| Resistivity method of geophysical prospecting is the most traditional and effective method in the investigation of underground water resources at home and abroad. In the region of Yuanbaoshan, Koshiketeng County, Chifeng City, there is serious drought for less rain, so the drinking water for living is very limited. Therefore, exploring and developing underground water is the main approach to solving the scarcity of water resources. Based on geology and hydrogeology features in this region, the authors utilize the resistivity method of geophysical prospecting, combined with electrical logging, to clarify aquifers and encircle the favorable areas of underground water development. All of results were attained by ascertaining the buried depth of Quaternary, the distribution laws of aquifers and the rising or sinking conditions of bedrock in the main region of the western depression plain, the eastern plain between mountains and the southern areas between rivers. General introductions to hydrogeology in investigating areas: Quaternary stratum in this region mainly belongs to Zhangjiakou Formation of Upper Jurassic system, and lithology is mostly tuff, rhyolite, andesite, etc. In Late Yanshan, intrusive masses are mainly granite porphyry. Neocathaysian structural system is the main structure, and Cathaysian strutures next to it. Quaterary stratum is widely extended and of great depth, its formation types are simple. Neocathaysian structural system and Cathaysian structures control the water system of mountainous regions. It is predicted that there perhaps exists comparatively deep aquifers in the central and marginal parts of depression basin, basin between hills, basin between rivers, and masses between rivers, while in areas of nearby ridges and divides, and blind ridgy bedrocks, there is less deep aquifers, so the latter having weak water-bearing capacity in general. Physical characteristics in investigating areas: After studying comprehensively the following curves, that is, curves of electric logs grads in 19 boreholes, curves of resistivity sounding in 28 boreholes, curves of resistivity sounding in 10 bedrock outcrop, the following results can be attained: the main stratum in this region, which include layers of dry sands with no water, water–bearing layers of Quaternary, and pre-Quaternary lithology, are shown apparently in the interfaces of different resistance and difference of electrical property in curves of electric logs and ones of electrical sounding. The electric characteristics of different stratum are corresponded to different curves of electrical sounding nearby boreholes. That is , the main stratum of depression basins and basins among hills corresponded to KQH type; the mainly marginal stratum of the basins above corresponded to KQ type; ridgy parts of blind bedrocks and front mountain region corresponded to KQ type; in areas of lake depression, where basement stratum is intrusive rocks or other ones with high resistor, it corresponded mainly to H type; where basement stratum is Jural tuff or basalt, it corresponded to Q type. When aquifer is more than 15 meters below the earth surface,the layers of dry sands is shown maximal K in electric sounding curves with maximal apparent resistivity more than 1000Ωm; When less than 10 meters below the earth surface, the curves are shown as QQ, Q, or H type. Lithology of water-bearing layers is simple and stable, and mainly is middle or tiny sands. Aquifers in Quaternary, whose apparent resistivity is between 120 to 140Ωm, more than 2 to 10 times smaller than the upper not-water-bearing sand layers, are usually shown in the descending parts of T or Q types. The varying thickness of aquifers can be shown by the relativedisplacement of horizontal coordinate. Most bedrock in this region are acidic tuff, and the like, in Upper Jurassic system, whose base plate is major electric marker. It is deep and widely extended, which is shown in the descending parts of the near end in KQ type curves, whose apparent resistivity exists between 60 to 280Ωm. The varied stratum interval of Quaternary is shown through displacement of Point Q in horizontal coordinate. Part of bedrock in this region is intrusive rocks with high resistive, whose apparent resistivity is between 400 to 680Ωm, more than 3 to 4 times higher than the overlying water-bearing layers. It is shown in the ascending part of the near end of KQH, KH types. Analyzing and explaining datum obtained: After analyzing quantatively geophysical prospecting datum, and, combined with geology and hydrogeology datum, features of electric sounding curves in different places can be obtained as follows: Type KQ1 is mainly in the west of Changxingta investigating unit; Type KQ2 is widely distributed, mainly in the central and southern parts of this unit; Type KQ3 is mainly in the northeastern part of this unit; Type KH1 is mainly in the front mountain region of east of this unit; Type H, Type Q are sparsely scattered in marsh areas of east of this unit and marsh areas nearby rivers of front mountain regions in mid-south of Yuanbaoshan investigating unit. By use of computer, master curve method, combine with electric reflection coefficient (K) method, and regression analytic method, taking account of known geology and hydrogeology datum, the following conclusion can be reached: the developing regularities of Quaternary stratumthickness in this region is its gradual increase from 20 to 200m. In general, the thickness of aquifers increases with growing thickness of Quaternary.
|
PDF Full Text Request