Analysis of the environmental conditions in Upper Permian deposits of NW Iran based on redox-sensitive trace metals


1 Assist. Prof., Dept., of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran

2 Ph. D. (graduated), Dept., of Geology, Faculty of Sciences, Lorestan University, Khorramabad, Iran


The lack of oxygen is considered as one of the main causes of mass extinction before Permian-Triassic boundary (ca. 251.9 million years ago). In this study redox conditions of Upper Permian shales of the Ali Bashi and Zal sections in SW Iran have been evaluated using redox-sensitive trace elements in order to examine the geochemical status of the seawater during Late Permian as well as before and after extinction horizon. According to V/Cr and V/(V +Ni) ratios the redox conditions throughout Upper Permian successions in both sections change from oxic/dysoxic to suboxic and in uppermost Changhsingian Aras Member which is located immediately after extinction horizon the increase of these for-mentioned rations are evident. The Mo/U authigenic ratios in both sections demonstrate their lower values than Mo/U molar ratio of seawater (~7.5-7.9) and MoEF and UEF covariate plots show the position of samples of two study sections in oxic/dysoxic to suboxic zones. Considering the obtained results, although there is evidence of low oxygen conditions in some parts of the Upper Permian deposits, the lack of oxygen and anoxic condition did not happen in extinction horizon and even in the Aras Member there was a suboxic status. Therefore, other mechanisms should be investigated for the low faunal diversity of the Upper portion of the Upper Permian deposits of the Ali Bashi and Zal sections.


Alavi, M (1991) Tectonic map of the Middle East, Geological Survey of Iran, Scale: 1:5000000.
Algeo, T. J (2004) Can marine anoxic events draw down the trace element inventory of seawater? Geology, 32: 1057-1060.
Algeo, T. J., Maynard, J. B (2004) Trace-element behavior and redox facies in core shales of Upper Pennsylvanian Kansas-type cyclothems. Chemical Geology, 206: 289-318.
Algeo, T. J., Tribovillard, N (2009) Environmental analysis of paleoceanographic systems based on molybdenum-uranium covariation. Chemical Geology, 268(3): 211-225.
Algeo, T. J., Li, C (2020) Redox classification and calibration of redox thresholds in sedimentary. Geochimica et Cosmochimica Acta, 287: 8-26.
Algeo, T. J.,  Hinnov, L., Moser, J., Maynard, J. B., Elswick, E., Kuwahara, K., Sano, H (2010) Changes in productivity and redox conditions in the Panthalassic Ocean during the latest Permian. Geology, 38(2):187-190.
Arefifard, S., Baud, A (2022) Depositional environment and sequence stratigraphy architecture of continuous Upper Permian and Lowermost Triassic deep marine deposits in NW and SW Iran. Palaeogeography, Palaeocli­matology, Palaeoecology, 603: 111187.
 Bond, D. P. G., Wignall, P. B (2014) Large igneous prov­inces and mass extinctions: an update. In: Keller, G, Kerr, A C, (Eds.), Volcanism, Impacts, and Mass Extinctions: Causes and Effects. Geological Society of America Special Paper, 505: 29-55.
Bond, D. P. G., Grasby, S. E (2017) On the causes of mass extinctions. Palaeogeography, Palaeocli­matology, Palaeoecology, 478: 3-29.
Bottrell, S. H., Raiswell, R (2000) Sulphur isotopes and microbial sulphur cycling in sediments. In: Riding, R E, Awramik, SM (Eds.), Microbial Sediment. Springer-Verlag, Berlin, 96-104.
Breck, W. G (1974) Redox levels in the sea. In: Goldberg, E D (Ed.), The Sea. Marine Chemistry, Wiley, New York, 5:153-179.
Brennecka, G. A., Herrmann, A. D., Algeo, T. J., Anbar, A. D (2011) Rapid expansion of oceanic anoxia immediately before the end-Permian mass extinction. Proceedings of the National Academy of Sciences, 108(43):17631-17634.
Burdige, D. J (1993) The biogeochemistry of manganese and iron reduction in marine sediments. Earth-Science Reviews, 35(3): 249-284.
Burgess, S. D., Bowring, S. A (2015) High-precision geo­chronology confirms voluminous magmatism before, during, and after Earth’s most severe extinction. Sci­ence Advances, 1: 1-14.
Burgess, S. D., Muirhead, J. D., Bowring, S. A (2017) Initial pulse of Siberian Traps sills as the trigger of the end-Permian Mass extinction. Nature Communi­cations, 8: 1-6.
Canfield, D. E., Thamdrup, B (2009) Towards a consistent classification scheme for geochemical environments, or, why we wish the term ‘suboxic’ would go away. Geobiology, 7(4): 385-392.
Canfield, D. E., Farquhar, J (2009) Animal evolution, bioturbation, and the sulfate concentration of the oceans. Proceedings of the National Academy of Sciences, 106(20): 8123-8127.
Canfield, D. E., Thamdrup, B., Hansen, J. W (1993) The anaerobic degradation of organic matter in Danish coastal sediments: iron reduction, manganese reduction, and sulfate reduction. Geochimica et Cosmochimica Acta, 57(16): 3867-3883.
Cao, C., Love, G. D., Hays, L. E., Wang, W., Shen, S., Summons, R. E (2009) Biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end-Permian mass extinction event. Earth and Planetary Science Letters, 281: 188-201.
Chen, J. H., Edwards, R. L., Wasserburg, G. J (1986) 238U, 234U and 232Th in seawater. Earth and Planetary Science Letters, 80: 241-251.
Chen, B., Joachimski, M. M., Shen, S. Z., Lambert, L. L., Lai, X. L., Wang, X. D., Chen, J., Yuan, D. X (2013) Permian ice volume and palaeoclimate history: oxygen isotope proxies revisited. Gondwana Research, 24: 77-89.
Chester, R (2000) Marine Geochemistry. Blackwell, London. 506 p.
Clarkson, M. O., Kasemann, S. A., Wood, R. A., Lenton, T. M., Daines, S. J., Richoz, S., Ohnemueller, F., Meixner, A., Poulton, S. W., Tipper, E. T (2015) Ocean acidifica­tion and the Permo-Triassic mass extinction. Science, 348: 229-232.
Courtillot, V (1999) Evolutionary Catastrophes: The Science of Mass Extinction. Cambridge, UK, Cambridge Uni­versity Press, 173 p.
Courtillot, V., Olson, P (2007) Mantle plumes link magnetic superchrons to Phanerozoic mass deple­tion events. Earth and Planetary Science Letters, 260: 495-504.
Diaz, R. J., Rosenberg, R (1995) Marine benthic hypoxia: a review of its ecological effects and the behavioural responses of benthic macrofauna. Oceanography and Marine Biology, 33: 245-303.
Ehrenberg S. N., Svånå, T. A., Swart, P. K (2008) Uranium depletion across the Permian–Triassic boundary in Middle East carbonates: Signature of oceanic anoxia. AAPG Bulletin, 92(6): 691-707.
Erwin, D. H (1994) The Permo-Triassic extinction. Nature, 367(6460): 231-236.
Erwin, D. H (2006) Extinction: How Life on Earth Nearly Ended 250 million years ago. Princeton, New Jersey, Princeton University Press, 296 p.
Erwin, D. H., Bowring, S. A., Jin, Y. G (2002) End-Permian mass-extinctions: A review. In: Koeberl, C, MacLeod, K G, (Eds.), Catastrophic Events and Mass Extinctions: Impacts and Beyond. Geological Society of America Special Paper, 356: 353-383.
Fraiser, M. L., Bottjer, D. J (2007) Elevated atmospheric CO2 and the delayed biotic recovery from the end Permian mass extinction. Palaeogeography, Palaeocli­matology, Palaeoecology, 252: 164-175.
Frank, K. T., Petrie, B., Shackell, N. L (2007) The ups and downs of trophic control in continental shelf ecosystems. Trends in Ecology & Evolution, 22(5): 236-242.
Ferry, J. G., Lessner, D. J (2008) Methanogenesis in marine sediments. Annals of the New York Academy of Sciences, 1125(1): 147-157.
Froelich, P. N., Klinkhammer, G. P., Bender, M. L., Luedtke, N. A., Heath, G. R., Cullen, D., Dauphin, P., Hammond, D., Hartman, B., Maynard, V (1979) Early oxidation of organic matter in pemagic sediments of the eastern Equatorial Atlantic: suboxic diagenesis. Geochimica et Cosmochimica Acta, 43: 1075-1090.
Gaines, R. R., Droser, M. L (2003) Paleoecology of the familiar trilobite Elrathia kingii: an early exaerobic zone inhabitant. Geology, 31(11): 941-944.
Ghaderi, A., Garbelli, C., Angiolini, L., Ashouri, A. R., Korn, D., Rettori, R., Gharaie, M. H. M (2014a) Faunal change near the end-Permian extinction: the brachiopods of the Ali Bashi Mountains, NW Iran, Rivista Italiana di Paleontologia e Stratigrafia, 120: 27-59.
Ghaderi, A., Leda, L., Schobben, M., Korn, D., Ashouri, A. R (2014b) High-resolution stratigraphy of the Changhsingian (Late Permian) successions of NW Iran and the Transcaucasus based on lithological features, conodonts and ammonoids, Fossil Record, 17: 41-57.
Gliwa, J., Ghaderi, A., Leda, L., Schobben, M., Tomás, S., Foster, W. J., Forel, M. B., Ghanizadeh Tabrizi, N., Grasby, S. E., Struck, U., Ashouri, A. R., Korn, D (2020) Aras Valley (northwest Iran): high-resolution stratigraphy of a continuous central Tethyan Permian/Triassic boundary section. Fossil Record, 23: 33-69.
Gooday, A. J., Jorissen, F., Levin, L. A., Middelburg, J. J., Naqvi, S. W. A., Rabalais, N. N., Scranton, M., Zhang, J (2009) Historical records of coastal eutrophication-induced hypoxia. Biogeosciences, 6(8): 1707-1745.
Gray, J. S., Wu, R. S. S., Or, Y. Y (2002) Effects of hypoxia and organic enrichment on the coastal marine environment. Marine Ecology Progress Series, 238: 249-279.
Grice, K., Cao, C., Love, G. D., Boettcher, M. E., Twitchett, R. J., Grosjean, E., Summons, R. E., Turgeon, S. C., Dunning, W., Jin, Y (2005) Photic zone euxinia during the Permian-Triassic superanoxic event. Science, 307(5710):706-709.
Hassanzadeh, J., Wernicke, B. P (2016) The Neotethyan Sanandaj-Sirjan zone of Iran as an archetype for passive margin-arc transitions. Tectonics, 35: 586-621.
Hatch, J. R., Leventhal, J. S (1992) Relationship between inferred redox potential of the depositional environment and geochemistry of the Upper Pennsylvanian (Missourian) Stark Shale Member of the Dennis Limestone, Wabaunsee County, Kansas, USA. Chemical Geology, 99: 65-82.
Heydari, E., Hassandzadeh, J., Wade, W. J (2000) Geochemistry of central Tethyan upper Permian and lower Triassic strata, Abadeh region, Iran. Sedimentary Geology, 137: 85-99.
Heydari, E., Hassanzadeh, J., Wade, W. J., Ghazi, A. M (2003) Permian-Triassic boundary interval in the Abadeh section of Iran with implications for mass extinction: part 1-sedimentology. Palaeogeography, Palaeoclimatology, Palaeoecology, 193: 405-423.
Hofmann, A. F., Peltzer, E. T., Walz, P. M., Brewer, P. G (2011) Hypoxia by degrees: Establishing definitions for a changing ocean. Deep Sea Research Part I, 58: 1212-1226.
Isozaki, Y (1994) Superanoxia across the Permo-Triassic boundary: record in accreted deep-sea pelagic chert in Japan. In: Embry, A. F., Beauchamp, B., Glass, D. J (Eds.) Pangea: Global Environments and Resources: Canadian Society of Petroleum Geologists Memoir, 17: 805-812.
Joachimski, M. M., Lai, X. L., Shen, S. Z., Jiang, H. S., Luo, G. M., Chen, B., Chen, J., Sun, Y. D (2012) Climate warming in the latest Permian and the Permian-Triassic mass extinction: Geology, 40: 195-198.
Joachimski, M. M., Alekseev, A. S., Grigoryan, A., Gatovsky, Y. A (2020) Siberian Trap volcanism, global warming and the Permian-Triassic mass extinction: new insights from Armenian Permian-Triassic sections. GSA Bulletin, 132 (1-2): 427-443.
John, E. H., Wignall, P. B., Newton, R. J., Bottrell, S. H (2010) δ34SCAS and δ18OCAS records during the Frasnian–Famennian (Late Devonian) transition and their bearing on mass extinction models. Chemical Geology, 275: 221-234.
Jones, B., Manning, D. A (1994) Comparison of geochemical indices used for the interpretation of palaeoredox conditions in ancient mudstones. Chemical Geology, 111(1-4): 111-129.
Kauffman, E. G., Sageman, B. B (1990) Biological sensing of benthic environments in dark shales and related oxygen restricted facies. In: Ginsburg, R. N., Beaudoin, B (Eds.), Cretaceous Resources, Events and Rhythms Kluwer, Dordrecht, 121-138.
Korn, D., Ghaderi, A., Leda, L., Schobben, M., Ashouri, A. R (2016) The ammonoids from the Late Permian Paratirolites Limestone of Julfa (East Azerbaijan, Iran). Journal of Systematic Palaeontology, 14: 841-890.
Korte, C., Kozur, H. W., Joachimski, M. M., Strauss, H., Veizer, J., Schwark, L (2004) Carbone, sulfur, oxygen and strontium isotope records, organic geochemistry and biostratigraphy across the Permian/Triassic boundary in Abadeh, Iran. International Journal of Earth Sciences, 9: 565-581.
Kozur, H. W (2007) Biostratigraphy and event stratigraphy in Iran around the Permian–Triassic Boundary (PTB): implications for the causes of the PTB biotic crisis. Global and Planetary Change, 55 (1-3): 155-176.
Leda, L., Korn, D., Ghaderi, A., Hairapetian, V., Struck, U., Reimold, W. U (2014) Lithostratigraphy and carbonate microfacies across the Permian-Triassic boundary near Julfa (NW Iran) and in the Baghuk Mountains (Central Iran). Facies, 60: 295-325.
Levin, L. A (2003) Oxygen minimum zone benthos: adaptation and community response to hypoxia. Oceanography and Marine Biology-An Annual Review, 41: 1-45.
Levin, L. A., Etter, R. J., Rex, M. A., Gooday, A. J., Smith, C. R., Pineda, J., Stuart, C. T., Hessler, R. R., Pawson, D (2001) Environmental influences on regional deep-sea species diversity. Annual Review of Ecology and Systematics, 32(1): 51-93.
Levin, L. A., Ekau, W., Gooday, A. J., Jorissen, F., Middelburg, J. J., Naqvi, S. W. A., Neira, C., Rabalais, N. N., Zhang, J (2009) Effects of natural and human-induced hypoxia on coastal benthos. Biogeosciences, 6: 2063-2098.
Little, S. H., Vance, D., Lyons, T. W., McManus, J (2015) Controls on trace metal authigenic enrichment in reducing sediments: Insights from modern oxygen-deficient settings. American Journal of Science, 315(2): 77-119.
Loope, G. R., Kump, L. R., Arthur, M. A (2013) Shallow water redox conditions from the Permian–Triassic boundary microbialite: The rare earth element and iodine geochemistry of carbonates from Turkey and South China. Chemical Geology, 351: 195-208.
Madison, A. S., Tebo, B. M., Mucci, A., Sundby, B., Luther, G. W (2013) Abundant porewater Mn (III) is a major component of the sedimentary redox system. Science, 341: 875-878.
Mamet, B., Préat, A (2005) Why is red marble red? Revista española de micropaleontología, 37: 13-21.
Mamet, B., Préat, A (2006) Iron-bacterial mediation in Phanerozoic red limestones: state of the art. Sedimentary Geology, 185: 147-157.
McLennan, S. M (2001) Relationships between the trace element composition of sedimentary rocks and upper continental crust. Geochemistry, Geophysics, Geosystems, 2: 1-24.
Millero, F. J (1996) Chemical Oceanography. CRC Press, Boca Raton, Florida. 469 p.
Morford, J. L., Emerson, S (1999) The geochemistry of redox sensitive trace metals in sediments. Geochimica et Cosmochimica Acta, 63: 1735-1750.
Morford, J. L., Emerson, S. R., Breckel, E. J., Kim, S. H (2005) Diagenesis of oxyanions (V, U, Re, and Mo) in pore waters and sediments from a continental margin. Geochimica et Cosmochimica Acta, 69: 5021-5032.
Murray, J. W., Codispoti, L. A., Friederich, G. E (1995) Oxidation-reduction environments: The suboxic zone in the Black Sea. In Aquatic Chemistry, Interfacial and Interspecies Processes. American Chemical Society, Advances in Chemistry Series, 244: 157-176.
Murray, J. W., Fuchsman, C., Kirkpatrick, J., Paul, B., Konovalov, S. K (2005) Species and d15N signatures of nitrogen transformations in the suboxic zone of the Black Sea. Oceanography, 18(2): 36-47.
Payne, J. L., Lehrmann, D. J., Follet, D., Seibel, M., Kump, L. R., Riccardi, A., Altiner, D., Sano, H., Wei, J.- Y (2007) Erosional truncation of uppermost Permian shallow-marine carbonates and implications for Perm­ian–Triassic boundary events. Geological Society of America Bulletin, 119: 771-784,
Penn, J. L., Deutsch, C., Payne, J. L., Sperling, E. A (2018) Temperature dependent hypoxia explains biogeogra­phy and severity of end-Permian marine mass extinc­tion. Science, 362: 1-6.
Poulton, S. W., Canfield, D. E (2011) Ferruginous conditions: a dominant feature of the ocean through Earth’s history. Elements, 7(2): 107-112.
Préat, A., Loreau, J. P., Durlet, C., Mamet, B (2006) Petrography and biosedimentology of the Rosso Ammonitico Veronese (Middle–Upper Jurassic, Northeastern Italy). Facies, 52: 265-278.
Préat, A., Mattielli, N. L., De Jong, J., Mamet, B (2008) Stable iron isotopes confirm microbial mediation in red pigmentation of the Rosso Ammonitico (Mid-Late Jurassic, Verona Area, Italy). Astrobiology, 8: 841-857.
Reichow, M. K., Saunders, A. D., White, R. V., Pringle, M. S., Al’Mukhamedov, A. I., Medvedev, A. I., Kirda, N. P (2002) 40Ar/39Ar dates from the West Siberian Basin: Siberian flood basalt province doubled. Sci­ence, 296: 1846-1849.
Reichow, M. K., Saunders, A. D., White, R. V., Pringle, M. S., Al'Mukhamedov, A. I., Medvedev, A. Ya., Kirda, N. P (2002) 40Ar/39Ar dates from the West Siberian Basin: Siberian Flood Basalt Province doubled. Science, 296: 1846-1849.
Renne, P. R., Basu, A. R (1991) Rapid eruption of the Siberian Traps flood basalts at the Permo–Triassic boundary. Science, 253: 176-179.
Repeta, D. J (1993) A high-resolution historical record of Holocene anoxygenic primary production in the Black Sea. Geochimica et Cosmochimica Acta, 57: 4337-4342.
Revsbech, N. P., Larsen, L. H., Gundersen, J., Dalsgaard, T., Ulloa, O., Thamdrup, B (2009) Determination of ultra-low oxygen concentrations in oxygen minimum zones by the STOX sensor. Limnology and Oceanography: Methods, 7: 371-381.
Rue, E. L., Smith, G. J., Cutter, G. A., Bruland, K. W (1997) The response of trace element redox couples to suboxic conditions in the water column. Deep-Sea Research Part I, 44: 113-134.
Saitoh, M., Isozaki, Y (2021) Carbon Isotope Chemostratigraphy Across the Permian-Triassic Boundary at Chaotian, China: Implications for the Global Methane Cycle in the Aftermath of the Extinction. Frontiers in Earth Science, 8: 1-22.
Savrda, C. E., Bottjer, D. J., Gorsline, D. S (1984) Development of a comprehensive oxygen-deficient marine biofacies model: evidence from Santa Monica, San Pedro, and Santa Barbara Basins, California Continental Borderland. AAPG Bulletin, 68(9): 1179-1192.
Schobben, M., Stebbins, A., Ghaderi, A., Strauss, H., Korn, D., Korte, C (2015) Flourishing ocean drives the end-Permian marine mass extinction. Proceedings of the National Academy of Sciences of the United States of America, 112: 10298-10303.
Shen, S. Z., Mei, S. L (2010) Lopingian (Late Permian) high resolution conodont biostratigraphy in Iran with comparison to South China zonation, Geological Journal, 45: 135-161.
Shen, J., Algeo, T. J., Zhou, L., Feng, Q., Yu, J., Ellwood, B. B (2012) Volcanic perturbations of the marine environment in South China preceding the latest Permian mass extinction and their biotic effects. Geobiology, 10: 82-103.
Sial, A. N., Chen, J., Lacerda L. D., Korte, C., Spangenberg, J. E., Silva-Tamayo, J. C., Gaucher, C., Ferreira, V. P., Barbosa, J. A., Pereira, N. S., Benigno, A. P (2020) Globally enhanced Hg deposition and Hg isotopes in sections straddling the Permian-Triassic boundary: Link to volcanism. Palaeogeography, Palaeocli­matology, Palaeoecology, 540: 109537.
Song, H. J., Wignall, P. B., Tong, J., Bond, D. P. G., Song, H. Y., Lai, X., Zhang, K., Wang, H., Chen, Y (2012) Geochemical evidence from bio-apatite for multiple oceanic anoxic events during Permian-Triassic transition and the link with end-Permian extinction and recovery. Earth and Planetary Science Letters, 353 (354):12-21.
Sperling, E. A., Knoll, A. H., Girguis, P. R (2015) The ecological physiology of Earth’s second oxygen revolution. Annual Review of Ecology, Evolution, and Systematics, 46: 215-235.
Svensen, H., Planke, S., Polozov, A., Schmidbauer, N., Corfu, F., Podladchikov, Y., Jamtveit, B (2009) Siberian gas venting and the end-Permian environ­mental crisis. Earth and Planetary Science Letters, 277: 490-500.
Sweere, T., van den Boorn, S., Dickson, A. J., Reichart, G. J (2016) Definition of new trace-metal proxies for the controls on organic matter enrichment in marine sediments based on Mn, Co, Mo and Cd concentrations. Chemical Geology, 441: 235-245.
Tribovillard, N., Algeo, T. J., Lyons, T., Riboulleau, A (2006) Trace metals as paleoredox and paleoproductivity proxies: an update. Chemical Geology, 232(1): 12-32.
Tribovillard, N., Algeo, T. J., Baudin, F., Riboulleau, A (2012) Analysis of marine environmental conditions based on molybdenum-uranium covariation—Applications to Mesozoic paleoceanography. Chemical Geology, 324: 46-58.
Taylor, S. R., McLennan, S. M (1985) The Continental Crust: Its Composition and Evolution. Blackwell, Oxford. 312 p.
Tyson, R. V., Pearson, T. H (1991) Modern and ancient continental shelf anoxia: an overview. In: Tyson R. V., Pearson T. H (Eds.), Modern and Ancient Continental Shelf Anoxia Geological Society of London Special. Publication, 58:  1-24.
Wignall, P. B., Myers, K. J (1988) Interpreting the benthic oxygen levels in mudrocks: a new approach. Geology, 16: 452-455.
Wignall, P. B., Hallam, A (1992) Anoxia as a cause of the Permian/Triassic extinction: Facies evidence from northern Italy and the western United States. Palaeogeography, Palaeoclimatology, Palaeoecology, 93: 21-46.
Wignall, P. B., Zonneveld, J. P., Newton, R. J., Amor, K., Sephton, M. A., Hartley, S (2007) The end-Triassic mass extinction record of Williston Lake, British Columbia. Palaeogeography, Palaeoclimatology, Palaeoecology, 253: 385-406.
Wignall, P. B., Bond, D. P. G., Kuwahara, K., Kakuwa, Y., Newton, R. J., Poulton, S. W (2010) An 80 million year oceanic redox history from Permian to Jurassic pelagic sediments of the Mino-Tamba terrane, SW Japan, and the origin of four mass extinctions. Global and Planetary Change, 71(1-2):109-123.
Yano, M., Yasukawa, K., Nakamura, K., Ikehara, M., Kato, Y (2020) Geochemical features of redox-sensitive Trace metals in sediments under oxygen-depleted marine environments. Minerals, 10: 1-20.
Zhang, F., Romaniello, S. J., Algeo, T. J., Lau, K. V., Clapham, M. E., Richoz, S., Herrmann, A. D., Smith, H., Horacek, M., Anbar, A. D (2018) Multiple episodes of extensive marine anoxia linked to global warming and continental weathering following the latest Permian mass extinction. Science Advances, 4: 1-9.
Zheng, Y., Anderson, R. F., van Geen, A., Kuwabara, J (2000) Authigenic molybdenium formation in marine sediments: a link to pore water sulfide in the Santa Barbara Basin. Geochimica et Cosmochimica Acta, 64: 4165-4178.
Zheng, Y., Anderson, R. F., van Geen, A., Fleischer, M. Q (2002a) Preservation of nonlithogenic particulate uranium in marine sediments. Geochimica et Cosmochimica Acta, 66: 3085-3092.
Zheng, Y., Anderson, R. F., van Geen, A., Fleischer, M. Q (2002b) Remobilization of authigenic uranium in marine sediments by bioturbation. Geochimica et Cosmochimica Acta, 66: 1759-1772.
Zhou, L., Wignall, P. B., Su, J., Feng, Q., Xie, S., Zhao, L., Huang, J (2012) U/Mo ratios and δ98/95Mo as local and global redox proxies during mass extinction events. Chemical Geology, 324 (325): 99-107.