AN ABRUPT VARIATION EVENT OF STROMATOLITIC MICROSTRUCTURES IN THE NEOPROTEROZOIC AND ITS ORIGINATION BACKGROUND
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Abstract:
A sharp reduce in both the diversity and abundance of the stromatolites occurred at the boundary of the Neoproterozoic Shisanlitai and Majiatun Formations in southern Liaoning, as well as Weiji and Shijia Formations in northern Anhui and Jiangsu respectively. The abrupt change of stromatolitic microstructure accompanied with a distinct negative shift of carbon isotope values of carbonate carbon, is the key marker of an oceanographic chemical change, and consequently is of an isochoronic event. More evidences include the near synchronous occurrence of tussocky microstructure in the Pre Sinian strata, and its correlated shift of carbon isotope values in Majiatun and Shijia Formations, as well as formation I 6 of the Upper Riphean Atar Group in Mauritania. The tussocky microstructure is thought to be a special calcified blue alga, and temporal oceanic stratification and upwelling of the anoxia deep water afterwards may be the provenances of its calcification and the corresponding negative shift of carbon isotope values. The anomaly high hydrothemal flux in a time span from 850 Ma to 800 Ma indicated by the strontium isotopic ratios coincides with production of large amount of juvenile crust and rifting of a super continent, and gave rise to the transient oceanic stratification and enhancement of calcification of blue algae.
