西藏羌塘盆地北部托纳木地区上侏罗统雪山组沉积相

Sedimentary facies of the Upper Jurassic Xueshan Formation in Tuonamu region of the Northern Qiangtang Depression,Xizang

羌塘盆地地处藏北高原，其南、北边界分别为班公错—怒江缝合带与拉竹龙—金沙江缝合带，盆地面积约18×104km2，可进一步分为羌北坳陷、中央隆起带和羌南坳陷3个二级构造单元。双湖托纳木地区地处羌北坳陷南部，与中央隆起带毗连，广泛发育上侏罗统雪山组沉积，垂向上由3个沉积旋回组合构成，总体显示为一个向上变粗的充填序列。雪山组发育扇三角洲相和冲积扇相，其中雪山组一段为前扇三角洲亚相沉积；二段为扇三角洲前缘亚相和扇三角洲平原亚相沉积，扇三角洲前缘亚相分为水下分流河道、河口坝和远砂坝沉积，扇三角洲平原亚相发育天然堤和分流河道沉积；三段为冲积扇相沉积，包括扇端和扇中沉积。雪山组沉积的物源来自西南部的中央隆起带。

The Qiangtang Basin is situated in northern part of the Qinghai-Xizang （Tibet）plateau, with the north and south boundaries being the Lazhulong--Jinshajiang and the Bangongcuo-- Nujiang suture belts respectively, and the square of the basin being about 18 × 10^4 km^2. The Qiangtang Basin could be further divided into the Northern Qiangtang Depression, the Central Rise and the Southern Qiangtang Depression. The studied area,Tuonamu region in Shuanghu, was in southern part of the Northern Qiangtang Depression,near the Central Rise. The Upper Jurassic Xueshan Formation was widespreadly developed there. Vertically, the formation was composed of three sedimentary cycles, and displayed a succession that the grain-size became coaser upwards. The deposits with sedimentary facies of fan delta and alluvial fan were devel- oped in the Xueshan Formation. The first member of the formation was sediments with pro-fan delta subfacies,the second member of the formation was sediments with subfacies of fan delta front and fan delta plain. The subfacies of fan delta front could be further divided into the microfacies of subaqueous distributary channel,distributary mouth bar and distal bar,and the subfacies of fan delta plain could be divided into the microfacies of natural levee and distributary channel. The third member of the formation was sediments with facies of alluvial fan, including the subfacies of outside fan and middle fan. The provenance of the Xueshan Formation was to the south ,namely ,the sources came from the Central Rise.