Cretaceous Strata SIMS Zircon U-Pb Dating In Northern Hebei Province And Songliao Basin

Cretaceous, is a very special period ranging between Jurassic and Paleogene in the geological history. It's global biosphere, ancient geography and ancient climate are changed dramatically and provide a good chance for the Earth system research.The establishment of the geological time scale provides high-precision geological coordinates to the significant studying of the relationships among geological events on the Earth's surface. The international Cretaceous geological time scale are mainly determined by marine fossils, but the distribution of Jurassic and Cretaceous marine sediments in China are very limited that it is difficult to establish the correlation of different area.Fengning Basin, in northern Hebei Province, has exposed a large number of fossils of the early Jehol Biota. The correlations between the fossil-bearing beds and interbedded tuffs are clear. Based on the previous study of stratigraphy and paleontology, we collected 8 samples from the interbedded bentonite and tuffaceous sandstones of the Protopteryx,Perpiaosteus and Mammal fossils-bearing deposits from top to buttom in three sections in the Basin, and carried out SIMS Zircon U-Pb dating, obtained the ages on the boundary of some important stratigraphic units and major the fossils:(1) Enantiornithes of Jehol Biota probably appeared at about 132 Ma, pushing back the history of the Enantiornithes between 128 Ma and 132 Ma.; the first probably appeared time of Jehol Biota can be pushed forward to 136 Ma, with the duration time of Jehol Biota at least 16 Ma. (2) 132 Ma is probably the maximal age estimate of the boundary between Dadianzi Formation and Dabeigou Formation; the horizon of Dadianzi Formation is maybe lower than the Yixian Formation, with the duration of 128～132 Ma; and the duration of Dabeigou Formation with 132～136 Ma, suggest that the time of Zhangjiakou Formation underlie Dabeigou Formation may be older than 136 Ma. The Jurassic-Cretaceous boundary (145 Ma) may be near the unconformity between the Zhangjiakou Formation and Tuchengzi Formation."SK-1", the first Chinese scientific drilling based the entire Cretaceous strata, is also the first continental Cretaceous scientific drilling wells in International Continental Scientific Drilling Program (ICDP). The drilling core mainly composed of deep lake mudstone and some sandstone. We selected five bentonite and tuffaceous sandstone layers from the core to conduct Zircon U-Pb dating by SIMS, and got important stratigraphic units'ages. (1) The bottom of Qingshankou Formation deposits at 91.4 Ma; and the boundary between the first and second bed of Qingshankou Formation is 90.2 Ma, which provide the isotopic age constraint for the boundary of Qingshankou Formation, suggest that the bottom of Qingshankou Formation is in the Turonian Stage. (2) The boundary of the first and second bed of Nenjiang Formation is 83.7 Ma.These age data provide chronological constraints to the main stratigraphic units, major fossil layer of the Upper Cretaceous in northern China. Besides, these precise ages improve the correlation between Chinese major Cretaceous geological events and global Cretaceous events.