Cretaceous Strata Sequence And Basin Evolution Of Yanji Basin

Yanbian region located in the junction parts of Paleao-Asian Ocean tectonic domain and Pacific tectonic domain, it belongs to the eastern parts of Xinan-Mongolia Orogenic belt and an important composition of Mesozoic volcanic belt circling west Pacific ocean. The main strata of Yanji Basin are composed of Cretaceous, it has clearly two basin evolution stages, namely: the early Cretaceous rifting basin stage and the late Cretaceous depression basin stage.Based on systematically geological survey and comprehensively analyzing and comparing the previous data, the author discussed the rock strata sequences of Yanji basin, biostratigraphic characteristics and regional comparison, and then analyzed its litho-palaeogeography and discussed its basin evolution cycle. The scientific achievements as follow:1. Summarized each of the Cretaceous litho-stratigraphic units of Yanji Basin, and rectified its standards, and then established the strata sequences of Yanji Basin.2. Through comprehensive isotopic chronologic and biostratigraphic discussions, the age of the Tuntianying formation of Yanji Basin is amended from the middle Jurassic to early Cretaceous.3. Through analyzing the typical elements of Dalazi Fauna, and after discussing its evolution sequence with the Jehol Fauna and the Songhuajiang Fauna, it is clear that the Dalazi Fauna is a transitional fauna between the Jehol Fauna and the Songhuajiang Fauna, and its age should be late Early Cretaceous. 4. After discussing the Cretaceous lithostratigraphic sequence of Yanji basin and its evolution of litho-paleaogeography, the author reckons that the Yanji basin in early Cretaceous is a set of stream facies, lacustrine facies, and peat facies with volcanic pyroclastic rocks deposition, however, the late Cretaceous is stream facies red coarse grain clastic deposition under dry climate condition.5. The author proposes that the Yanji basin should not be independent controlling basin faults, and its tectonic division is two uplifts and two depressions, and divides the Yanji basin evolution into two cycles, namely early Cretaceous rift basin and late Cretaceous depression basin.