陕西镇安二叠系碳酸盐岩粘土矿物特征及其对古气候指示

发布时间：2018-06-10 00:27

本文选题：粘土矿物 + 古气候　；参考：《合肥工业大学》2017年硕士论文

【摘要】：陕西镇安地区二叠纪时为古特提斯洋东部的一个孤立台地,二叠系地层连续发育,厚度巨大,是研究二叠纪古气候古环境的理想之地。本文通过对陕西镇安地区二叠系碳酸盐岩粘土矿物组合特征及相对含量的研究,来探讨研究区二叠纪的古气候特征及演化规律,并与华南、古特提斯地区进行对比,对探讨世界二叠纪古气候具有重要意义。本文对陕西镇安西口二叠系剖面(下二叠统三里冲组、石门垭组与垭子组,中二叠统五里坡组和水峡口组,下二叠统西口组、熨斗滩组和龙洞川组)进行了剖面测量和系统采样。实测剖面总长度7300m,地层总厚度3143m,采集样品272件,分离提取了其中172件碳酸盐岩样品中的粘土矿物。将分离得到的粘土矿物样品分别制备成自然定向片(N)、乙二醇定向片(EG)和高温定向片(550℃),对其进行XRD分析,并利用扫描得到的图谱进行定性分析和半定量计算。结果显示研究区粘土矿物组合为伊利石(平均含量70.9%)、高岭石(平均含量7.9%)、蒙脱石(平均含量4.4%)、绿泥石(平均含量8.6%)和伊蒙混层(平均含量8.3%)。样品的Kübler指数矫正前几乎均大于0.25Δθ°,矫正后均大于0.42Δθ°,伊利石结晶度高,且没有出现从下往上结晶度变小的趋势,说明研究区粘土矿物受到埋藏成岩和变质作用的影响较低,可以指示源区的风化条件。根据研究区粘土矿物组合特征,本文用伊利石相对含量作为恢复古气候指标,伊利石含量高指示气候寒冷干燥,反之则温暖潮湿。伊利石相对含量变化显示研究区二叠纪古气候变化可分为8个段:即阿舍尔期(Asselian)至空谷期(Kungurian)中期的干冷期(P1);空谷阶(Kungurian)中期至卡匹敦期(Capitanian)中期经历了湿热(P2)-干冷(P3)-干冷暖湿交替(P4)的变化;卡匹敦期(Capitanian)中期至吴家坪期(Wuchiapingian)早期的气候变冷(P5);吴家坪期(Wuchiapingian)早期的短暂暖湿期(P6);吴家坪期(Wuchiapingian)早期至吴家坪期(Wuchiapingian)末期的气候逐渐变冷(P7);以及长兴期(Changhsingian)干冷暖湿交替显著的气候(P8)。同时,对比研究表明,研究区二叠纪古气候变化受晚古生代冰期事件(LPIA)、Kamura事件及G-LB生物灭绝事件的影响。此外,研究区罗德期(Roadian)存在一个持续约2.4 Ma的短暂寒冷期,这与前人认为的空谷期(Kungurian)以来气候逐渐变暖不一致,该寒冷期恰好位于二叠纪的第3个冰期(P3),暗示其可能具有更广泛的对比意义。
[Abstract]:The Permian area of Shaanxi Province during the Permian period was an isolated platform in the eastern part of the PaleoTethys Ocean. The Permian strata developed continuously and its thickness was huge. It is an ideal place to study the Paleoclimate and paleoenvironment of the Permian period. Based on the study of the characteristics and relative contents of clay mineral assemblages of Permian carbonate rocks in Zhenan area, Shaanxi Province, this paper discusses the paleoclimate characteristics and evolution rules of Permian in the study area, and compares them with those in South China and PaleoTethys. It is of great significance to study the Permian paleoclimate in the world. The Permian section of Xikou, Zhenan, Shaanxi Province (Lower Permian Sanli Chong formation, Shimenya formation and Yazi formation, Middle Permian five Li Po formation and Shuixiakou formation, Lower Permian Xikou formation, etc. Section measurement and systematic sampling were carried out. The total length of measured section is 7300 m and the total thickness of stratum is 3143 m. 272 samples were collected and 172 of them were separated and extracted from carbonate rock samples. The samples of clay minerals were prepared into natural orientation tablets (NV), ethylene glycol oriented tablets (EGG) and high temperature oriented tablets (550C) respectively. The samples were analyzed by XRD, and analyzed qualitatively and semi-quantitatively by scanning spectra. The results show that the clay mineral assemblage in the study area is composed of Illite (average content 70.9g), kaolinite (average content 7.9m), montmorillonite (average content 4.4g), chlorite (average content 8.6C) and immonitic layer (average content 8.3g). The K 眉 bler exponents of the samples were almost more than 0.25 螖胃掳before correction and more than 0.42 螖胃掳after correction. The crystallinity of Illite was high and there was no tendency to decrease the crystallinity from the bottom to the top, indicating that the clay minerals in the study area were less affected by buried diagenesis and metamorphism. The weathering conditions of the source area can be indicated. According to the characteristics of clay mineral assemblage in the study area, the relative content of Illite is used as the index of recovering paleoclimate. The high content of Illite indicates that the climate is cold and dry, whereas the other is warm and humid. The change of Illite relative content indicates that the Paleoclimate change of Permian period in the study area can be divided into eight sections: the dry and cold period from the Asher period to the middle of the empty valley period Kungurian; the middle stage of the empty valley stage from Kungurianan to the middle period of Kapidon period, and the middle period of the period of Kapidon, the period of moist heat P2-dry and cold P3s. P4); From the middle period of Kapidon period to the early stage of Wujiaping stage, the climate became cold P5; the short warm and wet period of Wujiapingianingian was short; the climate of Wuchiapingianbetween the early Wujiapia period and the end stage of Wujiaping period gradually became cold P7N; and the climate of Changxing period Changhsingian1) changed significantly from dry, cold, warm and wet. At the same time, the comparative study shows that the Permian paleoclimate change in the study area is influenced by the late Paleozoic glacial events, the LPIAA Kamura event and the G-LB biological extinction event. In addition, there exists a brief cold period of about 2.4 Ma in the Luo De period in the study area, which is inconsistent with the gradual warming of the climate since the previous thought of the Hollow period (Kungurian). The cold period, which happens to be in the third glacial age of Permian, suggests that it may have wider contrasting significance.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P534.46;P532

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