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

摘要

Two positive δ~(13)C excursions are presented in records from the Frasnian-Famennian (F-F) marine carbonate sediments in Europe, America, Africa, and Australia, having been considered as a worldwide pattern, and attributed 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 investigation has been made on the Late Devonian section at Dongcun, Guilin, southern China to constrain perturbations in δ~(13)C of carbonates in the F-F deposited sequence. The result from this section also indicates two positive δ~(13)C excursions during the F-F transition. The first excursion with an amplitude of 1.5 per thousand 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 expected 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 per thousand is located at the F-F boundary, same as the records from other continents. This result strongly supports the view that two carbon isotope positive excursions during the F-F transition are common in carbonate sediments, resulting from worldwide increases of organic carbon burial intensity.