摘要
四川盆地三叠系蒸发岩发育,硫同位素δ^(34)S的变化幅度为14.5—34.9‰。其中以雷口坡组第四段最低约16.5‰,与现代海洋硫酸盐硫同位素值接近;雷一段至嘉四段26.1—29.5‰;嘉二段出现硫同位素的高异常值(32.4—34.9‰),可用以修改世界流行的δ^(34)S变化曲线.硫同位素的分布也表明了区内三叠纪属浅水盐湖环境。
The evaporite of the sedimentary basin of the upper Yangtze Platform has a wide distribution, which covers an area of 4 x 5km^2 particularly developes in Sichuan Basin. The evaporites occured from Feixianguan and Jialinjiang Formation of Lower Triassic, Leikoupo Formation of Middle Triassic. The thikness of anhydrite bed is 100-500m.
This paper provides a great deal of data of δ^(34)S, and established a δ34S column of Triassic evaporite in Sichuan Basin by analysing samples from deep bore.
Stratigraphic column of δ34S value indicates that δ34S value of anhydrite in the fourth member of Leikoupo Formation (namely T214) rages 14.5-18.9‰, commonly 16.5‰, T2I319.7-23.2‰, average 21.78‰, which is close to the isotopic value of sea sulphate. In T2l127.1-29.5‰.In the Fifth member of Jialinjiang For- mation (namely T1j5) δ34S value 26.1- 28.6‰, T1j4 28.0-28.5‰ commonly. But the δ34S value of T1j2 32.4-43.9‰, shows an abnomal high value.
As mentioned above, the sulfur isotope data are imoprtant for geologic research.
(1) In contemporary beds or a certain sedimentary basin. δ34S value varies very limited. So sulfur isotope may serve to stratigraphic division and correlation.
(2) δ34S value in the Triassic column decreases gradually from 34.9‰ at the lower to 14.5‰ at the upper.
(3) According to the view of modern sedimentary the deviation of sulfur isotope between evaporite and sea sulphate varies less than 1.6‰. The evaporation experiments on sea water indicate that in chloride sedimentary stage (such as carnallite etc.) the brine is bare of δ34S evidently. This represents the Salinization trend of the ancient saline lake and suggests that T2l4might be the higher deposition stage of salt-mineral.
(4) In the upper and middle part of Jialinjiang Formation δ34S value fix at about 28% constantly. In an anhydrite bed. δ34S is poor at some place. While a new sedimentary cycle start, δ34S value shows a new circulation from higher to lower. It may be proved that the dissolved sulphate of the ancient salt lake was supplied constantly. This may gives support to the hypothesis of shallow salt lake model. In other warde, in the lake of Early Triassic, the evaporative sedimentation of Sichuan Basin was a shalow water enviroment.
( 5) Comparing with sulfur isotopic data worldwide, δ34S value of the marine Triassic evaporite of Sichuan Basin has some character of the high abnomal value, and it is necessary to modify the sulfur isotopic curve prevailing all over th wold based on the data provided in the present paper.
出处
《沉积学报》
CAS
CSCD
北大核心
1989年第2期105-110,共6页
Acta Sedimentologica Sinica
