Sedimentary Characteristics and Evolution of Early Cretaceous Dalazi Formation in Songjiang Basin, Jilin Province

Key words: 
• sedimentary facies /
• sedimentary evolution /
• Dalazi Formation /
• Songjiang Basin /
• Early Cretaceous

Abstract: It is typically developed Dalazi Formation stratigraphy of Early  Cretaceous in Songjiang Basin of Yanbian region of Jilin Province. According to lithologic series, from bottom to top, the stratigraphy of Dalazi Formation is divided into sandstoneconglomerate sector and oilbearing shale sector. On the basis of the analyses of rock types of field sections and outcrops, grain features, primary sedimentary structure, paleontology fossil combination of Dalazi Formation, 4 sedimentary facies are recognized: luvial fan facies, fan delta facies, lake facies and lake subaqueous fan, with 9 sedimentary subfacies. Plan view, fluvial fan is mainly formed in the south of Toudaogou, southeast of Basin, the belt zone along Yangcaogou to Dongnancha and northeast of Basin; Fan delta chiefly occurs at the circum of Basin, the east of ShajingouYangcaogou and the south of YangcaogouXiaoshahe, and of which is much rich in northwest of Xiaoshahe; Lake facies mostly emergent at the center of Basin and the zone along Laopianpo, Dongshan, Shajingou, Songjiangtun; Lake subaqueous fan nearly concentrated in the zone north of SongjiangzhenShajingou, and some formed in the south of Dongnancha. The sedimentation and evolution of Dalazi Formation in Songliao Basin is obviously influenced and controlled by local tectonic activities, paleotopography, paleoclimate and baselevel change. Early of Dalazi Formation, the Basin developed fluvial fan and fan delta, but lake facies is confided .The deposit center located in the belt of XiaoshaheXinfeng and the sediments maily came from the northeast of the basin. After that, the basin expanded southwards, with deposit center moving to the zone of YangmutunShenglitun. The basin developed lake facies, with some lake subaqueous fans distributed in somewhere of moderate deep lake and deep lake.