Numerous sedimentary phosphorites in Southwest China were formed around the Precambrian–Cambrian transition(PC–C),including the upper Ediacaran Doushantuo Formation and lower Cambrian Gezhongwu Formation.The Gezhong...Numerous sedimentary phosphorites in Southwest China were formed around the Precambrian–Cambrian transition(PC–C),including the upper Ediacaran Doushantuo Formation and lower Cambrian Gezhongwu Formation.The Gezhongwu phosphorites in Zhijin exhibit marked rare earth element(REE)enrichment(>1000 ppm),and may represent new REE resources.Although the main characteristics of the Gezhongwu phosphorites have been well constrained,the REE enrichment mechanisms remain unclear.We undertook a comparative study of three typical sedimentary phosphorites with variable REE contents formed at the PC–C transition in central Guizhou Province,Southwest China.These include sections A and B of the Doushantuo phosphorites(560±8 Ma)from the Weng’an area(i.e.,WA-A and WA-B),and the Gezhongwu phosphorites(527±24 Ma)from the Zhijin area(ZJ).The phosphorites were investigated with state-of-the-art macroscale to nanoscale analytical techniques.In contrast to the extraordinary REE enrichment in the ZJ phosphorites(average RREE=1157 ppm),the phosphorites in WA-A(average RREE=234 ppm)and WA-B(average RREE=114 ppm)are REE-poor.Elemental mapping by laser ablation–inductively coupled plasma–mass spectrometry,along with transmission electron microscopy analyses,showed the REEs in the studied phosphorites are hosted in nanoscale francolites.The 87Sr/86Sr and Y/Ho ratios of the francolite grains indicate that greater terrigenous input may have led to more REE enrichment in the WA-A than WA-B phosphorites,but this cannot explain the extraordinary REE enrichment in the ZJ phosphorites.The F/P_(2)O_(5)values of the francolite grains in the ZJ phosphorites(~0.097)are higher than those in the WA-A(~0.084)and WA-B(~0.084)phosphorites,and the grain size of the francolite in the ZJ phosphorites(~89.9 nm)is larger than those in the WA-A(~56.6 nm)and WA-B(~57.4 nm)phosphorites,indicative of more intense reworking of the ZJ than WA phosphorites during early diagenesis.A plot of Nd concentration versus Ce/Ce^(*)reveals that lower sedimentation ra展开更多
基金This work was financially supported by the National Natural Science Foundation of China(Grant Nos.41825003,41921003)Key Research Program of the Institute of Geology&Geophysics,CAS(Grant No.IGGCAS-201901)+2 种基金Guangdong Special Support Program(Grant No.2019TX05L169)Science and Technology Planning Project of Guangdong Province,China(Grant No.2023B1212060048)Youth Innovation Promotion Association CAS(Grant No.2021353).
文摘Numerous sedimentary phosphorites in Southwest China were formed around the Precambrian–Cambrian transition(PC–C),including the upper Ediacaran Doushantuo Formation and lower Cambrian Gezhongwu Formation.The Gezhongwu phosphorites in Zhijin exhibit marked rare earth element(REE)enrichment(>1000 ppm),and may represent new REE resources.Although the main characteristics of the Gezhongwu phosphorites have been well constrained,the REE enrichment mechanisms remain unclear.We undertook a comparative study of three typical sedimentary phosphorites with variable REE contents formed at the PC–C transition in central Guizhou Province,Southwest China.These include sections A and B of the Doushantuo phosphorites(560±8 Ma)from the Weng’an area(i.e.,WA-A and WA-B),and the Gezhongwu phosphorites(527±24 Ma)from the Zhijin area(ZJ).The phosphorites were investigated with state-of-the-art macroscale to nanoscale analytical techniques.In contrast to the extraordinary REE enrichment in the ZJ phosphorites(average RREE=1157 ppm),the phosphorites in WA-A(average RREE=234 ppm)and WA-B(average RREE=114 ppm)are REE-poor.Elemental mapping by laser ablation–inductively coupled plasma–mass spectrometry,along with transmission electron microscopy analyses,showed the REEs in the studied phosphorites are hosted in nanoscale francolites.The 87Sr/86Sr and Y/Ho ratios of the francolite grains indicate that greater terrigenous input may have led to more REE enrichment in the WA-A than WA-B phosphorites,but this cannot explain the extraordinary REE enrichment in the ZJ phosphorites.The F/P_(2)O_(5)values of the francolite grains in the ZJ phosphorites(~0.097)are higher than those in the WA-A(~0.084)and WA-B(~0.084)phosphorites,and the grain size of the francolite in the ZJ phosphorites(~89.9 nm)is larger than those in the WA-A(~56.6 nm)and WA-B(~57.4 nm)phosphorites,indicative of more intense reworking of the ZJ than WA phosphorites during early diagenesis.A plot of Nd concentration versus Ce/Ce^(*)reveals that lower sedimentation ra
