Macroscopically, the crust in this area has been in a slow subsidence movement since Cenozoic, thus accumulating huge Quaternary sediments. Quaternary sediments are the most active layer of groundwater in modern times and the main place for the diffusion, migration and accumulation of fluorine, so Quaternary geology has become an important research object in this area.

1.Qh Holocene

A. Early Holocene alluvium (Qh 1)

It is distributed in the lower part of Holocene, and the surface is not exposed. This layer is mainly distributed in the south of the study area, south of Yanling-Fugou-Taikang line. Generally, tile shop, brick bridge and solid wall are divided into northeast and southwest parts: the northeast part (around Xihua County) is yellow-gray, gray-yellow, light-gray silt and fine sand deposited by the Yellow River, and some are medium-fine sand, with loose lithology, good sorting and grinding, clear bedding, buried depth below 5 ~ 15m, and the thickness is generally 5 ~ 65438. Horizontally, lithology becomes thinner from roughness to southeast; The soil in the main stream area of the river has coarse particles, loose structure and good water permeability. The flood plain has dense lithologic structure and poor permeability and hydraulic conductivity. The southwest (Luohe area) is yellow-brown, grayish yellow and brownish yellow loess clayey silt, containing ginger, which is generally buried below 5 ~ 10m, with a thickness of about 10m.

B. Middle Holocene sediments (Qh2a 1+h)

It is mainly distributed in the south of the study area, that is, Yanling County-Fugou County-south of Taikang County. Widely distributed in the whole region, most of them are buried, and some of them are exposed in Wadian in the northwest and Tanzhuang-Yao Ji-Guqiang in the southwest; Daguo-Chenglou area is mainly composed of yellowish gray, grayish brown clayey silt and grayish black, grayish brown muddy loam, which is porous, contains organic matter, smells like sapropelic mud, contains a small amount of calcium, iron and manganese nodules, and is generally 5 ~ 10m thick.

C. Late Holocene alluvium (Qh3al)

The Yellow River alluvial is distributed in the vast plain area east of Weishi. Its sedimentary thickness is controlled by the basement structure and the ancient channel of the Yellow River. The general rule is that the west and uplift areas are thinner, and the east and depression areas are thicker.

Shuanghe alluvial deposits are mainly distributed in the central and western parts of the study area, including the southwest of Weishi County, the east of changge city and Xuchang City, and most areas of Yanling County. The deposition thickness is 4 ~ 5m. The lithology is yellowish gray and grayish yellow clayey silty soil, and the silty soil is light. Clay silt is mixed with thin silt and coarse sand lens locally, and the thickness is less than1m.

The alluvial deposits of Shaying River are mainly distributed in the south of the study area, Xiaoyao-Tangzhuang-Xiangcheng and Dengxiang-North China-Dong 'an, and the lithology is light brown clayey silt and loam. Xiping-Xihong area is composed of brownish yellow clayey silt and light brownish red loam with a thickness of 3 ~ 5m.

D. Neoholocene Yellow River Alluvium (Qh4al)

It is mainly distributed in Liansi-Xihua-Bankou area, which was formed by flooding south of the Yellow River in 1938. The lithology is yellowish brown-grayish yellow clayey silt and silty sand, and the thickness is generally 1 ~ 3m. The lithology is loose, with horizontal bedding, rich in dispersed calcium and a small amount of calcareous nodules, and there are many traces of biological activities such as plant root holes and wormholes.

There is a layer of 1 ~ 2m modern sediments of the Yellow River between Jia Luhe and the Wohe River.

E. Holocene plain alluvium (Qh 1al)

The alluvial layer of the Yellow River floodplain is distributed in the northern part of the study area, including zhongmou county, Kaifeng City and Kaifeng County. The exposed depth of this layer is 0 ~ 50m. The buried depth of the bottom plate is generally 30 ~ 50m. The upper part is mainly yellowish brown and grayish yellow clayey silt and loam. The floodplain zone is dominated by fine sand mixed with thin loam, with 1 ~ 2 sand layer in the lower part, and its thickness is controlled by the structure of this area and the ancient channel of the Yellow River. The sand layer in the main stream area of the ancient road is thick and thick, and the sand layer in the flood plain area is thin and fine, generally 20 ~ 30m thick. The thickness of the depression area can reach about 40m, and the eastern part becomes thinner, generally less than 20 m.

F. Holocene aeolian deposits

It is distributed in Yao Jia, Huangdian, Zhuangtou, Xijiangzhai and Dagao Temple in Kaifeng County in the north and northwest of the study area. Accumulate on the surface in the form of sand dunes, sand ridges and flat sand fields. The lithology is fine sand and silty sand with a thickness of 1 ~ 8m. The sand layer was taken away by the Yellow River flood diversion, and later it was blown by the wind and accumulated into various forms of aeolian landforms. The areas around Zhongmou and Weishi are undulating sand dunes, most of which are fixed and a few are still moving.

2. Upper Pleistocene series (Qp3)

The upper Pleistocene sediments are controlled by basement structure, and the general rule is that the thickness is thinner in the west and thicker in the east, less than 20m in the west, 20-40m in Weishi, Tongxu and Taikang, and 60-70m in the east of Tongxu. The buried depth of the bottom is 20 ~ 40m in the west and 60 ~ 80m in the east, among which the buried depth of Yanling-Fugou-Taikang line is relatively deep, reaching 100m. The bottom interface inclines from southwest to northeast. The grain size of sediments changes from northwest to southeast, from upstream to downstream, and from coarse to fine.

3. Middle Pleistocene (Qp2)

In the northern part of the study area (Kaifeng and zhongmou county), the buried depth of the Middle Pleistocene strata is between 100 ~ 140m, and the buried depth of the floor is between 200 ~ 260m. The thickness of the Middle Pleistocene sand layer gradually becomes thinner from west to east and south, reaching 20m, and the thinnest in the southeast is only 10m.

In the central area of the study area (around Weishi County, Tongxu County and Fugou County), the Middle Pleistocene strata are thin in the west and thick in the east, and the surface is not exposed. The buried depth of this layer is 40 ~ 80m in Xigang of Weishi County, 140 ~ 150m in the east, and more than 150m in Zhuxian Town of Kaifeng County in the north and Fugou area in the south. This regularity shows that it is obviously controlled by the basement structure.

In the south of the study area, Zhaolinggang of this series is the thinnest, only more than 30 meters. The buried depth of Luohe, Xiping and Donghong areas is 100m, with a thickness of 50 ~ 60 m; the buried depth of Wangtian, Liansi and Xihuaying areas is 120 ~ 150 m, with a thickness of 70 ~ 100 m, and the buried depth and thickness gradually increase to the southeast.

4. Lower Pleistocene (Qp 1)

(1) North of the study area, Kaifeng and Zhongmou. The lower Pleistocene is not exposed to the surface. According to the drilling data, the buried depth of the roof is 200 ~ 260 m, most of the boreholes have not exposed the Lower Pleistocene, and some boreholes have penetrated, and the buried depth of the floor is 270 ~ 400 m .. and the thickness is 50 ~ 150m.

Lower Pleistocene alluvial lake layer: brown and brown loam, followed by clayey silt and clay. There are silty sand and medium-fine sand, and the thickness of sand layer is 4 ~ 8m. The distribution law of floor buried depth and sand thickness in the Lower Pleistocene is closely related to geological structure and consistent with the direction of provenance.

Ice-water accumulation layer of Lower Pleistocene: it is a set of grayish green, brownish red, brown clay and loam, containing a small amount of clayey silt, 1 ~ 2 layers of fine sand and medium fine sand. The clay contains iron, manganese nodules and calcium nodules, and the sand layer is muddy, so the sorting is poor.

(2) The Lower Pleistocene can be divided into the following parts: Kaifeng City, southern zhongmou county, Yanling County-Fugou County-northern Taikang County.

Upper part of Lower Pleistocene: Lower Pleistocene is buried under Middle Pleistocene, and its sedimentary thickness is obviously controlled by basement structure. The central uplift area is thin, and the southern and northern depressions are thick, from west to east 10m, from central to Tongxu 40-50m, and from north to 70-90m. The buried depth of the bottom is 40 ~ 50m in the west, 0/50 ~180m in the middle, more than 200m in the east and south, and 250m in the north.

Lower part of Lower Pleistocene: The lower part of this area is widely distributed with a large thickness, and this layer has not been exposed in all drilling holes. Judging from the buried depth of the roof, it is obviously controlled by the basement structure. Due to different reasons and material sources, it can be divided into the following three aspects:

Alluvium is distributed in Huangdian and Weishi Xingzhuang in zhongmou county. The lithology is brownish red, mixed with purplish red sandy clay and clay, grayish white and pink sand layers, containing gravels and clayey gravels. Aquifers mostly occur in multiple layers. Within the depth of 300 ~ 350 m, there are generally 4 ~ 5 layers, with a maximum of 8 ~ 10, with a total thickness of 60 ~100 m. The main aquifer is thick and coarse, showing the sedimentary characteristics of river bed facies.

Proluvial is distributed in the southern part of Daying-Weishi County to Zhuqu, with reddish brown lithology, mixed with purple sandy clay, clay and silty fine sand, medium fine sand and a small amount of coarse sand. There are 5 ~ 6 sand layers within 300m depth, with a total thickness of 60 ~ 80m. Mainly from the western mountainous area, the aquifer has fine particles, poor sorting and much mud.

Alluvial-lacustrine deposits are distributed in the vast plain area east of Weishi County. The upper part is brownish yellow mixed with gray-green disseminated thick sandy clay and clay, mixed with light yellow and gray-white medium-fine sand layer. The clay layer contains more calcareous nodules, ferromanganese nodules and disseminated substances, and there are 1 ~ 3 layers of paleosol, with loose structure and frequent cracks, and the cracks are filled with sand and calcium crystals. The lower part is red, blue-gray clay and brownish yellow argillaceous silty fine sand and medium fine sand layer. Thin layers are developed, and the main sand layers are thick and distributed stably. The particles are coarse and extend far, with coarse medium sand in the upstream and medium fine sand in the downstream. Total thickness of sand layer within 300-350m depth: less than 40m in the south and north, and 60-80m in the middle.

(3) In the south of the study area, south of Yanling-Fugou-Taikang line, the Lower Pleistocene can be divided into two parts.

Upper member of Lower Pleistocene: Zhaolinggang area, with a buried depth of150 ~ 200m and a thickness of 60 ~150 ~ 200m. The north, west and southwest are next, the buried depth of the bottom plate is 200 ~ 250 m, the thickness is 90 ~ 1 100 m, and the buried depth of Zhoukou-Xiangcheng northwest-southeast belt is 250 ~ 300 m, and the thickness is 100 ~ 130 m ... The southwest is deposited by ice water, and the lithology is mainly yellowish brown-reddish brown loam mixed with grayish green and rusty yellow loam, and the clay is mixed with thin clayey silt and extremely thick sand layer. The northeast is composed of yellowish brown and reddish brown thick loam, clay and silty fine sand. Generally, it contains calcareous and ferromanganese nodules, some clays are rich in integrated layers, and some clays have gray-green meshes and patches along the cracks. The sand layer has fine particles, good sorting and micro-bedding. It is caused by glacial lake sediments.

Lower member of Lower Pleistocene: limited by exploration depth, this member has not been exposed. The exposed thickness in the west is 50 ~100m; The exposed thickness in the east is100 ~ 200m. This section is deposited by rivers and lakes, mainly composed of brownish red, yellowish brown, grayish green clay and loam, with fine sand and medium fine sand layers, fine texture, grayish green network, patchy along clay cracks, and variegated appearance. Development level and wavy bedding, generally containing iron, manganese nodules and layered calcium tablets. The general characteristics are: mainly cohesive soil, compact structure, obvious grease luster and pressure surface, mostly in semi-cemented state. The sand layer has fine particles and good sorting, and some feldspar in the sand layer is weathered and semi-cemented.

(2) Neogene

1. Pliocene Minghuazhen Formation (N2m)

The lithology of this group changes slightly in Kaifeng and Zhoukou basins. Kaifeng basin consists of brown and gray claystone and sandy claystone interbedded with gray and light brown siltstone and sandstone, with gravel sandstone or gravel at the bottom. Zhoukou basin consists of brown-red and yellow-green claystone and sandy claystone interbedded with gray-yellow and gray-green fine sandstone and siltstone, with coarse sandstone or gravel sand layer at the bottom. Generally speaking, the formation is mainly composed of brownish red and grayish green claystone, with sandy claystone interbedded with siltstone and fine sandstone, and the bottom is mostly gravel sandstone or gravel sandstone. The grain size of sediments becomes finer from west to east, and Kaifeng basin is slightly finer than Zhoukou basin. Viewed vertically, it has the characteristics of tapering from bottom to top. This formation is a set of fluvial-lacustrine facies deposits. The eastern part is thicker than the western part, and the thickness changes little from north to south. Zhoukou basin is 640 ~11m, Kaifeng basin is 600 ~ 1428m.

2. Miocene Guantao Formation (N 1g)

The lithology and thickness of this group vary greatly in the region. Kaifeng basin is composed of light brownish red and light gray siltstone, which is interbedded with brownish red claystone and sandy claystone, with light gray, light brownish red calcareous sandstone and variegated gravel sandstone, with a thickness of 250 ~ 9 15m. The bottom of Zhoukou Basin is variegated conglomerate, with brownish yellow, grayish green and grayish white gravelly sandstone mixed with brownish red, grayish green claystone and sandy claystone, and locally mixed with black thin layer of inferior coal, with a thickness of124 ~ 342 m. Generally speaking, the granularity of clastic sediments in the west is coarse, with more sandstone and gravel, and the eastern part is thin, with more siltstone and claystone. Because of the different provenance and basin size, the grain size of sediments in Kaifeng basin is slightly finer than that in Zhoukou basin, but they all belong to river and lake facies.

(3) Paleogene

The Paleogene strata in the study area are not exposed, mainly distributed in Kaifeng and Zhoukou sag basins, under the Quaternary or Tertiary caprock. According to drilling, Eocene and Oligocene are relatively developed, but the Paleocene is not exposed, and the situation is unknown. According to the data of sedimentary lithofacies, structure and paleontology fossils, the Paleogene in this area is Kongdian Formation of Lower Eocene, Shahejie Formation of Middle Upper Eocene and Dongying Formation of Oligocene.

From the sedimentary characteristics, Zhoukou Basin is mostly a set of shallow lake facies red beds formed under oxidation conditions, with coarse rock particles, mainly dark purple and brown sandy claystone, siltstone, gravel sandstone, gray purple and reddish brown breccia limestone, marl and gray claystone, with a thickness of 342m ... Kaifeng Depression is mostly a shallow lake-deep lake facies formed under reducing environment, with dark gray and grayish brown claystone mixed with light gray and gray clay.

(4) Regional geological structure

The significance of studying regional structure on the distribution and formation of high fluorine groundwater mainly includes two aspects: ① the influence of basement on deep water circulation, the formation fluctuation caused by tectonic movement, and the influence of some fault structures on the deep water circulation; ② Influence on medium space and thickness distribution of underground hot water. With the change of structure, the stratum thickness will also change, and the stratum in the uplift will become thinner and the stratum in the depression will become thicker. The different spatial distribution of medium will also affect the distribution and dynamic change of underground hot water.

(5) General situation of basement structure

1. East-west Qinling structural belt

The northern part of the study area-Kaifeng depression zone is composed of many depressions and bulges. Among them, Zhongmou, Kaifeng Depression, Wang Luo Depression and Lankao Uplift are all near east-west, and will be partially deflected when disturbed by other tectonic systems or belts. East-west compressive and torsional thrust faults are relatively developed, accompanied by NE and NW torsional fault structures, which can be divided into several secondary structural units.

Most of the central and southern parts of the study area are mainly characterized by a series of east-west or nearly east-west fault zones and fold zones. The main faults are Yanling-Taikang fault, Yanling Beipengdian-Cao Li fault, Yao Jia-Zhuxianzhen fault, Linying-Shangshui fault, Wanggang fault, Taocheng syncline and Zhang Qiao fault.

2. Neocathaysian tectonic belt

The study area belongs to a part of the second subsidence zone of New China, and the main faults in the area are Zhuxianzhen-Zhuangtou fault and Qixian fault. There is Dayingxi fault in the west and Cao Xian-Suixian fault in Lu Yu in the east, which extends to this area.

In the southeast of the study area, the Neocathaysian tectonic belt consists of two faults (Fucaolou fault and Huaiyang fault) and one anticline (Anling anticline), with the anticline of n18 ~ 25 E, and the echelon tends to Huaiyang-Lin Caiyi belt, with a large fault scale of up to 20km.

3. North-South tectonic belt

The N-S structural belt was formed in Yanshan period and continued to move in Himalayan period, showing fault syncline structure, and its mechanical properties are mostly compressive and compressive-torsional faults. Distributed in Cao Nan area of Weishi.

4. NW-trending structural belt

This structural belt is undeveloped in the study area, mainly distributed in Zhoukou and the east of Xiating, and consists of two roughly parallel faults. One runs from Xihua via Zhoukou to Pingdian, and it runs northwest and northeast. One enters the country from Baotun-Daxinji, passes through Dongxiage to Wangdian, moves northwest, leans northeast, and the dip angle is 50, cutting off the east-west fault and making it move horizontally. It may have occurred in the late Yanshan period, and it is a compression-torsion fault. It obviously controls the distribution of water system in the study area, especially in Jia Luhe.

(6) Large structural units in the study area

The tectonic system in the study area is mainly controlled by the east-west structural belt of Xiaoqinling-Songshan, the Neocathaysian structural system and the north-central-western structural belt of Henan Province. Affected by this, there are three main structural units in the study area, namely Kaifeng sag, Tongxu uplift and Zhoukou sag. Tongxu uplift (or Tongxu anticline) occupies most of the study area, and only the north and south uplift intersect with parts of Kaifeng sag and Zhoukou sag respectively. Now described as follows.

1. Kaifeng sag

Kaifeng sag belongs to Jiyuan-Kaifeng sag and is a subunit of Jiyuan-Kaifeng sag, which is located in the southeast corner of Jiyuan-Kaifeng sag (Figure 2- 1 1). Kaifeng sag belongs to Mesozoic-Cenozoic fault depression.

Jiyuan-Kaifeng sag is distributed in Jiyuan-Kaifeng-Quan Min area along the east-west direction of the Yellow River, with an area of about 12000km2. This area is widely covered by Quaternary, and only Jurassic and Paleogene are scattered in the west of Jiyuan. The basement of Jiyuan-Kaifeng sag is mainly Paleozoic and Triassic, and some areas (Wuzhi uplift) are Archean metamorphic rocks. Among them, there are Paleozoic and Cenozoic continental debris, and the maximum thickness can reach more than 900m m.

Jiyuan-Kaifeng sag has nearly east-west structural lines and well-developed faults, which are mainly divided into three groups: near east-west, northeast and northwest. Near-east-west faults are normal faults with large scale, early formation and long activity time, which form the boundary of sag or secondary uplift and control the formation, development and shape of sag. In addition to the Jiaozuo-Shangqiu deep fault, there are also larger Zhongmu, Yangzhuang and Longtang faults on the north side. The small-scale and late-formed NE and NW faults are flat thrust normal faults, which have certain influence on the shape, Mesozoic and Cenozoic lithofacies and thickness changes of secondary uplift and sag in the sag.

Figure 2- 1 1 Schematic Diagram of Regional Geological Structure

Fault: f 1- lankao fault; F2- Zhongmou-Shangqiu fault; F3- solid box failure; F4- Shangshui fault; F5— Xiangjiang fault; F6- Lu Ye fault; F7- Zhengzhou fault; F8- Weiss fault; F9- Baotun fault; F10-fugou fault; F 1 1- Lu Yi fault; F12-Liaolan fault; F13-Suixian fault; F14-Shaji fault; F15-Yanji fault; F16-evolutionary fault. Fold: s1-Xuchang anticline; S2- fixed compartment anticline; S3— Shangshui syncline; S4- Quaternary anticline; S5-Cao Nan syncline; S6- Ningling anticline; S7- Duji anticline; S8— Yongcheng anticline; S9— Jishuiji anticline. 1- bedrock stratum; 2- Normal fault; 3- anticline; 4— Syncline

2. Tongxu bulge

Located in the east of Songjitailong and the west of Yongcheng sag. The area of Tongxu-Shangqiu between Jiyuan-Kaifeng and Zhoukou Depression is about 18000km2, as shown in Figure 2- 1 1.

The uplift basement is dominated by Paleozoic, and the eastern and western ends are Proterozoic and Archean in turn. It is mainly composed of Neogene red, brown and yellow clay rocks, sandstone and glutenite, with a thickness of 400 meters in the middle and 1300 meters in the south and north sides. The thickness of Quaternary fluvial clay and sand layer is100 ~ 200m. Paleogene continental clastic rocks with the thickness of 100 ~ 300 m are still developed in the southern and northern marginal zones and small depressions.

Tongxu uplift is actually the eastern extension of Songjitai uplift. The near east-west faults mainly include Zhongmu, Yangzhuang and Longtang faults in the north and Linying-Shangshui faults in the south. NE faults include Jiyang fault and Suixian-Cao Xian fault. The NW-trending faults are Caolibei and Eastern Xia Pavilion. Tongxu uplift is a latent uplift that sank after Paleogene.

3. Zhoukou sag

Located in the east of Mianchi-Queshan fault, between Tongxu and Xiping-Pingyu, with an area of nearly 10000km2.

The western part of the depression is dominated by negative aeromagnetic anomalies, while the eastern part is dominated by positive aeromagnetic anomalies. Gravity is a gravity area dominated by negative anomalies, with positive and negative phases. The gravity and magnetic anomalies in the south of Zhoukou-Shenqiu are NW-trending and NE-trending. Gravity and magnetic characteristics roughly reflect the face of Zhoukou sag. As shown in figure 2- 12.

Figure 2- 12 Structural Profile of the Study Area

The basement of the depression is Paleozoic and Triassic, and some areas are Archean (Dancheng Uplift). The depression is mainly composed of Paleogene fluvial clay rocks, sandstone mixed with marl and metastable dark red complex continental clastic rocks. Paleogene is a metastable complex continental clastic rock composed of variegated clay rocks and sandstone coal lines, and Quaternary is clay, sand and gravel layers. In addition, there may be Mesozoic in some areas of the depression. The maximum thickness of Cenozoic sediments is over 7000m.

In a word, Zhoukou sag is a Mesozoic-Cenozoic depression basin based on Paleozoic and developed by the main faults in the northwest and northeast directions in the region. It experienced two stages of development: pre-Neogene fault depression and Neogene and its subsequent depression, forming today's Duo Long, with numerous depressions and complex shapes. This landform has played a certain role in controlling the groundwater flow in the study area, thus indicating the migration and enrichment of salt in groundwater.