calendar Add meeting dates to your calendar.


Paper No. 27
Presentation Time: 8:00 AM-6:00 PM


BOSAK, Tanja1, LAHR, Dan J.G.2, PRUSS, Sara B.3, MACDONALD, Francis A.4 and AGRAMAKOVA, Yulia1, (1)Dept. of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, (2)Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts, Amherst, MA 01003, (3)Dept. of Geology, Smith College, Clark Science Center, Northampton, MA 01063, (4)Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, tbosak@MIT.EDU

Low latitude paleomagnetic data from Sturtian glacial deposits suggest that a global glaciation occurred 716.5 million years ago. The impact of this dramatic environmental change on biota remains virtually unknown. Here we report the discovery of microfossils of shell-forming eukaryotes, probable photosynthetic microbes and unornamented organic vesicles in organic-rich carbonates directly overlying Sturtian glacial deposits from four different paleocontinents: the Tsagaan Oolom Formation in Mongolia, the Rasthof Formation in Namibia, the Twitya Formation in Canada and the Numees Formation in Namibia.

The composition and the shapes of the most abundant shell-forming microfossils in these assemblages are consistent with testate amoebae, organisms that were abundant in the early Neoproterozoic sediments. The presence of rare sub-mm agglutinated tubes, curved tubes and cones in the Sturtian cap carbonates may indicate a greater morphological diversity of agglutinated microfossils with respect to the early Neoproterozoic deposits. This first robust and widespread morphological fossil record in the ~80 million year period between 716 and 635 Ma shows the presence of subtidal ecosystems dominated by diversifying shell-forming eukaryotes and morphologically simple acritarchs within ~ 20,000 kyr after the Sturtian glaciation. This glaciation thus does not appear to have severely challenged the survival of microbial eukaryotes.

Meeting Home page GSA Home Page