摘要： 甘肃和内蒙交界的北山地区早白垩世发育众多小型内陆沉积盆地,富含煤、铀、油气等能源资源,但由于该地区岩石地层系统划分较为混乱、时代归属不清,从而制约了近年来的大规模资源勘探工作。本研究基于众多钻孔及露头剖面的沉积序列特征和孢粉等古生物资料,系统清理了该地区的下白垩统归属关系,建议将该地区的下白垩统老树窝群划分为3个组,自下而上依次为驼马滩组、甜水井组(新名)以及马鬃山组(新名),驼马滩组和甜水井组呈不整合接触。驼马滩组以灰黑色、深灰绿色含煤泥岩、粉砂岩及粗砂岩为主,含早白垩世早期孢粉Aequitriradites,但早白垩世中晚期繁盛的Cicatricosisporites含量极低且类型单调,指示驼马滩组的时代为早白垩世早期(大致为贝里阿斯期晚期至瓦兰今期早期)。甜水井组以灰绿色泥岩、粉砂岩为主,Ephedripites、Cicatricosisporites等孢粉含量丰富且类型多样,指示其时代为早白垩世中期(大致为欧特里夫期至巴雷姆期)。马鬃山组以紫红色、浅灰色粉砂岩为主,含有少量三沟类早期被子植物花粉化石,指示其时代为早白垩世晚期(可能为阿普特期至阿尔布期)。以上研究初步整理了甘、蒙交界北山地区下白垩统地层系统,可为后期资源勘探、基础地质研究等工作提供参考。

关键词: 北山地区, 早白垩世, 孢粉化石, 岩石地层, 生物地层学

Abstract: Many small inland sedimentary basins,rich in coal,uranium,hydrocarbon and others, developed during the Early Cretaceous in Beishan area at the Gansu and Inner Mongolia border area. However,the chaotic subdivision of lithological stratigraphic systems and unclear age determination have seriously hindered resource exploration in recent years. Based on the stratigraphical and palynological data collected from boreholes and outcrop sections,the Lower Cretaceous Laoshuwo Group of this area was divided into three formations in an ascending order,including the Tuomatan Formation,the Tianshuijing Formation(a new name)and the Mazongshan Formation(a new name). The former two formations are probably in an unconformity contact. The Tuomatan Formation is mainly composed of dark gray,dark gray-green coal-bearing mudstone,siltstone and coarse sandstone,containing Aequitriradites that are common in the early Early Cretaceous. Cicatricosisporites that are more common in middle Early Cretaceous are rare in the Tuomatan Formation indicating the age of this formation is the earliest Early Cretaceous(probably late Berriasian to early Valanginian). The Tianshuijing Formation is characterized by gray-green fine-grained mudstone and siltstone,and rich in Ephedripites and Cicatricosisporites,indicating an age of middle Early Cretaceous(probably Hauterivian-Barremian). The Mazongshan Formation is characterized by purple-red,light-gray fine-grained siltstone,in which a few tricolpate pollen records of early angiosperms indicate a late Early Cretaceous age(probably Aptian-Albian). This new stratigraphic system in the Beishan area at the Gansu and Inner Mongolia border area will provide reference for later resource exploration and basic research.

Key words: Beishan area, Early Cretaceous, sporopollen fossils, lithological stratigraphy, biostratigraphy

中图分类号: 

• P534.53