EGU2020-2141, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-2141
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Refining the temporal relation between Large Igneous Provinces and carbon cycle perturbations: not every LIP triggers environmental crises, not every crisis is due to a LIP!

Urs Schaltegger1, Philipp Widmann1, Nicolas D. Greber2, Luis Lena1, Sean P. Gaynor1, Torsten Vennemann3, and Hugo Bucher4
Urs Schaltegger et al.
  • 1University of Geneva, Department of Earth Sciences, Geneva, Switzerland (urs.schaltegger@unige.ch)
  • 2University of Bern, Institute of Geology, Bern, Switzerland
  • 3University of Lausanne, Faculty of Geosciences and Environmental Sciences, Lausanne, Switzerland
  • 4University of Zürich, Paleontological Institute and Museum, Zürich, Switzerland

The connection between volcanic activity of large igneous provinces and the respective feedback from environment and biosphere contributing to the carbon cycle has been investigated at the present temporal resolution of high-precision U/Pb dating. Uncertainties of 0.05 % on the 206Pb/238U age from zircon dating allow a resolution of 30-50 ka pulses of magmatic activity; simultaneously, the duration of carbon isotope excursions (CIE) can be determined, the geological boundaries dated, or global sedimentary gaps can be quantified at the same level of precision. This contribution demonstrates with two case studies that we can refine the contemporaneity and start to reliably infer causality of consecutive events at the 104 year level.

Until the Anisian the aftermath of the Permo-Triassic Boundary Mass extinction (PTBME; ~251.94 Ma, Baresel et al., 2017) is characterized by profound fluctuations of the global carbon cycle with amplitudes of up to 8 ‰ in d13Ccarb values. These represent large variations in the global climate and biological crises, in particular during the end-Smithian extinction event (~249.1 Ma). A precise chronology from the southern Nanpanjiang basin (China) allows for a quantification of these fluctuations of Earth climate. Following the volcanic pulse causing the PTBME, several discontinuous episodes of volcanism of the Siberian Large Igneous Province (S-LIP) were generally assumed to have caused the subsequent Early Triassic carbon cycle fluctuations. This is, however, in disagreement with the geochronological database of precise zircon U/Pb dates that put an end to the volcanic activity at 250.6 Ma (Burgess & Bowring, 2015; Augland et al., 2019). Therefore, recurrent S-LIP volcanism is an unlikely explanation for the Early Triassic unstable carbon cycle.

The initial intrusive pulse of the Karoo Large Igneous Province (K-LIP) formed the sill/dyke complex of the Karoo basin, South Africa. New, precise U/Pb geochronology confirms its very short duration at around 183.2-182.8 Ma (Burgess et al., 2015; Corfu et al., 2016), as well as its synchronicity with the lower Toarcian oceanic anoxic event (T-OAE), and a carbon cycle disturbance of presumable global importance. Repeated excursions in d13Corg of up to 3 ‰ in the late Pliensbachian (~185.5 Ma) as well as at the Pliensbachian-Toarcian boundary (~183.5 Ma) are therefore at least partly older than any known magmatic activity of the K-LIP (Lena et al., 2019). We therefore, again, must invoke non-volcanic drivers in order to explain the instability of the carbon cycle.

These two case histories demonstrate that in order to invoke causality and global importance to carbon cycle instability, as well as for the testing of its correlation with volcanic episodes, we need to rely on geochronology of both sedimentary and volcanic records at the 104 years level of precision.

References: Augland et al. (2019) Scientific Reports, 9:18723 ; Baresel et al. (2017) Solid Earth, 8, 361–378, 2017; Burgess & Bowring (2015) Science Advances, 1(7), e1500470–e1500470; Burgess et al. (2015) Earth and Planetary Science Letters, 415(C), 90–99; Corfu, F. et al. (2016) Earth and Planetary Science Letters, 434(C), 349–352; Lena et al. (2019) Scientific Reports, 9:18430.

How to cite: Schaltegger, U., Widmann, P., Greber, N. D., Lena, L., Gaynor, S. P., Vennemann, T., and Bucher, H.: Refining the temporal relation between Large Igneous Provinces and carbon cycle perturbations: not every LIP triggers environmental crises, not every crisis is due to a LIP!, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2141, https://doi.org/10.5194/egusphere-egu2020-2141, 2020

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Presentation version 2 – uploaded on 01 May 2020
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  • CC1: Comment on EGU2020-2141, Mathieu Martinez, 01 May 2020

    Dear Urs,

    Many thanks for this very exciting study! I find interesting to see that the recently published ages on the Karoo-Ferrar suggest a duration of ~800 kyr for the activity of this Large Igneous Province. This province seems to be synchronous to the Toarcian Oceanic Anoxic Event and the duration of this event is debated between a short duration (300-500 kyr; Boulila et al., 2014) and a long duration (~900 kyr; Suan et al., 2008; Huang and Hesselbo, 2014; Thibaut et al., 2018). The reason for this discrepancy is how the cycles obtained from spectral analyses are interpreted. I’m thus wondering if constraining the duration of the Karoo-Ferrar activity can provide indirect constraints on the duration of the Toarcian-OAE.

    References:

    Boulila, S., et al., 2014. EPSL 386, 98-111.

    Huang, C., Hesselbo, S.P., 2014. Gondwana Res. 25, 1348-1356.

    Suan, G., et al., 2008. EPSL 267, 666-679.

    Thibault, N., et al., 2018. Proc. Geol. Assoc. 129, 372-391.

    • AC1: Reply to CC1, Urs Schaltegger, 01 May 2020

      Dear Mathieu

      Thanks for the comment. Given this years' format I had to stick to mostly published data... There is quite a bit of new stuff coming from our side in the next months. We are trying to structure the Karoo activity into pulses, some of it with great success. But I cannot tell more at the moment.... Anyway, magmatic activity is fractal, from huge volcanic provinces to single pulses to smallest melt increments. The question is which scale is transferred and discoverable in the environemntal response. Best, Urs

      • CC2: Reply to AC1, Mathieu Martinez, 01 May 2020

        Dear Urs,

        Many thanks for your answer, I greatly appreciate it

        All the best,

        Mathieu

Presentation version 1 – uploaded on 13 Apr 2020 , no comments