This study reviews the distribution of groundwater salinity in an arid desert transition zone. By combining field experiments and computer simulation models we make a comprehensive analysis of the formation mechanism of fresh groundwater in relation to the paleogeographic conditions of lithofacies, the geochemical characteristics of the aquifer media, salt deliverability in the vadose zone and prevailing hydrodynamic conditions. The results demonstrate that (1) the lacustrine facies deposition stratum of the Huanhe formation in the Cretaceous system provides a brackish-salt groundwater environment; (2) the average salinity of parent rocks are approximately 440 mg/kg and 4 371 mg/kg in the Quaternary eolian sand and the Cretaceous Huanhe formation respectively, suggesting that parent rocks are the principal controlling factor in the distribution of groundwater quality given that mineral and chemical composition of the eolian sand is simpler than that of the Huanhe formation; (3) average groundwater flow rates are approximately 0.25 m/d and 0.1 m/d in eolian sand and Huanhe formation aquifers respectively, indicating that hydrodynamic conditions play an important role in driving in the formation and evolution of fresh groundwater; (4) The salinity deliverability in the vadose zone overlying the aeolian sand and Huanhe formation aquifers are approximately 15.97 mg/L and 220.42 mg/L respectively, signifying that the combination of lithology and salt content of vadose zone, rainfall infiltration, evapotranspiration and concentration heavily influence the formation, distribution and evolution of groundwater quality. This study can provide a scientific basis for the sustainable development and utilization of groundwater resources in arid areas. 相似文献
Desert varnish of pristine sandstone and petroglyph surfaces from Takabart Kabort (Naturalistic Bubaline Art School) and Alamas (Tanzina Art School) can be well classified by their (SiO2+Al2O3):MnO2, Al2O3:SiO2, and P2O5:CaO ratios. Specific ratios are due to the occurrence of clay minerals like illite, kaolinite, smectite, and feldspar, quartz, carbonates like calcite and dolomite, manganese oxyhydroxides, and apatite. Their occurrence corresponds to the local origin and composition of the primary aeolian material.
In general, the analyzed desert varnish shows lamination patterns characterized by alternating MnO2-rich and -poor layers (25 wt% MnO2) at rather constant iron oxyhydroxide content (6 wt% Fe2O3). Varnish on non-engraved surfaces exhibits three MnO2-rich layers, whereas varnish-coated petroglyphs reveal minor lamination patterns corresponding to the dating of petroglyphs by rock art. The older Naturalistic Bubaline Art School petroglyphs (about 6–4 ka BP) and the younger Tazina Art School petroglyphs (about 3.8–3 ka BP) contain only two and one MnO2-rich layer, respectively. It is assumed that the occurrence of such microlaminations is caused by climate changes in North Africa. Three humid periods are discerned from the Terminal Pleistocene to Holocene in the literature. Such periods are suitable to induce manganese accumulation by biotic and abiotic processes. Accordingly, the distinct lamination patterns gained from this study verify the dating of petroglyphs by rock art. From another point of view, classification of the above petroglyphs may be provided by analyses of microlaminations independently on cultural historical aspects. 相似文献