广西桂林杨堤晚泥盆世弗拉期-法门期之交上、下 Kellwasser 事件的差异与海洋生产力变化

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

对广西桂林晚泥盆世弗拉期-法门期(Frasnian-Famennian,简称F-F)之交杨堤剖面的碳酸盐岩碳同位素、生物成因Ba、Al、Si和氧化还原指标的综合分析,表明该地区F-F之交生产力较低,且两次Kellwasser事件具有不同特点:下Kellwasser(LKW)事件时期并未出现明显缺氧环境,生态系统中初级生产力和最终生产力均相对较高,δ13 C小幅度正偏是由生产力上升引起;上Kellwasser(UKW)事件时期海平面上升,陆源输入物极少,氧含量急剧下降,初级生产力有所增加,最终生产力锐减,此时的δ13 C大幅正偏是由于缺氧条件下有机碳缓慢积累埋藏保存所致.

Extremely low productivity together with differences between the Lower and Upper Kellwasser events were found during the Late Devonian Frasnian-Famennian transition in the Yangdi section,Guilin,South China,which was paleogeographically situated at platform margin.Analysis of carbonateδ13C,biogenetic Ba,Al,Si and redox sensitive elements show oxic to dysoxic condition in the Lower Kellwasser event period with the small increase of both the primary productivity and the ecosystem ultimate productivity.The slightδ13C positive excursion of the Lower Kellwasser event was caused by the increased productivity.However during the Upper Kellwasser event period the primary productivity increased but the ultimate productivity sharply decreased,which means the great loss of biomass in the ecosystem.The remarkablyδ13C positive excursion was controlled by the accumulation of buried organic carbon in the anoxic circumstances with the simultaneous sea-level rise and reduced terrestrial input.