西藏羌塘盆地半岛湖地区索瓦组锶同位素组成与演化

Strontium Isotope Composition and Evolution in the Suowa Formation,Bandaohu Area,Qiangtang Depression,Tibet

西藏羌塘盆地中生代发育广泛的海相碳酸盐地层,前人对该区地层的对比研究多局限于古生物地层学,本文尝试通过锶同位素地层学方法对上侏罗—下白垩统索瓦组地层进行全球对比。根据锶同位素地层学的基本原理,本文在对样品进行显微组构分析、阴极发光分析、Ca、Si、Sr和Mn等元素含量分析及评估其对同期海水代表性和样品溶解过程合理性的基础上,测试了羌塘盆地半岛湖地区上侏罗—下白垩统锶同位素组成,并建立了相应的演化曲线,进行了全球对比研究。结果表明,样品的锶同位素组成与前人已公布的同期海水锶同位素组成数据较为接近,其演化曲线与国际上已公布的锶同位素演化曲线有着较好的可对比性,晚侏罗—早白垩世时期全球海平面的变化和侵蚀作用的强弱是控制锶同位素演化曲线的主要因素。此外,通过对索瓦组海相碳酸盐锶同位素的研究,我们认为索瓦组的顶部可能延伸到早白垩世欧特里夫期,近而说明了羌塘盆地在早白垩世欧特里夫期还存在大规模的海相地层。

The comparative study of the Mesozoic marine carbonate stratum has limited to paleostratigraphy in the Qiangtang depression of Tibet.Based on the strontium isotope stratigraphy,this paper was made correlation to the globe of the upper Jurassic-lower Cretaceous in Suowa Formation.On the basis of the analyzed the rock fabric,cathodeluminescence,chemical composition and preservative evaluation for coeval seawater information,this paper measured strontium isotopic composition of the samples and constructed the evolution curve.Results show that,these data of the samples are generally coincident with87 Sr /86 Sr ratios of coeval seawater from previous papers,and the curve is also similar to other previous curves,this indicates that the global sea level change and erosion intensity are the most important controlling factors to the strontium isotope evolution in the upper Jurassic-lower Cretaceous.In addition,we consider that the upper of Suowa Formation maybe extend to Hauterivian in the early Cretaceous through the study of strontium isotope,this suggests that there exist large-scale marine stratigraphy at the same of Hauterivian in the early Cretaceous,Qiangtang Depression.