论文部分内容阅读
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)锆石U-Pb年代学研究得出的该火山灰层沉积年龄为125.6±1.0Ma(巴雷姆期晚期—阿普特期最早期),这一结果与激光剥蚀-等离子体质谱(LA-ICP-MS)对同一样品分析得出的年龄一致.火山灰层保存的孢粉化石组合以裸子植物花粉和蕨类及苔藓的孢子为主,被子植物花粉非常稀少,且仅有棒纹粉Clavatipollenites 一种.这一孢粉组合支持火山灰层的年龄为巴雷姆期晚期至阿普特期最早期.本研究为认识整个霍林河组的年龄及火山灰层上覆地层保存的重要植物化石的最大年龄提供了重要数据.“,”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.