Carbon isotopic record from Upper Devonian carbonates at Dongcun in Guilin, southern China, supporting the world- wide pattern of carbon isotope excursions during Frasnian-Famennian transition

Two positive d 13C excursions are presented in records from the Frasnian-Famennian (F-F) marine carbon-ate sediments in Europe, America, Africa, and Australia, having been considered as a worldwide pattern, and attrib-uted to enhanced organic carbon burial during the F-F biological mass extinction. However, this worldwide pattern has not been revealed from the well-deposited Late Devonian sequences in southern China. In this paper, a detailed inves-tigation has been made on the Late Devonian section at Dongcun, Guilin, southern China to constrain perturbations in d 13C of carbonates in the F-F deposited sequence. The result from this section also indicates two positive d 13C ex-cursions during the F-F transition. The first excursion with an amplitude of 1.5 occurred at the bottom of linguiformis Zone, later than the early excursion existing in the Late rhe-nana Zone of the Late Devonian profiles in other continents, especially, in central Europe. This difference has been ex-pected to be a result as conodont Palmatolepis linguiformis occurred earlier in southern China than other sites. The second excursion with an amplitude of 2.1 is located at the F-F boundary, same as the records from other continents. This result strongly supports the view that two carbon iso-tope positive excursions during the F-F transition are com-mon in carbonate sediments, resulting from worldwide in-creases of organic carbon burial intensity.

广西上泥盆统F—F界线碳同位素的变化特征

发生在晚泥盆世弗拉期(Frasnian)—法门期(Famennian)之交的生物灭绝事件(简称F—F事件)是古生代以来五大生物集群灭绝事件之一,其原因仍含糊不清。碳同位素研究显示,伴随F—F事件全球碳循环发生了显著的变化。但对中国南方F—F事件地层碳同位素变化特征的认识不够,缺乏系统的研究。对广西桂林杨堤上泥盆统灰岩剖面的碳同位素的分析结果表明,在上泥盆统存在两次碳同位素正偏移,分别出现在下rhenana带和F—F的界线,其中,出现在F—F界线的碳同位素正偏移与广西垌村以及欧美和非洲等地的上泥盆统F—F界线附近的碳同位素记录一致,且具有相近的变化幅度。进一步对广西桂林附近的杨堤和垌村剖面F—F界线的碳同位素组成变化模式的分析发现,这次正偏移可能是由多次次级变化组成,与F—F事件中生物的灭绝步骤相似。