Samre area in northern Ethiopia with Neoproterozoic Tambien Group sedimentary rocks overlain by flat lying Paleozoic glacial sediments

Snowball Earth Geochronology

The Snowball Earth Hypothesis predicts that there were periods during Earth history where the entire planet was covered in ice. The primary evidence for this comes from paleomagnetic constraints on glacial rocks that indicate glaciers were present at low latitudes at sea level during certain time periods in the Neoproterozoic.

One of the key predictions of the Snowball Earth hypothesis is that glacial deposits from all around the world should have a very similar age, as the onset to glacial conditions should take thousands of years. This is well within the uncertainty of dating techniques, which is around 500000 years in the Neoproterozoic.

strat Figure 1: Summary diagram of our work in Ethiopia with other preSturtian sections with age constraints from around the world for context

The Neoproterozoic sedimentary rocks in northern Ethiopia are a great place to test this prediction out, as they consist of a relatively well preserved sequence of shallow water carbonates and siliciclastics, with occasional interbedded tuffs. So we’re able to get chemostratigraphic data from the carbonates, and U-Pb age constraints from the interbedded tuffs if there is zircon present.

We had some great success in Ethiopia, as we were able to find tuffaceous material stratigraphically very close to the Islay anomaly (a carbon isotope excursion that many used to think was associated with the onset of the first glaciation), as well as stratigraphically near the first unambiguous glacial sediments.

tuff Figure 2: A felsic tuff from the Tsaliet Group in northern Ethiopia. Note the lapilli at the base of the tuff layer


. The arc of the Snowball: U-Pb dates constrain the Islay anomaly and the initiation of the Sturtian glaciation. In Geology, 2018.

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