云南早震旦世早期的地层划分与沉积环境分析

云南牛头山地区的陆良组、牛头山组属下震旦统,沉积相类型为浅海—海岸相,而澄江等地的澄江组为河流相,两者为同时异相产物。滇中地区从西北向东南,早震旦世早期沉积相展布由古陆剥蚀区—河流相—海岸相—浅海相—半深海相,呈不对称的箕状断陷盆地。

STRATIGRAPHIC DIVISION AND SEDIMENTARY ENVIRONMENTAL ANALYSIS OF THE EARLY STAGE OF EARLY SINIAN PERIOD IN YUNNAN

The sedimentary facies of the silicilith and fine clastic rocks under Nantuo Group of SinianSystem in Niutoushan region, middle Yunnan is studied and thought to be shallow marine-littoral faciesof early stage of early Sinian. The division is reasonable which is proved by the characteristics of sedi-mentary facies distribution. Chengjiang Group developed in Chengjiang region is composed of purple massive conglomelates.Coarse lithoclast arenites and siltstones and mudstones as well. The maturity of texture and composi-tions of sandstones are low. The bedding. types are various. Such as parallel bedding, cross bedding. platecross bedding, etc.. Sand body is of upper-plane and bottom-concave lenticular in shape. The sequenceis coarsing-up. The dip of cross bedding is in the same direction. Grain size analysis also proves the flu-vial deposit. Luliang Group and Niutoushan Group in Niutoushan and Luliang regions are composed of green-grey. green-white quartzose sandstones, glauconite quartzose sandstones and silicalites and rare mud-stones. The texture and compositional maturities of sandstones are high. The sedimentary structurescaused by waves are rich. The dip of cross bedding is in bidirection. Grain size analysis shows shoaldeposit. Glauconlte is up to 15%. The age is 6.92 hundred million years mesured by rubidium-stron-tium method. It obviously belongs to early Sinian period. Based on the plane distribution of sedimentary facies, they are in the proper order fluvial (includ-ing Chengjiang region), littoral (including Luliang region), shelf, continental slope and trough-basinfrom northwest to southeast. All the characteristics of sedimetary build, volanic activity, tectonics and sedimentary facies dis-tribution show that it was intracontinental rift in middle Yunnan and passive continental margin insoutheast Yunnan in early Sinian.