济阳坳陷东营三角洲前缘斜坡重力流成因砂体特征及形成条件

运用最新的深水重力流理论开展系统研究,细分大型三角洲前缘斜坡重力流成因砂体类型,并建立各类型砂体的判识标准,探讨砂体展布的控制因素。研究表明:大型三角洲前缘斜坡发育一系列重力流成因砂体,砂体并非由单一流体形成,包含了塑性体、砂质碎屑流及浊流等多种流体的有序转化和多个岩相组合;根据纵向上序列组合的差异,可把重力流砂体类型划分为滑动成因砂体、滑塌成因砂体、碎屑流成因砂体和浊流;利用岩心沉积构造特征、粒度特征、测井相和地震相等多角度对比可识别砂体类型;三角洲前缘斜坡重力流成因砂体的形成与展布受控于古物源、古沉积坡角、同沉积断层和沉积基准面旋回变化等因素,其中充足的物源是重力流砂体发育的物质基础、适宜的古坡角是重力流砂体有序展布的必要条件、同沉积断层下降盘是砂体发育的有利区,而基准面旋回变化决定了重力流砂体的纵向分布样式。

Characteristics and formation condition of gravity flow developing in low-lying slope zone of Dongying delta in Jiyang Depression

The latest deep-water gravity current theory was used to subdivide the type of the gravity flow developed in the low-lying slope zone of large delta, and the discerning standards were established; and then the controlling factors of the distribution were discussed. The results show that a series of gravity flows can be developed in the low-lying slope zone of the large delta. The sand body formation however is not determined by one certain flow state, but always by several flow states including plastomer, debris flow and turbidite. They transform in order and have different lithofacies associations. According to the different longitudinal sequential patterns, the gravity flow could be divided into four types, which include the slide sand, the slump sand, the debris flow sand and turbidite. By comparative analysis of sedimentary structure characters, grain size characters, logging face and seismic face, the sand type could be identified. The controlling factors of the formation and distribution of gravity flow which developed in the low-lying slope zone of large delta include ancient material source, ancient sedimentary slope angle, contemporaneous fault and depositional base-level cycle. Ample material source is the material base for the development of gravity flow, and different types of sands could transform in order when the slope has suitable sedimentary angle. The decreasing plate of codeposition fault is the favorable development area, and the depositional base-level cycle controls the longitudinal distribution of the gravity flow sands.