南盘江盆地中北部三叠纪深水盆地古水流方向研究

Triassic Paleocurrent Study in the Middle-northern Part of the Nanpanjiang Deep Basin

南盘江盆地位于中国广西、贵州、云南三省毗邻地区,为晚二叠世—三叠纪期间演化的海相沉积盆地,建立在晚二叠世开始的裂谷系统基础之上,进入三叠纪中期,盆地范围进一步扩展、海水深度进一步加深,盆地内部主要沉积了一套深水复理石,晚三叠世沉积环境为前陆盆地,在盆地北部沉积有碎屑岩和碳酸盐岩建造。针对南盘江盆地中北部深水复理石沉积,测量了鲍马序列C段中的小型斜层理、爬升层理、包卷层理轴面倒向、槽模等反映古水流方向的沉积构造的产状,通过野外和室内复平面校正、古流向玫瑰花图的绘制,对研究区三叠纪古流向进行了系统研究,共获得49组古流向测量数据,通过古流向分析并结合沉积环境演化特征,对南盘江盆地物源区进行了讨论。研究结果认为中三叠世期间盆地南部广南、底圩、八达、富宁一线物源区来自南部的越北古陆;盆地东部的巴马、龙川、望谟一线物源区来自于东部及北东的江南古陆;盆地北部物源区位于盆地西北部和北部的扬子台地内部;盆地的沉积中心位于册亨以南、潞城以北地区;隆林县城和西林县城之间、阳圩和剥隘之间存在古隆起。晚三叠世期间盆地北部古流向发生明显变化,应与构造体制的变化密切相关。

The later Permian-Triassic Nanpanjiang deep marine basin is located in the adjacent areas among Guangxi,Guizhou,and Yunnan,which developed based on the rift system during the later Permian. The space and the depth of the basin increased during the middle-Triassic and a set of deepwater flysch sediment was preserved in the basin. The environment of the basin was identified as foreland basin where there was a set of clastic and carbonate sediment in the northern part of the basin. The main study areas lie in the northern and middle part of the Nanpanjiang Basin（ NPJB）.Some kinds of flysch sedimentary structures can be used in the field work to get paleocurrent such as small oblique bedding,small climbing ripple bedding,convolute bedding,flute cast and so on. Based on the field measurement,stratum attitude correction and the rose diagrams drawing of paleocurrent,this article discusses the paleocurrent of the sediment during the Triassic time. 49 sets of paleocurrent data were exhibited here by which sedimentary provenances of NPJB can be constrained. During the middle Triassic time the sedimentary provenance of the southern part of NPJB（ for example near Guangnan,Dixu,Bada,Funing） would be the Vietnam Block to the south of NPJB,the sedimentary provenance of the eastern part of NPJB（ for example near Bama,Longchuan,Wangmo） would be the Jiangnan Block to the east,and the sedimentary provenance of the northern part of NPJB would be the inner Yangtze Platform to the north. The centre of subsidence is located at the areas south to Ceheng and north to Lucheng. Two palaeohigh belts were indentified between Longlin city and Xilin city,between Yangxu town and Boai town. The paleocurrent changed significantly during the late Triassic time at the northern part of the NPJB which was considered as a consequence of the tectonic fragment change.