Abstract Aims Underground fissure soil is an important soil resource in karst rocky desertification area, but there are few reports on its physical and chemical properties and soil ecological stoichiometry. This study aims at investigating the physicochemical properties, nutrient content and stoichiometric characteristics of subsurface fissured soils in karst areas, which will help to understand their intrinsic linkage mechanisms and provide a scientific basis for making full use of fissured soils. Methods Typical karst fissures were selected through a combination of field investigation and in-laboratory analysis, and soil physicochemical properties were determined through field sampling and indoor tests. Results We found that as the depth of the fissure soil layer increases, the silt content and clay content increase and the sand content and soil water content continue to decrease. The fissure soil is basically weakly alkaline. The TN content does not change much from the surface to the lower part of the fissure, and the AN, TP and AP contents in the fissure generally decrease. In general, SOC, nitrogen and phosphorus are mainly concentrated in the surface soil compared to the other soil layers in the fissure; the C/N, N/P and C/P ratios are higher in the upper part of the fissure; C/P and N/P are higher and C/ N is lower in SL, while the opposite is true in AL. Conclusions The low nutrient content and high ecological stoichiometry of karst rift soils suggest that rift soils in karst areas need more soil nutrient management, and improvement of quality status.
Lower Ordovician dolomites in the central Tarim basin are of various types and extensively distributed.Seven dolostone types could be documented based on fabrics and structures,which are crystalline dolomite,residual-grain dolomite,residual calcite dolomite,algal dolomite,cloudy centers and clear rims dolomite,clitellum dolomite and gypes dolomite.It's characterised by middle-high δ18O negative value(-3.2%~-8.7‰),low-middle δ13C negative value(-3%~-0.77‰),and high Z value of 118~123.Most diagenetic temperature calculated by empirical formulas using δ18O values are between 118 to 123℃,which indicates that the temperature degree of dolomitization is low,and so the kind of dolomite belongs to low temperature dolostone.These dolomites have also characteristics of low Mg/Ca and variable Fe/Mn ratio values.According to mineral composition analyzed by electron microprobe,dolomite monomineral can be divided into high Fe content and low Fe content species.87Sr/86Sr ratios of most samples are low(among 0.708 8~0.709 7),which are similar to seawater strontium isotope composition,and some are of high ratios between 0.710 1 and 0.710 9.These characteristics reveal that the origin of dolomite in the study area can be classified into penecontemporaneous dolomitization and burial dolomitization.According to Ordovican palaeogeographical evolution,the penecontemporaneous dolomitization arised in the seafloor environment,mainly in tidal flats or beach environment.And this kind of dolomite characterised by low diagenetic temperature,low 87Sr/86Sr ratios,and low Fe content dolomite minerals.The burial dolomitization can be interpreted by two diagentic models.One is seepage-reflux dolomitization during early shallow burial stage and characterised by low diagenetic temperature but high 87Sr/86Sr ratios,and high Fe content dolomite mineral.Another is deep burial dolomitization which occured in more strong reducible diagenetic enviornment during late deep burial stage.In general,the degree of dolomitization in burial diagentic enviorment is further enhanced and adjusted.The deep burial dolomite is characterised by high diagenetic temperature and high homogenization temperature of fluid inclusions,but low salinity.
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