Earth History of Asia- II October 31 - November 3, Niigata, Japan 13 Mid-Cretaceous Charophyta Stratigraphy from Core SK1 (South) in Songliao Basin and its Correlation with Marine Chronostratigraphy ZHANG Yiyi 1' State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 1 00083, China [email protected] com Cretaceous plays a significant role during the sweep of geologic history in light of some major events such as global warming and mass extmction. Recent years, with the chronostratigraphy standard established, the marine Cretaceous is supposed to be well observed, while the non-marine Cretaceous is relatively poorly studied in part because there is a lack of comprehensive fossil records. In northeastern China, however, we found Charophyta fossils in the Songhao Basm, one of the biggest Cretaceous continental rift basins all over the world, in which the southern hole of Songke-1 (SKl(S)) is located in the centre. According to Gramast (1972), Charophyta may be an ideal instrument of dating non-marine strata, in particular those of the Cretaceous and valuable tool for intercontinental correlation. The target interval in this study is from the upper Quantou Formation to the lower Nenjiang Formation deposited during the depression stage in the Cretaceous. The member 3 of Quantou formation yields Atopochara restricta, Mesochara symmetriea, Obtuochara niaoheensis and Euaclistochara mundula; Member 4 is dominated by Amblyochara elliptica, Ambyochara quantouensis, Atopochara restricta and others; Member 2-3 of Qingshankou Formation contains mostly Aclistochara bransoni minor, Ambyochara elliptica, Atopochara restricta, Aclistochara songliaoensis, Maedlerisphaera ellipsoidalis; Member 1 of Yaojia Formation yields Aclistochara bransoni minor, Atopochara restricta, Obtusochara niaoheensis, Songliaochara heilongjiangensis, Songliaochara heilongjiangensis nonganensis; Member 2-3 of Yaojia Formation contains Aclistochara bransoni minor, Aclistochara songliaoensis, Obtusochara niaoheensis. Based on the high-resolution sampling from SKl (S) and the outcrops across the basin, four charophyta assemblages are classified: Obtusochara niaoheensis Assemblage in member 3 to lower member 4 of Quantou Formation, Amblyochara quantuoensis Assemblage in middle Member 4 of Quantou Formation, Maedlerisphaera ellipsoidalis Assemblage in upper Quantou Formation to lower Qingshankou Formation, and Aclistochara songliaoensis Assemblage in upper Qingshankou Formation to yaojia Formation. According to the previous research and the micro fossils involved in SKl(S), it is suggested that the age of the upper Quantou Formation possibly is from Cenomanian to lower Turanian, the Qmgshankou Formation is upper Turonian- lower Comacian; the Yaojia Formation is referred to upper Coniacian to middle Santoman, and the lower Nenjiang Formation rests in upper Santoman.
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