| 四川盆地川中地区须家河组古盐度特征及其地质意义 |
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| 引用本文： | 戴朝成,任军平,饶强,张怀胜.四川盆地川中地区须家河组古盐度特征及其地质意义[J].高校地质学报,2018,24(3):390. |
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| 作者姓名： | 戴朝成 任军平 饶强 张怀胜 |
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| 摘 要： | 在沉积学研究基础上,以粘土矿物为研究对象,利用X衍射分析和微量元素分析技术,采用Couch公式对四川盆地须家河组沉积期湖盆古盐度进行恢复,结果表明,须家河组古盐度介于4.8‰～19.7‰之间,平均值为12.8‰,远低于正常海水盐度。不同层位古盐度呈规律性变化,须二段至须六段古盐度逐渐降低,由咸水转变为微咸水。盐度的增高有利于蒙脱石向伊利石转化,使得须二段以伊利石为主,须四段—须六段伊利石平均含量逐渐降低,而以绿泥石为主。古盐度对绿泥石成分也有一定影响,随着古盐度的增高,绿泥石成分中的Si~(4+)逐渐减少,而Al~(Ⅳ)的含量逐渐增多,Fe~(2+)/Mg~(2+)+Fe~(2+)比值逐渐降低。结合四川盆地区域构造运动,认为须家河组古盐度变化主要由印支期构造所造成,须三段之后由于龙门山南段的抬升,四川盆地与外海失去联系成为独立沉积系统,须家河组二段和三段沉积应为陆相沉积物质,但受到海相潮汐叠加改造,而须四段—须六段则属于正常陆相沉积环境。
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| 关 键 词： | 四川盆地 上三叠统须家河组 古盐度 粘土矿物 Couch公式 |
Paleosalinity of the Xujiahe Formation in Central Sichuan Basin and Its Geological Significance |
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| DAI Chaocheng,REN Junping,RAO Qiang,ZHANG Huaisheng.Paleosalinity of the Xujiahe Formation in Central Sichuan Basin and Its Geological Significance[J].Geological Journal of China Universities,2018,24(3):390. |
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| Authors: | DAI Chaocheng REN Junping RAO Qiang ZHANG Huaisheng |
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| Abstract: | On the basis of sedimentological research, we study clay minerals by X-ray diffraction and trace element analysis to infer
paleosalinity of the lacustrine environment in which the Xujiahe Formation was deposited in Sichuan Basin. Paleosalinity was
determined using the Couch formula and the paleosalinity values range from 4.8 to 19.7 per thousand, with an average value of 12.8 per
thousand. The paleosalinity of different layers in the Xujiahe Formation changed regularly, and there is a gradual decrease trend from
the second to the sixth member, i.e., from saline to brackish water. The increase in salinity is favorable for the conversion of
montmorillonite to illite, suggesting that clay mineral of the second member of the Xujiahe Formation is mainly illite. The illite content
decreases gradually from the fourth member to the sixth member, indicating thatclay mineral in fourth member and sixth member is
mainly chlorites. Palaeosalinity also has a certain effect on the chlorite composition. with the increase of salinity, Si4+ , Fe2+/Mg2++Fe2+
content decreases and AlIV content increases in the chlorite composition. Combined with tectonic movement, the change in paleosalinity
of the Xujiahe Formation was probably caused by the Indosinian tectonism, the southern section of Longmen mountain uplift during the
third member period, the Sichuan Basin and the sea lost contact and became a separate deposition system. The sedimentary facies of
the second and the third member of the Xujiahe formation should be deposited in a terrestrial environment. However, it was
superimposed by tide. The fourth, fifth and sixth member of the Xujiahe Formation should belong to the normal continental sedimentary
environment. |
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| Keywords: | Sichuan Basin Upper Triassic Xujiahe Formation paleosalinity clay mineral Couch formula |
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