柴达木盆地北缘早奥陶世台地-斜坡-盆地相沉积特征及控制因素

Sedimentary characteristics and controlling factors of the Early Ordovician platform-slope-basin in the northern margin of the Qaidam Basin

通过对柴北缘地区的野外地质调查及室内实验分析,根据地质剖面中发育的岩石组合类型、沉积构造等特征,对研究区早奥陶世台地-斜坡-盆地相沉积体系进行了详细研究。认为研究区早古生代持续的海平面上升、柴北缘洋陆俯冲及陆弧碰撞是控制该时期盆山格局及沉积充填演化的重要因素。柴北缘早奥陶世台地边缘颗粒滩相发育在多泉山组中下部,岩性以生物碎屑灰岩、鲕粒灰岩以及泥晶灰岩为特征。而研究区斜坡相深水物质主要是由重力流搬运的碳酸盐岩再沉积物组成,共识别出包括细粒沉降微晶泥、滑塌角砾岩、颗粒流、瘤状灰岩、碎屑流以及浊积岩等不同类型的斜坡异地沉积物。研究区盆地相处于碳酸盐岩沉积体系-岛弧碎屑岩沉积体系两大沉积体系的转换位置。受到柴北缘洋陆俯冲及陆弧碰撞等影响,隆升的陆壳基底及大陆岛弧物质向盆地提供大量碎屑物质,因此在靠近岛弧边缘地区发育了砂质碎屑流、浊流等重力流沉积体系下的弧后盆地沉积产物。

Through geological field investigation and indoor experiments in the northern Qaidam Basin,the Early Ordovician platform-slope-basin facies sedimentary system was studied in detail,according to geological profiles of rock combination types and characteristics of sedimentary structures of the study area.The results show that the continuing sea level rise in the study area,subduction of the northern margin of the Qaidam Basin,and continental arc collision,were the important controlling factors for the basin mountain pattern development and sedimentary filling evolution during this period.In the northern margin of the Qaidam Basin,the Early Ordovician platform margin particle shoal facies developed in the lower part of the Duoquanshan Formation,and lithology included bioclastic,oolitic and micrite limestones.The carbonate rock materials on the deep water slope are mainly different slope sediments,including fine microcrystalline mud,slumps breccia,grain flow,nodular limestone,debris flow and turbidite,brought by gravity flow transportation and sedimentation from various locations.The study area basin lies in a transition area between the carbonate and arc clastic sedimentary systems.Affected by the North Qaidam oceancontinent subduction and continental arc collision,uplifted continental arc material and crust basement provided a large amount of detrital material to the basin.As a result,arc basin deposits developed in the areas close to the edge of the island arc,supported by the gravity flow depositional system of sandy debris flow and turbidity current types.