内蒙古东部霍林河盆地霍林河组的年龄:来自锆石U-Pb测年和孢粉组合的证据

内蒙古东部霍林河盆地霍林河组是我国最重要的下白垩统含煤地层之一.该组产出大量不同种类且保存完好的植物化石,但因为缺乏海相沉积和火山岩夹层,我们对这套地层的精确年龄认知不足.我们最近在扎鲁特旗扎哈淖尔露天煤矿霍林河组发现了火山灰层,基于钻孔数据的地层分析显示该火山灰层位于霍林河组下含煤段的底部.二次离子质谱(SIMS)锆...

AGE OF THE HUOLINHE FORMATION IN THE HUOLINHE BASIN,EASTERN INNER MONGOLIA,CHINA: EVIDENCE FROM U-Pb ZIRCON DATING AND PALYNOLOGICAL ASSEMBLAGES

The Huolinhe Formation in the Huolinhe Basin,eastern Inner Mongolia is one of the most im-portant Lower Cretaceous coal-bearing strata in China,yielding abundant,diverse,and well-preserved plant fossils.Its precise age,however,is poorly known due to lack of associated marine deposits and volcanic beds.Here we present U-Pb zircon ages,and the associated palynological assemblages of an ash layer of the Huolinhe Formation recently discovered at the Zhahanaoer open-cast coal mine in Jarud Banner.Strati-graphic analyses based on boreholes suggest that the ash layer occurs near the bottom of the"lower coal-bearing member"of the Huolinhe Formation.U-Pb zircon geochronology using the SIMS method con-strains the depositional age of the ash layer to be 125.6±1.0 Ma(late Barremian-earliest Aptian),and this is consistent with the result from LA-ICP-MS analyses of the same sample.A late Barremian-earliest Aptian age for the ash layer is also supported by the palynological assemblage associated with the layer,in which the pollen of gymnosperms and the spores of ferns and bryophytes are dominant,angiosperm pollen is very rare and represented by only Clavatipollenites.This study contributes important new data for understanding the age of the entire Huolinhe Formation and also provides a more precise maximum age for the key plant fossils preserved in the deposits above the ash layer.