Mid-Cretace。us char。ph桝a stra廿graphy fr。m c。re SKー (S。uth

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.