Cadmium Content Characteristics Of Carbonate Rocks In The Adjacent Karst Areas Of Yunnan,Guizhou And Guangxi

The distribution area of carbonate rocks in China is about 1.3 million km~2,and karst landforms are widely developed,mainly concentrated in Guangxi,Yunnan and Guizhou provinces(regions).A large number of related studies have shown that the soils covered by carbonate rocks generally have cadmium anomalies,which are mainly derived from the soil-forming parent material-carbonate rocks.In this paper,through field investigations of karst areas in the adjacent areas of Yunnan,Guizhou and Guangxi,carbonate samples from different locations in different locations were collected.After analyzing the content of cadmium in these carbonate samples,preliminary understanding of different areas and the characteristics of cadmium content in carbonate rocks in different eras,and a preliminary discussion on the factors affecting the cadmium content.The research results can provide necessary data for the in-depth study of the sources of soil cadmium anomalies in karst areas,and can provide a basis for the sources of cadmium pollution and the restoration and management of karst ecological environment.After preliminary data collection and field sampling,the paper collected a total of 184 rock samples and 35 soil samples.Through the detection and analysis of the sampled products,the distribution characteristics of cadmium content in carbonate samples and soil samples in the study area were compared and analyzed,and the following conclusions were mainly drawn:1.The maximum cadmium content in devonian carbonate rocks is 6.16mg/kg,and the average value is 0.405mg/kg.Compared with the average value of cadmium in crustal carbonate rocks(0.035mg/kg),the number of samples not less than the average value is 25,and the number of samples more than 10 times is 3,accounting for about 12%.The maximum content of cadmium in carboniferous carbonate rocks was 4.22mg/kg and the average value was 0.441mg/kg.Compared with the average value of cadmium in crustal carbonate rocks(0.035mg/kg),the number of samples exceeding the average value was 34,and the number of samples exceeding 10 times was13,accounting for 31%.The cadmium content of carbonate rocks in the Permian system ranged from 0.083 to 3.22mg/kg,with an average value of 0.793mg/kg.Compared with the average value of cadmium in the crust carbonate rocks(0.035mg/kg),all 38 samples exceeded the average value,and the number of samples over 10 times was 28,accounting for 74%.The maximum content of cadmium in Triassic carbonate rocks is 4.16mg/kg,and the average value is 0.208mg/kg.Compared with the average value of cadmium in the crust carbonate rocks(0.035mg/kg),the number of samples exceeding the average value is 47,and the number of samples exceeding 10times is 9,accounting for 12%.2.The statistical results show that cadmium in carbonate rocks of different ages in the study area is in the order of carboniferous>devonian>Triassic.The cadmium content of carbonate rocks of early devonian is higher than that of middle devonian.The content of cadmium in carbonate rocks of middle Permian is higher than that of early Permian.The cadmium content of Triassic carbonate rocks is as follows:the late Triassic>early Triassic>middle Triassic,and the cadmium content of the four late Triassic carbonate rocks is also as follows:the first stage of the franc formation(bamboo-slope section-wanyao section),the second stage of>the franc formation(laishicaceae section),the southern formation>the middle Triassic.3.The cadmium content in the Permian carbonate rocks of the three provinces is as follows:Guizhou>Yunnan;The cadmium content of carboniferous carbonate rocks is as follows:Guangxi>Guizhou>Yunnan;The cadmium content of devonian carbonate rocks is as follows:Guangxi>Yunnan;The cadmium content of Triassic carbonate rocks is as follows:Guizhou>Guangxi>Yunnan.4.The contents of cadmium in the soil of carbonate overburden areas in different ages were successively from the largest to the smallest:Carboniferous>Triassic>Devonian>Cambrian system,and the contents of cadmium in the soil all exceeded the contents of cadmium in the corresponding carbonate rocks.5.The content of cadmium in the soil of the study area was from the largest to the smallest:Guangxi>Guizhou>Yunnan.The collected soil total cadmium content reached 145.46 mg/kg,with an average content of 3.828 mg/kg,and the cadmium content ranged from 0.027 to 23 mg/kg.The maximum value was about 76.667 times higher than the national soil environmental quality level ii standard and 327.113 times higher than the supranational soil cadmium background value.