New group publications on the Toarcian Oceanic Anoxic Event

Recently two papers from our lab on the Toarcian Oceanic Anoxic Event (OAE) were published. This work was supported by the National Science Foundation’s Sedimentary Geology and Paleobiology program.

The Toarcian OAE or T-OAE occurred during the Early Jurassic Period approximately (~183 million years ago). The leading hypothesis for the cause of this event are massive volcanic eruptions associated with the emplacement of the Karro-Ferrar Large Igneous Provence. The gases emitted by these eruptions resulted in a transient interval of global warming and series of severe environmental changes that resulted in an extinction event. Our studies have sought to identify and quantify the environmental changes that occurred during this event. One of these environmental perturbations was the development or expansion of anoxia in parts of the oceans at time – hence the term oceanic anoxic event.

The first paper, published in Earth and Planetary Science Letters this past February, concerns the record of the carbon cycle during the T-OAE.

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Click on the title header above for link to the manuscript

This paper presents the carbon isotope stratigraphy from one of our study sites in Western North America (East Tributary of Bighorn Creek, Alberta, Canada). This study showed that the changes or excursions in the carbon isotope stratigraphy found elsewhere1,2,3,4 can be found in the North American record. This includes the large-scale excursion (see figure below), but also smaller-scale features in this record. This observation is important because this indicates that these excursions represent changes in the global carbon cycle. We also argue for an important role of the terrestrial carbon cycle in the overall carbon cycle and climate feedbacks during the event.

Screen Shot 2017-08-03 at 9.16.31 AMCarbon isotope stratigraphy and ammonite biostratigraphy from the East Tributary study site. Note the large carbon isotope excursion (CIE) that occurs in the T-OAE interval.


Click on the title header above for link to the manuscript

Our second paper, published in Scientific Reports in mid-July, involves reconstructing the changes in chemical weathering over the T-OAE using osmium isotopes. Chemical weathering is an important negative feedback to rising carbon dioxide levels in the atmosphere; these chemical reactions remove carbon dioxide from the atmosphere. We found an osmium isotope excursion – an increase in the ratio of the osmium isotope 187 (187Os) over 188 (188Os) (see plot below) – during the interval that contains the T-OAE.

Screen Shot 2017-08-03 at 9.28.31 AM

Carbon and osmium isotope stratigraphy from the East Tributary study site. Note the osmium isotope excursion that occurs at the same level as the T-OAE carbon isotope excursion.

This excursion indicates a transient increase in the weathering of continental rocks during the event; continental rocks are in enriched in 187Os relative 188Os as compared to other sources of osmium to the ocean. While similar signals have been previously found in locations in Europe6,7, it had yet to be identified elsewhere. Again, as for the carbon isotope record, this observation is critical to identify whether the excursion represents a global change in the osmium cycle. We also went a step further and used a numerical model of the osmium cycle to derive estimates of the change in chemical weathering during the event: our model suggests up to 3-fold increase in the weathering of continental material during the T-OAE.

Stay tuned for more work from our group on the Toarcian Oceanic Anoxic Event. We have several on going studies of this fascinating time interval in the history of the Earth.


  1. Kemp, D. B., Coe, A. L., Cohen, A. S., & Schwark, L. (2005). Astronomical pacing of methane release in the Early Jurassic period. Nature, 437, 396–399.
  2. Hesselbo, S. P., Jenkyns, H. C., Duarte, L. V., & Oliveira, L. C. V. (2007). Carbon-isotope record of the Early Jurassic (Toarcian) Oceanic Anoxic Event from fossil wood and marine carbonate (Lusitanian Basin, Portugal). Earth and Planetary Science Letters, 253(3-4), 455–470.
  3. Hermoso, M., Minoletti, F., Rickaby, R. E. M., Hesselbo, S. P., Baudin, F., & Jenkyns, H. C. (2012). Dynamics of a stepped carbon-isotope excursion: Ultra high-resolution study of Early Toarcian environmental change. Earth and Planetary Science Letters, 319-320(C), 45–54.
  4. Suan, G., Nikitenko, B. L., Rogov, M. A., Baudin, F., Spangenberg, J. E., Knyazev, V. G., et al. (2011). Polar record of Early Jurassic massive carbon injection. Earth and Planetary Science Letters, 312(1-2), 102–113.
  5. Al-Suwaidi, A. H., Hesselbo, S. P., Damborenea, S. E., Manceñido, M. O., Jenkyns, H. C., Riccardi, A. C., et al. (2016). The Toarcian Oceanic Anoxic Event (Early Jurassic) in the Neuquén Basin, Argentina: A Reassessment of Age and Carbon Isotope Stratigraphy. The Journal of Geology, 124(2), 171–193.
  6. Cohen, A. S., Coe, A. L., Harding, S. M., & Schwark, L. (2004). Osmium isotope evidence for the regulation of atmospheric CO₂ by continental weathering. Geology, 32(2), 157–160.
  7. Percival, L. M. E., Cohen, A. S., Davies, M. K., Dickson, A. J., Hesselbo, S. P., Jenkyns, H. C., et al. (2016). Osmium isotope evidence for two pulses of increased continental weathering linked to Early Jurassic volcanism and climate change. Geology, 44(9), 759–762.
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Congrats to Emma Tulsky

Congratulations to lab member Emma Tulsky who successfully defended and graduated this May. Her Masters thesis was on the effects of contact metamorphism had on the sulfur and carbon bearing species in the intruded sedimentary rocks.


I’m happy to say that Emma will be starting a job with Newmont Mining in June. She will be working on Carlin-type Gold deposits in Nevada.

Thanks Emma for sticking around to do a masters degree after doing your bachelors at Tech!

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New Publication: Elucidating the relationship between the later Cambrian end-Marjuman extinctions and SPICE Event


A study led by former lab group member Angela Gerhardt on the temporal relationship between a major perturbation to the marine carbon cycle (known as the SPICE) and extinctions that occurred during the late Cambrian has now been published online in the journal Palaeogeography, Palaeoclimatology, Palaeoecology. This study was the subject of Angela’s Master thesis.

Angela’s study investigated the stratigraphic relationship between the start of the SPICE and the extinctions in shallow marine communities of the trilobites and brachiopods that occurred around that time. She found that the first phase of the extinctions did not coincide with changes in the carbon cycle. However, the second and final phase of the extinctions coincided with the start of the SPICE, which suggests that the two events are mechanistically linked. Several other studies forward that the SPICE was caused by the spread of anoxia with the oceans. Therefore Angela’s findings suggest that anoxia may have been responsible for the final phase of these extinctions.

Here’s a link to paper:


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Congrats to Recent Lab Group Graduates

This is fairly belated, but congratulations are due to lab members Teddy Them and Sam Ritzer who successfully defended and graduated this spring.


Teddy will be starting a post-doc at Florida State starting this fall under the direction of my friend and colleague Jeremy Owens. He will be working on the thallium and vanadium isotope systems.

Sam will be going to Stanford to this fall to pursue a doctorate with another friend and colleague Erik Sperling.

Thanks to both of you for being great students and good luck with your future plans. You’ll both do great things!

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New Publication: Sulfur and carbon geochemistry of the Santa Elena peridotites: Comparing oceanic and continental processes during peridotite alteration

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A paper by Esther Schwarzenbach and I on sulfur and carbon cycling during the process of serpentinization was recently published in the journal Lithos.  This study was a collaboration with Esteban Gazel and Pilar Madrigal from the VT-Volcanoes Group.

This paper explores the carbon and sulfur cycles in the ultramafic rocks of the Santa Elena Ophiolite in Costa Rica during its complex geological history. Such environments are particularly interesting because the serpentinization processes can support microbial life since it can generate free hydrogen and methane. Therefore such environments may have hosted some of the earliest life on our planet and could potential  harbor life elsewhere in the universe.

Here’s a link to paper:

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Virginia Tech Scholar of the Week

This week, February 15th to 20th, I was selected as Virginia Tech Scholar of the Week. A bit of background. The Office of Vice President for Research at Virginia Tech selects faculty members weekly to highlight. They do a write up on the faculty member and it gets emailed in the weekly research e-mail that is sent across campus.

Here is a link to the article on me and my research group:

Oh yeah, you also get a cool coffee mug.



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VT Sedimentary Geochemistry Group at GSA 2105


This week the lab group is participating in the Geological Society of America’s Annual Meeting in Baltimore, Maryland. Here’s a list of the presentations.


Emma Tulsky is giving a poster on the using carbon and sulfur isotopes to track the chemical changes in sedimentary rocks during contact metamorphism

Contact Metamorphism and the release of carbon and sulfur volatiles: A study of the effects of diabase emplacement


Undergraduate Matt Petroff is giving a poster on carbon and sulfur cycles in subduction zones.

Syros, Greece: A geochemical window into subduction zone processes


Master student Sam Ritzer is presenting her work on accessing environment of deposition of a Triassic Lake and its relationship to deposit of well preserved fossils

Geochemical and sedimentological investigate of a lacustrine Triassic Lagerstatte in the Cow Branch Formation of the Danville-Dan River Basin

PhD student Matt LeRoy is presenting a study looking at the role of anoxia during a mass extinction event during the Cambrian.

Assessing the role of anoxia in the end-Marjuman extinction and SPICE Events

If you’re at the meeting stop by!

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Nature paper on oxygenation during the Proterozoic and Paleozoic published


A paper that I was a co-author was just published in Nature.  The study was led by Erik Sperling and statistically analyses geochemical data (specifically the iron content of shales) in order to track the redox evolution of the oceans during the Proterozoic through the Paleozoic. It then places this history into what we know about the evolution of animal life.

Here is a link to the article at Nature:

Here’s a link to write up that Virginia Tech did on the paper

Animals took first breaths after small oxygen blip in atmosphere, geoscientist discovers | Virginia Tech News | Virginia Tech.

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Lab Member Awarded AAPG Foundation Grant


Congratulations to Teddy Them who just received a grant from American Association of Petroleum Geologists from their Foundation Grants-in-Aid Program. This award, like his recent award from the Geological Society of America, will support his work on the Toarcian Oceanic Anoxic Event of the Early Jurassic.

Excellent work Teddy!

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Lab members awarded GSA Graduate Student Research Grants

Lab members Teddy Them and Matt LeRoy both received Graduate Student Research Grants from the Geological Society of America.

Matt’s student grant will support his study of environmental change during extinctions in the Late Cambrian Period.  Matt’s project is seeking evidence for the development of anoxia in the Rome Trough during one of these extinction events.

Teddy’s proposal was selected for the 2015 ExxonMobil/GSA Student Geoscience Grants.  These grants are awarded to 10 of the top 30 GSA student research grant proposals received each year.  This award will support his study on the Toarcian Oceanic Anoxic Event in the Early Jurassic.  Specifically he will use the grant for Re-Os isotope analyses that he will use to access paleoweathering rates during this event. The ultimate goal is will be understand links between volcanism, continental weathering and generation of anoxia in the ocean.

Way to go guys!

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