During this period, neotectonic movement was active, and the uplift amplitude of western and southern mountainous areas was obviously increased compared with before, which led to the formation of hillsides or the expansion of original hillsides in some piedmont areas. For example, the scope of Huolonggang was further expanded during this period, and some areas such as southern Anyang, northern and southern Zhumadian were eroded during this period.
On the whole, the western and southern piedmont areas are still inclined from west to east and from south to north, and the gradient is still large, with a height difference of 60 ~100 m. There are alluvial and diluvial fans near the outlet of large rivers (Figure 5), and the lithology is thin gravel, loam and clayey silt accumulation. Loess-like soil with cohesive soil as the main body is distributed on, between and in front of fans.
Due to the further development of rivers and the enhancement of accumulation in the central and eastern plains, the whole plain is almost shrouded by the accumulation environment of rivers. The front edge of the Yellow River alluvial fan extends from Xinxiang and Changyuan in the early days to hua county and Puyang in the northeast. Salt water also retreated to the front of the new fan with the expansion of the alluvial fan. But the main direction of the river is still the northeast, which is divided into four streams and enters Hebei. The current in the southeast direction is weak, and the sediments are mainly fine particles, extending from the western part of Sui County to Shangqiu and other places. The channel leading from the fan extends to the south of Huaiyang and Dancheng.
Since the formation and development of the Yellow River, it has basically reached a prosperous period. Compared with the previous period, the scope of fans has been significantly expanded and the river belt has become more developed. Lithology is mainly composed of medium coarse sand, medium fine sand, fine powder sand and clayey silt. In the middle and upper part of the fan, the thickness of sand layer is generally 10~30m ~ 30m, and the sand content is more than 60%. The sediment concentration in the river zone is generally 40% ~ 60%, which extends radially to the northeast, east and southeast, but its sediment concentration gradually decreases with the extension of the river.
Under the continuous accumulation of the Yellow River, the ancient lakes gradually retreated, and most of them became shallow marshes and depressions. At this time, except for the stable crustal movement in the south and the slight expansion of the shallow lake swamp area, due to the rapid accumulation of the Yellow River in the north, the lake area retreated eastward to the vicinity of Shangqiu, consisting of thick and medium-thick clayey soil. Lakes in other areas are basically extinct.
Due to the strong accumulation of the Yellow River in the west, the Laishan River in the northeast is relatively weak. And to a certain extent, it does inhibit the passing capacity of Laishan River in the northeast of Thailand, and its accumulation and distribution range becomes very small.
In short, in the late Zhoukoudian period, the Henan Plain was transported and accumulated by rivers such as the Yellow River, and the lake area gradually decreased, the accumulation increased day by day, and the terrain became flatter. The elevation near the mountain area is about 1.20m, which gradually decreases eastward, with the lowest elevation of about -20 m, and the maximum elevation difference in the whole plain area is about 1/65438+. The general feature of terrain slope is that it inclines to the east. However, due to the different material sources of the north and south and the east and west when the plain was formed, each place maintained its own unique characteristics. Roughly bounded by Shangqiu north-south line, the terrain on the east and west sides is slightly inclined to it; In front of Dabie Mountain, it leans to the northeast in a fan shape, with a relatively large slope of about11000.
The lithofacies palaeogeographic features of the above five members all show provenance problems in different directions. According to the combination of heavy minerals and their comparison in profile, the percentage content and weathering coefficient of some major heavy minerals such as garnet, epidote, amphibole and metal minerals are obviously reflected in the plane.
Table 6. Statistical results of1Qinyang-Kaifeng-Shangqiu section show that the contents of garnet and metal minerals increase from west to east. However, the content of unstable minerals such as epidote and amphibole is from more to less, and the weathering coefficient is from small to large. This shows that the Quaternary sediments in this area mainly come from the western mountainous areas and change regularly with the increase of transportation distance. However, in Yongcheng and Shangqiu areas in the east of the plain, the percentage of amphibole has increased, which is similar to the material characteristics in the west of Jiangsu-Anhui plain, indicating that the sediments in this area came from the eastern mountainous areas.
Fig. 6.8 The contour map of the bottom boundary elevation in the Lower Sarawusu stage of Quaternary in Henan Plain.