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
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
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
Sm-Nd isotopic determination on small shelly fossils and collophanites collected from 3 Precambrian-Cambrian boundary sections,namely Meishucun of Jinning in Yunnan,Maidiping of Emei in Sichuan and Wushi of Kalpin in ...Sm-Nd isotopic determination on small shelly fossils and collophanites collected from 3 Precambrian-Cambrian boundary sections,namely Meishucun of Jinning in Yunnan,Maidiping of Emei in Sichuan and Wushi of Kalpin in Xinjiang,shows that the seawater masses of these three remotely separated areas were co-oceanic in the Precambrian-Cambrian transitional period,with a common seawater ε_(Nd)(T) val- ue of -6.6±0.5.The ε_(Nd)(T) value of the China's seawater ranges from -5.7 to-6.6 during the period from 610 Ma B.P.to 500 Ma B.P.The research suggests that there could be an 'Asiaustralian Ocean' be- sides the Panthalassa Ocean and the Iapetus Ocean at that time,and the China's seawater possibly belonged to the Asiaustralian Ocean.The Sm-Nd model age of the determined samples is about 1.8 Ga,which reflects the mean age of the continental source areas around the China's seawater.展开更多
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.
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 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
基金the National Natural Science Foundation of China
文摘Sm-Nd isotopic determination on small shelly fossils and collophanites collected from 3 Precambrian-Cambrian boundary sections,namely Meishucun of Jinning in Yunnan,Maidiping of Emei in Sichuan and Wushi of Kalpin in Xinjiang,shows that the seawater masses of these three remotely separated areas were co-oceanic in the Precambrian-Cambrian transitional period,with a common seawater ε_(Nd)(T) val- ue of -6.6±0.5.The ε_(Nd)(T) value of the China's seawater ranges from -5.7 to-6.6 during the period from 610 Ma B.P.to 500 Ma B.P.The research suggests that there could be an 'Asiaustralian Ocean' be- sides the Panthalassa Ocean and the Iapetus Ocean at that time,and the China's seawater possibly belonged to the Asiaustralian Ocean.The Sm-Nd model age of the determined samples is about 1.8 Ga,which reflects the mean age of the continental source areas around the China's seawater.
