Brugia Malayi - Clark Science Center - Smith College

Constraining the Record of Neoproterozoic Life: New Insights from
Neoproterozoic Strata of Northern Namibia
Maggie Sawdy
Global events and anomalies throughout time have been recorded in the geologic record and have shaped the evolution of life
on earth. During the Cryogenian period (750-635 Ma), unusual, low latitude glacial deposits capped by carbonates appeared
twice (Hoffman et al., 1998). The snowball earth hypothesis suggests that the earth experienced extremely cold periods followed
by rapid warming (Hoffman et al., 1998). The severity and extent of the glaciers is debated, but the rapid climatic changes are
undisputed and would have had dramatic consequences for the diversity and ecology of organisms.
The Otavi Group of northern Namibia spans both Snowball earth events. The Beesvlakte Formation (Tonian) and Okakuyu
Formation (Cryogenian) are pre-Sturtian glacial age while the Rasthof Formation (Cryogenian) and Ombaatjie Formation
(Ediacaran) are post-Sturtian glacial age. Recent work on the Okakuyu Formation has yielded possible sponge-like microfossils
dated at ca. 760 my old (Brain et al., 2012). Also diverse and abundant microfossil assemblages have previously been found
in the microbialaminates of the Rasthof Formation (Pruss et al., 2010; Bosak et al., 2011a). The assemblages included testate
microfossils and possible foraminifera (Bosak et al., 2011b). At different localities, differences in ecological diversity have been
observed (Bosak et al., 2011a, Dalton et al., in review). The presence of microfossil assemblages shows that eukaryotes and their
ecological communities were present immediately after the first glaciation in the Snowball earth event. Furthermore, sponge-like
microfossils have been found in the Ombaatjie Formation similar to the microfossils in the Okakuyu Formation (Brain et al.,
2012). This suggests that similar organisms were present before and after the glaciation.
In my work, thirty-seven samples from across the four formations were examined. One set of samples from the Beesvlakte
Formation (Beesvlakte), one set of samples from the Okakuyu Formation (Otjize), five sets of samples from the Rasthof
Formation (Okakuyu, Heuwels, Otjomatemba, Okatjovandu, and Okaaru), and two sets of samples from the Ombaatjie
Formation (Heuwels and Danube) were examined. Except for the Rasthof Formation at Okaaru, none of the localities had
previously been examined for microfossils. The samples were all dissolved in 10% acetic acid buffered with 10% ammonium
acetate. Residues were collected using suction filtration at >100µm and 41-100µm. Microfossils were extracted from the residues
under a dissecting scope and examined in more detail under the SEM.
Every locality except for Otjize yielded microfossils, and at least nineteen residues have been categorized as fossiliferous. The
fossiliferous material included testate microfossils and unidentified organic material. The presence of microfossils in the three
formations further illustrates that eukaryotes and their resulting ecological communities were present both before and immediately
after the Sturtian glacier despite the dramatic climatic changes. Further work on the biological affinities of these organisms will
help constrain the role of climate change in influencing diversity during this critical yet understudied period of evolution. In
summary, my work is helping to fill in gaps in the fossil record while adding to the understanding of the snowball earth events and
hypothesis. (Supported by the Schultz Foundation)
Advisor Sara Pruss
References:
Bosak, T., Lahr, D.J.G., Pruss, S.B., Macdonald, F.A., Dalton, L., & Matys, E., 2011a. Agglutinated tests in post-Sturtian cap carbonates of Namibia and Mongolia.
Earth Planet. Sci. Lett. 308(1), 29-40.
Bosak, T., Lahr, D.J.G., Pruss, S.B., Macdonald, F.A., Gooday, A.J., Dalton, L., & Matys, E., 2011b. Possible early foraminiferans in post-Sturtian cap carbonates.
Geology, 40(1), 67-70.
Brain, C.K., Prave, A.R., Hoffmann, K.H., Fallick, A.E., Botha, A., Herd, D.A., Sturrock, C., Young, I.,
Condon, D.J., & Allison, S.G., 2012. The first animals: ca. 760-million-year-old sponge-like fossils from Namibia. S. Afri. J. Sci. 108(1/2).
Dalton, L. A., Bosak, T., Macdonald, F. A., Lahr, D. J. G., and Pruss, S. B., in review at Palaios, Preservational and morphological variability of assemblages of
agglutinated eukaryotes in Cryogenian cap carbonates of northern Namibia, 43 pp.
Hoffman, P.F., Kaufman, A.J., Halverson, G.P., & Schrag, D.P., 1998. A Neoproterozoic snowball Earth. Science 281(5381), 1342-1346.
Pruss, S.B., Bosak, T., Macdonald, F.A., McLane, M., & Hoffman, P.F., 2010. Microbial facies in a Sturtian cap carbonate, the Rasthof Formation, Otavi Group,
northern Namibia. Precambrian Research 181, 187-198.
2012
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