Life and climate evolved dramatically during the Tonian Period (1000–717 Ma). Sedimentary rocks from this period record the diversification of eukaryotic life, large-scale fluctuations of the carbon cycle, and major changes to the configuration of the continents during the lead-up to a pair of severe global “Snowball Earth” glaciations in the Cryogenian Period (717-635 Ma). Understanding global change leading up to these glaciations is critical for interpreting the boundary conditions that allowed these extreme environmental conditions to occur, especially since no ice sheets are known to have existed for ~1.5 billion years between ~2200 Ma Paleoproterozoic glaciation and the ~717 Ma start of the Cryogenian glaciations.
The Tonian-Cryogenian Tambien Group of the Tigray region of northern Ethiopia is a sequence of carbonate and siliciclastic sedimentary rocks deposited in an arc-proximal basin that culminates in glacial deposits associated with the first of the Cryogenian glaciations – the Sturtian Snowball Earth. The presence of tuffs suitable for high-precision U-Pb geochronology within the stratigraphy makes the Tambien Group an ideal target for temporally constraining stratigraphic and isotopic data sets of the interval preceding, and leading into, the Sturtian glaciation.
Our team has mapped the stratigraphy of the Tambien Group in high detail in the Negash Syncline and the Samre Fold-Thrust Belt (Figs. 1 and 2). While mapping, we make detailed observations of the stratigraphy, and collect rock samples to analyze their chemical compositions (Fig. 3). The lithostratigraphy (i.e. the types of rocks) gives us important information on the evolution of the local depositional environment, whereas the chemostratigraphy (i.e. the chemical composition of the rocks) gives us important information on the evolution of the global surface environment.
Our work in the Tambien Group has placed important new constraints on the evolution of the global surface environment leading up to the Sturtian glaciation by refining the timing and trajectory of the chemostratigraphic record (Fig. 4). In particular, we find that rapid and large-magnitude perturbations to the carbon cycle (as recorded in the δ13C of marine carbonates) are not responsible for the Sturtian glaciation. Furthermore, an analysis of
Details about the project coming soon – please check back later!
- Park, Y., Swanson-Hysell, N. L., MacLennan, S. A., Maloof, A. C., Gebreslassie, M., Tremblay, M. M., Schoene, B., Alene, M., Anttila, E. S. C., Tesema, T., Condon, D. J., Haileab, B., 2019, The lead-up to the Sturtian Snowball Earth: Neoproterozoic chemostratigraphy time-calibrated by the Tambien Group of Ethiopia: GSA Bulletin, doi:10.1130/B35178.1.
- MacLennan, S. A., Park, Y., Swanson-Hysell, N. L., Maloof,A. C., Schoene, B., Gebreslassie, M., Anttila, E. S. C., Tesema, T., Alene, M., and Haileab, B., 2018, The arc of the Snowball: U-Pb dates constrain the Islay anomaly and the initiation of the Sturtian glaciation: Geology, vol. 46, pp. 539–542, doi:10.1130/G40171.1.