松辽盆地断陷期火石岭组时代归属探讨

Chronostratigraphy of Huoshiling Formation in the Songliao Basin,NE China:An overview

通过对松辽盆地火石岭组生物地层、同位素年代地层、岩石地层及古地磁等资料的系统总结分析，结合上覆营城组底界年龄，基于井间对比、沙河子组和火石岭组的沉积厚度和沉积速率，探讨火石岭组的纵向序列、空间展布及其地质时代。火石岭组是东北地区及邻区断陷盆地群早期的一套局部以火山岩为主的充填序列。在平面展布上，火石岭组具有大范围分布、断陷间火山作用特征和时间差异性显著等特点。火石岭组植物化石时代意义不明显，孢粉化石显示早白垩世的特征，特征大孢子分子、古地磁资料则显示侏罗纪的特征。根据营城组的底界年龄（130Ma），沙河子组时间跨度（10Ma），计算火石岭组的顶界年龄在140Ma左右，又根据火石岭组最小的时间跨度（8Ma），计算火石岭组底界年龄应在150Ma左右，这与同位素年龄分析结果相吻合。综合来看，火石岭组具有跨时代的特征，主体年龄在140～150Ma，对应于Tithonian-Berriasian期，可能上延至Valanginian期。松辽盆地侏罗系-白垩系界线（J／K界线）可能存在于火石岭组内部。

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, litbostratigraphy 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 {ossil and magnetostratigraphy indicate the age o{ the Jurassic. Overlying sequence of the H-Form is also concerned in order to constrain its time span. The bottom of Yingcheng Formation is 130 Ma, the duration of Shahezi Formation is about 10 Ma, so that the top age of the H-Form should be ca. 140 Ma. The minimum duration of H-Form is calculated ca. 8 Ma, and its bottom age ought to approach about i50 Ma. The isotopic age dating on the volcanic rocks of H-Form mainly ranges from 140 Ma to 150 Ma. 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.