Differences between the Upper and Lower Kellwasser Events and Productivity  Variations during the Late Devonian Frasnian-Famennian  Transition in Yangdi of Guilin, South China

Extremely1ow productivity together with differences between the Lower and Upper Ke11wasser events were found during the LateDevonian Frasnian-Famennian transition in the Yangdi section, Guilin, South China, which was paleogeographica11y situated at platform margin.Analysis of carbonate013C, biogenetic Ba, A1, Si and redox sensitive elements show oxic to dysoxic condition in the Lower Ke11wasser event period with the sma11 increase of both the primary productivity and the ecosystem ultimate productivity.The slight013C positive excursion of the Lower Ke11wasser event was caused by the increased productivity. However during the Upper Ke11- wasser event period the primary productivity increased but the ultimate productivity sharply decreased, which means the great1oss of biomass in the ecosystem. The remarkably013C positive excursion was contro11ed by the accumulation of buried organic carbon in the anoxic circumstances with the simultaneous sea-1eve1 rise and reduced terrestria1 input.