辽西—冀北地区土城子组的地质时代、年龄及其国际地层对比  

Dating of Tuchengzi Formation in Western Liaoning-Northern Hebei and correlation with the International strata

作　　者：王思恩[1] 高林志[1] 万晓樵[2] 宋彪[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学,北京100083

出　　处：《地质通报》2013年第11期1673-1690,共18页Geological Bulletin of China

基　　金：全国地层委员会项目(编号:1212011120142);国家自然基金委项目(批准号:41172037)

摘　　要：辽西—冀北地区土城子组(后城组)含有各类化石,包括植物、孢粉、介形类、叶肢介、昆虫及恐龙类等,各门类化石都对土城子组的时代提出归属与生物演化依据。通过与国内外相关生物群(组合)的研究与对比,尤其是孢粉、介形类微体化石大区域的国际对比,将土城子组的地质时代划归为晚侏罗世早—中期(Oxfordian-Kimmeridgian)。土城子组的地磁年代学研究,也得出大致相同的时代结论。笔者在辽西金岭寺—羊山盆地土城子组剖面中,采用SHRIMP锆石U-Th-Pb同位测定技术,对凝灰岩中的锆石进行了年龄测定,获得的206Pb/238U年龄为:第22层140.2Ma±1.3Ma(N=13,13个数据加权平均值);第30层139.6Ma±1.9Ma(N=12);小刘家沟剖面土城子组上部凝灰岩139.6Ma±0.7Ma(N=11);第83层137.3Ma±1.0Ma(N=13)。由于第22层距土城子组底界369m,据沉积速率推算约为1.5Ma。因此,土城子组底界年龄应为141.7Ma±1.3Ma。第83层接近土城子组顶界,137.3Ma±1.0Ma年龄值可大致视为土城子组顶界的年龄。如此推断,上侏罗统牛津阶(Oxfordian)底界年龄应接近141.7Ma±1.3Ma,基默里奇阶(Kimmeridgian)上界年龄应为137.3Ma±1.0Ma左右,而国际地质年表中推导、标注的两者年龄分别为163.5Ma±1.0Ma和152.1Ma±0.9Ma,与笔者实测的年龄值分别相差21Ma和15Ma,对此进行了深入的探讨。Various fossils such as plants, spore-pollen, ostracods, conchostracans, insects and dinosaurs are well developed in the Tuchengzi Formation （Houcheng Formation）, and fossils of each kind has their own evolutional orbit and ages. According to the study and correlation of different assemblages in the whole globe, mainly biostratigraphic correlation of spore-pollen and ostracods both in China and abroad, the Tuchengzi Formation should belong to the early-middle Late Jurassic Oxfordian-Kimmeridgian, identical with the age obtained by paleomagnetism and geochronology. The authors obtained some SHRIMP U-Pb zircon ages of tuff, such as 140.2Ma±l.3Ma from Horizon 22 and 139.6Ma±1.9Ma from Horizon 30 of the Tuchengzi Formation in Jinlingsi-Yangshan basin of western Lioaning Province, and 139.6Ma±0.7Ma from the upper part of the Tuchengzi Formation and 137.3Ma±1.0Ma from Horizon 83 along the Xiaoliujia valley section （about 6km north of Sanbaoying Town）. Because Horizon 22 is 369m from the bottom of the Tuchengzi Formation and, according to the depositional rate, the authors hold through calculation that its deposition took place at about 1.5Ma. Therefore, the boundary age should be 141.7Ma. In addition, Horizon 83 is close to the top boundary, so the SHRIMP U-Pb zircon age 137.3Ma±1.0Ma should be regarded as the top boundary age of the Tuchengzi Formation. However, the bottom boundary age of Oxfordian is nearly 141.7Ma＋l.3Ma, and that of the top boundary of Kimmeridgian is 137.3Ma±1.0Ma; nevertheless, Oxfordian age is 163.5Ma±1.0Ma and Kimmeridgian age is 152.1Ma±0.9Ma in International Geological Time Scale, so there exists the age difference of 21Ma and 15Ma between the authors＇ calculation and the age indicated by International Geological Time Scale for Oxfordian and Kimmeridgian respectively.

关 键 词：土城子组 生物地层学 SHRIMP锆石U—Pb年龄 侏罗纪 

分 类 号：Q911.6[天文地球—古生物学与地层学] P597.3[生物学—古生物学]