Dating permian ru
The Tongbai range is separated from the Funiu by a gap some 75 to 100 miles (120 to 160 km) wide cut by the Tang and Bai rivers, which are tributaries of the Han River.This gap gives easy access from the Henan Plain to the central basin of the Yangtze River (Chang Jiang), a route much used from Han times onward in Chinese expansion southward. Until fairly recent geological times the mountains in the west formed the coast of a sea that, essentially, was the western extension of the present Bo Hai (Gulf of Chihli) and Yellow Sea.There is a Chinese saying that “if you fall into the Huang He, you never get clean again.” Prior to the damming of the river at Sanmen Gorge, the river was fast flowing through the gorge, and it was able to carry its load of silt until it issued onto the plain; at that point, its pace was checked, it could no longer carry the silt, and flooding occurred.Throughout historical times, this menace was met by building levees to contain the waters.Consequently, soil salinity and alkalinity affect the whole area.There are large areas of bleak, white saline sands.The floor of this zone is sinking at a rate equal to that of deposition.
It is part of the great subduction zone (downwarping part of the Earth’s crust) that extends from Heilongjiang to Jiangxi provinces.The Huang He (Yellow River) divides the province into two unequal parts—one-sixth north and five-sixths south of the river—and thus to some extent belies the name Henan (“South of the River”). They are part of the Taihang fold system of Permian times (i.e., about 250 to 300 million years ago), have a general northeast-to-southwest trend, and mark the northern border of the province.