六盘山地区中生代煤系地层时代归属重新厘定

发布时间：2018-01-31 22:01

  本文关键词： 六盘山地区 地层时代 延安组 U-Pb同位素定年 再旋回化石　出处：《地学前缘》2017年05期 　论文类型：期刊论文

【摘要】：为正确划分六盘山地区具"上三叠统或下-中侏罗统"之争的中生代煤系地层,通过野外沉积现象观察、镜下矿物学研究并结合砂岩碎屑锆石LA-ICP-MS U-Pb同位素定年,重新厘定了该套煤系地层的时代。六盘山地区争议地层普遍发育铁质结核,砂岩差异风化严重,这与邻区下-中侏罗统延安组地层相似,而与邻区上三叠统延长组差异较大;争议地层砂岩样品中含13颗中生代年轻碎屑锆石((188±3)~(254±8)Ma)(占总数17%),其中3颗碎屑锆石U-Pb年龄小于200 Ma,最年轻的碎屑锆石年龄限制了争议地层最大沉积年龄小于(188±3)Ma。争议地层中发育的晚三叠世孢粉组合,是三叠系孢粉化石再旋回的结果,鄂尔多斯盆地西南缘强烈的印支运动导致三叠系很快抬升至地表遭受剥蚀,为近区早—中侏罗世地层提供物源,古生物化石亦随之混入近区沉积地层中。根据上述证据和讨论,将六盘山地区中生代煤系地层时代重新归为早—中侏罗世,这一结论具有重要科学研究和油气勘探价值。
[Abstract]:In order to correctly divide the Mesozoic coal measures strata in the Liupanshan area with "Upper Triassic or Lower Middle Jurassic" dispute, the field sedimentary phenomena were observed. The mineralogical study under microscope and LA-ICP-MS U-Pb isotopic dating of sandstone zircon have redefined the age of the coal-bearing strata. Iron nodules are commonly developed in the disputed strata in Liupanshan area. The sandstone differential weathering is serious, which is similar to the lower and middle Jurassic Yan'an formation in the adjacent area, but is quite different from the Yanchang formation of the Upper Triassic in the adjacent area. The sandstone samples of the disputed strata contain 13 young Mesozoic detrital zircons (188 卤3) and 254 卤8 Majiao (17 in total). The U-Pb age of three detrital zircons is less than 200 Ma. The youngest clastic zircon age limits the maximum sedimentary age of the disputed strata to less than 188 卤3 Ma. The late Triassic sporopollen assemblage developed in the disputed strata is the result of the recycle of the Triassic sporopollen fossils. The strong Indosinian movement in the southwest margin of the Ordos Basin caused the Triassic to rise to the surface of the earth to be eroded quickly, which provided a material source for the early and Middle Jurassic strata in the near area. According to the above evidence and discussion, the Mesozoic coal-bearing strata in Liupanshan area were reclassified to early and middle Jurassic. This conclusion has important scientific research and oil and gas exploration value.
【作者单位】： 西北大学大陆动力学国家重点实验室西北大学地质学系;
【基金】：国家自然科学重点基金项目(41330315) 中国地质调查局项目(12120113039900,12120114009201)
【分类号】：P597.3;P618.11
【正文快照】： GUO Pei,LIU Chiyang*,WANG Jianqiang,DENG Yu,ZHAO Xiaochen,WANG Wenqing,WANG LeiState Key Laboratory of Continental Dynamics;Department of Geology,Northwest University,Xi，

本文编号：1480094