Palaeodimatic and chronostratigraphic interpretations from strontium, carbon and oxygen isotopic ratios in molluscan fossils of Quaternary Seoguipo and Shinyangri Formations, Cheju Island, Korea

Palaeotemperatures and chronostratigraphies of the Quaternary Seoguipo and Shinyangri Formations, Cheju Island, South Korea were investigated in terms of the strontium, oxygen and carbon isotopic compositions of carbonate mol lusc shells. The Sr-87/Sr-86 ratios of mollusc shells from the Seoguipo For mation range from 0.70911 to 0.70914, which yield carbonate ages of 0.5-1.2 Ma (Early to middle Pleistocene) using the linear equation between ages an d 87Sr/86Sr ratios of Quaternary seawater. The 87Sr/86Sr ratio (0.70917) of aragonitic shells from the Shinyangri Formation provide late Pleistocene a ges (0.04 Ma). Based on AMS C-14 dates of mollusc fossil shells from the Sh inyangri Formation, the depositional age of the formation has been extended to 1570 yr BP. Palaeotemperatures calculated on the basis of the oxygen is otopic composition of the calcitic mollusc shells from the Seoguipo Formati on give a range of values from 12.6 to 19.1 degrees C, which is lower than the present-day shallow seawater temperature (14.9-25.5 degrees C) in the v icinity of the Seoguipo coast. Aragonitic mollusc shells from the Shinyangr i Formation provide oceanic temperatures ranging from 22.5 to 29.8 degrees C, which is higher than present-day seawater temperatures (14.1-23.2 degree s C). The calculated palaeotemperatures of the Seoguipo and Shinyangri Form ations are inferred to reflect cold and warm currents flowing over Cheju Is land during the Pleistocene to Holocene. (C) 1999 Elsevier Science B.V. All rights reserved.