Initial Conference Of The Ecostratigraphic Framework And Primary Productivity, Silurian, Upper Yangtze Region, China

As the representative area of the Silurian in China, significant progresses in various respects have been achieved during the passed decades that focused mainly on the lithostratigraphy and biostratigraphy. However, the ecostratigraphy is relatively lack studied, and in particular, both the ecostratigraphic framework across different facies belts and the estimation of the primary productivity are nonexistent.Three typical outcrop sections, the Wengxiang of Kaili in Guizhou, the Wangjiagou of Wangcang in Sichuan, as well as the Bajiaokou of Ziyang in Shaanxi, have been selected from the south towards the north in the Upper Yangtze Platform. They represent the different facies belts from the near-shore area, the off-shore or inner-shelf, to the slope-basin area, respectively. Following the principal methods of the ecostratigraphy, all the different eco-communities with different habitant-types (HT) at the typical section have been recognized. Based on the biosgratigraphic data, all the three sections have been tried to correlate with each other. Consequently, the Silurian ecostratigraphic framework across different facies belts in the Upper Yangtze Platform has been established preliminarily.On the basis of the ecostratigraphical framework, the primary productivity of the Silurian habitant-types in the Upper Yangtze Platform has been estimated preliminarily, which represented by the Wangjiagou section, Wangcang, Sichuan. Referring the previous examples, the bio-Barium is chosen as the proxy for the initial estimation of the primary productivity. Meanwhile, the trace elements Al and P, and the ratio of Al / Ti, have been tried to estimate it qualitatively. The results show that the primary productivity of the habitant-type in the peritidal-subtidal area is 973-1110 gCm-2y-1, the inner shelf is 960-1300 gCm-2y-1, and the outer shelf, 139-197 gCm-2y-1. On the other hand, according to the data in the present South China Sea and the south of the East China Sea, the primary productivity in the peritidal-subtidal area is 600-1000 gCm-2y-1, the inner shelf is 400-600 gCm-2y-1, and the outer shelf, 100-400 gCm-2y-1. Because both the primary productions of the Silurian habitant-type estimated by the bio-Barium and that of the present seas around China are comparable, it suggests that the bio-Barium can be served as a quite good proxy of the primary paleoproductivity. Moreover, it also suggests that the primary productivity may be estimated and recovered with the comparison between the same habitant-type in different areas. The present analysis of the primary productivity can lay the foundation for the further evaluation of the potential source rock levels from the viewpoint of the geobiology.