辽河盆地宋家洼陷上侏罗统扇三角洲和浪控三角洲

FAN-DELTA AND WAVE-DORMINATED DELTA DEPOSITS OF THE UPPER-JURASSIC IN SONGJIA DEPRESSION, LIAOHE BASIN

宋家洼陷是辽河盆地西部凸起上的一个 NE向小型断陷。通过岩芯研究 ,发现洼陷中上侏罗统属扇三角洲成因 ,而扇三角洲的前缘受高能湖浪作用发育典型的浪控三角洲。浪控三角洲的平原部分以分流河道和含植物根系和生物扰动构造的泛滥平原沉积为特征。河口坝相以含砾粗砂岩为代表 ;滨滩 -上滨面为含粉砂条带的粗砂岩 ,沙质前积斜坡为平行纹层状细砂和粉砂岩 ,这些条带和平行纹层属破波区和激浪带冲洗层理成因 ;泥质前积斜坡为夹粉砂的泥岩。当湖泊向盆地中退缩时 ,边缘扇三角洲可暴露于水面上 ,经历古土壤化过程 ,故对扇三角洲的定义 (“伸入静水体中的冲积扇”)不能机械地理解。

The Songjia depression is a NE oriented small rift in the west protrude of Liaohe Basin. The typical wave dorminated delta deposits of the Jurassic were discovered by core section studies. The delta plain facies is characterized by distributary channel sands and rooted and bioturbated flood plain sediments. The mouth bar facies is represented by gravelly coarse sandstone, the shore beach to upper shore face facies by banded siltstone bearing coarse sandstone, and the sandy off shore slope by parallel laminated fine sandstone and siltstone. The muddy off shore slope facies consists of mudstone with siltstone intercalations . This paper points out that as the lake regressed basinward, the marginal fan delta could undergo subaerial exposure and palaeopedogensis, so the original definition of fan delta ('alluvial fan built in standing water body') should not be understood mechanically. In the paper, the interrelationship between systems tract and microfacies and the reservoir aspects of wave dorminated delta have also been referred to.