Arctic Ice Cap And The Early Evolution Of The South China Sea Basin In Southern South China Sea In Response To The Late Miocene Benthic Foraminifera Records

This thesis discusses paleoceanography of the South China Sea (SCS) during the past14-5million years (Ma) on the basis of stable oxygen and carbon isotopes on foraminifers (518O and513C) from Ocean Drilling Program (ODP) Leg184Site1143, which is located in south of SCS. Isotope measurements were done in the Laboratory of Marine Geology of Tongji University on tow to seven foraminifers in a total of1615samples from191.25-432.29mcd (meter composite depth) of Site1143, including benthic species Cibicidoides wuellerstorfi and Uvigerina peregerina and planktonic species Globigerinoides obuliquus. The results show that:①Oxygen and carbon isotopes on benthic foraminifers are closely related to the initial appearance of the Arctic ice cap and uplift of Bashi channel;②Oxygen and carbon isotopes on planktonic foraminifers are not so close to the initial appearance of the Arctic ice cap, but they both display classic precession period of0.02Ma. The reason may be that the local environmental factors exerted a strong impact on planktonic foraminifers;③Carbon isotopes on both benthic and planktonic foraminifers changed before oxygen isotopes curve. This may be due to that carbon dioxide in atmosphere changed first, causing change in global temperature, and in turn change in global ice volume.Benthic foraminiferal assemblages were analyzed using the same set of samples, but with sampleing interval assemblages were of2.5m.136species were identified from104samples, including30dominant species whose percentage is over3%in more than2samples. According to faunal structure benthic foraminiferal, assemblages were grouped into five types:Group1. O. umbonatus is the major component, accompanied by one or several species of C. mundulus, C. wuellerstorfi, E. bradyi and G. Subglobosa;Group2. C. wuellerstorfi is the major component, accompanied by one or several species of O. umbonatus, C. mundulus and G. subglobosa;Group3. G. subglobosa is the major component, accompanied by one or several species of O. umbonatus, C. wuellerstorfi and C. mundulus;Group4. G. praegeri is the major component, accompanied by one or several species of G. subglobosa, C. wuellerstorfi and C. mundulus;Group5. C. mundulus is the major component, accompanied by one or several species of C. wuellerstorfi, G. subglobosa and O. umbonatus.These five groups account for82.69%in a total of86samples. The initial appearance of the Arctic ice cap may have exerted a great influence on faunal structure of benthic foraminifers, but uplift of the Bashi channel had little influeuce.