The Ediacaran and early Cambrian black shales are widespread across the South China Craton （Yangtze and Cathaysia blocks）. However, the trace element distribution patterns of the Ediacaran and early Cambrian black s...The Ediacaran and early Cambrian black shales are widespread across the South China Craton （Yangtze and Cathaysia blocks）. However, the trace element distribution patterns of the Ediacaran and early Cambrian black shales in the Cathaysia Block are still unclear. In this study, thirty- four black shale samples in the Lechangxia Group （Ediacaran） and thirteen black shale samples in the lower Bacun Group （early Cambrian） from Guangning area, western Guangdong Province, South China, were analyzed for major and trace elements concentrations. Compared to the upper continental crust, the Ediacaran black shales exhibit strongly enriched Se, Ga, and As with enrichment factor values （EF） higher than 10, significantly enrichedBi and Rb （10〉EF〉5）, weakly enriched Mo, Ba, Cs, V, In, Be, TI, and Th （5〉EF〉2）, normal U, Cr, Cd, Sc, Pb, Cu, and Li （2〉EF〉0.5）, and depleted Ni, Zn, Sr, and Co. Early Cambrian black shales display strongly enriched Se, Ga, and As, significantly enriched Ba, Bi, and Rb, weakly enriched Mo, Cs, Cd, V, U, Be, In, and TI, normal Sc, Th, Cr, Li, Cu, Ni, and Pb and depleted Co, Zn, and Sr. Moreover, Se is the most enriched trace element in the Ediacaran and early Cambrian black shales： concentrations vary from 0.25 to 30.09 ppm and 0.54 to 5.01 ppm, and averaging 4.84 and 1.72 ppm, with average EF values of 96.87 and 34.32, for the Ediacaran and early Cambrian shales respectively. The average concentration of Se in the Ediacaran black shales is 2.8 times higher than that of early Cambrian black shales. Se contents in the Ediacaran and early Cambrian black shales exhibit significant variation （P = 0.03）. Provenance analysis showed that Se contents of both the Ediacaran and early Cambrian black shales were without detrital provenance and volcanoclastic sources, hut of hydrothermal origin. The deep sources of Se and the presence of pyrite may explain the higher Se contents in the Ediacaran black shales. Similar with the Se-rich characteristics of the contemporaneous black shales in the south Qingling Mountain and Yangtze block, the Ediacaran and early Cambrian black shales in Guangning area, Cathaysia, are also enriched in Se, which may provide a clue for looking for the selenium-rich resources in western Guangdong Province.展开更多
The distribution and enrichment patterns of selenium(Se) in the E-?1 strata in the Yangtze Gorges area of South China were obtained. The geochemical characteristics of the significantly and non-significantly enriched ...The distribution and enrichment patterns of selenium(Se) in the E-?1 strata in the Yangtze Gorges area of South China were obtained. The geochemical characteristics of the significantly and non-significantly enriched strata of Se were analyzed.The observed enrichment factor(EF, relative to the upper continental crust) and concentration coefficient(CC, relative to the similar lithology in Eastern China) both suggest that Se is the most enriched/concentrated(SeEF=26.97, SeCC=48.04) among the analyzed23 trace elements the E-?1 strata. The normalized enrichment factor(EF′, EF after Al or Th normalized) shows Se is secondly enriched(SeEF′=218.73), which is slightly lower than cadmium(CdEF′=288.46) but significantly higher than the third enriched trace element arsenic(AsEF′=97.49). Se concentrations in the E-?1 strata vary from <10.5 to 30.08 ppm with an arithmetic mean value of 1.35 ppm. Compared to the Nantuo Formation, Se increased 11.78 times in the whole E-?1 strata and the average EF values are displayed as Shuijingtuo(92.58)>Yanjiahe(54.45)>Doushantuo(24.72)>Dengying(2.48)>Shipai(1.95)>lower Tianheban(1.24)Formations. Se concentrations in the E-?1 strata are best displayed on natural logarithm normal quantile-quantile(Q-Q) plots and shown as a positive-skewed distribution pattern. The Se significantly enriched(EF>10) strata sequences mainly include the lower and upper Doushantuo member II(DST-II), top DST-III, DST-IV, the basal and upper Yanjiahe Formation, and lower and upper Shuijingtuo Formation. Geochemical characteristics indicate that Se concentrations in the significantly enriched strata were generally influenced by terrigenous detrital as well as the combined action of single or multiple factors, such as hydrotherm,volcanic debris and deep source. Moreover, pyrite and organic matter promoted the enrichment of Se in the upper DST-II, DST-IV,upper Shuijingtuo Formation and lower DST-II, upper Shuijingtuo Formation, respectively. The Se concentrations in the not significantly enriched strata(except for DST-I, middle Shuijingtuo Formation, Shipai Formation and lower Tianheban Formation)were also influenced by terrigenous detrital, but other enrichment activities(e.g., hydrothermal, volcanic debris, and deep source)were generally insignificant.展开更多
基金the National Natural Science Foundation of China (Grant No.41172310, 41472322 and 40872210)the National Basic Research Program of China (Grant No.2014CB238906)the Local Science and Technology Tasks "Distribution Patterns and Prospect of Exploitation and Utilization of Selenium in Foshan area, Guangdong" and "Construction for Laboratory of Selenium Resources Comprehensive Utilization"
文摘The Ediacaran and early Cambrian black shales are widespread across the South China Craton （Yangtze and Cathaysia blocks）. However, the trace element distribution patterns of the Ediacaran and early Cambrian black shales in the Cathaysia Block are still unclear. In this study, thirty- four black shale samples in the Lechangxia Group （Ediacaran） and thirteen black shale samples in the lower Bacun Group （early Cambrian） from Guangning area, western Guangdong Province, South China, were analyzed for major and trace elements concentrations. Compared to the upper continental crust, the Ediacaran black shales exhibit strongly enriched Se, Ga, and As with enrichment factor values （EF） higher than 10, significantly enrichedBi and Rb （10〉EF〉5）, weakly enriched Mo, Ba, Cs, V, In, Be, TI, and Th （5〉EF〉2）, normal U, Cr, Cd, Sc, Pb, Cu, and Li （2〉EF〉0.5）, and depleted Ni, Zn, Sr, and Co. Early Cambrian black shales display strongly enriched Se, Ga, and As, significantly enriched Ba, Bi, and Rb, weakly enriched Mo, Cs, Cd, V, U, Be, In, and TI, normal Sc, Th, Cr, Li, Cu, Ni, and Pb and depleted Co, Zn, and Sr. Moreover, Se is the most enriched trace element in the Ediacaran and early Cambrian black shales： concentrations vary from 0.25 to 30.09 ppm and 0.54 to 5.01 ppm, and averaging 4.84 and 1.72 ppm, with average EF values of 96.87 and 34.32, for the Ediacaran and early Cambrian shales respectively. The average concentration of Se in the Ediacaran black shales is 2.8 times higher than that of early Cambrian black shales. Se contents in the Ediacaran and early Cambrian black shales exhibit significant variation （P = 0.03）. Provenance analysis showed that Se contents of both the Ediacaran and early Cambrian black shales were without detrital provenance and volcanoclastic sources, hut of hydrothermal origin. The deep sources of Se and the presence of pyrite may explain the higher Se contents in the Ediacaran black shales. Similar with the Se-rich characteristics of the contemporaneous black shales in the south Qingling Mountain and Yangtze block, the Ediacaran and early Cambrian black shales in Guangning area, Cathaysia, are also enriched in Se, which may provide a clue for looking for the selenium-rich resources in western Guangdong Province.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41172310 & 41472322)the National Basic Research Program of China (Grant No. 2014CB238906)
文摘The distribution and enrichment patterns of selenium(Se) in the E-?1 strata in the Yangtze Gorges area of South China were obtained. The geochemical characteristics of the significantly and non-significantly enriched strata of Se were analyzed.The observed enrichment factor(EF, relative to the upper continental crust) and concentration coefficient(CC, relative to the similar lithology in Eastern China) both suggest that Se is the most enriched/concentrated(SeEF=26.97, SeCC=48.04) among the analyzed23 trace elements the E-?1 strata. The normalized enrichment factor(EF′, EF after Al or Th normalized) shows Se is secondly enriched(SeEF′=218.73), which is slightly lower than cadmium(CdEF′=288.46) but significantly higher than the third enriched trace element arsenic(AsEF′=97.49). Se concentrations in the E-?1 strata vary from <10.5 to 30.08 ppm with an arithmetic mean value of 1.35 ppm. Compared to the Nantuo Formation, Se increased 11.78 times in the whole E-?1 strata and the average EF values are displayed as Shuijingtuo(92.58)>Yanjiahe(54.45)>Doushantuo(24.72)>Dengying(2.48)>Shipai(1.95)>lower Tianheban(1.24)Formations. Se concentrations in the E-?1 strata are best displayed on natural logarithm normal quantile-quantile(Q-Q) plots and shown as a positive-skewed distribution pattern. The Se significantly enriched(EF>10) strata sequences mainly include the lower and upper Doushantuo member II(DST-II), top DST-III, DST-IV, the basal and upper Yanjiahe Formation, and lower and upper Shuijingtuo Formation. Geochemical characteristics indicate that Se concentrations in the significantly enriched strata were generally influenced by terrigenous detrital as well as the combined action of single or multiple factors, such as hydrotherm,volcanic debris and deep source. Moreover, pyrite and organic matter promoted the enrichment of Se in the upper DST-II, DST-IV,upper Shuijingtuo Formation and lower DST-II, upper Shuijingtuo Formation, respectively. The Se concentrations in the not significantly enriched strata(except for DST-I, middle Shuijingtuo Formation, Shipai Formation and lower Tianheban Formation)were also influenced by terrigenous detrital, but other enrichment activities(e.g., hydrothermal, volcanic debris, and deep source)were generally insignificant.
