新疆库车坳陷晚白垩世沉积的地球化学特征及意义

库车坳陷广泛发育的晚白垩世巴什基奇克组是新疆塔里木盆地北部地区克拉苏大型气田的主要储层,其沉积环境一直存在争议。本文依据塔里木盆地北部地区库车坳陷巴什基奇克组地球化学资料,对塔北地区晚白垩世时期发育海侵沉积进行了分析。结合野外露头剖面和钻井剖面巴什基奇克组上段新发现的大量海相钙质超微化石和沉积相特点,认为塔北地区晚白垩世时期曾发生明显的海侵作用,海水分布范围向东可达库车河地区,但沉积环境比较闭塞,古盐度指数反映水介质为咸水,古气候以干旱高温为特点。这一研究为塔西南地区和塔北地区晚白垩世地层对比奠定了基础,对本区的油气勘探和远景分析具有重要意义。

Geochemical Characteristics and Significance of Late Cretaceous Deposits in the Kuqa Depression, Xinjiang

The Bashijiqik Formation developed in Kuqa depression is the main reservoir of the large-size Kelasu gas field in northern Tarim basin of Xinjiang. Nevertheless, its sedimentary environment is a problem of long controversy. Based on geochemical data of the Bashijiqik Formation in Kuqa depression, the authors analyzed the Late Cretaceous transgressive sediments in this depression. Combined with lots of marine calcareous nannofossils in the upper member of the Bashijiqik Formation recently discovered in the outcrop and drillhole sections and the features of sedimentary facies, it is held that the transgression must have happened in Late Cretaceous in northern Tarim basin, and that the sea water was widely distributed over the Kuqa River area. The sedimentary environment, however, was relatively closed. The paleosalinity indices indicate that the medium was salt water, and the paleoclimate was dry and of high temperature. This research has laid a foundation for the correlation of Cretaceous strata between southwestern and northern Tarim basin and hence is of great significance in the oil-gas exploration and perspective analysis.