This paper gives a brief report on the latest results in litho-, bio-, and chrono-stratigraphy obtained fromthe authors' further research on the Meishucun section during 1987-1988. More attention was paid to the s...This paper gives a brief report on the latest results in litho-, bio-, and chrono-stratigraphy obtained fromthe authors' further research on the Meishucun section during 1987-1988. More attention was paid to the studyof the microtexture of Lapworthella and some new materials of trace fossils. Phycodes pendum Seilacher, animportant index for correlation, was also discovered in the Zhongyicun Member. In the Yu' anshan Membermany worms, medusas and arthropods of the Chengjiang fauna have been found by other workers. Asupplemental study was made on the fossil zones of the Meishucunian stage. Based on new isotopic data, theage of the Precambrian-Cambrian boundary should now be 597 Ma. It is further suggested that point 'B' re-mains as an optimum selection for defining the Precambrian-Cambrian boundary.展开更多
The Meishucun section in Yunnan is the stratotype section for stratigraphic correlation of the Lower Cambrian strata across the Yangtze Block. Known for enriched small shelly fossils, it is a prominent section for inv...The Meishucun section in Yunnan is the stratotype section for stratigraphic correlation of the Lower Cambrian strata across the Yangtze Block. Known for enriched small shelly fossils, it is a prominent section for investigating the Early Cambrian phosphogenic event.Pasˇava et al.(Econ Geol 105:1047–1056, 2010) reported anomalously high PGE concentrations in this section, up to576 9 10-9(434 9 10-9Pt, 142 9 10-9Pd) for the total PGE concentrations of a K-bentonite sampled from the bottom of Bed 5. This finding can illustrate two significant statements:(1) in addition to the attested polymetallic NiMo-PGE ore layer, another potential PGE enrichment layer exists with PGE concentrations up to the mineralization level; and(2) acid volcanics have high PGE contents overturning conventional views. To inspect whether the anomalous PGE concentration is pervasive, we investigated Bed 5 of the Meishucun section systematically, and sampled from a profile with a thickness of 3.5 m. The major and trace element geochemistry indicate the Bed5 K-bentonite is derived from acid volcanic ash. PGE concentrations were determined repeatedly by isotope dilution-ICP-MS using improved digestion technique(Qi et al., in J Anal At Spectrom 26:1900–1904, 2011), and were duplicated by fire assay method. The results showed that each sample had total PGE concentrations of less than0.90 9 10-9, and Pt ? Pd concentrations of no higher than0.70 9 10-9. Combined with the petrological and mineralogical features, and trace and rare earth element analyses,it is inferred that no generality of PGE enrichment exists in Bed 5 and that the anomalous PGE concentration is likely due to the nugget effect of volcanic ash modified by currents in a shallow coastal environment.展开更多
This paper gives the detail description of Meishucun section , Yunnan , China . By studying biotic characteristics , analyzing isotopic age and comparing with the main Precambrian - Cambrian boundary sections in the w...This paper gives the detail description of Meishucun section , Yunnan , China . By studying biotic characteristics , analyzing isotopic age and comparing with the main Precambrian - Cambrian boundary sections in the world , we construct a global stratotype section and a point for the Precambrian-Cambrian boundary at Meishucun , which are of the convenient assessibility , abundant fossils of diverse groups , continuous sedimentation . perfect outcropping , lock of tectonic and metamorphic alteration , and have been deep studied in all related disciplines of sciences .展开更多
Determination of the age of the Precambrian-Cambrian boundary is critical in understanding early evolution of life on Earth. SIMS U-Pb zircon analyses of the Bed 5 tuff layer of the Meishucun section were carried out ...Determination of the age of the Precambrian-Cambrian boundary is critical in understanding early evolution of life on Earth. SIMS U-Pb zircon analyses of the Bed 5 tuff layer of the Meishucun section were carried out closely following the guidance of cath展开更多
The Meishucun secton has been recommended as an international candidate stratotype secton of thePrecambrian-Cambrian boundary. The paper deals with the palaeomagnetic study on the section. A total of159 palaeomagnetic...The Meishucun secton has been recommended as an international candidate stratotype secton of thePrecambrian-Cambrian boundary. The paper deals with the palaeomagnetic study on the section. A total of159 palaeomagnetic samples were successively collected from the platform-facies sequence of carbonates andphosphates at the section. Thermal demagnetization results indicate a great majority of the rocks at the sectionhave been strongly overprinted by recent magnetic field, but 57 samples have preserved remanentmagnetization with antipodal directions (mean D/I=4.2°/ 7.1°, K=9, α_(95) = 6.6°). Baaed on calculation,the location of the palaeomagnetic pole was at 68.8°N and 270.7°E, which is different from any palaeopolesobtained from younger Phanerozoic rocks in South China. The results reveal a polarity zonation which in-cludes at least 9 reversal events. A comparison of China's magnetostratigraphic records with those fromSiberia, Australia and the western U.S.A. shows that all the sections are characterized by frequent polarity re-versals.展开更多
文摘This paper gives a brief report on the latest results in litho-, bio-, and chrono-stratigraphy obtained fromthe authors' further research on the Meishucun section during 1987-1988. More attention was paid to the studyof the microtexture of Lapworthella and some new materials of trace fossils. Phycodes pendum Seilacher, animportant index for correlation, was also discovered in the Zhongyicun Member. In the Yu' anshan Membermany worms, medusas and arthropods of the Chengjiang fauna have been found by other workers. Asupplemental study was made on the fossil zones of the Meishucunian stage. Based on new isotopic data, theage of the Precambrian-Cambrian boundary should now be 597 Ma. It is further suggested that point 'B' re-mains as an optimum selection for defining the Precambrian-Cambrian boundary.
基金supported by National Science Foundation of China (Nos. 41072054, 40963002)
文摘The Meishucun section in Yunnan is the stratotype section for stratigraphic correlation of the Lower Cambrian strata across the Yangtze Block. Known for enriched small shelly fossils, it is a prominent section for investigating the Early Cambrian phosphogenic event.Pasˇava et al.(Econ Geol 105:1047–1056, 2010) reported anomalously high PGE concentrations in this section, up to576 9 10-9(434 9 10-9Pt, 142 9 10-9Pd) for the total PGE concentrations of a K-bentonite sampled from the bottom of Bed 5. This finding can illustrate two significant statements:(1) in addition to the attested polymetallic NiMo-PGE ore layer, another potential PGE enrichment layer exists with PGE concentrations up to the mineralization level; and(2) acid volcanics have high PGE contents overturning conventional views. To inspect whether the anomalous PGE concentration is pervasive, we investigated Bed 5 of the Meishucun section systematically, and sampled from a profile with a thickness of 3.5 m. The major and trace element geochemistry indicate the Bed5 K-bentonite is derived from acid volcanic ash. PGE concentrations were determined repeatedly by isotope dilution-ICP-MS using improved digestion technique(Qi et al., in J Anal At Spectrom 26:1900–1904, 2011), and were duplicated by fire assay method. The results showed that each sample had total PGE concentrations of less than0.90 9 10-9, and Pt ? Pd concentrations of no higher than0.70 9 10-9. Combined with the petrological and mineralogical features, and trace and rare earth element analyses,it is inferred that no generality of PGE enrichment exists in Bed 5 and that the anomalous PGE concentration is likely due to the nugget effect of volcanic ash modified by currents in a shallow coastal environment.
文摘This paper gives the detail description of Meishucun section , Yunnan , China . By studying biotic characteristics , analyzing isotopic age and comparing with the main Precambrian - Cambrian boundary sections in the world , we construct a global stratotype section and a point for the Precambrian-Cambrian boundary at Meishucun , which are of the convenient assessibility , abundant fossils of diverse groups , continuous sedimentation . perfect outcropping , lock of tectonic and metamorphic alteration , and have been deep studied in all related disciplines of sciences .
基金Supported by National Natural Science Foundation of China (Grant Nos. 40730211 and 40821091)
文摘Determination of the age of the Precambrian-Cambrian boundary is critical in understanding early evolution of life on Earth. SIMS U-Pb zircon analyses of the Bed 5 tuff layer of the Meishucun section were carried out closely following the guidance of cath
文摘The Meishucun secton has been recommended as an international candidate stratotype secton of thePrecambrian-Cambrian boundary. The paper deals with the palaeomagnetic study on the section. A total of159 palaeomagnetic samples were successively collected from the platform-facies sequence of carbonates andphosphates at the section. Thermal demagnetization results indicate a great majority of the rocks at the sectionhave been strongly overprinted by recent magnetic field, but 57 samples have preserved remanentmagnetization with antipodal directions (mean D/I=4.2°/ 7.1°, K=9, α_(95) = 6.6°). Baaed on calculation,the location of the palaeomagnetic pole was at 68.8°N and 270.7°E, which is different from any palaeopolesobtained from younger Phanerozoic rocks in South China. The results reveal a polarity zonation which in-cludes at least 9 reversal events. A comparison of China's magnetostratigraphic records with those fromSiberia, Australia and the western U.S.A. shows that all the sections are characterized by frequent polarity re-versals.
