西准噶尔阿舍勒阔尔勒斯地区石炭系—下二叠统沉积环境变迁及物源

Changes in sedimentary environments and provenances of the Carboniferous-Lower Permian strata in Ashelekuoerlesi area,West Junggar

在西准噶尔阿舍勒阔尔勒斯地区,下石炭统姜巴斯套组与下伏黑山头组和上覆下二叠统哈尔加乌组之间均为不整合接触,而在黑山头组顶部、姜巴斯套组底部和哈尔加乌组顶部的砂岩样品中,最年轻碎屑锆石组给出的年龄分别为328 Ma(早石炭世谢尔普霍夫期)、318 Ma(晚石炭世巴什基尔期)和297 Ma(早二叠世阿瑟尔期)。显然,姜巴斯套组的时代不是早石炭世,建议将其归为上石炭统莫老坝组。黑山头组顶部为含海相碎屑岩;莫老坝组只保留了下部退积型充填序列,缺失上部进积型充填序列,是准噶尔残余洋盆于晚石炭世消失并发生构造抬升和剥蚀所致;哈尔加乌组为典型的陆相沉积。石炭系—二叠系碎屑岩均为近源沉积的产物,各组中最年轻的锆石来自同时代的火山岩。

In the Ashelekuoerlesi area,West Junggar,the Lower Carboniferous Jiangbasitao Formation unconformably overlies the Heishantou Formation and underlies the Lower Permian Haerjiawu Formation.The youngest detrital zircon clusters from three sandstone samples yielded U-Pb ages of 328 Ma(Serpukhovian Stage)for the top of the Heishantou Formation,318 Ma(Bashkirian stage)for the bottom of the Jiangbasitao Formation and 297 Ma(Asselian stage)for the bottom of the Haerjiawu Formation,respectively.Therefore,the Jiangbasitao Formation is Late Carboniferous in age,rather than Early Carboniferous,and is equivalent to the Upper Carboniferous Molaoba Formation in the West Junggar area.The Heishantou Formation is a set of fossil-bearing marine deposits.The Molaoba Formation is a retrograding filling sequence from fan delta facies to shallow marine facies,but there is no preservation of the progressive filling sequence above,which may have resulted from the denudation after the tectonic uplift of the Junggar residual ocean basin in the Late Carboniferous.The Haerjiawu Formation is continental alluvial fan facies.The provenances of the Carboniferous and Lower Permian strata were confined to a neighboring area,and the youngest detrital zircons were derived from the contemporaneous volcanic rocks.