松辽盆地白垩系营城组再搬运火山碎屑与相模式

Reworked Pyroclastics Deposits and Facies Model of Cretaceous Yingcheng Formation in Songliao Basin,NE China

以松辽盆地东南缘营城组二段两类火山碎屑岩(沉凝灰岩、凝灰质砂岩)为研究对象,进行了火山碎屑粒度特征、碎屑组成和火山碎屑岩相研究.结果显示,火山碎屑搬运除受火山作用激发控制外,还受牵引流、重力流以及牵引流和重力流的双重机制影响.火山碎屑微观特征、成因分析和岩相分析认为,本区火山碎屑堆积主体为热基浪堆积和热碎屑流堆积,部分为空落堆积.火山碎屑组成特征为晶屑含量多,玻屑和岩屑含量少,且岩屑仅在较粗粒级颗粒组成中存在.研究认为,本区发育的火山碎屑为沉积环境中的再搬运火山碎屑,共识别出4种火山碎屑岩相,河流故道上的热基浪,河流故道上的热碎屑流,冲积平原上的热基浪和空落相.建立了松辽盆地东南缘露头区营城组二段河流-冲积平原沉积环境的再搬运火山碎屑岩相模式.

The pyroclastics grain size characteristics, the pyroclastics composition and the pyroclastics rocks facies of two types of pyroclastics rocks samples of Yingcheng Formation in the southeast edge of Songliao basin, tufts and tuffaceous sandstone, had been studied. The results show that, the pyroclastics had been transported at the beginning by volcanism excitation, however, traction flow, gravity flow and the double mechanism of traction flow and gravity flow controlled the transportation process. The conclusion drawn from pyroclastic microscopic characteristics study, genetic type analysis and lithofacies analysis of those samples in study area calculates that, the majority volcanic debris accumulation was composed of hot base surge and pyroclastic flow deposition and a small portion had been composed of fallout. The characteristics of detrital composition were those, there were a large amount of crystal fragments, a small amount of shard and lithic fragments, and the lithic fragments existed only in coarse grain composition. Studies suggest that, the pyroclastics outcropped in this area were the reworked pyroclastics in the depositional environment. There were 4 types of pyroclastics facies, the hot base surge in the previous valley, the pyroclastics flow in the previous valley and the base surge and fallout on the alluvial plain had been distinguished in this area. Based on the member II of Yingcheng Formation in the southeast edge of Songliao basin, facies models of the reworked pyro clastics in these fluvial-alluvial plain sedimentary environments were established.