GSA Connects 2021 in Portland, Oregon

Paper No. 15-1
Presentation Time: 8:05 AM


HOWARD, Cecilia1, SHELDON, Nathan1, SMITH, Selena Y.1 and NOFFKE, Nora2, (1)Earth and Environmental Sciences, University of Michigan, 1100 N University Ave, Ann Arbor, MI 48109, (2)Ocean & Earth Sciences, Old Dominion University, 4600 Elkhorn Avenue, Norfolk, 23529

While multicellular life can be preserved in fossils that can be used to understand its functioning and structure, microbial body fossils are not easily preserved, making the study of more ancient life challenging. Early rocks (before ~2.5 Ga) require extensive geochemical and/or morphological evidence to support the involvement of life in their deposition. Sedimentary structures in the 3.2 Ga tidal sandstones of the Moodies Group, Barberton Greenstone Belt, South Africa are proposed to have been produced by microbial mats. This determination has been based on a number of analysis techniques, including microprobe imaging, SEM imaging following HF maceration, and chemical analysis (including Raman and stable isotope mass spectrometry). Imaging of samples following HF maceration and in thin section has revealed microbially induced sedimentary structures (MISS) such as wrinkles and roll-ups, but these imaging techniques are destructive and/or capture only two-dimensional morphology. μCT imaging has been used to great effect in paleontology in order to examine fossils non-destructively and in three dimensions. Two previously described specimens from the Moodies Group were analyzed at UM’s CTEES facility using a Nikon XT H 22ST μCT and images were analyzed using Dragonfly to determine how the 3D morphology of ancient MISS relates to the traditional 2D orthoslices. Preliminary results include the identification of sub-mm scale ripples and dome structures consistent with previous 2D analysis of these samples. Using μCT scanning may enable the identification of microbially influenced rocks non-destructively as well as aiding in the identification of complex MISS such as multi-dimensional ripples and roll-ups that may not be apparent in 2D slices.