New stratigraphic evidence refines the timing of a major ancient carbon isotope shift (2.445–2.018 Ga), tightening its link to the Great Oxidation Event—and Earth’s first snowball glaciations.
In PNAS: https://ow.ly/AOb050XWizf
This work doesn't "solve" the cause of the LJE, but it does provide clean constraints that explanatory models must match. All of the data, models, and code is open source so others can build on it: github.com/sedmonsond/s...
Additionally, Stacey ran her inference separately for deep, intermediate, and shallow depositional environments, and the LJE (a long-lived positive excursion) appears in each.
This revised timing puts the start of the δ¹³C rise before or around the earliest clear signs of oxygenation, tightening the temporal link between the LJE and the Great Oxidation Event.
The timing of the LJE also shifts earlier than many common depictions. Best estimate: it begins around 2,445 million years ago, peaks near 2,130 Ma, and returns toward baseline by about 2,018 Ma.
The main result is that the excursion does look global, but the global peak is more modest than the most extreme local δ¹³C values suggest. In other words, some basins likely amplify the signal beyond what the whole ocean was doing.
Stacey’s approach was to build a statistical model that asks what common signal exists amongst global records of the LJE, if any, while explicitly accounting for the age uncertainty of these records.
However, the cause, and global nature of the LJE remain contentious due to significant uncertainties in the excursion’s timing and magnitude, as well as the the incomplete and spatially variable nature of the shallow-water sedimentary record.
The Lomagundi-Jatuli excursion (LJE) describes an interval of unusual carbon isotope ratios (high δ¹³C) that are broadly the same age as the sediments that record the rise of atmospheric oxygen during the Great Oxidation Event.
As a quick primer: carbon comes in two (isotopic) forms, and the ratio of these two forms in the ocean is controlled by the way that carbon enters, reacts, and leaves Earth's surface. This ratio gets stored in carbonate sediments, so the rock record gives clues about how the ancient carbon worked.
My grad student Stacey Edmonsond just published a new paper about the carbonate sediments that were deposited around the time that Earth first starts accumulating oxygen on the surface: "Timing and magnitude of the Lomagundi-Jatuli carbon isotope excursion"
www.pnas.org/doi/10.1073/...
4/4 Fun backstory: this idea started as a final project in our Advanced Sedimentology & Stratigraphy course (EOS 423) at UVic (@seos-uvic.bsky.social). Really fun to see the classroom project grow into a full paper, and I learned a lot about numerical modeling and stratigraphy along the way!
3/4 A key prediction is that transport-driven isotope excursions should occur in very specific stratigraphic contexts: tied to changes in the coastline (transgression/regression). If the same signal appears outside those contexts, a global driver is more likely.
2/4 We built a simple numerical sediment-transport model to track tracers (like δ13C of carbonates) through sediment formation, transport, erosion and deposition. The key result: erosion, reworking, and lateral transport alone can generate stratigraphically correlative isotope excursions.
1/4 Excited to share a new paper led by my student Connor S. van Wieren in Earth and Planetary Science Letters: "Correlative isotope excursions driven by transport, not global environmental change."
www.sciencedirect.com/science/arti...
I really wonder what the GOP's vision of America in 30 years is. Do they want a country that doesn't do fundamental research, without the world's best research universities, with the citizens working in factories assembling iPhone cases?
I honestly believe our most powerful position in a toxic time that feeds on cynicism, apathy,& despair is to genuinely care and act for a better world.
Cynicism is our enemy. We should check it, incl. on the left. It’s not intellectually superior. It’s the virus they’re trying to infect us with. NO
🚨 BREAKING: OMB has just issued a memo *rescinding* the previous memo freezing all federal financial assistance programs.
Full text, per government source:
I think some people hear “grants” and think that without them, scientists and government workers just have less stuff to play with at work. But grants fund salaries for students, academics, researchers, and people who work in all areas of public service.
“Pausing” grants means people don’t eat.
Each agency must "assign responsibility and oversight to a senior political appointee" and "cancel awards already awarded that are in conflict with Administration priorities". Where does science fall on that priority list...? 🧐
your papers and teaching material were a great resource and inspiration for me when I designed my 2nd year geochemistry course. thank you for your work! 🏳️⚧️
Passionate about Earth history? Dr. Blake Dyer's @blakedyer.bsky.social inclusive research team uses cutting-edge models & fieldwork to unravel sedimentary records, from life’s evolution to glacial cycles. Explore Masters & PhD opportunities www.blakedyer.com/index.html www.blakedyer.com/me.jpg
🧐.. this is very true 😐
1/n The installation of the Multi-Collector Inductively Coupled Mass Spectrometer (MC-ICP-MS) continues @seos-uvic.bsky.social This instrument uses an Argon plasma torch to ionize elements and molecules that are then accelerated along a flight path toward a big (450 kg) magnet shown here
The unboxing of the Nu Sapphire continues. The laboratory space in the Bob Wright Centre at #UVic was designed with this instrument in mind. The company manufactured the instrument to be able to be separated near the flight tube to fit in our elevator. Dr. Anne-Sofie Ahm looking on
It’s not every day you unbox a Nu Sapphire Multi-Collector ICP-MS. Congratulations to Drs. Anne-Sofie Ahm and Blake Dyer on their NSERC CFI-JELF success 🌊
