Chronostratigraphy of Huoshiling Formation in the Songliao Basin,NE China:An overview
The chronostratigraphy,sequence and distribution of Huoshiling Formation(H-Form)in the Songliao Basin are discussed and summarized on the basis of biostratigraphy,isotopic dating,lithostratigraphy as well as magnetostratigraphy.The H-Form is the first rifting basin stage with the filling sequence of mainly volcanic rocks in northeastern China and adjacent areas.Laterally,it is characterized by the widespread distribution,remarkable variation in volcanic eruption time and scale between fault depressions.The H-Form yielded plant megafossils in a wide range of periods.The sporo-pollen assemblages show a blooming age of the early Cretaceous.Characteristic megaspore fossil and magnetostratigraphy indicate the age of the Jurassic.Overlying sequence of the H-Form is also concerned in order to constrain its time span.The bottom of Yingcheng Formation is 130Ma,the duration of Shahezi Formation is about 10Ma,so that the top age of the H-Form should be ca.140Ma.The minimum duration of H-Form is calculated ca.8Ma,and its bottom age ought to approach about 150Ma.The isotopic age dating on the volcanic rocks of H-Form mainly ranges from140Ma to 150Ma.All these evidences above suggest that the age of H-Form can be well constrained from the Tithonian to the Berriasian or to the bottom of the Valanginian.The Jurassic-Cretaceous boundary(J/K boundary)in the Songliao Basin probably exists inside the Huoshiling Formation.