Basin pattern and evolution of Triassic in North China

Triassic is an important transition period in the structural evolution of North China.The basin pattern and evolution of Triassic in North China is discussed based on the study of the development characteristics of the residual strata of the Triassic.It is held that the Indosinian movement happening during Triassic is the dominant factor of the basin evolution in North China.From the Early Triassic to the Middle Triassic,there possibly exists a large-scale NWW-trending sedimentary basin in the North China Plate,which presents steeper in the south and gentler in the north,and higher in the northwest and lower in the southeast.The evolution of the basin inherits the structural and sedimentary pattern in late Hercynian.The original thickness of Lower and Middle Triassic is 1 500~2 000 m.During late Triassic,the scissors-type collision splicing occurs between the Yangtze Plate and the North China Plate,which leads to the uplifting of the North China Plate.The uplifting is heterogeneous:the uplifting in the east is earlier and higher than that in the west.And the basin retracts to the west:there is still a basin in the west of North China,there developed the sediments of fluvial-lacustrine facies under the warm and humid climate,but its scale become smaller compared with the basin in Early--Middle Triassic;in the eastern most areas of North China,the strata of the Lower and Middle Triassic are denuded,and even some strata of the Paleozoic are also denuded.There developed small-scale intermountain basin sediments only in the eastern local areas of North China.