The modern Black Sea has a mixed upper layer in the top 150-200 m of the water column, below which the water is anoxic, separated from the mixed layer by a redox boundary. There is limited vertical movement of water. Pyrite framboids form in the water column of the anoxic zone, then have been traditionally interpreted to sink immediately and accumulate in the sediments of the Black Sea. Thus the occurrence of framboids in sediments in the rock record is widely interpreted to indicate poorly oxygenated to anoxic conditions in ancient environments. However, in the Permian-Triassic boundary (PTB) microbialites of South China, which formed in shallow marine conditions in contact with the atmosphere, the published occurrence of framboids is inconsistent with abundant gastropod and ostracod shells in the microbialite. Furthermore, in the modern Black Sea, (a) framboids may be suspended, attached to organic matter in the water column, thus not settle to the sea floor immediately after formation; and (b) the redox zone is an unstable complex area subject to rapid vertical water movement including occasional upwelling. The model presented here supposes that upwelling through the redox zone can lead to upward transport of suspended pyrite framboids into the mixed layer. Advective circulation could then draw suspended framboids onto the shelf to be deposited in oxygenated sediments. In the Permian-Triassic transition, if framboids were upwelled from below the redox boundary and mixed with oxygenated waters, sediment deposited in these conditions could provide a mixed signal for potentially misleading interpretations of low oxygen conditions. However, stratigraphic sampling resolution of post-extinction microbialites is currently insufficient to demonstrate possible separation of framboid-bearing layers from those where framboids are absent.
Profound differences between microbialite constructors and sequences between the western and eastern Tethys demonstrate barriers to migration of microbial organisms. However, framboid occurrences in both areas indicate upwelling and emphasize vertical movement of water from the lower to upper ocean, yet the mixed layer advective motion may not have been as effective as in modern oceans. In the modern Black Sea, such advection is highly effective in water mixing, and provides an interesting contrast with the PTB times.
I am most grateful to scientists at the P. P. Shirshov Institute of Oceanology, Moscow, for support and discussions during research visits to the Black Sea in 2012 and 2013. I particularly thank Alexander Ostrovskii for discussion on Black Sea processes and am indebted to Victoria Putans, Nikolai Esin and Kolya Esin for logistic support. Max McGuire, Noel Healy, Maria Zhdan and Tanya Zhdan are thanked for their support in Russia. Russian work was supported by EU-funded project PIRSES-GA-2009-247512. Prof. Zeng-Zhao Feng and Prof. Yong-Biao Wang are thanked for their comments on an earlier draft. This paper contributes to: (a) project “CLIMSEAS”: Climate Change and Inland Seas: Phenomena, Feedback and Uncertainties, the Physical Science Basis; and (b) project IGCP630: “Permian-Triassic climatic and environmental extremes and biotic response”.
Algeo, T. J., Kuwahara, K., Sano, H., Bates, S., Lyons, T., Elswick, E., Hinnov, L., Ellwood, B., Moser, J., Barry Maynard, J. B., 2010. Spatial variation in sediment fluxes, redox conditions, and productivity in the Permian-Triassic Panthalassic Ocean. Palaeogeography, Palaeoclimatology, Palaeoecology, 308: 65-83.
Baud, A., Bernecker, M., (eds), 2010. The Permian-Triassic transition in the Oman Mountains. IGCP 572 Field Guide Book 2: GUtech, Muscat, 109 pp.
Bond, D. P. G., Wignall, P. B., 2010. Pyrite framboid study of Permian-Triassic boundary sections: A complex anoxic event and its relationship to contemporaneous mass extinction. GSA Bulletin, 28: 1265-1279.
Collin, P. -Y., Kershaw, S., Tribovillard, N., Forel, M. -B., Crasquin, S., 2012. Geochemistry of post-extinction microbialites as a powerful tool to assess the oxygenation of shallow marine water in the immediate aftermath of the end-Permian mass extinction. 29th IAS Meeting of Sedimentology, Schladming Dachstein, 10-13 September 2012, Theme 8: Hazards, events, climate signatures. Poster Abstract T8 S3 from the Late Permian to the Middle Triassic: Perturbations around the Permian/Triassic boundary, 458 pp.
Crasquin-Soleau, S., Kershaw, S., 2005. Ostracod fauna from the Permian-Triassic boundary interval of South China (Huaying Mountains, eastern Sichuan Province): Palaeoenvironmental significance. Palaeogeography, Palaeoclimatology, Palaeoecology, 217: 131-141.
Danovaro, R., Dell’Anno, A., Pusceddu, A., Gambi, C., Heiner, I., Kristensen, R. M., 2010. First metazoa living permanently in anoxic conditions. BMC Biology, 8: 30, doi: 10.1186/1741-7007-8-30.
Falina, A., Sarafanov, A., Volkov, I., 2007. Warm intrusions in the intermediate layer (150-500 m) of the Black Sea eastern gyre interior. Geophysical Research Letters, 34: 22.
Forel, M. -B., Crasquin, S., Kershaw, S., Feng, Q. L., Collin, P. -Y., 2009. Ostracods (Crustacea) and water oxygenation in the earliest Triassic of South China: Implications for oceanic events at the end-Permian mass extinction. Australian Journal of Earth Sciences, 56: 815-823.
Forel, M. -B., Crasquin, S., Kershaw, S., Collin, P. -Y., 2013. In the aftermath of the end-Permian extinction: The microbialite refuge? Terra Nova, 25: 137-143.
Gingras, M., Hagadorn, J. W., Seilacher, A., Lalonde, S. V., Pecoits, E., Petrash, D., Konhauser, K., 2011. Possible evolution of mobile animals in association with microbial mats. Nature Geoscience, 4: 372-375.
Ivanova, E. V., Murdmaa, I. O., Chepalyga, A. L., Cronin, T. M., Pasechnik, I. V., Levchenko, O. V., Howe, S. S., Manushkina, A. V., Platonova, E. A., 2007. Holocene sea-level oscillations and environmental changes on the eastern Black Sea shelf. Palaeogeography, Palaeoclimatology, Palaeoecology, 246: 228-259.
Kershaw, S., 2000. Oceanography: An Earth Science Perspective. Stanley Thornes, Cheltenham, UK, 276 pp.
Kershaw, S., Crasquin, S., Li, Y., Collin, P. Y., Forel, M. -B., Mu, X., Baud, A., Wang, Y., Xie, S., Maurer, F., Guo, L., 2012. Microbialites and global environmental change across the Permian-Triassic boundary: A synthesis. Geobiology, 10: 25-47.
Kidder, D. L., Worsley, T. R., 2004. Causes and consequences of extreme Permo-Triassic warming to globally equable climate and relation to the Permo-Triassic extinction and recovery. Palaeogeography, Palaeoclimatology, Palaeoecology, 203: 207-237.
Knoll, A. H., Fischer, W. W., 2011. Skeletons and ocean chemistry: The long view. In: Gattuso, J. -P., Hansson, L., (eds). In Ocean Acidification. Oxford: Oxford University Press, 67-82.
Liao, W., Wang, Y., Kershaw, S., Weng, Z., Yang, H., 2010. Shallow marine dysoxia across the Permian-Triassic boundary; evidence from pyrite framboids in the microbialite in South China. Sedimentary Geology, 232: 77-83.
Luo, G., Wang, Y., Grice, K., Kershaw, S., Algeo, T. J., Ruan, X., Yang, H., Jia, C., Xie, S., 2013. Microbial-algal community changes during the latest Permian ecological crisis: Evidence from lipid biomarkers at Cili, South China. Global and Planetary Change, 105: 36-51.
Mihailov, M. -E., Tomescu-Chivu, M. -I., Dima, V., 2012. Black Sea water dynamics on the Romanian littoral — Case study: The upwelling phenomena. Romanian Reports in Physics, 64: 232-245.
Ostrovskii, A., Zatsepin, A., 2011. Short-term hydrophysical and biological variability over the northeastern Black Sea continental slope as inferred from multiparametric tethered profiler surveys. Ocean Dynamics, 61: 797-806.
Paytan, A., Gray, E. T., Ma, Z., Erhardt, A., Faul, K., 2011. Application of sulphur isotopes for stratigraphic correlation. Isotopes in Environmental and Health Studies, doi: 10.1080/10256016.2011.625423.
Tuzhilkin, V. S., 2008. General Circulation. In: Hutzinger, O., (ed). The Handbook of Environmental Chemistry, Volume 5: Water Pollution, Part Q, 159-194.
Tang, H., Tan, X., Yang, X., Zhang, Q., Su, C., Li, H., Chen, H., 2014. Can microbialites represent a harsh environment? The evidence from the Permian-Triassic boundary section, northwestern Sichuan Basin, South China. Abstract, page 685, 19th International Sedimentological Congress, 18-22 August, Geneva, Switzerland.
Tian, L., Tong, J., Algeo, T. J., Song, H., Song, H., Chu, D., Shi, L., Bottjer, D. J., 2014. Reconstruction of Early Triassic ocean redox conditions based on framboidal pyrite from the Nanpanjiang Basin, South China. Palaeogeography, Palaeoclimatology, Palaeoecology, 412: 68-79.
Volkov, I. I., Rimskaya-Korsakova, M. N., Grinenko, V. A., 2007. Chemical and isotopic uniformity of the bottom convective water layer in the Black Sea. Doklady Earth Sciences, 414: 625-629.
Volkov, I. I., Neretin, L. N., 2008. Hydrogen sulphide in the Black Sea. In: Hutzinger, O., (ed). The Handbook of Environmental Chemistry, Volume 5: Water Pollution, Part Q, 309-331.
Wang, Y., Tong, J., Wang, J., Zhou, X., 2005. Calcimicrobialite after end-Permian mass extinction in South China and its palaeoenvironmental significance. Chinese Science Bulletin, 50: 665-671.
Wilkin, R. T., Barnes, H. L., Brantley, S. L., 1996. The size distribution of framboidal pyrite in modern sediments: An indicator of redox conditions. Geochimica et Cosmochimica Acta, 60: 3897-3912.
Zatsepin, A. G., Arashkevich, E. G., Kremenetskiy, V. V., 2007. Black Sea dynamics and its impact on plankton communities. Rapp. Comm. int. Mer Médit., 38: 23.
2015, Vol. 4 
