下寒武统黑色岩系沉积环境与控烃差异--以塔里木盆地西北缘和东北缘为例

The differences of sedimentary environment and hydrocarbon control of Lower Cambrian black rock series:a case study of northwestern and northeastern margin,Tarim Basin

基于对露头剖面的精细观测,文中开展了塔里木盆地西北缘和东北缘下寒武统黑色岩系沉积环境与控烃差异的研究。结果表明:黑色岩系的沉积环境差异整体反映在岩性、沉积相、厚度等方面。西北缘发育潮坪、陆棚等海相烃源岩,岩性以薄层泥页岩和薄层碳酸盐岩互层为主,厚度普遍在15~25 m,经历造陆运动,黑色岩系连片分布;东北缘发育欠补偿盆地烃源岩,岩性以硅质岩和泥岩为主,较西北缘厚,经历强烈的造山运动,黑色岩系不及东北缘发育。沉积环境差异影响了烃源岩的发育模式。热液作用有利于激发海洋底栖藻的大量繁盛,缺氧的水体环境有利于优质烃源岩的形成。上升洋流虽然是形成缺氧环境的重要因素之一,但强烈的岩浆活动破坏了东北缘的有机质保存环境,使西北缘黑色岩系中烃源岩的品质优于东北缘。

On the basis of detailed observation and measurement of outcrop profiles,the paper has studied the differences of sedimentary environment and hydrocarbon control of the Lower Cambrian black rock series in northwestern and northeastern margin,Tarim Basin.The results show that the differences are generally reflected in lithology,sedimentary facies,and thickness.In northwestern margin,the marine hydrocarbon source rocks such as tidal flat and shelf are developed,and thin shale and thin carbonate rocks interbedded are the dominant lithology combination,of which thickness is generally from 15 m to 25 m.The black rock series is distributed in successive patches during the epeirogenic movement.In northeastern margin,the hydrocarbon source rocks are deposited in the starved basin,and the lithology is mainly siliceous rocks and shales,which are thicker than that in northwestern margin.The black rock series is not developed as well as that in the northwestern margin due to the intense orogeny.The differences of sedimentary environment have influenced the modes of the hydrocarbon source rocks.Hydrothermal process is advantageous to stimulate benthic algae flourished of sea and anoxic environment is conducive to the formation of high-quality hydrocarbon source rocks.Although the rising ocean current is one of the most important factors for the formation of anoxic environment,the strong magmatic activity has destroyed the preservation environment of hydrocarbon source rocks in northeastern margin.Therefore,the quality of hydrocarbon source rocks in northwestern margin is better than that in northeastern margin.