早期热河生物群时代的磁性地层学约束

Magnetostratigraphic Dating of the Early Jehol Biota

早期热河生物群保存于冀北的中生代地层大北沟组—大店子组,层位时代的磁性地层学研究对限定热河生物群的演化、鸟类的起源与进化以及被子植物的起源等重大科学问题的年代框架具有重要的科学意义。同时,将为中国陆相侏罗系—白垩系界线及早白垩系地层划分提供可以进行全球对比的磁性地层学证据。此外,还将为限定华北克拉通破坏提供可靠"深时(Deep-time)"约束。基于1 100余块样品的测试与分析结果,建立了冀北滦平盆地大北沟组—大店子组高精度的磁极性序列。磁性地层对比分析方案表明,大北沟组、大店子组和西瓜园组的磁极性序列对应于标准磁极性柱的M12—M9,属于Valanginian中期至Hauterivian中期。从磁性地层学的综合研究认为早期热河生物群的时代归属于早白垩世的Valanginian期。本文的研究结果不支持中国陆相侏罗—白垩系界线位于大北沟组与大店子组之间的划分方案。

The early record of the Rehol Biota has been well preserved in the Mesozoic Dabeigou Formation and Dadianzi Formation.The magnetostratigraphic study can provide age control for the evolution of the Rehol Biota,the origin of birds,and the evolution of angiosperm.Meanwhile,it will offer chronological evidence for the terrestrial Jurassic Cretaceous boundary in China,the Early Cretaceous division and global stratigraphic correlation.Additionally,it can also afford“deep-time”age control for the timing of destruction of the North China Craton.Based on magnetostratigraphic results from more than 1 100 oriented samples of the Luanping Basin,northern Hebei Province,the authors established a high-resolution magnetic polarity sequence of Dabeigou and Dadianzi Formations.By magnetostratigraphic correlation,the magnetic polarity sequence of the Dabeigou,Dadianzi and Xiguayuan Formations is correlated to M12 M9 in standard magnetic polarity time scale.The Dabeigou Dadianzi Formation belongs to Mid-Valanginian Mid-Hauterivian.The authors hold that the early age of the Rehol Biota is younger than the Early Cretaceous Valanginian Age.The studies conducted by the authors refute the stratigraphic subdivision that the terrestrial Jurassic Cretaceous boundary in China would be set between the Dabeigou and the Dadianzi Formations.