摘要：

陕北地区上三叠统延长组是以河流－湖泊沉积体系为主的陆源碎屑岩系。依据野外剖面和井下资料，本文对陕北地区上三叠统延长组进行了层序地层划分，共划分出了四个三级层序，其中一个属于湖相层序，另外三个为冲积层序。每个层序包括三个体系域，它们分别是低位体系域、水进体系域和高位体系域，每个体系域由不同的相组合构成，呈现不同的堆砌样式。湖相层序和冲积层序的层序界面和层序内部单元的构成特征均不相同。由于河流冲刷在陆相地层中普遍发育，以冲刷面为层序界面时要综合考虑多种因素进行综合判断，如砂体厚度的展布和相的构成等，而且纵向的比较也很重要，纵向的相变是划分陆相层序的一个重要标志。最大洪泛面和水进面在冲积地层中较难确定，往往以一套地层的出现为标志，而不是某个单层为代表。在陕北地区延长组陆相层序地层中，控制层序形成的主要因素是构造运动和气候变化。陕北地区陆相层序对盆地含油气性的控制主要表现在三个方面：1、层序控制了生储盖的组合；2、层序控制着储层的展布；3、层序影响着储层的储集性能。

Abstract:

Based on the research of outcrop and underground data, four 3-order sequences are recognized in the Yanchang Group of Upper Triassic in Shaanxi that is continental clastic sediment composed of fluvial and lacustrine system. The first one is lacustrine sequence while others are fluvial ones. According to the surfaces and genetic units of sequence, stratigraphic sequence can be divided into three part: Low Stand System, Transgressive System and High Stand System. The fluvial sequence develops overflow and marshy sediments during maximum flooding period while the lacustrine sequence develops dark shale. Sequence boundary is the key to recognize sequence on which develops thick multi-storey sandstone. To determine the sequence boundary is challenge because the fluvial surface is so normal in continental sediments and using comprehensive ways is necessary. The main controls of sequence formation is tectonics and climate change in continental sequences. Sequence controls development of petroleum accumulation. This is clear in three aspects: the control for the assemblage of source, reservoirs and caps, the control for distribution of reservoirs and the control for performance of reservoirs.