新疆准噶尔盆地北缘第三纪磁性地层学

【作者】 张睿；

【导师】 岳乐平；

【作者基本信息】 西北大学 ， 第四纪地质学， 2004， 硕士

【摘要】 对含动物化石的剖面进行绝对年代的测定是目前地层学研究的发展趋势，在北美陆相及欧洲海相地层中类似的研究已经进行的比较完善，80年代以来，古地磁及同位素等测年工作在我国大部分地区也已开展起来，对于新生代千百万年来的陆相地层，古地磁手段由于其可靠记录全球性变化的一致性以及与标准年代的可比性，成为地层工作者(尤其是新生代的古生物学者们)们最常借助的工具之一。 新疆地区新生代地层年代学研究成果较为缺乏，研究基础较为薄弱。本论文对新疆准噶尔盆地北缘含哺乳动物化石的2条主要剖面和2条辅助剖面进行了磁性地层方面的研究。通过岩石磁学x-T曲线的分析以及样品退磁强度曲线的分析，认为原岩的铁磁性矿物以赤铁矿及磁铁矿为主，反应了其时炎热的气候条件。对样品采取主向量分析手段，得到样品稳定的特征剩磁磁场方向。 结合古生物化石的证据，将特征剩磁极性方向与标准的极性年表(Cande-kent95年表)进行了对比。结果显示，乌伦古河地区铁尔斯哈巴合剖面很好地记录了极性年表中C5Cn3n～C8r的18个正极性和18个负极性段，最下部的负极性段记录了C8r，始自26.6Ma，最上部的正极性段记录了C5Cn3n，终于16.6Ma，时间跨度10Ma，自晚渐新世至中中新世早期。剖面记录了可可买登组(时代晚于16.4Ma，中中新统)、哈拉玛盖组(18.5～16.4Ma，早中新统)、索索泉组(23.8～18.5Ma，早中新统)、铁尔斯哈巴合组(早于26.8～23.8Ma，晚渐新统)四组地层，其中连续沉积的铁尔斯哈巴合组与索索泉组地层的界线为渐新世与中新世的界线(23.8Ma)。剖面底部两个晚渐新世动物群的年代分别为26Ma和25.5Ma。辅助剖面播塔莫音剖面应在始新世与渐新世界限附近。很好地记录了年表中C6r～C6Br的4个负极性和3个正极性段，最下部的负极性段记录C6r，始自24.7Ma，最上部的负极性段记录了C6Br，终于23.2Ma，时间跨度约1.5Ma。 布尔津地区克孜勒托尕依剖面的磁性地层记录了年表中C20n～C10r，最下部的正极性段记录C20n，始自约43Ma，最上部的正极性段记录了C11n1n，终于约29.6Ma，时间跨度13Ma，自中始新世至早渐新世晚期，包含了始新世与渐新世的界线(33.6Ma)，剖面中部的晚始新世哺乳动物群化石年代为34Ma。更多还原

【Abstract】 Dating the absolute time of mammalian fossils in the stratum is the tendency of stratigraphic research at present, identical research have been developed well in North American land facies and Europe sea facies. Since 1980s, dating studies such as magnetostratigraphy and isotope-stratigraphy have been carried out in many localities in China. For its coherence with global change and comparable with time scale, palaeomagnetism is mostly used by paleontologist to do the research in the Cenozoic land deposits.In this paper, we have researched 2 major sections and 2 assistant sections with mammalian fossils in north Junggar Basin by the means of magnetostratigraphy, analyzed its x-T curves and remnant magnetism, and thought that the hematite and magnetite were the main magnetic mineral and were the sign of hot climate. By virtue of main vectors analyzing, we have got the characteristic remnant magnetism of all the samples.Associated with some evidences from mammalian fossils, we correlate the geomagnetic results with the GPTS(Geomagnetic Polarity Time Scale). Tieersihabahe section (Ulungur district) had recorded the polarities C5Cn3n~C8r (26.6-16.6 Ma), from late Oligocene to early of middle Miocene, including the Tieersihabahe Formation (ie. 26.8-23.8 Ma, Late Oligocene), Suosuoquan Formation(23.8~18.5Ma, early Miocene), Halamagai Formation(23.8~18.5Ma, early Miocene), Kekemaideng Formation(<16.4 Ma, middle Miocene). The border of Oligocene and Miocene was in the continuous sediments between Tieersihabahe Fonnation and Suosuoquan Fonnation (23.8 Ma). The ages of the two faunas of late Oligocene in the bottom of the section were 26Ma and 25.5Ma. The short assistant section of Botamoyin was in the border of Oligocene and Miocene and had recorded the polarities C6r~C6Br (24.7-23.2Ma).Keziletuogayi section in the Burqin district had recorded the polarities C20n~C10r (43-13 Ma), from middle Eocene to early Oligocene, including the border of Eocene and Oligocene (33.6 Ma). The age of the mammalian fossils of lateEocene in the section was 34Ma.更多还原