【摘要】 湘西上震旦统层状硅质岩化学成分纯净,硅质矿物平均含量95%以上,且FeO/Fe2O3比值大于1,MnO/TiO2比值为6.1,P2O5含量极低。微量元素Sr/Ba比值小于1,稀土以总量低(5.64～31.54μg/g)和铈亏损为特征。硅质岩的δ30Si值变化在0.0‰～0.7‰之间,硅质岩中有机碳含量较高,介于0.443%～1.993%之间,Pr/Ph比值小于1。硅质岩的上述特点反映其沉积于大陆边缘斜坡半深海至大洋盆地深海环境中。更多还原

【Abstract】 Siliceous rocks are widely distributed intrabasinal rocks, and may occur in all kinds of sedimentary environments. Some significant achievements have already been made by using sedimentary geochemical characteristics of siliceous rocks to analyze the sedimentary environment. The aims of this paper are to discuss the sedimentary environment of the Upper Sinian bedded siliceous rocks inwestern Hunan Province on the basis of previous studies. The ratios of FeO/Fe2O3 and MnO/TiO2 of siliceous rocks ranging from 1.13 to 7.34, 2.4 to 10, averaging 3.92 and 6.1, respectively, very low contents of P2O5 and the development of phosphatic nodule and thin bedded phosphorite interbed indicate that the rocks deposited in the marine environment with a feature of deeper water depth, deficiency of oxygen, low energy and reduction intense reduction. The ratios of Sr/Ba are much less than 1.0, reflecting that the rocks formed between deep sea and detained shallow environment. The Hf/3 Th Ta triangular diagram shows thatthe rocks deposited in the tectonic environment of disintegrated plate margin. The total REE contents and δCe values range from 5.64 μg/g to 31.54 μg/g and 0.4 to 0.85, averaging 15.01 μg/g, and 0.72, respectively, manifesting thatthe rocks mainly formed in ocean basins of a deep sea environment to continental marginal slopes of a bathyal environment. The δ30Si values range from 0.0‰ to 0.7‰, averaging 0.3‰, reflecting that the depositional environment isa transitional zone from the bathyal to the deep sea environment. The organiccarbon contents and ratios of Pr/Ph ranging from 0.443% to 1.993% and 0.198to 0.638, averaging 1.260% and 0.350, respectively, and sapropel type organic matter indicate that the rocks deposited in the intense reduction environmentof deeper water depth. To sum up, analyses of the depositional environment of siliceous rocks in the study area using the sedimentary geochemical characteristics yield the same conclusion that the rocks formed in environments from continental marginal slopes of a bathyal environment to oceanic basins of a deep sea environment.更多还原