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Geology, Stratigraphic-Proterozoic, Snowball Earth (Geology), Paleontology-Proterozoic, Fossils-Namibia, Glaciers-Namibia, Amoeba, Micropaleontology-Namibia, Paleobotany-Namibia-Proterozoic, Neoproterozoic, Microfossils, Namibia, Rasthof Formation, Testate amoeboe
In the late Neoproterozoic (~750 to 635 Ma), geochemical, paleomagnetic, and sedimentological evidence suggests that global glaciations occurred at least twice during what is known as Snowball Earth. The climatic changes would have had dramatic impacts on organisms and ecosystems. The Otavi Group in northern Namibia contains deposits from the first glaciation, the Sturtian glaciation (~720 Ma). Two pre-glacial formations (Beesvlakte and Okakuyu formations) and two post-glacial formations (Rasthof and Ombaatjie formations) were examined in this work. Two major types of microfossils were found: black organic matter with polygonal vesicles and the ability swell when hydrated, which is presumed to represent the remains of red algae, and spheroidal testate microfossils. The black organic matter, although only found in a few samples, is preserved in units deposited both before and after the Sturtian glaciation (Beesvlakte and Rasthof formations). The spheroidal microfossils have been found in the Rasthof Formation only and were rigid, hollow, and composed of mineral grains agglutinated to an organic matrix. Previous work has shown the spheroidal microfossils are consistent with agglutinating lobose testate amoebae, and this study shows that their occurrences were even more ubiquitous than previously suspected. The testate microfossils have a variety of morphotypes and displayed lateral variation from locality to locality, much like extant communities. Describing the microfossil assemblages from before and after the Sturtian glaciation provides critical insights into microbial ecosystems that existed during this important interval and may provide a deeper understanding of the effects of global glaciation on the marine realm.
Sawdy, Maggie Anne, "Constraining the record of neoproterozoic life : new insights from cryogenian strata (~850 to 635 Ma) of northern Namibia" (2013). Honors Project, Smith College, Northampton, MA.
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