乌尔逊凹陷北部下白垩统层序地层发育特征

Sequence Stratigraphy of Lower Cretaceous in the Northern Wuerxun Sag

陆相断陷盆地层序的形成和发育主要受控于幕式构造活动，边界断裂的活动强度和基底的沉降速度是形成不同类型层序的主要原因。通过层序地层学分析，乌尔逊凹陷北部下白垩统地层可划分出４ 个三级层序。这些层序由于形成时所经历的构造背景不同，因此形成的层序特征也不同，层序内部体系域的构成和规模也不同。在充分利用钻井、测井、地震资料的基础上建立了乌北地区层序地层充填模式。并指出油气在这些层序和体系域类型中的赋集规律，认为快速断坳层序和同生断坳层序能形成最有利的生储盖组合。

The formation and evolution of the sequences in continental down faulted basin are mainly controlled by eposodic tectonism.The strength of boundary fault activity and the velocity of basement depression are the main reason that lead to the formation of different sequences.Principal marks to identify sequence types are the sequence boundary characters.The mechanisms of formation of sequence boundary and sequence surface are the uplift of whole lacustrine basin,the cease of the movement of boundary fault and the depression of basement.Based on these studies,four types of sequences have been identified from the lower Cretaceous strata in the northern Wuerxun sag,i.e.,simply faulted sequence,quickly faulting depressed sequence,syngenetic faulting depressed sequence and simply depressed sequence.The development of simply faulted sequence and simply depressed sequence are mainly controlled by sag boundary fault and basement depression respectively,whereas the formation of quickly faulting depressed sequence and syngenetic faulting depressed sequence are dependent on both boundary fault and basement depression.Due to different tectonic background,these sequences are different in scale and composition. Different kinds of sequences have different system tracts and petroleum potential,and the most favorable sequence types are the quickly faulting depressed sequence and syngenetic faulting depressed sequence,for they both contain best source,reservoir and seal rocks.