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Geological Age and Palaeoenvironment of the Lower Seogwipo Formation, Cheju Island, Korea

LI Bao hua 1) , PARK Byong Kwon 2) , KIM Dongseon 2) , and WOO Han Jun 2) ( 1) Nanjing Institute of Geology and Palaeontology, the Chinese Academy of Sciences, Nanjing, 210008; 2) Korea Ocean Research & Development Institute, Ansan  
Oceanic microfossil bearing deposits of the lower Seogwipo Formation along the Cheju Island are used to reconstruct palaeoenvironment and evolution of the island. Analyses of fifteen samples of planktonic foraminifera fossil bearing deposits from the lower Seogwipo Formation indicated that it was formed during the middle Pleistocene (late N22 Zone, i.e. Globigerina calida calida Subzone, and older than 400 ka BP) based on the presence of Globigerina calida calida, Beella digitata, Globigerina bermudezi and Globoquadrina conglomerata in the samples examined. The ratio of planktonic to total foraminiferal fauna decreased from the lower to the upper units in the section. Warm water species of Globigerinoides ruber and G. trilobus decreased while the temperate species of Neogloboquadrina dutertrei, Globigerina quinqueloba increased upwards. Quantitative analyses of foraminifera revealed that warm middle shelf (or offshore) waters were dominant during the deposition of the lower layers, and shallower inner shelf (or nearshore) waters with temperate water layers in the upper parts of the section came to dominate the palaeoenvironment. These varying conditions recorded a sedimentary history of regression of the lower Seogwipo Formation including three subregressions and two subtransgressions.
【Fund】: 韩国海洋研究所与中国科学院南京地质古生物研究所博士后 经费资助
【CateGory Index】: P534.63
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