Preliminary Study Of The Ecostratigraphic Framework And The Primary Productivity Of The Ordovician In The Upper Yangtze Platform, South China

During the passed decades, many progresses have been achieved significantly in various respects of the Ordovician in China, including the biostratigraphy, the chronostratigraphy, the ecostratigraphy and the palaeoecology, as well as the sequence stratigraphy. However, the recognition of the related habitant-types （HT） in the Ordovician successions, the ecostratigraphic framework across different facies belts, as well as the estimation of the primary paleoproductivity is still nonexistent.Based on the classification of biological communities and the recognition of the habitat types of the Ordovician successions across the near-shore, off-shore, as well as the slope-basin facies belts, the initial Ordovician ecostratigraphic framework from the west to the east has been established preliminarily in the Upper Yangtze Platform. Furthermore, with the geochemical parameters （trace elements, stable isotopes, etc.） and the related data of the present seas, the primary productivity of the different Ordovician habitant-types in the Upper Yangtze Platform has been analyzed initially.With Ba, Al, Ti and other elements, the primary productivity of the succession at the Huanghuachang section in Yichang, Hubei Province, has been calculated. The productivity in the outer-shelf area （HTâ…£₁² -â…£₂²ï¼‰ is from 180 to 250 gCm^-2y^-1, the inner-shelf （Ⅲ12 -â…¢22） 65-280 Cm^-2y^-1, and the peritidal area （Ⅱ₁² -â…¡₂²ï¼‰ 120-390 Cm^-2y^-1. The overall trend of the productivities is in agreement with that of the present marine environments. It may indicate that the bio-Barium （Ba） can be regarded as a proper proxy to estimate the primary paleoprodoctivity of the geohistory time.On the other hand, the development of theδ¹³C （inorganic carbon） is coordinate with the change of the element Fe. While the negative shift of theδ¹³C corresponds to the relatively low productivity, the curve of the Fe has a similar shift, and vise versa. It may suggest that the element Fe can be also a proxy of the primary productivity of the Ordovician succession in the Upper Yangtze Platform.