Organic fraction of the total carbon burial flux deduced from carbon isotopes across the Permo-Triassic boundary at Meishan, Zhejiang Province, China

Abstract

By combining the carbon cycle model with the records of carbonate and organic (kerogen) carbon isotope, this paper presents the calculation of the fraction of organic carbon burial (forg) of beds 23–40 at the global boundary stratotype section and point (GSSP) of the Permian-Triassic boundary at Meishan, Zhejiang Province. The resulting calculation produces two episodes of forg maxima observed to occur at beds 23–24 and 27–29, which respectively corresponds to the two episodic anoxic events indicated by the flourish of green sulfur bacteria. Two episodic forg minima occurred at beds 25–26 and 32–34, generally coincident with the flourish of cyanobacteria (bed 26 and upper part of beds 29 to 34) as shown by the high value of 2-melthyhopnoanes. It appears that the forg is related to the redox conditions, with greater forg values observed under the reductive condition. The relationship between forg and the total organic carbon (TOC) content was complex. The forg value was low at some beds with a high TOC content (such as bed 26), while high observed at some beds with a low TOC content (e.g. bed 27). This association infers the important contribution of primary productivity to the TOC content. The original organic burial could be thus calculated through the configuration of the function of the primary productivity and forg, which can be used to correct the residual TOC measured today. This investigation indicates that compiling the organic-inorganic carbon isotopes with the carbon cycle model favors to understand the fraction of organic carbon burial, providing information for the reconstruction of the coupling among biota, environments and organic burial.