鄂尔多斯盆地延长期沉积中心迁移及其动力学背景

延长期（T₃y）是鄂尔多斯盆地中生界优质烃源岩的主要发育时段。本文在大量钻井和测井等资料研究的基础上，结合露头剖面与岩心观察，建立了盆地延长组地层对比格架，综合最新沉积相研究成果，进一步发现在中-晚三叠世延长期盆地主体发生了两次明显的沉积中心迁移，形成了3个沉积中心。其中以长9期为代表的早期（长10—长8期）沉积中心位于吴起—志丹—富县—洛川一带，以长7期为代表的盆地发育鼎盛时期（长7—长2期）沉积中心位于姬塬—华池—宜君一带，以长1期为代表的湖盆萎缩期的沉积中心位于横山—子长之间。前两期沉积中心明显控制着盆地优质烃源岩的形成和分布，进而控制着盆地中生界常规和非常规油气资源的总体分布。结合周邻山系演化历史分析认为，晚三叠世初长9—长7期沉积中心向西南（向山）迁移，与扬子板块向华北板块俯冲汇聚、在秦岭造山带后陆（即华北仰冲板块南部）因汇聚的巨量物质部分上拱和能量释放而导致的沉降有关；至晚三叠世末长1期沉积中心转向北东（离山向陆）迁移，为华北与扬子板块间的有限洋消失及之后持续汇聚的结果，秦岭造山带挤压隆升增强引起北邻鄂尔多斯盆地南部抬升，致使盆地消亡，沉积中心相应向北东迁移。两次沉积中心迁移的动力学环境，主要受鄂尔多斯盆地南侧秦岭造山带形成演化的控制，沉积中心迁移是盆山耦合演化彼此响应的结果和记录。

Depocenter migration of the Ordos Basin during the Yanchang period and the geodynamic settings

The Yanchang period（T₃y）is the main development period of the high-quality oil source rocks in the Ordos Basin. With abundant data of drills, logs, outcrops, cores and so on, the present study established the stratigraphic correlation framework of the Yanchang Formation in the Ordos Basin. Three different depocenters were found to have formed during the Middle-Late Triassic Yanchang period in the basin, with two significant depocenter migration events. The early depocenter represented by the deposition of the Chang9 unit（from the Chang10 to Chang8 units）was located in the area of Wuqi-Zhidan-Fuxian- Luochuan. The heyday depocenter represented by the deposition of the Chang7 unit（from the Chang7 to Chang2 units）was located in the area of Jiyuan-Huachi-Zhengning-Yijun. And the shrinking depocenter represented by the deposition of the Chang1 unit and was formed in the Hengshan-Zichang area. The former two depocenters（the early and the heyday ones）have affected the formation and distribution of the high-quality source rocks as well as the distribution of the conventional and unconventional oil-gas resources in the Ordos Basin. According to the tectonic analyses of the basin and its periphery mountains, these depocenter formation and migration events in the Late Triassic in the Ordos Basin mainly resulted from the southward movement of the Qinling orogenic belt. The first depocenter migration event（from the early to the heyday depocenter）is interpreted as a response to the northward subduction and convergence of the South China block to the North China block. Because of the convergence, large amount of materials and energy gathered around the south part of the North China block. Its shallow lithosphere arched, fractured and then extended laterally, resulting in local subsidence and formation of a backland basin. The other depocenter migration event（from the heyday to the shrinking depocenter）occurred in the period of the Chang1 unit, which is also believed to relate to the continuous convergence of the South China block and North China block, but with a different mechanism. As the compression of the Qinling orogenic belt strengthened, the south part of the Ordos Basin uplifted. The ever-large Ordos paleolake shrank and the sedimentation migrated northeastward. Overall, the evolution of the Qinling orogenic belt caused the depocenter formation and migration of the Ordos Basin. The Ordos Basin and the Qinling orogenic belt can be seen as a good example of the basin-range coupling.