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Based on the detailed field survey and laboratory analysis, the authors studied lithology, sedimentary conformation and palaeontological characteristics of the sedimentary strata of Yixian Formation in northern Hebei and the sedimentary environment has been analyzed. Results indicate that Senjitu Basin in northern Hebei has experienced enormous changes of sedimentary environment and frequent replacements of lithofacies types and rock combination, showing the evolution model of rapid deposition basin-filling. The sedimentary environment divided into fluvial deposit and lacustrine deposit. The sedimentary evolution of each depositional circle usually began with alluvial channel to fluvial deposit, and evolved into lacustrine deposit which is mainly made up of shore-shallow lake sedimentary model with relatively stirring hydrodynamic condition. The volcanism also had greater impact on the depositional environment during this period.

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