Document Type


Publication Date


Publication Title



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 preSturtian 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.





First Page


Last Page




© 2017, SEPM (Society for Sedimentary Geology)


Archived as published.

Included in

Geology Commons


To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.