1 Nature 2001 Vol: 411(6838):675-677. DOI: 10.1038/35079548

Stability of atmospheric CO2 levels across the Triassic/Jurassic boundary

The Triassic/Jurassic boundary, 208 million years ago, is associated with widespread extinctions in both the marine and terrestrial biota. The cause of these extinctions has been widely attributed to the eruption of flood basalts of the Central Atlantic Magmatic Province1, 2, 3, 4. This volcanic event is thought to have released significant amounts of CO2 into the atmosphere, which could have led to catastrophic greenhouse warming5, 6, 7, but the evidence for CO2-induced extinction remains equivocal. Here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations, spanning a 20-Myr period across the Triassic/Jurassic boundary. Using a standard diffusion model8, 9, we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000–4,000 p.p.m. increase4, 5. The relative stability of atmospheric CO2 across this boundary suggests that environmental degradation and extinctions during the Early Jurassic were not caused by volcanic outgassing of CO2. Other volcanic effects—such as the release of atmospheric aerosols or tectonically driven sea-level change—may have been responsible for this event.

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Figures
Figure 1: Location of basins containing the sampled palaeosols.Right, exposed basins of the Newark Supergroup. Sampled basins: 1, Durham sub-basin of the Deep River basin (Chatham Group samples from the eastern Durham sub-basin); 2, Hartford basin (New Haven Formation); and 3, Fundy basin (McCoy Brook Formation). Left, part of the Chinle basin with the outcrop pattern of the Chinle Group shown in black. Location of the sample area of the Owl Rock Formation is indicated (4).
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References
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    • . . . The cause of these extinctions has been widely attributed to the eruption of flood basalts of the Central Atlantic Magmatic Province1, 2, 3, 4 . . .
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    • . . . The cause of these extinctions has been widely attributed to the eruption of flood basalts of the Central Atlantic Magmatic Province1, 2, 3, 4 . . .
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    • . . . Recent estimates of the maximum volume of CAMP basalt3 are comparable to the largest estimates for the Deccan Traps flood basalts27, the eruptions of which are estimated to have increased atmospheric CO2 by only 200–250 p.p.m.v. (against a Late Cretaceous background of about 600 p.p.m.v.)28 . . .
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    • . . . The cause of these extinctions has been widely attributed to the eruption of flood basalts of the Central Atlantic Magmatic Province1, 2, 3, 4 . . .
    • . . . Using a standard diffusion model8, 9, we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000–4,000 p.p.m. increase4, 5 . . .
    • . . . A frequently cited deleterious effect of these widespread, massive eruptions is a sudden increase in atmospheric CO2 (pCO2) from outgassing, resulting in intense global warming4, 5, 6, 7. . . .
    • . . . The isotopic composition of oolitic goethite has been cited as evidence for greatly elevated (possibly 18 times the modern level) pCO2 during the Early Jurassic4; however, the age of these data are not well constrained and are still subject to interpretation . . .
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    • . . . Using a standard diffusion model8, 9, we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000–4,000 p.p.m. increase4, 5 . . .
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    • . . . However, dating of the best-candidate impact structure (the Manicouagan crater) places the impact roughly 14 Myr earlier16, and sea-level change fails to explain the fern spike in the terrestrial boundary record6 . . .
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    • . . . Using a standard diffusion model8, 9, we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000–4,000 p.p.m. increase4, 5 . . .
    • . . . The estimation of atmospheric palaeo-pCO2 using 13C of pedogenic carbonate and the diffusion-reaction model is now common practice8, 9, 18 . . .
    • . . . Elevated palaeo-pCO2 for the Late Triassic has been estimated previously from the isotopic analysis of calcite in palaeosols8, 9, 18, but reliable data gathered with modern sampling protocols9, 18 are lacking for the Early Jurassic. . . .
    • . . . Owing to the temperature control on isotope fractionation8, the difference between the Upper Triassic and Lower Jurassic palaeosols is eliminated if the mean temperature of pedogenic calcite precipitation were 2 °C lower in the more northerly Fundy basin . . .
    • . . . Our results are similar to previous estimates of palaeo-pCO2 for the Late Triassic8 and the Late Jurassic25; however, these earlier estimates lacked the stratigraphical resolution necessary to examine changes in palaeo-pCO2 across the Triassic/Jurassic boundary . . .
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    • . . . Using a standard diffusion model8, 9, we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000–4,000 p.p.m. increase4, 5 . . .
    • . . . The estimation of atmospheric palaeo-pCO2 using 13C of pedogenic carbonate and the diffusion-reaction model is now common practice8, 9, 18 . . .
    • . . . Elevated palaeo-pCO2 for the Late Triassic has been estimated previously from the isotopic analysis of calcite in palaeosols8, 9, 18, but reliable data gathered with modern sampling protocols9, 18 are lacking for the Early Jurassic. . . .
    • . . . We selected samples from depths of 30 cm or greater, below the top of the Bk or K horizon, thereby minimizing the effects of soil depth9, 18 . . .
    • . . . The 13Catmos is set at -6.5 PDB9, although variation in the composition of marine carbonates suggests that this value varied slightly during the early Mesozoic18 . . .
    • . . . The 13C value for organic matter was taken as -24 PDB, consistent with direct measurements9 and proxy measurements18 for Upper Triassic and Lower Jurassic palaeosols . . .
    • . . . Fractionation of soil CO2 by 1 relative to organic matter is assumed9 . . .
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    • . . . The mass extinction at the end of the Triassic claimed about 80% of all species10, including most non-dinosaurian archosaurs11 . . .
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    • . . . Although extinctions in the terrestrial and marine environments may be slightly asynchronous, they are closely related temporally and undoubtedly share causality12 . . .
    • . . . CAMP volcanics include the basalts of the Newark Supergroup of eastern North America whose ages of around 200 Myr and stratigraphical proximity to the Triassic/Jurassic boundary are well constrained12, 17 . . .
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    • . . . This biotic crisis has been attributed previously to bolide impact6, 13 and sea-level change14, 15 . . .
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    • . . . This biotic crisis has been attributed previously to bolide impact6, 13 and sea-level change14, 15 . . .
    • . . . Although little evidence has been presented to support the former14, the latter hypothesis has the advantage of explaining the transgressive–regressive couplet that spans the Triassic/Jurassic boundary14, 15 and the widespread record of Early Jurassic marine anoxia14. . . .
  15. Hallam, A. & Wignall, P. B. Mass extinctions and sea-level changes. Earth Sci. Rev. 48, 217-250 , (1999) .
    • . . . This biotic crisis has been attributed previously to bolide impact6, 13 and sea-level change14, 15 . . .
    • . . . Although little evidence has been presented to support the former14, the latter hypothesis has the advantage of explaining the transgressive–regressive couplet that spans the Triassic/Jurassic boundary14, 15 and the widespread record of Early Jurassic marine anoxia14. . . .
  16. Hodych, J. P. & Dunning, G. R. Did the Manicouagan impact trigger end-of-Triassic mass extinction? Geology 20, 51-54 , (1992) .
    • . . . However, dating of the best-candidate impact structure (the Manicouagan crater) places the impact roughly 14 Myr earlier16, and sea-level change fails to explain the fern spike in the terrestrial boundary record6 . . .
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    • . . . CAMP volcanics include the basalts of the Newark Supergroup of eastern North America whose ages of around 200 Myr and stratigraphical proximity to the Triassic/Jurassic boundary are well constrained12, 17 . . .
  18. Ekart, D. D., Cerling, T. E., Montanez, I. P. & Tabor, N. J. A 400 million year carbon isotope record of pedogenic carbonate: implications for paleoatmospheric carbon dioxide. Am. J. Sci. 299, 805-827 , (1999) .
    • . . . The estimation of atmospheric palaeo-pCO2 using 13C of pedogenic carbonate and the diffusion-reaction model is now common practice8, 9, 18 . . .
    • . . . We selected samples from depths of 30 cm or greater, below the top of the Bk or K horizon, thereby minimizing the effects of soil depth9, 18 . . .
    • . . . The 13Catmos is set at -6.5 PDB9, although variation in the composition of marine carbonates suggests that this value varied slightly during the early Mesozoic18 . . .
    • . . . The 13C value for organic matter was taken as -24 PDB, consistent with direct measurements9 and proxy measurements18 for Upper Triassic and Lower Jurassic palaeosols . . .
    • . . . The morphologies of these palaeosols suggest formation in well-drained arid to semi-arid soils in which S(z) may vary from 3,000–7,000 p.p.m (ref. 18) . . .
  19. Berner, R. A. Enriched: GEOCARB II; a revised model of atmospheric CO2 over Phanerozoic time. Am. J. Sci. 294, 56-91 , (1994) .
    • . . . Values of palaeo-pCO2 derived from 13C are similar to values from other sources, such as geochemical modelling19 . . .
    • . . . These estimates and ours are contained within the range of error for average palaeo-pCO2 for the latest Triassic and earliest Jurassic calculated by carbon-cycle modelling of 3–8 times the modern level19 . . .
  20. Hubert, J. F. Paleosol caliche in the New Haven Arkose, Newark Group, Connecticut. Palaeogeogr. Palaeoclimatol. Palaeoecol. 24, 151-168 , (1978) .
    • . . . These soils all formed on alluvial floodplains at low palaeolatitudes ( 15°) and most profiles show features such as gradational lower boundaries, rhizoliths, and circumgranular cracking, which suggest semi-arid to arid conditions, and so have been inferred to represent well-drained soils20, 21, 22, 23. . . .
  21. Coffey, B. P. & Textoris, D. A. Paleosols and paleoclimatic evolution, Durham sub-basin, North Carolina. Geol. Nat. Hist. Sur. Connecticut Misc. Rep. 1, 6 , (1996) .
    • . . . These soils all formed on alluvial floodplains at low palaeolatitudes ( 15°) and most profiles show features such as gradational lower boundaries, rhizoliths, and circumgranular cracking, which suggest semi-arid to arid conditions, and so have been inferred to represent well-drained soils20, 21, 22, 23. . . .
  22. Tanner, L. H. in The Continental Jurassic (ed. Morales, M.) 656-574 (Museum of Northern Arizona, Flagstaff, Arizona, 1996) , .
    • . . . These soils all formed on alluvial floodplains at low palaeolatitudes ( 15°) and most profiles show features such as gradational lower boundaries, rhizoliths, and circumgranular cracking, which suggest semi-arid to arid conditions, and so have been inferred to represent well-drained soils20, 21, 22, 23. . . .
  23. Tanner, L. H. Palustrine-lacustrine and alluvial facies of the (Norian) Owl Rock Formation (Chinle Group), Four Corners region, southwestern U.S.A.: implications for Late Triassic paleoclimate. J. Sedim. Res. 70, 1280-1289 , (2000) .
    • . . . These soils all formed on alluvial floodplains at low palaeolatitudes ( 15°) and most profiles show features such as gradational lower boundaries, rhizoliths, and circumgranular cracking, which suggest semi-arid to arid conditions, and so have been inferred to represent well-drained soils20, 21, 22, 23. . . .
  24. Olsen, P. E. Stratigraphic record of the early Mesozoic breakup of Pangea in the Laurasia-Gondwana rift system. Annu. Rev. Earth Planet. Sci. 25, 337-401 , (1997) .
    • . . . The consistent isotopic compositions of pedogenic calcite is notable because these basins extend across about 17° of palaeolatitude, from the equatorial Deep River basin to the Fundy basin at about 15° N (ref. 24) . . .
  25. Ekart, D. D. & Cerling, T. E. PCO2 during deposition of the Late Jurassic Morrison Formation and other paleoclimatic/ecologic data as inferred by stable carbon isotope analyses. Geol. Soc. Am. Abs. Prog. 28, 252 , (1996) .
    • . . . Our results are similar to previous estimates of palaeo-pCO2 for the Late Triassic8 and the Late Jurassic25; however, these earlier estimates lacked the stratigraphical resolution necessary to examine changes in palaeo-pCO2 across the Triassic/Jurassic boundary . . .
  26. Suchecki, R. K., Hubert, J. F. & De Wet, C. B. Isotopic imprint of climate and hydrogeochemistry on terrestrial strata of the Triassic-Jurassic Hartford and Fundy rift basins. J. Sed. Res. 58, 801-811 , (1988) .
    • . . . Most significantly, our results differ substantially from previously published analyses for the McCoy Brook Formation (Lower Jurassic), which were obtained by bulk analyses of samples collected without the constraint of position within the palaeosol profile26. . . .
  27. Coffin, M. F. & Eldholm, O. Scratching the surface: estimating dimensions of large igneous provinces. Geology 21, 515-518 , (1993) .
    • . . . Recent estimates of the maximum volume of CAMP basalt3 are comparable to the largest estimates for the Deccan Traps flood basalts27, the eruptions of which are estimated to have increased atmospheric CO2 by only 200–250 p.p.m.v. (against a Late Cretaceous background of about 600 p.p.m.v.)28 . . .
  28. Caldeira, K. G. & Rampino, M. R. Deccan volcanism, greenhouse warming, and the Cretaceous/Tertiary boundary. Geol. Soc. Am. Spec. Pap. 247, 117-123 , (1990) .
    • . . . Recent estimates of the maximum volume of CAMP basalt3 are comparable to the largest estimates for the Deccan Traps flood basalts27, the eruptions of which are estimated to have increased atmospheric CO2 by only 200–250 p.p.m.v. (against a Late Cretaceous background of about 600 p.p.m.v.)28 . . .
  29. Wallace, P. & Anderson, A. T. in Encyclopedia of Volcanoes (ed. Sigurdsson, H.) 149-170 (Academic, New York, 2000) , .
    • . . . This calculation, moreover, is based on an estimate of 0.5% CO2 in the basaltic magma that may be overgenerous29 . . .
  30. Parfitt, E. A. & Wilson, L. Impact of basaltic eruptions on climate. Geol. Soc. Am. Abs. Prog. 32, 501 , (2000) .
    • . . . Alternative mechanisms for extinction need to be explored more fully, particularly short-term cooling or acidification of the atmosphere and oceans from SO2 aerosols6, 30, and rapid sea-level change driven by plume-driven thermal doming and collapse7 . . .
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