Abstract:

The Songliao Basin was a big lake during the midCretaceous, where Jehol, Songhuajiang and Mingshui biotas were developed in the Cretaceous; the organic of the lake expressed the sequence, the explosion and the extinction of the three biotas. The Songhuajiang Biota consisted of ostracodes, conchostracans, bivalves, charophytes, dinoflagellates, palynoflora, angiospermae etc. with distinct regional features. The angiospermae fossils such as Trapa angulata, Platanus septentrionalis, and the angiospermae pollen such as Crenwellia, Xinjiangpollis, Quantonenpollenites, Lythraites, Gothanipollis have been obtained from the Quantou Formation, with the age of the Late Cretaceous. SHRIMP zircon UPb ages of nine volcanic rock samples from Yingchen range from (1151±12) Ma to (1111±09) Ma, falling into the Late Aptian to the Early Albian stage. The magnetostratigraphic research indicated that the polarity from the Denglouku to the Yaojia Formation is normal, but twice brief reversed polarity occurred in the Upper Part of the Denglouku Formation and the Lower Part of the Yaojia Formation. The dark shales and oilshales in the Lower Part of the Qingshankou Formation are of high organic carbon, and positive excursion of kerogen isotopes. It is suggested that the dark shales in the Lower Part of the Qingshankou Formation are the products of the lake anoxic period. Based on the study of biostratigraphy, chronostratigraphy, magnetostratigraphy and event stratigraphy, the Lower/Upper Cretaceous boundary in the Songliao Basin is, therefore, between the Quantou and the Denglouku Formation, instead of between the Quantou and the Qingshankou Formation.

Key words: Key words: Denglouku Formation; Quantou Formation; Qingshankou Formation; UpperLower Cretaceous boundary; Songliao Basin