中条山地区武系地球化学特征与沉积环境研究

Geochemical Characteristics and Sedimentary Environment of the Cambrian Carbonates in Zhongtiaoshan Area

华北地区沉积岩石特征表明：早寒武世辛集期主要为潮间-潮下带沉积,馒头期海平面相对稳定,毛庄期—张夏期大量的潮下鲕粒滩发育,中寒武世张夏期为寒武纪最大海侵期。随后海平面下降,晚寒武世主要表现潮坪相的白云岩沉积。通过地球化学分析表明：碳酸盐岩δ13 C多数为-1.23～0.34,总体上反映相对水体较浅的环境。早寒武世δ13C为负值,中寒武世逐渐正漂移,晚寒武世又逐渐负偏,表明该地区寒武纪海平面经历了由浅变深再变浅的变化过程,最大海侵面时期为中寒武世张夏期,与岩石特征所反映的结果一致;低负值的δ18 O说明该区域均为较为局限的海域。LREE/HREE值反映了轻稀土富集、重稀土亏损,与碳酸盐岩球粒陨石标准化后的稀土元素配分曲线一致;δEu和δCe异常、La/Yb值显示早寒武世和晚寒武世海平面均发生过几次明显波动,表明寒武纪碳酸盐岩沉积时期,沉积水体经历了几次氧化-还原环境变化。

The characteristics of sedimentary lithology in north China reveals that intertidal-sub- tidal deposition dominated the Xinji period of early Cambrian; while sea level was relatively stable during the Mantou period, large amount of subtidal oolitic shoals began to develop in the Maozhuang-Zhangxia period; in the early-middle Cambrian, Zhangxia period experienced the maximum transgression of this era; then with the fall of sea level, the tidal facies dolostones were deposited during the late Cambrian. To discuss the redox environment of Cambrian deposition in north China, the Cambrian carbonate samples in Zhongtiaoshan mountain area are systematically collected, and geochemically analyzed. The geochemical research indicates that most δ13C isotopeof these carbonates are between --1.23 and 0.34 and reflect the relative shallow sedimentary en- vironment ; the negative δ13C isotope during early Cambrian is changed step by step into a positive value during the middle of Cambrian, and become negative again in the end of the era, which demonstrate that the Cambrian sea level in this area had undergone a transition from shallow to deep, and then from deep to shallow. The maximum transgression took place in the mid-Cambri- an Zhangxia period, which is consistent with the implications from lithological characteristics. The lower negative δ18O value shows that the Zhongtiaosban area used to situate in relatively re- stricted waters. LREE/HREE ratios indicating enrichment of the light REE and deficiency of the heavy REE agrees with the Chondrite-normalized pattern. The δEu, δCe and La/Yb ratios sug- gest that the sea level during early and late Cambrian have both experienced several obvious fluc- tuations, which indicates that the redox environment of the sedimentary water body might occur repeatedly during the Cambrian carbonate deposition.