鄂尔多斯盆地西南缘中奥陶统等深流沉积及其主控因素研究

Contourite is an important part of the deep-sea deposits and the best carrier of information to analyze the paleoceanography, paleoclimate and paleotectonics. At present, the major problem focuses on far less study on the breadth and depth of contourites in stratigraphic records than that of modern contour current deposits, in which examples are less found out in the stratigraphic records and identification marks are imperfect, especially little study of the forming mechanism of contourite drifts. In allusion to situation stated above, in this project, the modern sedimentological theory and the theory of contour current deposit of oceanography is used as a guidance, and by combining field geology with laboratory integrated study, macroscopic study with microscopic study, modern sedimentary study with ancient sedimentary study and conventional analysis with advanced test, the case study of contourites of the Middle Ordovician in the Southwest margin of the Ordos Basin is emphatically analyzed. And rock types, characteristics, its sedimentary sequence and the distribution rules of contourite are deeply studied. The result is contrasted with those of the case study of modern contourite drifts and other ancient contourite drifts found. And the control factors of ancient landform, paleotectonics, ancient circulation and cyclic variations forming contourite drifts, the relations between the control factors and glaciation and interglaciation, and between its special time and space distribution rules and oil and gas are studied, for the purposes of promoting the development of research on contour current deposit in the stratigraphic record and laying a base for finding new areas of oil and gas exploration.

等深流沉积是深海沉积的重要组成部分，是解析古海洋学、古气候和古构造信息的最佳载体。目前对地层记录中等深流沉积的研究广度和深度远逊于对现代等深流沉积的研究，地层记录中发现的实例少，相关的鉴别标志不完善，尤其对等深岩丘的形成机理研究甚少。本项目针对这种现象，以现代沉积学理论和海洋学中关于等深流沉积的理论为指导，采取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、常规分析与先进的分析测试相结合的方法，对鄂尔多斯盆地西南缘中奥陶统等深流沉积进行解剖，重点研究等深流沉积的岩石类型、特征、沉积层序、分布规律，并与现代等深流沉积和其它已发现的古代等深流沉积实例对比分析，研究等深流沉积形成的古地形、古构造、古环流、周期性变化的控制因素以及与冰期、间冰期之间的关系，等深流沉积的时空分布规律及与油气的关系。促进地层记录中等深流沉积研究的发展，同时为寻找新的油气勘探领域奠定基础。

等深流沉积是一种重要的深水沉积类型，自20世纪60年代以来，对现代海洋中的等深流沉积做了大量的研究，取得了不少的研究成果。然而，对地层记录中的等深流沉积的研究却比较少，严重制约了等深流沉积研究的更一步发展。鄂尔多斯盆地西南缘中晚奥陶世等深流沉积较为发育，是研究地层记录中等深流沉积的理想地区。开展此项研究，对于探索中晚奥陶世鄂尔多斯盆地西南缘环流体系、古气候和古大地构造具有重要的意义，将促进地层记录中等深流沉积的研究，还可为深水沉积的油气勘探提供基础地质依据。. 基于丰富的野外露头资料和现代沉积研究成果，对鄂尔多斯盆地西南缘奥陶系平凉组等深流沉积及等深流与重力流交互作用沉积的特征、类型、过程、机理及主控因素进行了研究。研究认为，等深流沉积、重力流沉积、内潮汐沉积、等深流与重力流交互作用沉积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。等深流沉积以细粒沉积为主，包括灰泥等深积岩、粉屑等深积岩、砂屑等深积岩、砾屑等深积岩4种类型，沉积构造及生物扰动发育，多呈细—粗—细沉积序列，可进一步划分出4类等深积岩层序。受米兰科维奇旋回影响，等深流强度呈多周期“弱-强-弱”递变，体现为三个不同尺度的周期性变化，研究区等深流强化周期约为0.1Ma。等深流从东向西大致平行斜坡运动，东部由于富平裂陷，能量较低，以灰 泥等深积岩为主；中部地形开阔，重力流规模大，能量高，等深流能量较弱，导致重力流沉积发育，等深流沉积少见；西部由于限制性环境，等深流能量较高，发育砂屑等深积岩和浊积岩。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等深流与重力流相对能量的大小。改造砂、浊流沉积及粗粒等深流沉积具有较好的储集性能，是潜在的油气勘探领域。