摘要
关于准噶尔盆地西北缘风城组沉积环境的属性,以往认为系海相沉积.笔者通过几年的工作,认为这一结论值得商榷.文章从沉积特点与岩石、矿物标志及元素地球化学标志诸方面论述了风城组陆相咸化湖泊沉积的证据.
Fengcheng Formation(P2') which is located in the northwest margin of the Junggar Basin is a set of dark mudstone and dark-gray dolomitic mudstone stratum. Geologists have made much study on this area, but the opinons about the sedimentary facies of the stratum are different. The author consides that the stratum is of ter-restrial facies dom inated by saline lacustrine facies.
1 .Characters of sediment and marks of mineral and petrology
(1) The sea water receded eastwards and southwards in the Junggar Basin at the Late Carboniferous Epoeh, but in the southeast margin of the basin, the water receded late, dominated by marine facies. In the
soushwest margin.there was no marine sedimental paleogeographyic condition at the middle Permain Epoch. (2)The Fengcheng Formation has distribution limited, synch rone and out-of-phase.
(3) Dark mudstone and dolomitic miudstone are rich in organie matter and scattered pyrite with fine hori-
zontal stratification wave and laminated bedding. It suggests that there was a quiet water and lower-energy en-
yironments under reducing condition.
(4) Dolostone is distributed with spotted and stripped, and unstable in, horizon. Its content is less than
30% in rocks by chemical analysis, and it contains more terrestrial fragments.
(5) The claymineral is composed of montmorillonite-illits and illite-chlorite, and a few of samples contain
a few mixture of montmorillonite and illite, kaolinite is few.All of these shows that the clay mineral developed in
a lacustrain deposition under perch groundwater and quiet water environments.
2.Geochmical marks of elements
(1)There are twenty-eight belonging to sr/ba>1 and seventy two pereent belonging to
Sr/Ba/1.The ratio changes sharp from 0.05 to 16.67 in vertical section .It shows the feature of salty lacustrine
deposite.
(2) Ca, Mg contents in Fengcheng Formation are twice as high as that in Xiazijie Formation and it shows
the feature of medium of saline water.
(3) Al, Fe, Ti, Zr, Mn elements content in Fengcheng Formation is the same as that in the upper and lower formaion. Both the Fengcheng Formation and Xiazijie Formation are terrestrial facies deposit.
(4) The ratio of V / Ni in Fengcheng Formation is 0.7 to 3.8, the average is 2. The ratio of V / Ni in Xiazijie Formation and Wuerhe Formation is 0.3 to 3.6, the average is 1.4. So all of them may be terrestrial facies deposit.
(5) Coefficient of carbonate and aluminium as well as alkaline-eanhmetal of Fengcheng Formation is similar as Xiazijie and Wuerhe Formation. All of them are terrestrial facies deposit.
(6) The analysis of a group Q= 1, Q = 2, Ca, Mg, K, V,Ni, Sr, Ba elements shows the Fengcheng Formation, Xiazijie and Wuerhe Formation are terrestrial deposit.
Sum up above, Fengcheng Formation is the terrestrial deposit of saline lake which had fresh water turning into saline water late.
出处
《沉积学报》
CAS
CSCD
北大核心
1989年第1期61-70,共10页
Acta Sedimentologica Sinica
