鄂尔多斯盆地西南缘中奥陶统重力流与等深流交互作用沉积研究

Interaction between gravity flow and contour current deposits is an important part of the deep-sea deposits which carries significant information to analyze the paleoceanography, paleclimate and paletectonics. At present, the stratigraphic records of interaction between gravity flow and contour current deposits are much less focused on than that of modern. Furthermore, the identification marks are imperfect, mechanism and mainly controlling factors are still little clear. The modern sedimentological theory and the theory of oceanography, sequence stratigraphy are used as guidance, and by combining field geology with laboratory integrated study, macroscopic study with microscopic study, modern sedimentary study with ancient sedimentary study, the case study of interaction between gravity flow and contour current deposits of the Middle Ordovician in the southwest margin of the Ordos Basin is analyzed. And rock types and characteristics are mainly investigated. The relationship between the deposit and relatively sea level, tectonic activity and climate, forming mechanism, mainly controlling factors, sedimentary model and sandbody distribution are obverted, which aim to promoting development of research on the interaction between gravity flow and contour current deposits in the stratigraphic record and providing basis for deep-water oil and gas exploration.

重力流与等深流交互作用沉积是深海沉积的重要组成部分，其承载了古海洋、古气候及古构造等重要信息。目前地层记录中的重力流与等深流交互作用沉积研究远逊于现代沉积。在研究内容上还存在鉴别标志不完善、形成机理不清楚及主控因素不明确等问题。本项目以沉积学、海洋学及层序地层学理论为指导，采用野外地质工作与室内综合研究相结合、宏观与微观研究相结合、现代沉积与古代沉积研究相结合的方法，对鄂尔多斯盆地西南缘中奥陶统重力流与等深流交互作用沉积进行解剖，重点研究其沉积类型及特征，探讨其与相对海平面升降、构造运动强弱及气候变化等的联系，揭示其形成机理，分析其主控因素，建立其沉积模式，研究其砂体展布规律，促进地层记录中重力流与等深流交互作用沉积研究的发展，并为油气勘探提供理论依据。

重力流与等深流交互作用沉积是深水沉积研究的热点和难点，目前研究的主要为现代沉积，古代地层记录中的交互作用研究极为薄弱。本项目基于丰富的露头资料，采取野外和室内、宏观和微观、现代与古代研究相结合，对鄂尔多斯盆地西南缘奥陶系平凉组等深流与重力流交互作用沉积特征、类型、过程、机理及主控因素进行了研究，进而探讨了其有利储层分布规律。研究认为等深流、重力流、等深流与重力流交互作用及深水原地沉积在岩性、沉积构造、古生物、古流向及地化特征等方面具有明显不同。研究区等深流从东向西大致平行斜坡运动，东部由于富平裂堑，能量较低，以细粒泥晶等深流沉积为主；中部地形开阔，能量较弱，等深流沉积不发育；西部由于限制性环境，等深流能量较高，发育砂屑等深流沉积。而碎屑流沉积在研究区东部较为发育，中部发育碎屑流及浊流沉积，西部以浊流沉积为主。等深流与重力流运动方向大致垂直。等深流与重力流交互作用直接影响因素为两个相对能量的大小。研究区东部等深流与重力流能量较弱，发育泥晶等深流沉积及碎屑流沉积互层；中部重力流规模大，能量高，破坏作用强，导致重力流沉积发育，等深流沉积少见。西部由于等深流能量增加，发育砂屑等深流及浊流沉积，少量碎屑流沉积互层。在陇县地区发现等深流改造浊流沉积，即改造砂。改造砂、浊流沉积及粗粒等深流沉积具有较好的储集性能，是潜在的油气储层。