Differences between the Upper and Lower Kellwasser Events and Productivity Variations during the Late Devonian Frasnian-Famennian Transition in Yangdi of Guilin, South China
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摘要:
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,δ13C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δ13C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.
Abstract: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.
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Key words:
- Devonian /
- Kellwasser event /
- δ13C /
- anoxic /
- productivity /
- Guilin /
- stratigraphy
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