鄂尔多斯盆地白垩系主要含水岩组沉积岩相古地理对地下水水化学场形成和水质分布的影响

通过典型水文钻孔和露头剖面沉积地质、水文地质调查、样品测试及综合研究表明,鄂尔多斯盆地白垩系含水层形成时,北部环河组、洛河组均广泛发育河流相沉积,而南部环河组湖泊相为主、洛河组沙漠沙丘相广泛分布的沉积古地理格局,这对含水岩石中长石、粘土矿物、方解石、石膏等重要矿物组成和易溶盐含量及其空间分布形成明显控制,也控制了含水层和隔水层空间分布,并显著影响了深层地下水循环交替条件的区域分布变化。在沉积-成岩环境条件下,影响地下水水化学场形成和水质分布变化的主要水-岩作用包括硫酸盐、碳酸盐及硅酸盐矿物的溶解溶滤和阳离子交换作用等水文地球化学作用。受含水层沉积岩相古地理、地下水循环及水岩作用等因素控制,环河组、洛河组地下水总体表现为盆地北区TDS低、淡水发育、以HCO3型为主,南区TDS高、微咸水和咸水发育、以HCO3.SO4型为主的分布规律,地下水水化学和水质分布在北区分布变化小、在南区上下含水层分布变化复杂。

The effects of sedimentary facies and palaeogeography on the formation and distribution of the deep groundwater of the Cretaceous strata in the Ordos Basin

The integration of sedimentary geological and hydrogeological survey and sample analysis of the representative Cretaceous hydrological boreholes and outcrops has disclosed that during the formation of the Cretaceous aquifers, the fluvial deposits were wide-spread in the Huanhe and Luohe Formations in the northern part while the lake deposits occupied in the Huanhe Formation, and desert deposits occurred in the Luohe Formation in the southern part of the Ordos Basin. The framework of sedimentary facies and palaeogeography has exercised a major control not only on mineral compositions such as feldspar, clay minerals, calcite and gypsum in the aquifer systems, soluble salt contents and their spatial distribution, but also on the spatial distribution of the aquifers and impermeable beds, regional distribution of the deep groundwater circulation and alternation. The water-rock interactions influencing the formation of the hydrochemical fields and distribution of the groundwater include the dissolution of sulfate minerals, carbonate minerals and silicate minerals, rock salt leaching and cation exchange. Controlled by sedimentary facies and palaeogeography, groundwater circulation and water-rock interaction, the groundwater from the Huanhe and Luohe Formations are characterized by lower TDS, enriched freshwater and dominant HCO3type in the northern part whereas higher TDS, enriched brackish water-saline water, and HCO3 ＂ SO4type in the southern part of the basin.