High influx of carbon in walls of agglutinated foraminifers during the Permian–Triassic transition in global oceans

Abstract

The Permian–Triassic mass extinction is postulated to be related to the rapid volcanism that produced the Siberian flood basalt (Traps). Unrelated volcanic eruptions producing several episodes of ash falls synchronous with the Siberian Traps are found in South China and Australia. Such regional eruptions could have caused wildfires, burning of coal deposits, and the dispersion of coal fly ash. These eruptions introduced a major influx of carbon into the atmosphere and oceans that can be recognized in the wall structure of foraminiferal tests present in survival populations in the boundary interval strata. Analysis of free specimens of foraminifers recovered from residues of conodont samples taken at a Permian–Triassic boundary section at Lung Cam in northern Vietnam has revealed the presence of a significant amount of elemental carbon, along with oxygen and silica, in their test wall structure, but an absence of calcium carbonate. These foraminifers, identified as Rectocornuspira kalhori, Cornuspira mahajeri, and Earlandia spp. and whose tests previously were considered to be calcareous, are confirmed to be agglutinated, and are now referred to as Ammodiscus kalhori and Hyperammina deformis. Measurement of the ²⁰⁷Pb/²⁰⁴Pb ratios in pyrite clusters attached to the foraminiferal tests confirmed that these tests inherited the Pb in their outer layer from carbon-contaminated seawater. We conclude that the source of the carbon could have been either global coal fly ash or forest fire-dispersed carbon, or a combination of both, that was dispersed into the Palaeo-Tethys Ocean immediately after the end-Permian extinction event.

Keywords:

• foraminifers
• carbon
• lead isotopes
• pyrite clusters
• Permian–Triassic transition
• Vietnam

Acknowledgements

We thank Sue Ellwood for designing the sample method used and her aid in sampling. LTPL thanks Dr Dang Tran Huyen for his help in understanding the palaeobiology in the Lung Cam section. Drs B. Sen Gupta (Louisiana State University), M. Robinson (US Geological Survey), and V. Vuks (VSEGEI, Saint Petersburg, Russia) are graciously thanked for their constructive and valuable comments, which improved the manuscript. We are grateful to Dr R. Blakey (Northern Arizona University) for providing literature and a palaeogeographical map for the late Permian. We thank the Editor-in-Chief, Dr R. Stern, for suggestions to improve the manuscript.

Additional information

Funding

This work was partly supported by the National Science Foundation [grant number EAR-0745393]. LTPL thanks the Vietnam Institute of Geophysics for partial funding for this project.