Using high resolution Sr isotope data from the Nama Group, South Africa, to constrain global stratigraphic relationships and continental weathering rates in the terminal Ediacaran

Master Thesis


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Although life on Earth evolved in the Archean, complex hard bodied animals only emerged in shallow marine environments during the late Ediacaran (~550 Ma). The trigger for the appearance of these hard-bodied animals is still debated but it was probably related to ecological and/or environmental change. Continental weathering fluxes into the oceans can influence redox conditions and seawater chemistry and can be tracked using the strontium isotope ratio of seawater, which can be faithfully captured by carbonate minerals. However, analysis of strontium isotopes in ancient carbonates can be complicated by diagenetic alteration. To ensure that the 87Sr/86Sr ratios generated in this study were reflective of primary seawater signals, a sequential leaching procedure, first proposed by Bailey et al., (2000), was tested on Ediacaran bulk rock carbonate samples. The successful implementation of the sequential digestion technique was verified through careful examination of samples for diagenetic alteration using petrography, trace element ratios and  18O. The sequential digestion technique was then applied to a high-resolution stratigraphic transect through terminal Ediacaran carbonate rocks from the Nama Group, collected in South Africa and Namibia. The isotopic signature of these rocks is consistent with other terminal Ediacaran age rocks, with typically slightly positive  13C and relatively high 87Sr/86Sr ratios (~0.7085). Correlation with other Ediacaran basins reveals a drop in 87Sr/86Sr from ~0.7090 to ~0.7085 ca. 550 Ma. The drop was likely due to location of palaeocontinents compounded by palaeoclimatic cooling during the terminal Ediacaran. These changes provide important context for a critical period in metazoan evolution and may have influenced the cost-benefit ratio of producing hard body parts.