| Groundwater in the Cretaceous Basin is vital to the construction of the energy and chemical industry base, and is an important factor which holds out coordinate development of the society and economy. The construction of groundwater circulation mode and reasonable evaluation of groundwater resources can provide useful guidance and is helpful to the allocation of water resources. Meantime, the groundwater circulation process and its value in use then can be found according to the groundwater circulation mode. Therefore, the groundwater circulation mode of the northern cretaceous basin and the hydrochemical evolution mechanism are focused in this thesis, which can provide basis for the groundwater utilization.The groundwater is in close relationship with local setting throughout the long geologic history, when moving in the stratum and forms the typical characteristics of hydrochemistry and isotopes which can provide important evidence for groundwater circulation. Therefore, the distribution characteristics of hydrochemical field and D,18O isotopes of different water bodies were firstly analyzed as well as the variation of TDS, D and 18O isotopes along chief rivers to find out the dynamitic connections of precipitation, surface water and groundwater. Then the ages of groundwater in different aquifers and their sources were calculated using 3H, CFCs and 14C to ascertain the groundwater flow direction and its circulation rate. The typical profile (Ⅱ-Ⅱ') was chosen to proceed a groundwater mathematic simulation. In the end, the groundwater circulation mode in the research field was constructed.The groundwater hydrochemical field is formed after long history with various characteristics and formation mechanism. Therefore, it's necessary to take advantages of several different methods to conclude a correct result. This thesis applied the mineral saturation index method, the ion combination and ratio method and the isotopic hydrologic method to analyze the hydrochemical formation effects and the sources of partial hydrochemical constituents. Then two samples on the same flow path were selected to analyze the geochemical actions with the combination of the result from the groundwater flow field model of the typical profile.The main conclusions of this thesis are stated as follow:1. The sources of groundwater and surface water and relationships between tehm are found out based on the analysis of hydrochemic components, D and 18O in these waters.The surface water and groundwater originate both from precipitation and are both affected by evaporation. The river is mainly recharged by groundwater which can be concluded from the contribution variation of hydrochemistry,δD andδ18O isotopes along the river flow direction. The portion of modern precipitation in groundwater decreases with depth revealed from CFCs isotopes.2. The special distribution characters of groundwater ages are analyzed by determining the shallow groundwater ages using the 3H and CFCs isotopes and theages of groundwater in Huanhe aquifer and Luohe aquifer using 14C.Age of shallow groundwater within the circulation depth of modern water is very small concluded from the calculation of 3H and CFCs. The age of shallow young groundwater is less than 20a in the area around the watershed and increases to morea than 50a along the flow line to the boundary and rivers. The 14C age of groundwater in Huanhe and Luohe aquifers is less than 5 000 years old and increases towards the rivers and boundaries in eastern, western and northern direction. The groundwater age is generally more than 10 000 years in the discharging area. The distributing characters of groundwater in Luohe aquifer is similar to the Huanhe aquifer, but the the area of groundwater with age less than 5 000 years in Huanhe aquifer is bigger than that in Luohe aquifer. The distributing rule reflects that the recharge time is earlier in Luohe aquifer and the groundwater flow rate is slower.3. Based on the analysis of geologic and hydrogeologic conditions, the groundwater circulation mode is estabilished according to the isotopic and hydrochemical characters on the profile. The groundwater circulation system can be divided into the local circulation system,the intermediate circulation system and the regional circulation system based on the circulation depth.The local circulation system arises between mesa and low-lying vicinity (river valley, lakes, and depressions) including Cenozoic aquifer system and shallow Cretaceous aquifer system (embedding depth within 100m), with circulation depth up to 100m and strong groundwater movement. In the research field, there are some lakes in different scales recharged by the local circulation system, which protects the lakes from being dry up.The intermediate circulation system underlies under the local circulation system with larger incidence, depth and circulation depth up to 600m. Precipitation is the main source in this circulation system, secondly the infiltration from the local circulation system. The main rivers and relatively larger lakes in the area are the discharge datum plane of the intermediate groundwater system. The regional circulation system underlies under the intermediate circulation system with quite slow groundwater runoff, and the circulation depth is between 500 to 1000m until it reaches the bottom of Cretaceous stratum. The recharge mainly depends on the precipitation in the Etuoke-Sishililiang area and lateral seepage from middle circulation system. And the groundwater discharges to the regional rivers and lakes (such as Dusituhe River, Wudinghe River and Hongjiannao Lake).4. The sources of main ions in groundwater is analyzed by applying the chemical components and the tracing characters of Sr and S isotopes.Then the regional representive flow path was selected and the hydrochemical path simulation model is constructed by analyzing the main factors effecting the hydrochemical evolution. At last, the main effects controlling the formation of hydrochemical and the evolutionary process in study area are found out.On the basis of water circulation mode research, this thesis synthesizes the application of the saturation index method, ion combination and ratio method, Sr,S isotopes technique and anti-hydrochemical path simulation to analyze the groundwater chemical formation effect, find out the basic discipline and formation mechanism of groundwater chemical evolution in the northern Cretaceous Basin of Ordos. (1).Lixiviation, evaporation, the cation alternative asorption influences and the mixing influence are the chief geochemistry actions controlling the groundwater hydrochemical characteristics in the northern Cretaceous Basin of Ordos.(2). The chief actions on the simulated flow path are the precipitation of calcite, dolomite, the solution of gypsum and potassium feldspar, the cation exchange of Ca-Na, and the solution of NaCl or plagioclase.Based on the conclusions mentioned above, the groundwater resource can be considered to be the chief source for the energy construction, and the water supply field can be designed in the Wudinghe-Wulanmulunhe groundwater system with good groundwater quality and fast groundwater circulation.
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