle interval(250-200 cm) since the latest Pleistocene.

울릉분지 00GHP－01 코아에서 산출된　규조군집의 수직분포상 변화에　근거하여　후기 플라이스토세부터　현세까지　동해의　고환경　변천과　해수면의 변동에　대한　연구가 이루어졌다. 규조　군집조성은 근해 및 연안종으로 주로 조성되어 있으며 난류종과 한류종이 혼합된 양상을 보인다. 규조군집의　산출양상을　근거로　6개의　화석군집대와　2개의　무화석대가　설정되었으며, 각각의 화석군집대는 다음과 같다. 1) Pseudoeunotia doliolus Assemblage Zone (AZ): 하부 502 cm에서 410 cm까지로 대마난류가 풍부하게 유입되고 동시에 북쪽으로부터 한류가 유입되는 공해 환경. 2) Paralia sulcata AZ (410-360cm): 해수면 하강시기에 대륙주변부의 퇴적물이 풍부하게 유입되는 연안 혹은 조간대 환경. 3) Rhizosolenia hebetata var. hiemalis AZ(360-280 cm): 대마난류의 유입은 차단되고 동중국해에서 기원된 저염분수가 유입되었으며 동시에 오호츠크해로부터 한류가 유입된 시기. 4) Paralia sulcata- Cyclotella striata- Thalassiothrix longissima AZ(260-100 cm): 해수면 상승으로 대마난류가 조금씩 유입되기 시작하는 플라이스토세-홀로세 경계. 5) Paralia sulcata- Thalassionema nitzschioides AZ(100-40 cm): 해수면 하강으로 담수가 유입되고 동시에 한류의 영향도 많이 받은 조간대 환경이며 저탁류의 영향을 많이 받은 환경. 6) Pseudoeunotia doliolus -Thalassionema nitzschioides AZ(28-0 cm): 대마난류가 유입되는 현재와 유사한 바다환경. 7) 무화석대(270 cm, 30 cm): 해수면 하강으로 인한 해수순환이 차단되어 무산소 해저 환경을 이루었다. 이상의 규조화석 연구로 볼때 울릉분지가 퇴적될 당시 3번의 대마난류가 유입되었으며 이들 변화는 빙하기-간빙기의 해수면 변화에 기인된 것으로 보여 진다.

Keywords

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