| 阜平群条带状铁建造中硅质鲕粒特征及其成因 |
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| CHARACTERISTICS AND ORIGIN OF SILICEOUS OOUTHS IN THE BANDED IRON FORMATION OF THE FUPING GROUP |
| Siliceous ooliths occur sporadically in the banded iron formation of the Nanying Formation of the Fuping Group of Archaean, accounting for 3-5%. They are composed primarily of cryptocrystalline siliceous matters with SiO2 content up to 60-70% and FeO and SOz as of secondary importance. Most of them occur in fan and ear forms or as irregular fragments and only a few of them show spherical and ellipsoidal forms. The ooliths are often included in quartz, cummingtonite, magnetite and other minerals or preserved in the interstitials between minerals. They generally ranges form 100 to 300 μm and sometimes form 20 to 30 μm in diameter. Concentric laminations are fairly developed and the lamination of an individual oolith is generally divided into 5-10 layers. The color of each lamina always changes from a light to dark shade outward, ie., from grey and yellow to brown yellow or brown black. As the color becomes darker, the SiO2 content decreases gradually form 60% to 52% while the FeO content increases form 6% to 19%. The highest SO2 content in the dark lamination zone is from 8% to 11%.The dark brown or brown black lamination zone is characterized by cross extinction.Based upon the investigation of forms and structures of the siliceous oo-liths, it is suggested that the specimens of the presert study area were formed in the tide zone of a shallow-sea turbulent environment. The ooliths are similar in character to those of the Bahamian type found in the Bahama Islands and are also comparable to those of the Proterozoic Gunflint Iron Formation of Canada. A further study on forms, structures, composition, distribution and origin of ooliths of the Precambrian Iron Formation will have a great signfiicance for clarifying the original environment of the Precambrian Iron Formation and the law of its distribution and for studying the character of Precambrian hydrosphere and atmorsphere, biotic origin and other matters. |
| WU Jia-shan,DI Yuan-sheng,JIN Long-guo.1987.CHARACTERISTICS AND ORIGIN OF SILICEOUS OOUTHS IN THE BANDED IRON FORMATION OF THE FUPING GROUP[J].Acta Geoscientica Sinica,9(2):179-188. |
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