A previously undescribed carbonate-shrub facies has been discovered in the lower member of the Noonday Dolomite—a Neoproterozoic post-glacial cap carbonate. This unusual facies consists of centimeter-scale structures composed of micrite and encased in early-marine cement, and exhibits an overall clotted, mottled appearance. Shrub architecture is characterized by occurrence of a central stalk with diverging branches that are composed of micrite leaves. A combination of biological, environmental, and diagenetic influences contributed to the growth and present appearance of Noonday Dolomite carbonate shrubs. Comparison with modern and ancient known abiogenic and biogenic shrub-like structures indicates that microbial communities were most likely responsible for at least localizing and initiating calcium carbonate growth in the Noonday Dolomite shrubs, although no undisputable microbial fossils have yet been discovered. Diagenetic processes may have obliterated Noonday Dolomite shrub microstructure and obscured any former fossil evidence. Unusual seawater conditions (high alkalinity/extreme calcium carbonate supersaturation) were vital for shrub growth. This research highlights a possible biologic component in Neoproterozoic post-glacial cap carbonates where most studies have focused on abiogenic processes.

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