Strontium Isotope Evolution and Global Sea-level Changes of Carboniferous and Permian Marine Carbonate, Upper Yangtze Platform
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摘要: 地质历史中海水的锶同位素组成是时间的函数,全球海平面变化是其最主要的控制因素,上扬子地区石炭—二叠纪海相碳酸盐的锶同位素演化曲线与海平面变化曲线有着很好的一致性。锶同位素演化曲线说明:1)早石炭世是一个海水逐渐加深的全球海平面上升时期,锶同位素最小值所显示的最大海泛面的年龄为 34 2Ma,位于杜内阶和韦宪阶的界线上 ;2 )晚石炭世是一个全球海平面下降时期 ;3)整个二叠纪都是全球海平面上升时期,晚二叠世的海平面上升不仅幅度大,而且海水在短时间内迅速加深 ;4)晚二叠世具有古生代海相碳酸盐的锶同位素最小值,显示晚二叠世末的全球淹没事件,最大海泛面的年龄为 2 5 0Ma,正好在二叠 /三叠纪界线附近 ;5 )二叠 /三叠纪之交的全球生物绝灭事件可能与二叠世末的全球淹没事件有关。Abstract: The evoIution of strontium isotopic composition of originaI seawater is a function of geoIogicaI time, and mainIy controIIed by the gIobaI sea-IeveI changes. The evoIutionaI curves of the strontium isotopic composition of Carboniferous and Permian marine carbonate rocks, Upper Yangtze PIatform is guite consistent with trend of the sea-IeveI changes. This variation curve of the strontium isotope shows the foIIowing facts： 1）The gIobaI sea-IeveI rise is corresponding to the faIIing of strontium isotope. The point of the minimum vaIue of 87 Sr /86 Sr in the earIy Carboniferous is just the position of maximum fIooding surface for the period of earIy Carboniferous, of which the numeric age is 342 Ma. This key point is just Iocated at the boundary of Tournaisian and Visean, for the Huishui section in Guizhou of Province, which is Iocated at the boundary between Jiusi and Shangsi formation. 2）The Iate Carboniferous is a period of gIobaI sea-IeveI faIIing. 3）The Permian, from the beginning to the end, is a period of gIobaI sea-IeveI rise. During the Iate Permian, we can see that the sea IeveI was rising unceasingIy and the marine water became deepIy in short time. 4）The Iate Permian is provided with the strontium isotopic minimum of marine carbonate rocks throughout the Late PaIaeozoic, representing the gIobaI marine fIooding event. The numeric age of the fIooding is 250 Ma, which nears to the Permian-Triassic boundary. 5）The mass extinction at the boundary of Permian-Triassic is probabIy due to the gIobaI marine fIooding event of Iate Permian.
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