西藏羌塘盆地依仓玛地区中上侏罗统碳酸盐岩特征及其环境意义

Characteristics of Mid-Upper Jurassic carbonate rocks in the Yichangma area, Qiangtang Basin, Tibet: Implications for the sedimentary environment

在野外详细测量剖面基础上,对碳酸盐岩宏观特征、矿物和碎屑组分、结构、碳氧稳定同位素、生物古生态等特征进行系统研究。研究显示碳酸盐岩主要为泥晶灰岩、颗粒泥晶灰岩和泥晶颗粒灰岩等岩类,δ13C和δ18O值呈现低→高→低→高→低(雀莫错组→布曲组→夏里组→索瓦组→雪山组)的规律性变化。雀莫错组和雪山组以河控三角洲相沉积为主,布曲组为碳酸盐缓坡相沉积为主,夏里组主要为潮坪-三角洲相沉积,索瓦组主要为潮坪-泻湖相沉积,中晚侏罗世羌塘盆地古水深在下降的总趋势中呈现浅→深→浅→深→浅的升降旋回,盆地沉积中心由东向西迁移,区域构造演化和全球海平面变化共同控制了沉积面貌。

The macroscopic characteristics, mineral and clastic compositions, textures, carbon and oxygen stable isotopes and paleontological and paleoecological characteristics of Mid-Upper Jurassic carbonates in the Qiangtang basin, northern Tibet, have been studied systematically based on detailed field section surveys. Study shows that the carbonate rocks mainly include micrite, grainstone and packstone. The δ^13C and δ^18O values show two cyclic variations from low→high→low→high→low from the Quemo Co Formation→the Buqu Formation→Xiali Formation→Suowa Formation→Xueshan Formation. The Quemo Co and Xueshan formations are dominated by fluvial-dominated deltaic deposits, the Buqu Formation by carbonate ramp deposits, the Xiali Formation by tidal flat-deltaic deposits and the Suowa Formation by tidal flat-lagoonal deposits. The water table in the Mid-Late Jurassic Qiangtang basin showed the rising and falling cycles from shallow→deep→shallow→deep→shallow in the general trend of water table lowering. Meanwhile, the depocenter of the basin migrated from east to west and the Jurassic sedimentary environment of the Qiangtang basin is controlled by the combined regional tectonic evolution and global sea level change.