Abstract: The sedimentary history of Wuerxun Depression includes a few stages corresponding with structural evolution.The result of sequence stratigraphy research shows that the Cretaceous strata in this area involve two first-order sequences,five second-order sequences and twelve sequences.These sequences take on many obvious surface characteristics and abundant sedimentary systems.The sedimentary history includes two major growth cycles.The first cycle started from T₄,and the second cycle is a non-integrated cycle started from T₀₄.The general tectonic framework controls the form of the depression and the distribution of the depositional systems in the accommodation,which is the fundamental reservoir formation condition.Furthermore,the strata and the depositional systems are the essential physical reservoir formation condition.The major potential hydrocarbon resources are the dark mudstones of the condensed sections in sequence 4 and sequence 5 of second-order sequence Ⅱ and Ⅲ.The favorable reservoirs are mainly involved with lowstand fan,lowstand wedge,highstand delta front,highstand fan delta front and the turbidity fan in these two second-order sequences.

Key words: Wuerxun Depression, sequence stratigraphy, depositional evolution, sequence model, reservoir condition

摘要： 乌尔逊凹陷沉积过程与构造演化对应,具有阶段性。层序地层学分析结果表明,凹陷南部白垩系发育2个一级层序(TSq1和TSq2)、5个二级层序(Ⅰ—Ⅴ)和12个三级层序(Sq1—Sq12)。层序界面特征明显,层序内部沉积体系类型丰富。凹陷沉积演化经历了2个旋回,分别从T₄时期和T₀₄时期开始,其中后者为不完整旋回。总的构造格局决定了凹陷形态与沉积物在可容纳空间内的分布,这是油气成藏的先决条件;地层充填沉积,沉积体系叠置匹配,为成藏提供了必要的物质条件。二级层序Ⅱ和Ⅲ中各层序的密集段是烃源岩的主要分布区,尤以其中的Sq4和Sq5的暗色泥岩为最佳;这2个二级层序内的低位扇、低位楔,高位三角洲前缘、扇三角洲前缘沉积以及湖底浊积扇体系是形成油气藏的有利部位。

关键词: 乌尔逊凹陷, 层序地层, 沉积演化, 层序模式, 成藏条件