冀北滦平盆地榆树下剖面大北沟组岩石地层、生物地层及其地质年代探讨

发布时间：2018-05-01 15:31

  本文选题：滦平盆地 + 榆树下剖面　； 参考：《地学前缘》2017年01期

【摘要】：滦平盆地榆树下剖面大北沟组出露完全、沉积连续、化石丰富,是研究热河生物群的起源、早期演化以及中国陆相晚侏罗世—早白垩世过渡地层的关键层位。论文对人工新揭露出的榆树下剖面进行了精细的实测;阐明了大北沟组与张家口组界线的标志,为凝灰质碎屑岩(沉积岩)的出现与晶屑岩屑熔凝灰岩(火山岩)的结束;大店子组与大北沟组界线的标志,为"蜂窝梁砾岩"或与之相当的粗碎屑岩的出现。剖面的主体大北沟组总厚度为224.51m,可分为3段46层。大北沟组二段与一段界线的标志,为正常沉积岩(不含或很少火山物质,开始出现丰富化石)的出现并取代凝灰质碎屑岩成为主要的岩层;大北沟组三段与二段界线的标志清晰,为一套青灰色粉砂凝灰岩的出现。依据新采集到的化石并结合前人资料,完成了榆树下剖面大北沟组综合生物地层的建立。首次在大北沟组二段中上部发现了介形类化石,并可延伸到三段顶部;初步鉴定出介形类化石9属17种,可划分为Luanpingella-Pseudoparacypridopsis-Eoparacypris组合带,并可进一步细分为Luanpingella postacuta和Pseudoparacypridopsis mountfieldensis 2个亚带。叶肢介化石的首现面在二段底部,可贯穿至三段顶部;叶肢介组合带的划分参考前人的结果,由下至上分为Nestoria pissovi-Jibeilimnadia ovata、Nestoria pissovi-Keratestheria gigantea和Yanshania xishunjingensis-Y.subovata3个化石带。昆虫化石主要分布在二段中部至三段中上部的页岩中,仅为三尾拟蜉蝣(Ephemeropsis trisetaris)一个种,据此建立昆虫类Ephemeropsis trisetaris化石带。此外,参考前人资料,尝试建立了大北沟组孢粉、双壳类和鱼类化石带。在大北沟组介形类、叶肢介、孢粉等生物的年代特征分析的基础上,结合大北沟组同位素测年结果、磁性年代特征和生物归属的认识,将大北沟组的地质时代归为早白垩世。
[Abstract]:The Dabigou formation in Yushushi section of Luanping Basin is completely exposed, continuous sedimentary and rich in fossils. It is the key horizon to study the origin, early evolution and transitional strata of late Jurassic to early Cretaceous in China. In this paper, the detailed measurement of the newly exposed Yushu section is carried out, and the mark of the boundary between the Dabigou formation and the Zhangjiakou formation is clarified, which is the appearance of the tuff clastic rock (sedimentary rock) and the end of the crystalline clastic tuff (volcanic rock). The boundary between Damianzi formation and Dabeigou formation is marked by the occurrence of "honeycomb conglomerate" or equivalent coarse clastic rock. The total thickness of the Dabigou formation, the main body of the section, is 224.51 m, which can be divided into 3 sections and 46 layers. The boundary between the second member and the first member of the Dabigou formation is marked by the occurrence of normal sedimentary rocks (no or very little volcanic material and the appearance of rich fossils) and the replacement of tuffaceous clastic rocks as the main rock formations. The boundary between the third member and the second member of Dabigou formation is clear, which is a set of bluish gray silt tuff. Based on the newly collected fossils and previous data, the comprehensive biostratigraphy of the Dabigou formation in the Yushou section was established. For the first time, ostracods were found in the middle and upper part of the second member of the Dabigou formation, which can be extended to the top of the third member, and 9 genera and 17 species of ostracoda fossils were identified, which can be divided into Luanpingella-Pseudoparacypridopsis-Eoparacypris assemblage zone and further subdivided into Luanpingella postacuta and Pseudoparacypridopsis mountfieldensis subzones. The first present surface of the phyllodes is at the bottom of the second stage, which can run through the top of the third section, and the division of the lamellar assemblage zone can be divided into Nestoria pissovi-Jibeilimnadia ovata Nestoria pissovi-Keratestheria gigantea and Yanshania xishunjingensis-Y.subovata3 fossil belts from the bottom up according to the previous results. The insect fossils are mainly distributed in the shale from the middle part of the second member to the upper part of the third member, and are only a species of Ephemeropsis trisetaris (Ephemeropsis trisetaris). Based on this, the Ephemeropsis trisetaris fossil belt of insects has been established. In addition, the sporopollen, bivalve and fish fossils of the Dabigou formation have been established with reference to previous data. Based on the analysis of the age characteristics of ostracods, lobes, sporopollen and other organisms in the Dabigou formation, combined with the results of isotopic dating, magnetic chronology and biological attribution of the Dabigou formation, the geological age of the Dabigou formation is classified as early Cretaceous.
【作者单位】： 中国地质大学(北京)地球科学与资源学院;北京盛元金土能源投资有限公司;
【基金】：国家重点基础研究发展计划“973”项目(2012CB822000) 国家自然科学基金项目(41302008,41172015,41172037) 中国地质大学(北京)优秀导师基金项目(53200859507)
【分类号】：Q91;P534.5

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