Timing and tempo of the Great Oxidation Event
Ashley P. Gumsley a,1, Kevin R. Chamberlain b,c, Wouter Bleeker d, Ulf Söderlund a,e, Michiel O. de Kock f, Emilie R. Larsson a, and Andrey Bekker g,f
aDepartment of Geology, Lund University, Lund 223 62, Sweden;
bDepartment of Geology and Geophysics, University of Wyoming, Laramie, WY 82071;
cFaculty of Geology and Geography, Tomsk State University, Tomsk 634050, Russia;
dGeological Survey of Canada, Ottawa, ON K1A 0E8, Canada;
eDepartment of Geosciences, Swedish Museum of Natural History, Stockholm 104 05, Sweden;
fDepartment of Geology, University of Johannesburg, Auckland Park 2006, South Africa;
gDepartment of Earth Sciences, University of California, Riverside, CA 92521
Edited by Mark H. Thiemens, University of California, San Diego, La Jolla, CA, and approved December 27, 2016 (received for review June 11, 2016)
We present U-Pb ages for the extensive Ongeluk large igneous province, a large-scale magmatic event that took place near the equator in the Paleoproterozoic Transvaal basin of southern Africa at ca. 2,426 Ma. This magmatism also dates the oldest Paleoproterozoic global glaciation and the onset of significant atmospheric oxygenation. This result forces a significant reinterpretation of the iconic Transvaal basin stratigraphy and implies that the oxygenation involved several oscillations in oxygen levels across 10−5 present atmospheric levels before the irreversible oxygenation of the atmosphere. Data also indicate that the Paleoproterozoic glaciations and oxygenation were ushered in by assembly of a large continental mass, extensive magmatism, and continental migration to near-equatorial latitudes, mirroring a similar chain of events in the Neoproterozoic.
The first significant buildup in atmospheric oxygen, the Great Oxidation Event (GOE), began in the early Paleoproterozoic in association with global glaciations and continued until the end of the Lomagundi carbon isotope excursion ca. 2,060 Ma. The exact timing of and relationships among these events are debated because of poor age constraints and contradictory stratigraphic correlations. Here, we show that the first Paleoproterozoic global glaciation and the onset of the GOE occurred between ca. 2,460 and 2,426 Ma, ∼100 My earlier than previously estimated, based on an age of 2,426 ± 3 Ma for Ongeluk Formation magmatism from the Kaapvaal Craton of southern Africa. This age helps define a key paleomagnetic pole that positions the Kaapvaal Craton at equatorial latitudes of 11° ± 6° at this time. Furthermore, the rise of atmospheric oxygen was not monotonic, but was instead characterized by oscillations, which together with climatic instabilities may have continued over the next ∼200 My until ≤2,250–2,240 Ma. Ongeluk Formation volcanism at ca. 2,426 Ma was part of a large igneous province (LIP) and represents a waning stage in the emplacement of several temporally discrete LIPs across a large low-latitude continental landmass. These LIPs played critical, albeit complex, roles in the rise of oxygen and in both initiating and terminating global glaciations. This series of events invites comparison with the Neoproterozoic oxygen increase and Sturtian Snowball Earth glaciation, which accompanied emplacement of LIPs across supercontinent Rodinia, also positioned at low latitude.
Great Oxidation Event Snowball Earth Paleoproterozoic Kaapvaal Craton Transvaal Supergroup
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Author contributions: A.P.G., U.S., and M.O.d.K. designed research; A.P.G., K.R.C., W.B., U.S., M.O.d.K., and E.R.L. performed research; K.R.C., W.B., U.S., and M.O.d.K. contributed new reagents/analytic tools; A.P.G., K.R.C., W.B., U.S., M.O.d.K., E.R.L., and A.B. analyzed data; and A.P.G., K.R.C., W.B., U.S., M.O.d.K., E.R.L., and A.B. wrote the paper.
The authors declare no conflict of interest.
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