重力流沉积岩相划分及其发育规律

Lithofacies classification and development rule of gravity flows deposits

在Tailling等分类的基础上建立基于沉积过程中的流变学特征和沉积物支撑机制的滑塌流-浊流-碎屑流三分(滑塌岩相、碎屑流岩相和浊积岩相)14个序列的重力流岩相划分体系;结合鄂尔多斯盆地合水地区长7段大量的岩心资料,并借助于测井曲线和录井数据,对合水地区长7段重力流沉积的岩相及岩相组合进行识别。结果表明:合水地区主要发育5类重力流沉积岩相组合类型,即低密度浊流组合、高密度浊流组合、黏滞性碎屑流组合、弱黏滞性碎屑流组合以及滑塌岩组合;对比合水地区重力流沉积空间发现,滑塌岩相发育范围相对局限,主要发育于三角洲前缘失稳区,碎屑流沉积主要发育于斜坡带-坡折带处,浊流沉积的分布范围最广;'浅水凸形'坡折带位于三角洲前缘或三角洲平原附近,是重力流重要的触发区,主要控制正常牵引流三角洲前缘中松散的水下分流河道砂体沉积;'深水凹形'坡折带位于前三角洲深水区,是深水重力流砂体主要的卸载沉积区。

Building upon prior investigations of Talling and others,a three-fold classification of gravity flow lithofacies was established based primarily on fluid rheological characteristics and sediment-support mechanisms of depositional processes. The new classification mainly contains slumps lithofacies,debris flow lithofacies and turbidite lithofacies,corresponding to the deposits of slump,debris flow and turbidity current respectively,and can be further subdivided into 14 lithofacies. Using the abundant core data and logging data,lithofacies and lithofacies associations of gravity flows deposits were identified in Chang 7Member of Heshui region,Ordos Basin. The results show that there are five types of lithofacies associations developed in Heshui region,including the low density turbidite association,the high density turbidite association,the viscous debris flow association,the weakly viscous debris flow association and the slumps association. The slumps lithofacies are located restrictively in the instable area of delta-front,the debris flow deposits are mainly developed in the slope to slope break zone,and the turbidites are on the other hand most widely distributed. The shallow water and convex slope break is located in the delta-front or the delta-plain,which is the initiating area of the gravity flow and mainly controls the distribution of loose sandy depositions of subsea distributary channels in delta-front caused by normal traction currents. The deep water and concave slope break is located in the deep water area of prodelta,which is the major unloading and deposition area of the gravity flows sand.