PYRITIZED CRYOGENIAN CYANOBACTERIAL FOSSILS FROM ARCTIC ALASKA
Author(s)
Macdonald, Francis; Du, Kimberly; Lahr, Daniel J. G.; Pruss, Sara B.; Moore, Kelsey Reed; Bosak, Tanja; Newman, Sharon; ... Show more Show less
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The Cryogenian was a time of climatic extremes, with two extended and severe global glaciations bracketing hothouse conditions. The effect of these extreme climate conditions on ocean chemistry and the marine biosphere remain poorly understood. Most of the previous studies of the fossil record from this interval focus on benthic organisms, with few examples of organisms with an inferred planktonic lifestyle and no firm evidence for photosynthetic organisms. Here, we present helically coiled, straight, and curved fossils composed of fine crystalline or framboidal pyrite in limestone samples from the Ikiakpuk formation of Arctic Alaska. These structures are morphologically identical to fossils of Obruchevella, a cyanobacterial form genus reported in pre-Sturtian and post-Marinoan strata, but not in deposits from the Cryogenian non-glacial interlude. We interpret fossils of the Ikiakpuk formation as planktonic cyanobacteria based on their morphology, which is identical to that of some modern planktonic cyanobacteria. Further evidence for a planktonic lifestyle comes from the preservation of these pyritized fossils in deep-water facies that lack evidence of microbial lamination. They provide the first direct evidence for bacterial primary productivity in the pelagic realm during the Cryogenian non-glacial interlude. Keywords: Alaska; metasomatism; paleoecology; United States; Cryogenian; Neoproterozoic; Proterozoic; upper Precambrian; Precambrian
Date issued
2017-11Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary SciencesJournal
PALAIOS
Publisher
Society for Sedimentary Geology
Citation
Moore, Kelsey R. et al. “PYRITIZED CRYOGENIAN CYANOBACTERIAL FOSSILS FROM ARCTIC ALASKA.” PALAIOS 32, 12 (December 2017): 769–778 © 2017 Society for Sedimentary Geology
Version: Author's final manuscript
ISSN
0883-1351