PALEOGEOGRAPHIC CONSTRAINTS FROM THE KAAPVAAL CRATON (SOUTH AFRICA) IN THE IMMEDIATE AFTERMATH OF THE GREAT OXIDATION EVENT

Between 2.4 and 2.1 Ga, Earth’s climate and surface environments underwent dynamic changes with large-scale glaciations and global perturbations in the oxygen, sulfur, and carbon cycles (e.g. Lomagundi-Jatulli Event.) Existing geologic and paleogeographic constraints have suggested this was a time period of breakup of ancestral supercratons, perhaps even a supercontinent (e.g. Gumsley et al. 2017). Additional data are needed to probe the paleogeographic history of continental fragmentation, the latitudinal extent of Paleoproterozoic ice sheets, and any tectonic drivers of paleoenvironmental change. To this end, we performed paleomagnetic analyses on basaltic volcanic rocks of the Pretoria Group of the Transvaal Basin, South Africa. Data were collected from the 2.22 Ga Hekpoort Formation and the ca. 2.1 Ga Machadodorp Member of the Silverton Formation, which overlie the record of the Great Oxidation Event (ca. 2.4 to 2.3 Ga) in the stratigraphic succession. Study sites spanned along-strike zones from the Mpumalanga, Guateng, and Northwest provinces. Data from the Hekpoort Formation reveal a high unblocking temperature component (11 sites where n > 6) with a steep northwest-up direction. Combining these results with previously published data from the southwestern part of the Transvaal Basin (Humbert et al. 2017) provides a strong paleomagnetic pole of 20 sites. Bolstering these data is a fold test. Pervasive overprints from the 2.05 Ga Bushveld Igneous Complex, modern lightning strikes, and interpreted hot emplacement of pyroclasts foiled attempts at other supporting field tests. The Machadodorp Member is closer stratigraphically to the Bushveld intrusion; although 20 sites were sampled, almost all are completely remagnetized. If the Hekpoort Formation pole is primary, it would be the highest paleogeographic latitude for a craton in Paleoproterozoic time raising questions about whether four Snowball Earth events are necessary, providing evidence against the high-obliquity hypothesis, and affecting craton configurations during the rise of atmospheric oxygen on Earth.

Gumsley, A. P., Chamberlain, K. R., Bleeker, W., Söderlund, U., de Kock, M. O., Larsson, E. R., & Bekker, A. (2017). PNAS, 114(8), 1811-1816.

Humbert, F., Sonnette, L., De Kock, M. O., Robion, P., Horng, C. S., Cousture, A., & Wabo, H. (2017). Geophys. J. Int., 209(2), 842-865.