塔里木盆地沙雅隆起北部震旦纪地层特征与锆石U-Pb年龄约束

SINIAN STRATIGRAPHY AND ZIRCON U-Pb AGES FROM THE SHAYA UPLIFT OF THE TARIM BASIN,NW CHINA

综合钻井岩芯、岩石薄片、测井、地震资料和野外露头资料,对塔里木盆地沙雅隆起北部的震旦纪地层进行划分对比和时代研究。该区震旦系分别以角度不整合位于变质岩基底之上、寒武系玉尔吐斯组泥岩或中生代地层之下,由下部的陆相碎屑岩和上部的台地相碳酸盐岩组成,厚度约在220~260m。其中碳酸盐岩厚度约在200m左右,自上而下分为藻云岩段、泥质云岩段、白云岩和灰岩夹白云岩段4个岩性段,相当于塔里木盆地西北缘的奇格布拉克组;震旦系下部的碎屑岩厚度20m左右,以褐色泥岩为主,相当于塔里木盆西北缘的苏盖特布拉克组。利用锆石测年对震旦系底部碎屑岩及其下伏变质岩时代进行限定,其基底年龄不早于776 Ma,相当于青白口系阿克苏群。研究区震旦系与塔里木盆地西北缘露头地层的对比表明,在震旦系苏盖特布拉克组沉积期,沙雅隆起北部可能处于隆起区,具有较长时间的沉积间断,至奇格布拉克组沉积期整个塔北才开始沉降并重新接受海相沉积。

Sinian strata in the northern Tarim Basin are described on the basis of drill cores,thin section observations,well logs,and seismic data.Stratigraphic division and correlation of Sinian strata in the Tarim Basin are proposed based on zircon U-Pb ages.The results show that Sinian strata in the northern Shaya uplift and in the Aksu region of northwestern margin of the Tarim Basin can be correlated.The Sinian System unconformably overlie metamorphic rocks of the Aksu Group of the Qingbaikouan System,and underlie Cambrian or Mesozoic strata in the northern Shaya uplift.Sinian strata in the Shaya uplift consist of a set of shallow marine clastic rocks and carbonate rocks,and their thickness is between 220 mand 260 m.The carbonates are about 200 mthick and can be divided into four lithologic units including,from the top to the bottom,an algal dolostone unit,an argillaceous dolostone unit,a dolostone unit,and an interbedded dolostone and limestone unit.These four carbonate units are equivalent to the Sinian Qigebulake Formation in the Aksu area of northwestern Tarim basin.The clastic rocks are about 20 mthick and are composed of brown mudstone and thin-bedded sandstone.They can be correlated with the Sinian Sugetebulake Formation in the Aksu area in northwestern Tarim basin.The age of the clastic rocks and underlying metamorphic basement is constrained by zircon U-Pb dates.The minimum age of the metamorphic rock is 776 Ma,indicating that the clastic sedimentary rocks are no earlier than 776 Ma.The metamorphic rocks are equivalent to the Qingbaikouan Aksu Group in northwestern Tarim basin.The differences in stratigraphic thickness between the northern Shaya uplift and Aksu area indicate that the Shaya region was located in an uplift zone,where marine deposition started in the late Sinian Period.